Larger displacement for better mpgs?

Here is an intresting topic, we were all tought that smaller displacement engines made less power but got better fuel effecency, and larger engines would always burn more fuel, back in the days when a Holly 750cfm was high tech that was certainly the case, but now we are starting to see the opposite in many cases. I work at a chevy dealership and I noticed several examples of this. The Colorado with the Z71 offroad package gets better effecency with the inline 5 than the base model with the four banger (crew cabs), the Tahoe gets better effecency with the larger 5.3L than the 4.8, and the full size Impala with its 3.5L V6 only gets one mpg less than the tiny cobalt with its wimpy I4. The Z28 for its weight has to be one of the most effecent cars of all time, even before displacement on demand the nearly two ton cars was getting 28mpg with proformance gearing and tires!! And lets remamber that it was a front engine rear wheel drive so it had alot more powertrain loss than an FF car. I may not be an engineer but it seems to me that higher displacement engines that run much lower RPMs have much more potential to be effecent. OK here is my questions, how much energy does an engine loose in friction from the swept area, I have heard that if speed doubles the friction in the swept area is increased four times is that true?
Question #2 in the avrage engine there is supposed to be around a 63% thermal loss, say we cut the surface to volume ratio in half, aproxamatly how much more effecent would it be all other factors being equal?
Could someone build a very lage bore engine that could run highway speeds with 500-800 rpms and get better ecconomy than a Toyota 1.3L inline 4, or is there a law of deminishing returns that I am overlooking?

Lets assume that I had the resources (aka money) to build a project engine lets say I build an inline or horazontaly opposed four cylinder with an absolutly insane 7 inch bore and 6 inch stroke, we would have over 800 cu in displacement, and about half the surface to volume ratio as a 5.7L V8, mathamaticly speaking we could put it in a camaro and run highway speeds at or below 700 rpm, in addition to the crazy low opporation speed we would have an exisessve amout of power just a downshift away, I know that an engine with pistons that size and a stroke that deep probably would come unglued past 3500-4000 RPM, but the upside is that you would probably never need any more revs than that since hp is just a multiple of torque (torque=hp at around 5200 rpm) even if could only make 900 ft-lbs (direct injection with around a 12.5:1 CR I would say 900 is a very safe bet) and we maxed out at only 3500rpm we would still be making over 600HP! I don't think weight would be a problem with this engine, we have about the same surface area as a small block v8 and the LS2 fully dressed weighs less than 400 lbs, so it is not out of the realm of possability to make our project engine a comprable weight. This engine could not be made street legal because of emissions laws, big bore/long stroke engines tend to have a problem with unburnt hydrocarbons, but with the advent of gasoline direct injection, and multi pulse injectors, not to mention the use of E85 a street legal engine of this type might be possable. Does anyone out there in internet land see any problems with a project like this?

well 4 cylinders at inch bore and 6 inch stroke gives you 15.1 liters.
i think the sheer size of that engine might ruin any hopes of good gas mileage. just think, you need to fill those enormous cylinders with 15 liters of air and fuel.

you would have a huge problem with the flame spreading.
i dont know the technical term, but with larger bores, the amount of time it takes for the flame to spread and ignite the fuel actually becomes a variable.
you would have to use multiple spark plugs and have to advance the timing so that the flame was not still spreading as the cylinder reached the bottom of travel.

essentially you are talking about building a boat motor into a car.
personally, i would use a 3-4 cylinder diesel with a massive bore and short stroke (for the size of the bore)

a 5 inch bore with 4 inch stroke and 3 cylinders gives you 4 liters.
put that into an any early 80's japanese sports car, and you have yourself a mileage queen. (hehe)

your unburnt hydrocarbons could be taken care of by using multiple spark plugs (on a gas) or high compression (on a diesel)

If you want better fuel economy, buy a Volvo 2-litre diesel. 48mpg combined.

Case closed.

or to make 2.2's statement broader, if you want fuel efficiency, you cut gasoline out of the equasion, and go for lean-burn compression ignition fuels aka diesel.

well 4 cylinders at inch bore and 6 inch stroke gives you 15.1 liters.
i think the sheer size of that engine might ruin any hopes of good gas mileage. just think, you need to fill those enormous cylinders with 15 liters of air and fuel.

you would have a huge problem with the flame spreading.
i dont know the technical term, but with larger bores, the amount of time it takes for the flame to spread and ignite the fuel actually becomes a variable.
you would have to use multiple spark plugs and have to advance the timing so that the flame was not still spreading as the cylinder reached the bottom of travel.

I think the technical term you are looking for is flame front velocity, I don't think that will be nearly the problem you think.
Reason #1 direct injection sprays directly onto the sparkplug(s) so the flamefront would not have to reach into the far edges of the cylinder to catch up with all the fuel, plus with a multi-pulse injector, and a multi-spark ignition I don't think buriing the fuel will be much of a problem.
Reason #2 Since this thing is in theory swinging massive 7" pistons it's opperating speed would be much slower than a 1.6L honda I4, the flame would have several times the amount of time before we hit BDC, remember I am talking about 500-700 RPM crusing speed.
Reason #3 Last I heard a higher CR helped the air/fuel mixture burn faster, so by using a direct injection system which allows for a very high CR (and hotter spark) we should be able to keep the fuel nearly completly burnt up to our 3500-4000RPM redline, afterall if the flame front can travel 4" at 7000RPM why not 7" at 3500??
As far as the huge amounts of power it takes to move 15.1L of air per rotation, think about it this way my 03 Rodeo has a 3.2L V6 that has to turn 2600 RPM on the highway just to maintain 70mph (3.2L x2600RPM/2 = 4160L of air per min assuming 100%VE. My concept engine would be 15.1L x500RPM/2=3775L per min assuming 100%VE. Now which one sounds like more of a gas guzzler? The difference is that the larger displacement engine will loose less energy through the cylinder walls, loose less energy through swept area friction (rings rubbing the cylinder walls), loose less energy through valvetrain friction due to softer springs in the cam (remember around 4k RPM would be this things max anyway) ,and loose less energy through blowby (less ring to leak around per cubic in), so in thory the project engine would be noticeably more fuel effecent and have aprox three times the HP and over four times the torque as my modern DOHC V6!

or to make 2.2's statement broader, if you want fuel efficiency, you cut gasoline out of the equasion, and go for lean-burn compression ignition fuels aka diesel.

