Engine Displacement and Cylinders


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TrvlynAlec
05-16-2002, 07:51 AM
"There is no replacement for displacement" is what many people say, but many times it is not so. Some engines like the lamborgini have 6.0L and 12 cylinders. Others like the Honda F-1 race car is a 1.5L V6. My father has a Chevy 6.5L turbo disel V-8(i think). The honda prelude is a 2.2L 4 cylinder. I dont get why some engines have small displacement any many cylinders. And others have a large displacement and few cylinders. Why do they do this, and what are the advantages of each? Thanks

Steel
05-16-2002, 08:03 AM
well there really IS no replacement for displacement ;), just that with the more cylinders, the engine runs smoother and iirc, a bit more efficiently. If you had a 6.1 litre 4 banger, your car would be jumping all over the road. But it depends on the manufacturer. usually 0-2.5 litres is 4 cylinder, 2.6-4.0 is 6, 4.1-5.7 is 8 (with exceptions) like your dad's v8 diesel. the 6's are usually race engines used by v12's excpet the Viper with has an 8 liter V10, or a hemi 528 which is an 8.6 liter V8!! frickin big cylinders i tell you now! There ARE 3 and 5 cylinder engines too, so dont forget those. Like i said, it depends on the manufacturer and what they want out of the engine.

ivymike1031
05-16-2002, 08:46 AM
well heck, there used to be a 66L (not 6.6L) 3cyl sitting about 100ft from my desk, but they gave it to a university to use for research. It was a running prototype for a 22L/cyl V16. Obviously not well suited for a small vehicle application...

I guess the point is just that there are different constraints for different designs. Often a very slow moving engine can have really high displacement per cylinder, and medium to high speed engines have lower displacement per cylinder. More cylinders can mean more cost to build the engine, but having less cylinders can limit power output and/or engine speed... there are really lots of factors that go into the decision.

enginerd
05-16-2002, 09:53 AM
I saw a natural gas pump here once. It was the size of a house and was nothing more than a flat 8. One side was powered by what else but natural gas and the other was a gas pump to get the gas out of the ground.

TrvlynAlec
05-16-2002, 01:51 PM
"engine runs smoother and iirc" what is iirc? And if ivymike1031 is correct when he says "having less cylinders can limit power output and/or engine speed" then why is everyone crazy over a 8.6L V8 hemi engine? Does that mean a lamborghini engine is better than a 8.6L V8 engine? I mean it does have more cylinders. Yeah the hemi will have tons of torque, but the lambo should have more overall power/speed becuase of the extra cylinders.

ivymike1031
05-16-2002, 02:24 PM
perhaps I should have said "for a given displacement..." I'd say that in general, for a given total engine displacement, an engine with large, slow slugs will produce more torque than an engine with a bunch of little, high-speed pistons, and the high-speed engine will have a higher peak power output. Additionally, in general, the large displacement/cyl, slower engine will be undersquare, while the faster, many-cyl engine will be oversquare.

Before anyone starts in with counter-examples - I realize that if you start comparing dissimilar engine configurations, my general statement will seem incorrect (turbo vs na, diesel vs gas, etc)

fieroturbo
05-16-2002, 10:01 PM
Well, yet another topic that's "nucking futs!"

To my knowledge, the reason F-1 racers (An Ferrari 360 Modenas) use more pistons, with less stroke and bore (displacement per cylinder), is because the shorter the stroke, the higher RPM's you can get to. And a smaller bore, or thicker cylinder walls, increase reliablity of the block.

Now, trucks (pickups or semi's) perform their duties better with fewer pistons with larger diameters.

I'm not a scientist, I'm a hobbyist. So I can't tell you why, I can just tell you what.

I do know however, the larger the piston surface, the more surface there is to push down on, which I guess results in more torque. The combinations I've seen on my engine, the Pontiac Iron Duke (both truck engine and NASCAR engine), makes me assume that there's a ratio between Bore and Stroke that is equivalent to Horsepower and Torque.