BTW direct injection gas engines can lean-burn by injecting just a small amount of fuel right around the sparkplug Mitsu engineers ran a gas engine with as low as a 30:1 air to fuel ratio using direct injection, that is well under half the recomended 12 or 13 to one ratio.

Four words: Power to Weight Ratio.

A small engine in a heavy car has to work harder to make it move, and therefore uses more fuel.
A big engine in a small car doesn't have to work as hard, and so uses less fuel to achieve the same performance.
I used to have a 700kg car, with a 100ish hp Toyota twin cam in it. If driven gently it used to get crazy mpg, 40+ easily. But if I opened it up, I could drain the fuel tank just driving it home from work.
Basically a 20L tank could last me 7 days, or half a day depending on how I drove it.

The smaller engine will always give better fuel economy if run in the same way.

But if run with an auto which kicks down sooner (effectively lower gearing) and a computer which richens the mixture a lot when full throttle is used, then the comparison becomes distorted.


As far as efficiency, a larger engine can be more efficient than a small one for the reasons you mentioned (volume to surface ratio). But a large engine requires a large load to run efficiently (otherwise the standby losses are too big a proportion).
Running a large engine with a large load puts economy right out the window (even though efficiency has increased).

For example.
Isuzu have a 2.8 litre diesel engine which has a lowest BSFC (brake specific fuel consumption) of around 240 g/kwH.
Isuze also have a 4.3 litre diesel engine which has a lowest BSFC of around 215 g/kwH.

Of course diesel has a wide and flat efficiency curve, petrols have a small island of best efficiency whch is very easy to miss.

The smaller engine will always give better fuel economy if run in the same way.

But if run with an auto which kicks down sooner (effectively lower gearing) and a computer which richens the mixture a lot when full throttle is used, then the comparison becomes distorted.


As far as efficiency, a larger engine can be more efficient than a small one for the reasons you mentioned (volume to surface ratio). But a large engine requires a large load to run efficiently (otherwise the standby losses are too big a proportion).
Running a large engine with a large load puts economy right out the window (even though efficiency has increased).

A few things you are not taking into consideration standby losses are reduced with a direct injection (remember the 30:1 AF ratio) Also remamber we are in the age of hybrids once the battery is charged who is to say it wont have an auto shut off, and just run it on the battery for a while, but even with regular port injection and no hybrid system I would put it aginst any proformance minded 4 cylinder anyday, for effecency or proformance I would bet the larger engine would stomp a mudhole in it in every event exept for standby fuel consumption, and you know what I could live with that. I don't know about you but I don't spend much time at a dead stop. During my hour drive to work everyday I probably do not spend any more than three munites at a stop.

30:1 is nothing. Diesels regularly idle at 80:1 or higher, and get down to 15:1 when under full load. It's easy once you only have one variable to change, the amount of fuel, as opposed to a gasoline engine, fuel AND air.

30:1 is nothing. Diesels regularly idle at 80:1 or higher, and get down to 15:1 when under full load. It's easy once you only have one variable to change, the amount of fuel, as opposed to a gasoline engine, fuel AND air.

It would be so much easier to just make it a diesel and get it over with, the harsh reality is that most people hate diesels, I don't I think they are great, compression ignition takes out so many dificult challenges: hot spots, swirl heads, squash area, ignition timing, load vs comprssion compromise.... it just makes too much good sence, but if I built the perfect diesel 85% of the American population would not give it a second look I dont care it it got 3,000,000,000,000 mpg and the exaust smelled like flowers. Untill the American public has a change of heart they are going to buy gas engines.

It would be so much easier to just make it a diesel and get it over with, the harsh reality is that most people hate diesels, Untill the American public has a change of heart they are going to buy gas engines.

Becasue they are stupid. SHeeps that let the EPA and Society of Concerned Scientists (a crock!) make their opinion for them. Never mind that VW/Audi is making a new SUV with a 6 liter V12 TDI diesel making 500 HP and 738 torques! and still gets 20mpg!

http://imgup-lb.automotive.com:8080/files/1004291.w492.jpg
:eek:

As completly sweet as that is I am trying to beat that for power and fuel effecency, without the use of a turbo. With less than half the friction, and half the heat loss of a conventional V8, I need to figure out how much energy is lost through the cylinder walls in in swept area friction berore I can give a solid estamate on fuel effecency, but I do know that a 20mpgs is not unrealistic, an 07 tahoe with a 5.3L 320hp V8 gets up to 22mpg. SO if anybody has any figures on swept area friction on thermal loss let me know. Another concern that I have is the rev willingness on such a long stroke engine, even with it's insane power if it does not behave like a proformance engine with WOT it will not catch on. Even with a high CR, undersquare bore to stroke ratio, and lightweight forged internals, I am still not sure it will rev like a V8. Using either an in line or horozontaly opposed design it sould not require any counter weights, that will help a little, but the prospect of 7" postons probable weighing better than 2lbs each sounds very imposing, especaly since nobody that I know of has ever tried anything like this that I am aware of. Oh I am sure that someone else in history has built larger pistons but not for combined proformance and fuel ecconomy.

PERformance

Intresting tid bit of info, I just did a few mathmatical equations, and even with it's insane 6 inch stroke, this engine could run aprox 5000 rpms without exceding the internal g-forces of other production engines! 6"x 5000rpm x2cycles=5000ft per min. I would probably have to go with a long rod design to deal with those rpms though and that would slightly compromise low end torque, but a good thing for engine life (less laterial force aginst the rings and pistons, and less stress on the wristpins and just about any other moving part because of the more gradual g-forces at TDC and BDC) the higher RPM would allow to push the redline power to 800-900HP!! OK without advanced VVTi and variable length intake runners maby more like 700hp but that is still major kick.

any chance of showing us the maths you have done and what they mean and relate to, so that those of us who does know a bit about the mechanics of these things can take a look and see what you're doing?