I'll find a way to explain it. I'll look through the dyno charts I have and see if I can explain it somehow.

Polygon
05-17-2002, 02:07 AM
Originally posted by TrvlynAlec
"engine runs smoother and iirc" what is iirc? And if ivymike1031 is correct when he says "having less cylinders can limit power output and/or engine speed" then why is everyone crazy over a 8.6L V8 hemi engine? Does that mean a lamborghini engine is better than a 8.6L V8 engine? I mean it does have more cylinders. Yeah the hemi will have tons of torque, but the lambo should have more overall power/speed becuase of the extra cylinders.

Not so. The Plymouth Superbird in the late 60s/early 70s broke 200 mph with a 426 Hemi under the hood. The 528 Hemi would murder a 426 Hemi. So imagine what the 528 Hemi would do under the hood of the Superbird. The 528 Hemi has over 700HP and 700 torque out of the box and they also use the 528 Hemi in top fuel drag cars and pull 7000HP out of them. So that statement does not always apply but sometimes does.

enginerd
05-17-2002, 09:18 AM
Also consider that Formula cars as the name implies must follow a formula. Normally the participants are given a choice between a larger, normally aspirated engine, or a small turbo engine. Almost always the engineers choose the small, turbo engine. 'Normal' conditions do not apply. Pump gas is not fed to formula engines. These are not real world engines that last 100,000 miles. Cylinder bore, stroke, engine configuration and countless other varibles are considered in engine design to best fit the demands and expectations of that engine in it's intended application. Early in American auto engineering, cars were equipped with slow-turning, long stroke, small bore engines. These were ideal for pulling tree stumps, treading through muddy bogs (before modern roads) and hauling supplies. In the middle of the twentieth century, engineers were developing better and better gasoline and auto makers decided to capitalize on it. Engines with a large bore and a small stroke were developed. Horspower figures jumped and the muscle-car era was in full bloom. Later in the twentieth century, engines began to have "square" or close to square dimensions ie. square being bore and stroke being close in numbers. This compromise leads to good gas mileage and a good power. Supply and demand really dictate engineering. We don't want gas hogs or slow turning engines today, so engineers give us what we will buy.

fieroturbo
05-17-2002, 11:54 AM
Hey, I think somewhere on this "fup ucked" site is a Formula 1 forum. Maybe they know!

SaabJohan
05-17-2002, 06:55 PM
Fewer cylinders means higher efficiency but very few cylinders means problems with the forces created by the reciprocating piston.

The power of an engine depends of the amount of fuel that can be burnt, and the amount of fuel depends of the amount of air.

A naturally aspiranted 6 litre 4-stroke engine at 6000 rpm will use 18'000 litres air / minute if we consider the VE to be 100%.
We can compare that to one of the old F1 engines, 1,5 litre, 12000 rpm and around 4 bar boost pressure. That engine will use 45'000 l /m, that is 2,5 times the amount of air used by the 6l engine.

With tha amount air used per time unit we can estimate the engine power if we know the fuels energy content, SAFR and the engines effiency. In theese cases the power can be estimated to 470 hp and 1180 hp if gasoline is used.

Steel
05-17-2002, 08:35 PM
Originally posted by TrvlynAlec
"engine runs smoother and iirc" what is iirc? And if ivymike1031 is correct when he says "having less cylinders can limit power output and/or engine speed" then why is everyone crazy over a 8.6L V8 hemi engine? Does that mean a lamborghini engine is better than a 8.6L V8 engine? I mean it does have more cylinders. Yeah the hemi will have tons of torque, but the lambo should have more overall power/speed becuase of the extra cylinders.

iirc=if i remeber correctly. And people are crazy over 528 hemi's cause anyone who wants one HAS to be crazy ;) (like me) But the sheer power of the engine overcomes the lack of 4 more cyliders, and i never said that the 528 is gonna run as smooth as a baby's ass. Far from even. and it wont spin at nearly as fast as the lambo engines, and THAT's why the lambo's would have a speed advantage. There is a point where enough is enough. There ARE v16's (mostly in old planes) and V24's and other crazy numbers, but after V12, the size and weight of the engine works against itself.

MBTN
05-17-2002, 09:06 PM
V12 engine is usually the practical limit in cylinder numbers. An engine with a high number of cylinders (let's say V12) has a smoother firing order, which allows the engine to run smoother than let's say an I4. Given the same displacement:

More cylinders: smoother and higher horse power
Less cylinders: More torque, not as smooth.

TrvlynAlec
05-17-2002, 10:50 PM
More cylinders: smoother and higher horse power
Less cylinders: More torque, not as smooth.

Ok..so say if we have a 2.0L engine..one has 4 cylinders and the other has 6 cylinders. Will the 6-banger be able to achieve higher horsepower, even though they both have the same displacement? Second, if you have a engine with a bore bigger than the stroke, will it have higher a top speed than a engine with a stroke bigger than the bore? Thanks for the post :D

ivymike1031
05-17-2002, 11:14 PM
Ok..so say if we have a 2.0L engine..one has 4 cylinders and the other has 6 cylinders. Will the 6-banger be able to achieve higher horsepower, even though they both have the same displacement?

If both engines are consistent with general trends, then yes. There are plenty of factors that could make a given pair of engines go against the general trend, of course.

Second, if you have a engine with a bore bigger than the stroke, will it have higher a top speed than a engine with a stroke bigger than the bore?

(I assume you meant for a given displacement) Yes, in general that is the way things go. A longer stroke means that at a given engine rpm, the pistons will be moving faster, and they'll undergo greater accelerations when they reverse direction. This translates to larger loads on the mechanical components that control the pistons' motion (cylinder wall, wrist pin, conrod, crankshaft, etc). Thus it is generally easier to make the smaller-stroke engine rev higher. As always, there are other factors - a major limiting factor on engine top speed is the ability to maintain control of the valvetrain. If your valvetrain can't run at the higher speeds, then your engine can't (because you'll start to run valves into pistons, etc). The valvetrain speed capability is independent of bore, stroke, and the price of tea in china.

ivymike1031
05-17-2002, 11:18 PM
V12 engine is usually the practical limit in cylinder numbers.

There are, of course, exceptions. I don't think I've ever seen a modern engine with more than 24 cylinders. I did see a W-18 at the detroit auto show, which is about the most cylinders I've ever seen in a road vehicle.

SaabJohan
05-18-2002, 08:54 AM
Basicly more cylinders -> lower effiency -> less power

this is because more cylinders means bigger surface area, and that means that more heat will go into the cylinderwalls and into the engines coolingsystem instead for going to the crankshaft.

But we can't make too big cylinders either because then the travelpath for the combustionflame will be too long so combustion will take too long time. It's wanted that the combustion goes fast, this means that small cylinders with small bore are good (and centrally placed sparkplugs), but the speed also depends of the turbulence created before ignition.

Steel
05-18-2002, 11:19 AM
unless of course you have 2 plugs per cylinder, like my suzi bike engine.

454Casull
05-18-2002, 11:22 AM
Is it possible to place two spark plugs into a car engine cylinder?

ivymike1031
05-18-2002, 12:33 PM
Is it possible to use 2 plugs per cyl on a car engine? yes, Honda does that on the 2nd-generation IMA drivetrain. (Civic hybrid) It's also done on rotary engines, but that's not really the same thing...

enginerd
05-18-2002, 01:23 PM
Mercedes also uses two plugs per cylinder. One fires before TDC and another fires shortly after TDC.

Tom_S8
05-18-2002, 02:10 PM
Originally posted by enginerd
Mercedes also uses two plugs per cylinder. One fires before TDC and another fires shortly after TDC.

Alfa romeo also uses the same thing...

TheMan5952
05-21-2002, 12:06 PM
So do the 4 cyl ford rangers, it helps reduce emissions.