I never thought of the equations dealing with bore, stroke, or even the size of the engine compared to its fuel mileage. A car with a more powerful engine gets you to where you are going quicker, which means it travels more miles in a shorter time then a less powerful engine. The only really problem I see is the speed limit. It won't matter how fast your car goes if you're both at a constant speed (65mph) and the engine built to conserve energy (and fuel) wins.

any chance of showing us the maths you have done and what they mean and relate to, so that those of us who does know a bit about the mechanics of these things can take a look and see what you're doing?

OK here we go surrface to valume ratio 7(bore) x3.14 (pie)=21.98x6(stroke)x4(cylinders)=527+(3.5x3.5)3. 14x2x4 (surface area area of piston and combustion chamber) Total 834 sq in for 923 cu in. The importance of that is that with lager cylinders and more stroke the surface to volume ratio is decreased which helps with fuel effecency since there is less heat loss through the cylinder walls, a typical V8 has aprox twice that surface to volume ratio.
As far as the RPM goes take your stroke (6") times your cycles per rotation (2) times your RPM devided by 12 (12"=1foot) and you have your piston speed in this case 5000 FPM (feet per min). 6600 FPM is where things usualy start to come unglued, depending on what material are used for the internals. As far as the rod to stroke ratio, Longer rods mean less G-forces at Top dead center and bottom dead center TDC and BDC, 1.5-1.8 rod to stroke ratio is pretty standard.
Are there any other equations you are looking for??

I never thought of the equations dealing with bore, stroke, or even the size of the engine compared to its fuel mileage. A car with a more powerful engine gets you to where you are going quicker, which means it travels more miles in a shorter time then a less powerful engine. The only really problem I see is the speed limit. It won't matter how fast your car goes if you're both at a constant speed (65mph) and the engine built to conserve energy (and fuel) wins.
There is more to it than which engine will get you there faster, I already pointed out several examples in my first post, lower engine speeds mean less friction, less friction means better effecency, better effecency usualy means better MPG. If a 1.3L Yaris could cruse highway speeds at 1600 RPM like a Z28 you would have fuel effecency approching the tripple digits, but the 1.3L engine does not make enough low end torque to do that. Even with Toyota engineering a 1.3L engine could not push a nearly two ton car while getting 28mpg, it would have to work way too hard (4000+RPM), but a 5.7L 300hp LS1 can. What I am attempting to do is to step up the engine size even more and reduce the engine rpm at cruse, basicly make an engine that could push a car at highway speeds at below 700 RPM, it sounds really weird but if you look at the physics behind it, it makes alot of sence, a large engine can opperate with less friction at 700 rpm than a small engine can at 3600 RPM (in the yaris or XAs case) Rember friction is not a linier equation, if engine speeds double friction quadruples!

i was thinking more along the lines of the real spoddy bits of maths dealing with masses, inertia, vibrations, amount of fuel needed per cycle that sort of thing.
you started this thread by stating a "want" for a more efficient engine but so far, i don't really see anything that follows on from this apart from mentioning the theoretical reduction of loss of energy through heat.

where are you getting that your idea would more fuel efficient than a "regular" engine?

i was thinking more along the lines of the real spoddy bits of maths dealing with masses, inertia, vibrations, amount of fuel needed per cycle that sort of thing.
you started this thread by stating a "want" for a more efficient engine but so far, i don't really see anything that follows on from this apart from mentioning the theoretical reduction of loss of energy through heat.

where are you getting that your idea would more fuel efficient than a "regular" engine?

I don't have all the mathamatical equations, that is why I started this thread, if I had all the anwsers I would not humble myself and ask for anwers, if you know anything I don't please let me know. I have a pretty good idea as far as things like inertia goes, but this is so upscale from from anything of its kind ever built that I don't know for sure, I would assume that a piston with twice the mass as a typcal 4" piston with twice the barring area and twice the structural strength could support the same g-forces, but again I am not sure maby there is a variable that I overlookerd, as far as effecency goes I have mentioned plenty of things other than surface to volume ratio, like swept area friction, valvetrain friction, Using direct injection to reduce the required fuel to air ratio. None of this is crazy science fiction it is all based on pre-existing ideas and facts, all put togeather into one concept. I can show you the basis for any one of the facts that I mentioned. The most important factors I am looking for are how much energy the avrage internal combustion engine looses through swept area friction, valvetrain friction, and thermal loss through the internal surface of the engine. Any additional factors you know of I would love to hear about them.

i'm not saying this is far fetched science fiction; after all, they used to make 27 litre V12s pumping out 1000+ bhp easily 60+ years ago.
it's just that the first thing that comes to mind is that thermal efficiency doesn't automatically equal good fuel economy.
by the same token, super efficient use of fuel in modern engines also doesn't automatically equal good thermal efficiency or fuel economy.

first thing's first.
what kind of efficiency are you looking at specifically?

i'm not saying this is far fetched science fiction; after all, they used to make 27 litre V12s pumping out 1000+ bhp easily 60+ years ago.
it's just that the first thing that comes to mind is that thermal efficiency doesn't automatically equal good fuel economy.
by the same token, super efficient use of fuel in modern engines also doesn't automatically equal good thermal efficiency or fuel economy.

first thing's first.
what kind of efficiency are you looking at specifically?

Extreme (highway speed) fuel effecency. And or marine crusing speed. Combining high thermal effecency with modern direct fuel injection. All in one neat package that would provide cuting edge proformance witout sacraficing economy. Most importantly I wanted to find the upper limits of thermal effecency in an automotive sized engine. Although I admit 15.1L is a touch excesive, but to achieve max thermal effecency I would need a low surface to volume ratio platform, and the reason I chose this size is it has aprox 1/2 the surface to volume ratio and swept ares (per cu in) as your avrage V8.

A few things you are not taking into consideration standby losses are reduced with a direct injection (remember the 30:1 AF ratio) Also remamber we are in the age of hybrids once the battery is charged who is to say it wont have an auto shut off, and just run it on the battery for a while, but even with regular port injection and no hybrid system I would put it aginst any proformance minded 4 cylinder anyday, for effecency or proformance I would bet the larger engine would stomp a mudhole in it in every event exept for standby fuel consumption, and you know what I could live with that. I don't know about you but I don't spend much time at a dead stop. During my hour drive to work everyday I probably do not spend any more than three munites at a stop.

Standby losses are the amount of power it takes to turn the engine. They are not changed by direct injection, battery charging or any other such factors.

Anything a petrol can gain by using hybrid drive, a diesel can also gain.

You may not spend much time at a dead stop, but the average car engine spends almost all of it's time heavily throttled. In these situations a large engine is nothing but a waste of space and fuel.

Comparing highway MPG is not the whole story. There are many standards worldwide for fuel consumption tests, a large engine will do poorly in all of them.

It takes me 15 minutes to pedal to work on a mountainbike. The same journey in a car takes 7 minutes and consumes over half a litre of petrol.

Intresting tid bit of info, I just did a few mathmatical equations, and even with it's insane 6 inch stroke, this engine could run aprox 5000 rpms without exceding the internal g-forces of other production engines! 6"x 5000rpm x2cycles=5000ft per min. I would probably have to go with a long rod design to deal with those rpms though and that would slightly compromise low end torque, but a good thing for engine life (less laterial force aginst the rings and pistons, and less stress on the wristpins and just about any other moving part because of the more gradual g-forces at TDC and BDC) the higher RPM would allow to push the redline power to 800-900HP!! OK without advanced VVTi and variable length intake runners maby more like 700hp but that is still major kick.

Linear speed isn't the problem in an engine revving.

Linear acceleration at the top of the stroke is.

The thermal efficiency of a petrol engine is appalling. You are flogging a dead horse. But that same dead horse is being flogged in much better ways by thousands of professional engineers world-wide.

In case you didn't realise. The thermal efficiency is very closely linked to the compression ratio. A diesel has typically twice the compression of a petrol engine.

As completly sweet as that is I am trying to beat that for power and fuel effecency, without the use of a turbo. With less than half the friction, and half the heat loss of a conventional V8,

Are you going to cure cancer and world hunger while you're at it?

Your goals are completely unrealistic and unacheivable.

Standby losses are the amount of power it takes to turn the engine. They are not changed by direct injection, battery charging or any other such factors.

Anything a petrol can gain by using hybrid drive, a diesel can also gain.

You may not spend much time at a dead stop, but the average car engine spends almost all of it's time heavily throttled. In these situations a large engine is nothing but a waste of space and fuel.

Comparing highway MPG is not the whole story. There are many standards worldwide for fuel consumption tests, a large engine will do poorly in all of them.

It takes me 15 minutes to pedal to work on a mountainbike. The same journey in a car takes 7 minutes and consumes over half a litre of petrol.

I would have to disagree with you several large engines have done well on the highway, the massive 6.0L 400hp LS2 gets 28 mpg in the 07 vette, the 5.3L V8 Chevy gets as good or better fuel ecconomy than their smaller 4.8 V8 or even their v6. I work at a GM dealership I see examples of this all the time, I got a trade in the other day a full size GMC pickup with 168,000 mile on it with a 5.3L V8 that was still getting over 23mpg without displacement on demand (it had the drivers information center with exact fuel consumption) the 4.3L v6 only gets 21 mpg so how are you going to tell me that it is not possable for a larger engine to get better fuel effecency??? There are plenty of other examples I can point out if you want me too.

so how are you going to tell me that it is not possable for a larger engine to get better fuel effecency???

There are thousands of engineers out there who have been working for the last 100 years to get the best possible efficiency out of the petrol internal combustion engine.

The petrol engine is so close to it's peak that there is no large gain possible.

Put those vehicles through a combined cycle fuel economy test and your results will be very very different.
The fact that the occasional owner spends all their time driving on the highway and gets good numbers doesn't matter when the same vehicle won't get 4 km/l in an urban environment.

So what if a 6.0l vette can get 28 USmpg. A smaller petrol engine in the same car could almost double that. A diesel engine in the same car would more than double that.

Linear speed isn't the problem in an engine revving.

Linear acceleration at the top of the stroke is.

The thermal efficiency of a petrol engine is appalling. You are flogging a dead horse. But that same dead horse is being flogged in much better ways by thousands of professional engineers world-wide.

In case you didn't realise. The thermal efficiency is very closely linked to the compression ratio. A diesel has typically twice the compression of a petrol engine.

I know that compression ratio is linked to thermal effecency, but higher compression is only part of the story if you did your reserch you would see that after 17:1 compression you actualy loose a small amount of power, that is why you see the move to turbocharged diesels running between 16.5 and 17:1 CR, but if you did your homework you would also know that with direct injection you could the same 17:1 compression as a diesel since pre ignition is not even possable with a proper setup. I never said that linear speed was a problem with engien reving I was concerned with recprocating mass, if you had actualy read my post you would know that, if you are going to make smart ass coments on someone elses idea make sure you read the idea first. As far as thousands of professional engineers world wide goes they are too blinded by pre-formed ideas of how things should be, that is why many of the great inovations come from other sources, and once the idea is proven engineers improve on it. Inventors and pioneers are not usualy engineers, but everyday people that have a great idea, yeah maby 99% of the time we are wrong, but that 1% is the next big thing. I invented two different types of the CVT transmision when I was 12 years old, (variable pully and twin cone) and my dad (a gearhead) told me that they could not work, within the next ten years both had been built and tested, one is in production and the other is in testing. So don't tell me that if an engineer did not come up with it ignore it, if a 12 year old that never drove a car can come up with an idea years before any engineers do, don't assume they are all knowing OK. Oh and in case you did not notice diesels are on the decline here in the US due to our emmissions laws. FYI do your own reserch before you bash someone elses.

There are thousands of engineers out there who have been working for the last 100 years to get the best possible efficiency out of the petrol internal combustion engine.

The petrol engine is so close to it's peak that there is no large gain possible.