454Casull
05-21-2002, 04:54 PM
How does that work? Doesn't the resulting combustion push the piston backward (against its proper cycle)? I can understand if the plug fires at TDC and after, but not before and after.

ivymike1031
05-21-2002, 05:39 PM
The spark plugs in every automobile that I can think of fire many degrees before TDC, even at idle. In general, the faster the engine is running, the more the timing is advanced.

The thing that you may be missing - it takes time for the charge to burn, and you want the peak pressure to happen at a useful point in the cycle (a little after TDC). You've got to give the flame a head start if you want that to happen. That's the big reason why spark-induced knock happens, and why faster-burning fuel helps to reduce knock. If you give the spark too much of a head start, you'll reach too high of a temp&pressure as you approach TDC, resulting in knock. If your fuel burns faster, you don't have to give the spark so much of a lead, and you can thus give yourself a bigger margin to avoid knock. If your mixture burned so fast that you could always ignite the mixture after TDC, you could run much higher compression ratios w/o fear of knock (you'd probably start to get a diesel-like pressure trace, but I'm not sure).

SaabJohan
05-21-2002, 07:08 PM
The only time when the spark is fired very late is when you're starting your engine. If the fuel is ignited to early during startup the engine may go backward or create enough resistance so that startermotor will eventually break. And this is only done to engines with EMS.

Twin sparkplugs can be used on two ways, the can ignite both on the same time or not. Twin sparkplugs gives a few advantages under low and mid rpm and under part-load but not during high rpm and full-load.
Twin sparkplugs was used first/invented by Alfa Romeo.

454Casull
05-21-2002, 07:26 PM
Ohhhhhhhhh!!!

/chalk one up for the dumbass

TrvlynAlec
05-21-2002, 07:52 PM
this is probably going to sound really stupid, but what does TDC mean?

ivymike1031
05-21-2002, 08:15 PM
top dead center: when the piston pin is farthest from the crankshaft axis of rotation.

454Casull
05-22-2002, 04:32 PM
Twin sparkplugs gives a few advantages under low and mid rpm and under part-load but not during high rpm and full-load.
Why not?

SaabJohan
05-23-2002, 01:12 PM
Originally posted by 454Casull

Why not?

That's what tests have shown, doesn't have an explanation why.

454Casull
05-23-2002, 03:25 PM
All else being the same, having an extra spark plug in there would increase the compression ratio slightly, would help cool down the engine (an additional heatsink), leads to more efficient burning, so what's to lose?

SaabJohan
05-25-2002, 07:29 PM
Originally posted by 454Casull
All else being the same, having an extra spark plug in there would increase the compression ratio slightly, would help cool down the engine (an additional heatsink), leads to more efficient burning, so what's to lose?

Since compression ratio depends on cylinder volume and volume when piston is at TDC I can't se how the c.r. would increase with an extra plug.

A sparkplug is rather a hotspot than heatsink.

Twin sparkplugs is used when a cleaner and more efficient combustion is wanted at low and mid rpms, and if there is hard for one plug to ignite the fuel and/or if the fuel is burning slow like in Top Fuel dragsters.

454Casull
05-26-2002, 12:03 AM
Sorry, I forgot. :)

Why are there heat ratings for spark plugs then?

texan
05-26-2002, 01:29 PM
They're for controlling tip temperature, to prevent them from becoming so cold that they foul and so hot that they cause ignition pre-ignition.

There's nothing wrong with two spark plugs per cylinder, it's just that they don't really fit properly if you have more than three valves per cylinder. Mercedes found it beneficial for efficiency and emmisions to remove one valve in order to add a spark plug, which isn't surprising given that it does help low to midrange engine operation (where their engines spend about 90% of their life).

SaabJohaan- For combustion to travel fastest and exert maximum pressure on the piston crown during high RPM operation, a large bore and small stroke are what you're looking for (not the other way around). Additionally, such a setup has a smaller surface area to volume ratio, which if you're that worried about efficiency would be the way to go. Remember its not just about surface area, its about volume vs. surface area. On a displacement vs. surface area basis, old pushrod 2 valve V8's have a significantly better ratio than most any modern four cylinder motor.