Put those vehicles through a combined cycle fuel economy test and your results will be very very different.
The fact that the occasional owner spends all their time driving on the highway and gets good numbers doesn't matter when the same vehicle won't get 4 km/l in an urban environment.

So what if a 6.0l vette can get 28 USmpg. A smaller petrol engine in the same car could almost double that. A diesel engine in the same car would more than double that.

Show me a freaking 400hp diesel that can push a 3000lbs car on 285 series tires with 56mpg I dare you. Or better yet show me ANY 3000lbs High proformance car that gets 56 mpg on any fuel. Dude you are starting to reak of $hit, I would recomend that you do some reserch before start bashing someone else.

Lets get this thread back on track without any more Interruptions from people that don't even know what I am talking about.

I know that compression ratio is linked to thermal effecency, but higher compression is only part of the story if you did your reserch you would see that after 17:1 compression you actualy loose a small amount of power, that is why you see the move to turbocharged diesels running between 16.5 and 17:1 CR, but if you did your homework you would also know that with direct injection you could the same 17:1 compression as a diesel since pre ignition is not even possable with a proper setup. I never said that linear speed was a problem with engien reving I was concerned with recprocating mass, if you had actualy read my post you would know that, if you are going to make smart ass coments on someone elses idea make sure you read the idea first. As far as thousands of professional engineers world wide goes they are too blinded by pre-formed ideas of how things should be, that is why many of the great inovations come from other sources, and once the idea is proven engineers improve on it. Inventors and pioneers are not usualy engineers, but everyday people that have a great idea, yeah maby 99% of the time we are wrong, but that 1% is the next big thing. I invented two different types of the CVT transmision when I was 12 years old, (variable pully and twin cone) and my dad (a gearhead) told me that they could not work, within the next ten years both had been built and tested, one is in production and the other is in testing. So don't tell me that if an engineer did not come up with it ignore it, if a 12 year old that never drove a car can come up with an idea years before any engineers do, don't assume they are all knowing OK. Oh and in case you did not notice diesels are on the decline here in the US due to our emmissions laws. FYI do your own reserch before you bash someone elses.
You need to do a little more research.
Power does not drop off over 17:1 compression. The reason turbo engines run a lower [b]static[/b>\] compression ratio is because the boost gives you a dynamic compression ratio that is much higher.

Without a high compression ratio, you're going to be exhausting very hot air. This ensures you will never get good efficiency.

I don't know how old you are, but belt and cone CVT's have been around for around a century. To claim you "invented it' as a 12 year old before engineers did is truely silly. Indeed impossible given you are most certainly not the worlds oldest living person.

Claiming that professional engineers are blinded by "how things should be" is again rather silly. I suggest you spend a few days working with a some engineers, you may learn a lot. But only if you are capable of learning.

Show me a freaking 400hp diesel that can push a 3000lbs car on 285 series tires with 56mpg I dare you. Or better yet show me ANY 3000lbs High proformance car that gets 56 mpg on any fuel. Dude you are starting to reak of $hit, I would recomend that you do some reserch before start bashing someone else.

We were discussing fuel economy, not power output.

Yes there are many diesels which could push a corvette along the highway and get 56mpg. But they won't have 400hp.

The title of this thread is "larger engines for better mpgs?"
Not "mixing performance and economy".

You need to do a little more research.
Power does not drop off over 17:1 compression. The reason turbo engines run a lower <b>static</b> compression ratio is because the boost gives you a dynamic compression ratio that is much higher.

Without a high compression ratio, you're going to be exhausting very hot air. This ensures you will never get good efficiency.

I don't know how old you are, but belt and cone CVT's have been around for around a century. To claim you "invented it' as a 12 year old before engineers did is truely silly. Indeed impossible given you are most certainly not the worlds oldest living person.

Claiming that professional engineers are blinded by "how things should be" is again rather silly. I suggest you spend a few days working with a some engineers, you may learn a lot. But only if you are capable of learning.

I am not claming that professional engineers never invent anthing usefull, but they are given R&D projects that are just slight improvments over curent ideas, and I am sure that the CVT was not invented a centure ago, otherwise they would be perfected by now, I remember a few years ago reading in a magazine that Audi was just starting working on the variable pully design, I have spent many hours talking with engineers. My girlfriends dad is an engineer for Chrysler, he engineers gears for their transmissions, and he still knows nothing of CVTs. They are usualy very narrow minded in their feilds, mind you I am not being arrogant, he knows more about the working of gears than I will ever know, but that is his specality. BTW if you read GMs assesment of compression ratios and their effect on torque you will see that at aprox 17:1 CR you stop gaining torque, it is called diminishing returns if you study engineering you will see what I am talking about. I know a little more about the internal combustion engine than what I am letting on so don't try to debate me without some serous ammo OK, anyway lets get back to the subject at hand.

We were discussing fuel economy, not power output.

Yes there are many diesels which could push a corvette along the highway and get 56mpg. But they won't have 400hp.

The title of this thread is "larger engines for better mpgs?"
Not "mixing performance and economy".

Yes but if you actualy READ my posts I am talking about cutting edge proformance and fuel effecency, besides the most fuel effecent diesel car I have ever seen gets 49 MPG and only has about 98hp, far from 56MPG.
Look dude I am not trying to be rude but everything you have said thus far has been third grade crap.
Diesels get better fuel economy.... well no $%^@ higher BTU fuels have that tendency
High compression ratios provide more torque..... you don't say

I am not claming that professional engineers never invent anthing usefull, but they are given R&D projects that are just slight improvments over curent ideas, and I am sure that the CVT was not invented a centure ago, otherwise they would be perfected by now, I remember a few years ago reading in a magazine that Audi was just starting working on the variable pully design, I have spent many hours talking with engineers. My girlfriends dad is an engineer for Chrysler, he engineers gears for their transmissions, and he still knows nothing of CVTs. They are usualy very narrow minded in their feilds, mind you I am not being arrogant, he knows more about the working of gears than I will ever know, but that is his specality. BTW if you read GMs assesment of compression ratios and their effect on torque you will see that at aprox 17:1 CR you stop gaining torque, it is called diminishing returns if you study engineering you will see what I am talking about. I know a little more about the internal combustion engine than what I am letting on so don't try to debate me without some serous ammo OK, anyway lets get back to the subject at hand.

I am a professional engineer.
Diminishing returns are completely different to your claim of "losing power".
Yet the diminishing returns is exactly what is happening with the petrol engine.

You are assuming that because CVT was not in production in an automobile that it was not invented.
That is a very poor assumption.

Belt/pulley and cone CVT's have been used for speed control in machinery for a century.
They haven't been used in automotive because until recently they haven't been made small enough, light enough, cheap enough and at the same time maintenance free for the 300,000km or so an automobile has to last for.

Buy yourself a thermodynamics book and start reading.
The Carnot cycle will tell you straight away that what you propose is not going to work.
The Otto cycle will give you a few more ideas why it's not going to work.

When you're done with those, get out a fluids book and figure out what the pumping losses are with a throttled petrol engine. This will show you what an appalling waste of space a throttled idling petrol engine is and why large petrol engines use a massive proportion of their output literally strangling themselves.

Then start drawing.
Do the layout of your six inch stroke engine and tell us how tall it is going to be.
I have a 120mm stroke pushrod diesel which is approximately 800mm tall from sump to rocker cover. That seriously restricts what vehicles can use the engine.
A 150mm stroke engine is suitable for only large commercial trucks. Large commercial trucks are not interested in petrol and never will be.

Yes but if you actualy READ my posts I am talking about cutting edge proformance and fuel effecency, besides the most fuel effecent diesel car I have ever seen gets 49 MPG and only has about 98hp, far from 56MPG.
VW have diesel cars which use only 2.6 litres of diesel per 100km on a straight level run

I see you edited your post to include the BTU's of diesel.
Diesel fuel has roughly 10% more energy than petrol by volume. Weight for weight they're about equal.

I am a professional engineer.
Diminishing returns are completely different to your claim of "losing power".
Yet the diminishing returns is exactly what is happening with the petrol engine.

You are assuming that because CVT was not in production in an automobile that it was not invented.
That is a very poor assumption.

Belt/pulley and cone CVT's have been used for speed control in machinery for a century.
They haven't been used in automotive because until recently they haven't been made small enough, light enough, cheap enough and at the same time maintenance free for the 300,000km or so an automobile has to last for.

Buy yourself a thermodynamics book and start reading.
The Carnot cycle will tell you straight away that what you propose is not going to work.
The Otto cycle will give you a few more ideas why it's not going to work.

When you're done with those, get out a fluids book and figure out what the pumping losses are with a throttled petrol engine. This will show you what an appalling waste of space a throttled idling petrol engine is and why large petrol engines use a massive proportion of their output literally strangling themselves.

Then start drawing.
Do the layout of your six inch stroke engine and tell us how tall it is going to be.
I have a 120mm stroke pushrod diesel which is approximately 800mm tall from sump to rocker cover. That seriously restricts what vehicles can use the engine.
A 150mm stroke engine is suitable for only large commercial trucks. Large commercial trucks are not interested in petrol and never will be.

Oh goody you are a pro, so mr pro since you are doing such a great job (LOL) at bashing my ideas why don't you tell me how much heat a cylinder looses during a power stroke, or how much energy is lost in the swept area or anything usefull...come on anything if you are a pro why don't you know anything about compression ratios?? why have you not contributed one usefull fact to this thread thus far??? I have to say I do not beleve you, what do you engineer chew toys???

Guys... you are both starting to pi$$ me off. Stop flaming and get back to being objective or I'll close the thread.

There are no set rules. You can't calculate everything like heat losses unless you know the efficiency of the coolant, the specific heat gravity of the alloy in the cylinder walls, how much of the time the flame spends touching the walls integrated with the rod/stroke ratio and what part of the cylinder is uncovered at any given time, not to mention adiabatic changes in the volume of the cylinder. Factor in VE, induction type, cam timing, and all the other things and there is no real way to quantify everything.

That's why the same basic small block chevy can get as little as 1 mpg or 100 mpg depending on how its set up.

The bottom line here (if I read the posts correctly) is that we're talking about converting the stored energy in the fuel into motion in the most efficient means possible, right? So let's talk about it rationally, not by throwing bricks.

Oh goody you are a pro, so mr pro since you are doing such a great job (LOL) at bashing my ideas why don't you tell me how much heat a cylinder looses during a power stroke

The energy lost to heat depends on too many factors to simply throw out a value. You need to lock down the exact situation before you can calculate anything meaningful. So when you know the materials, temperatures, geometry of everything, gas velocities, specific heats and the rate of expansion then you might be able to start.

But I can tell you that it's a whole lot less than the energy that gets thrown out as hot exhaust.

if you are a pro why don't you know anything about compression ratios?? why have you not contributed one usefull fact to this thread thus far??? I have to say I do not beleve you, what do you engineer chew toys???

I have told you about compression ratios. But you chose not to believe it because it doesn't fit with your own theories.

Read this
https://me.queensu.ca/courses/MECH435/notes/Thermodynamic_Cycles.ppt

Well said, I was waiting for you to show up Curtis, you usualy have an anwser to just about everything, I have a rough idea how much torque it takes to overcome the friction in a cam, but I have no idea how much it takes to overcome the friction in the swept area of an engine, do you have any clue?

The energy lost to heat depends on too many factors to simply throw out a value. You need to lock down the exact situation before you can calculate anything meaningful. So when you know the materials, temperatures, geometry of everything, gas velocities, specific heats and the rate of expansion then you might be able to start.

But I can tell you that it's a whole lot less than the energy that gets thrown out as hot exhaust.

OK lets take out the variables, assuming the same aloy, same combustion dynamics, same compression ratio, how much more energy will we loose with twice the surface to volume ratio? Or a better way of saying it how much more energy will we retain with half the surface to volume ratio? I don't need an exact number, I know that would be nearly imposable, the process by which the block was cast or forged could effect the conductivity of heat I am just trying to get a rough figure, in the avrage internal combustion engine we loose 63% of the energy as heat though our exaust and coolent systems, I am just trying to figure how much of that can be saved if it has fewer ways of getting out. BTW your link does not work.