454Casull
05-26-2002, 02:37 PM
On a another note: Why is the Viper's V10 still using pushrods?

texan
05-26-2002, 04:05 PM
Originally posted by 454Casull
On a another note: Why is the Viper's V10 still using pushrods?

If you're looking for the positive aspects of it, the pushrod configuration naturally lends itself to a lighter and more compact engine package. They probably decided early on to make the motor a 2 valve per cylinder setup, and given the height and width considerations didn't see the need to move to SOHC valvetrain. The Viper V10 is actually closer in design and tune to a truck engine than a performance car motor, but it's so damn big it can still hurl a car around at ludicrous speeds.

454Casull
05-27-2002, 06:29 AM
It's already big enough...

I've got a question though - why does it only make ~60HP/L?

SaabJohan
05-27-2002, 11:29 AM
Originally posted by texan
SaabJohaan- For combustion to travel fastest and exert maximum pressure on the piston crown during high RPM operation, a large bore and small stroke are what you're looking for (not the other way around). Additionally, such a setup has a smaller surface area to volume ratio, which if you're that worried about efficiency would be the way to go. Remember its not just about surface area, its about volume vs. surface area. On a displacement vs. surface area basis, old pushrod 2 valve V8's have a significantly better ratio than most any modern four cylinder motor.

The flamepath will be shorter for an engine with small bore since the flame path is from the sparkplug to the furtest point which is the cylinderwalls when using a centrally placed spark plug.

Large bore with small stroke have a larger surface area/volume than small bore and large stroke, but is anyway better in a high rpm operation like you said.

A four cylinder engine will always have better surface to volume ratio than an eight cylinder engine if they have the same volume and have the same type of head.

I didn't mentioned the volume since my comparison was between few and large cylinders against small and many cylinders.

GPrince
06-08-2002, 01:08 PM
these are generalizations.
larger displacement makes more torque
air flow makes more power
it's easer to get air in to a small cylinder than a larger one at higher engine speeds.
also larger bore size can make it easer to get air into an engine. for a given dispalcement.
a V12 6 L is just 12 smaller one cylinder engines added together.
a V8 6 L is just 8 larger one cylinder engines added together.
torque is about the same.
the v 12 will almost aways be able to breath better at higher R.P.M. and make more HP.
every thing else being the same.

.........ft/lb of torque * R.P.M.
HP= --------------------------
....................5252...............
how does one get sucked in to answring a question. that has no real answer?

454Casull
06-08-2002, 05:52 PM
a V12 6 L is just 12 smaller one cylinder engines added together.
a V8 6 L is just 8 larger one cylinder engines added together.
You missed the whole point.

GPrince
06-08-2002, 06:22 PM
I think I got my threads crossed.
I was repling to something else.

Hudson
06-21-2002, 10:58 AM
Originally posted by 454Casull
On a another note: Why is the Viper's V10 still using pushrods?

Just for additional information:

When the Viper's engine was designed, it was derived from an existing OHV V8. In order to develop the V10 as a SOHC unit, it would have been much more expensive and taken longer. The Viper went from concept to assembly line in 3 years. Very good for a vehicle that was on a unique platform using a unique (albeit based on an upcoming volume engine's design) engine.

I forget the exact numbers, but the cost of the Viper project was relatively low.

GPrince
06-21-2002, 05:26 PM
the v 10 iis big enough already.
I have been thinking about this
so what if your engine is smaller on the inside
it matters how big it is on the outside. that and weight. and fuel consumption are the only real things worth thinking about

Steel
06-22-2002, 02:10 PM
fuel consumption schmuel consumtion! When i get me a deuce and a hlaf, ill be mkaing a good 8 miles a gallon! If that! or mabbe an M1 abrahms, 2 gallons a mile...hmm

GPrince
06-23-2002, 05:46 PM
1 your not paying for the fuel

2 the abrahams m1a1 uses turbine engine = High power dencity

454Casull
06-24-2002, 08:39 PM
High power density? Wrong term. :)

ivymike1031
06-24-2002, 10:45 PM
sounds like an appropriate term to me... what was your complaint?

454Casull
06-25-2002, 10:27 AM
My mistake. I thought power density and power-to-weight ratio were different.

..mmustt... get.... of... crraa

Gravitom
07-16-2002, 11:24 AM
Just a little clarification

Modern F1 cars use 3L V10s with an extremely short stroke that lets them rev to about 18,000 rpms and produce about 850hp.

Late 80's/Early 90's F1 cars used 1.5L V6 Turbos producing 1500hp. They were eventually banned because they were too fast and getting expensive. But they were wrong and modern V10s cost just as much.

Jimbo_Jones
07-19-2002, 10:27 AM
heavier pistons are harder to get moving but have more weight... therefore more torque... whereas, little pistons are easier to get moving but have little weight... therefore more horsepower

Gravitom
07-19-2002, 10:31 AM
Originally posted by Jimbo_Jones
heavier pistons are harder to get moving but have more weight... therefore more torque... whereas, little pistons are easier to get moving but have little weight... therefore more horsepower

Does that mean when you put in lighter forged pistons you are actually reducing your torque for more horsepower?

texan
07-19-2002, 04:27 PM
Originally posted by Gravitom


Does that mean when you put in lighter forged pistons you are actually reducing your torque for more horsepower?

No, piston weight has nothing directly to do with power output.

SaabJohan
07-19-2002, 05:18 PM
Originally posted by Gravitom
Just a little clarification

Modern F1 cars use 3L V10s with an extremely short stroke that lets them rev to about 18,000 rpms and produce about 850hp.

Late 80's/Early 90's F1 cars used 1.5L V6 Turbos producing 1500hp. They were eventually banned because they were too fast and getting expensive. But they were wrong and modern V10s cost just as much.

The bore is usually around 92-96 mm and the stroke 42-45 mm, and at 18000 rpm this gives forces in the 8000 G area. The old F1 turbos usually had max rpm at around 12000 and this gives forces in around 5000 G but today the parts like pistons, piston pins and connection rods are lighter. To make them light materials like metal matrix composite and titanium are used, and these materials aren't cheap..

454Casull
07-19-2002, 09:08 PM
You say metal matrix composite; which part[s] use this material? And what is the metal matrix? What is the composite?

ivymike1031
07-20-2002, 12:01 AM
I don't know very much about these mat'ls, so I don't have a whole lot to add to the discussion.

The whole shebang is the composite (metal and all).

Definition I looked up online: Metal Matrix Composites: Materials in which continuous carbon, silicon carbide, or ceramic fibers are embedded in a metallic matrix material.

Try this site for more info on Al-SiC MMCs: http://www.x-lite.com/materials.html#mat

I don't know for sure (and right now I don't feel like searching to find out), but I would guess that in an F1 engine, MMCs are used in the conrods and pistons, but probably not the crankshaft or piston pin. It wouldn't surprise me to find out that you can make an aluminum cylinder wall into a MMC cylinder wall through some special treatment processes. I wonder how well MMCs wear, and how well parts that run against MMCs wear.

SaabJohan
07-20-2002, 08:42 AM
MMC is used in pistons, cylinderliners and possibly also in block and cylinderhead.

http://www.perfectbore.com/motorsport2.htm

Conrods are titanium and the crankshaft is made of steel.

454Casull
07-20-2002, 09:22 PM
MMCC's Al/SiC MMC has a density of 2.9g/cc, while 2618 Al alloy, which is what many racing pistons use, has a density of 2.81g.

ivymike1031
07-20-2002, 11:09 PM
ok... was there a point you were planning to make?

454Casull
07-20-2002, 11:40 PM
No, I'm just wondering why it's used.

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