Going to bed, I have work in a few hours. I'll continue debating tomarow TTYL

BTW your link does not work.

It works fine. It's a powerpoint presentation.

If you don't have powerpoint, download openoffice.

It's a well known fact that a smaller engine will be more efficient when it's used in car. This is based on the simple fact that the otto engine is more efficient at higher loads than on part load. The efficiency of an engine at full load is typically around 30% or so, at very low loads the efficiency can be as low as 10%.

It's also well known that most car engines spend most of their time running at very low loads since only a small amount of power (5-20kW is enough for most cases) is needed to keep a car at a constant speed. So by using a smaller engine engine load can be kept much higher and the fuel consumption can be reduced.

With the smaller engine funning at higher load friction losses will be smaller, the heatlosses will be smaller, the pumping losses will be smaller and so on.

When it comes to estimation of heat losses and friction there are some softwares that can calculate those with quite good results, these softwares are commonly used by automotive engineers. Lotus Engine Simulation is such a software, and there's a single cylinder freeware availible for download on http://www.lesoft.co.uk

As for diesel engines and their compression ratios, the use of a high compression ratio is needed if a compression ignited engine should be able to run and especially to cold start when it's cold outside.

A high compression ratio, and thereby a high expansion ratio means a higher thermal efficiency. But high compression ratios also means high cylinder pressures. High cylinder pressures means that the engine must be structurally stronger (heavier), it also means that the friction losses increase (piston ring friction). Since friction increase with cylinder pressures, mechanical efficiency goes down when cylinder pressures become really high. Because of that reason a compression ratio should be chosen so:
1. The engine easily can be cold started
2. That the thermal + mechanical efficiency is high

A very simple way to estimate the friction losses is by:

FMEP = 0.3 + 0.04*(vP)^1.3

where

vP = piston velocity in m/s
FMEP = Friction Mean Effective Pressure in bar

FMEP is the difference between BMEP and IMEP:

IMEP - BMEP = FMEP

where

IMEP = Indicated Mean Effective Pressure
BMEP = Brake Mean Effective Pressure

Engine power, power lost though friction or engine power with no friction losses can be calculated

P [kW] = BMEP [bar] x V [litres] x n [rpm] / 1200
P [kW] = FMEP [bar] x V [litres] x n [rpm] / 1200
P [kW] = IMEP [bar] x V [litres] x n [rpm] / 1200

^ i like this guy :)

And no offense, but i trust Kiwi's knowledge, experience and intuition more than someone who doesnt have a complete understanding of what's going on. I'm sure he busted his rump in school to get his engineering degree, which isn't easy i know, and the fact that he even finished it says to me that he isn't bullshitting with this stuff. He probably comes off a little testy because of people that keep feeding him pipe dream engineering projects and then get all butthurt when he shoots down their dreams with facts and experience.

And the only reason the Corvettes are pulling 28 mpg on the highway (and ONLY on the highway) is because their overdrive is so insanely tall that the engine is just above idle at 65-70mph, and its aerodynamics mean that it doesnt need THAT much torque to keep it going. If you actually drive it 'normally' it wouldnt get near 28 mpg.

I work at a chevy dealership...

what do you do at that chevy dealership?

Car sales. It is my job to know the cars stats off the top of my head. I used to be a mechanic but that really sucks sometimes, so I got into sales. I think we all know that engines are most effecent when they are put under heavier loads, that is why in my concept engine it is designed to opperate at such extreamly low RPMs, the higher thermal effecency of a larger bore, and the load percentage of a small 4 cylinder. I am not for sure that I would totaly surpass the most effecent four bangers out there, but I know I could get close with a very powerfull, very exciting engine, Just imagine Mclaren F1 power and Toyota Yaris ecconomy, and the really great thing about it is that it would not cost a fortune to produce. No need for titanium valve springs, pistons and rods balanced to .5g, it's power comes from it's unbeatable torque not from a 9000RPM readline.

as i see it, you (the thread starter) are talking about a slow revving (1000 tops) engine with a long stroke and huge bore.
engines like this are currently being used in a much larger scale in ocan vessels.
i imagine that the queen mary and similar ship engines dont rev much past 700 rpm. ( i think the queen mary uses boilers, but W/E)
lower rpms are better anyway because you can get more acurate timing and can get away with less overlap and have the valves shut instantly, meaning less wasted energy.

as for huge engine bay problems, use an inline and mount it way low. put the accessories on the side. a cowl induction hood could add some clearance.



i'm not claiming to have any credentials or anything, but i do have logic, and a firm grasp of mechanical devices and how they work.
i would go ahead with the huge bore, but i think a short stroke would be more do-able.
the chevy 302 has a 4" bore and a 3" stroke. it has been taken past 10,000 rpms in racing applications.
i would keep stroke between 4 and 5 inches, but go crazy with the bore.
it would fit into an engine bay better.
i'd use diesel, and go crazy with compression.
a turbo can increase thermo efficiency, so it would be good to have too.

^ i like this guy :)

And no offense, but i trust Kiwi's knowledge.....

He probably comes off a little testy because of people that keep feeding him pipe dream engineering projects and then get all butthurt when he shoots down their dreams with facts and experience.

Damn straight.

Most people also get testy when told their super-dooper perpetual motion machine is never going to work.

as i see it, you (the thread starter) are talking about a slow revving (1000 tops) engine with a long stroke and huge bore.
engines like this are currently being used in a much larger scale in ocan vessels.
i imagine that the queen mary and similar ship engines dont rev much past 700 rpm. ( i think the queen mary uses boilers, but W/E)
lower rpms are better anyway because you can get more acurate timing and can get away with less overlap and have the valves shut instantly, meaning less wasted energy.

as for huge engine bay problems, use an inline and mount it way low. put the accessories on the side. a cowl induction hood could add some clearance.



i'm not claiming to have any credentials or anything, but i do have logic, and a firm grasp of mechanical devices and how they work.
i would go ahead with the huge bore, but i think a short stroke would be more do-able.
the chevy 302 has a 4" bore and a 3" stroke. it has been taken past 10,000 rpms in racing applications.
i would keep stroke between 4 and 5 inches, but go crazy with the bore.
it would fit into an engine bay better.
i'd use diesel, and go crazy with compression.
a turbo can increase thermo efficiency, so it would be good to have too.

You still don't quite get it, The stroke is not excessive in fact it is undersquare, the reason for this? To allow it to rev to 4000+RPM when you want excessive power :) but being able to cruse at or below 500 RPM to maxamize fuel ecconomy. Direct injection and a very low idel speed will prevent the massive engine from burning excesive amounts of fuel when the vehicle is stoped.

I have a suggestion:

kachok25, why don't you stop talking and start doing? Go to the drawing board and try to draw your engine first. I'm sure you'll realize you need to read something on the subject as a result. And when you read and understand everything that needs to be understood to build an engine, come back and re-read the thread. I bet you'll be surprised.:grinyes:

I'm sure you can find a machine shop willing to do this. and i give another +1 towards Kiwibacon. you'd be surprised what you learn in university. if you took an engineering course you'd learn things that'll help you understand 1)your own ideas better and why they will or will not work and 2)what other people are telling you. it's a hell of alot easier to explain things to someone who has the base knowledge required.

And i know how tough engineering can be. i'm in first year engineering, easy for now, but once you hit second and subsequent years it gets intensive, you have to be smart to get through, which is why i'll take kiwi's professional engineering over your mechanics and car sales for discussions about theoretical engines and whatnot.

I have a suggestion:

kachok25, why don't you stop talking and start doing? Go to the drawing board and try to draw your engine first. I'm sure you'll realize you need to read something on the subject as a result. And when you read and understand everything that needs to be understood to build an engine, come back and re-read the thread. I bet you'll be surprised.:grinyes:

Well put.:)

Even drawing the simple 2d layout of such an engine (crank, conrod, piston, head, valvetrain) would prove it unworkable.
That's without getting into the thermodynamics and mechanics of it.

It's a well known fact that a smaller engine will be more efficient when it's used in car. This is based on the simple fact that the otto engine is more efficient at higher loads than on part load. The efficiency of an engine at full load is typically around 30% or so, at very low loads the efficiency can be as low as 10%.

The efficiency of an idling engine is 0%.
Give an idling engine a small load and you efficiency might rise to 1-2%

Well put.:)

Even drawing the simple 2d layout of such an engine (crank, conrod, piston, head, valvetrain) would prove it unworkable.
That's without getting into the thermodynamics and mechanics of it.
I've been doing engines for a living...:wink:

the same basic small block chevy can get as little as 1 mpg or 100 mpg depending on how its set up.
Surely you mean 0.3-30mpg.

*edit for typing*

I have a suggestion:

kachok25, why don't you stop talking and start doing? Go to the drawing board and try to draw your engine first. I'm sure you'll realize you need to read something on the subject as a result. And when you read and understand everything that needs to be understood to build an engine, come back and re-read the thread. I bet you'll be surprised.:grinyes:

If you don't have any usefull scientific information why don't you just go away, pointless unfounded bashing is pointless, if you don't think it will work give me a ratonal reason why and not some off the top of your head BS, I am not trying to be rude but I am tired of peoples crap, yeah I understand that this is not the normal way things are done that is why I am asking question and not telling everyone how it should be done. Even if I had the funds to build this right now I would still be checking out the mathamatics first, which is what I am doing now.

as i see it, you (the thread starter) are talking about a slow revving (1000 tops) engine with a long stroke and huge bore.
engines like this are currently being used in a much larger scale in ocan vessels.
i imagine that the queen mary and similar ship engines dont rev much past 700 rpm. ( i think the queen mary uses boilers, but W/E)
lower rpms are better anyway because you can get more acurate timing and can get away with less overlap and have the valves shut instantly, meaning less wasted energy.

as for huge engine bay problems, use an inline and mount it way low. put the accessories on the side. a cowl induction hood could add some clearance.



i'm not claiming to have any credentials or anything, but i do have logic, and a firm grasp of mechanical devices and how they work.
i would go ahead with the huge bore, but i think a short stroke would be more do-able.
the chevy 302 has a 4" bore and a 3" stroke. it has been taken past 10,000 rpms in racing applications.
i would keep stroke between 4 and 5 inches, but go crazy with the bore.
it would fit into an engine bay better.
i'd use diesel, and go crazy with compression.
a turbo can increase thermo efficiency, so it would be good to have too.

The largest of the ship engines are turbocharged 2-stroke direct injection compression ignition engines running on fuel oil. One of the largest ship engines in this class is the Wärtsilä-Sulzer RT-flex96C. It has bore of 960 mm and a stroke of 2500 mm, it runs at 92-102 rpm and it's designed to operate at high loads.

As you can see it has a very long stroke, about 2.5 times the bore. This means that when the engine is running the piston mean velocity is around 8.5 m/s, similar to that of a car engine.

The engine isn't efficient because it's large, its size and power output is of benefit though. As we increase the size of an engine displacement increases faster than cylinder surface area, and if the power ouput increases proportionally against the displacement, heat losses decrease. Of the same reason a large displacement car engine which only needs to develop a certain power output the heat losses will increase, especially if we have an increase in bore rather than stroke.

The ship engine is also efficient because it's a two stroke, two stokes per cycle means that you only need half the engine speed for a certain power output and that equals less friction.

The engine has overlapping port/valve timing, naturally since it's a two stroke, but since it is direct injected no fuel is lost though the exhaust.

The engine is turbocharged, these turbochargers are used as scavenge pumps and force feed the engine with a high density charge. This increases power output while friction and heat losses remains small.

In a car an engine with a huge bore or stroke would not be efficient. It's much better to design a very small direct injected turbo engine, this concept would save you probably 10-20% fuel compared to a NA engine with similar power output.