High Rev's possible with high displacement?

[nubtuner]

Before anybody flames me I looked through the forums, but I did not see anything particularly useful to my question, which is.....

What generally prohibits High displacement engines from making high revs? I say generally because I know it won't be just one engine part, but a combination of things. I've heard of things like weight of parts? Position of the block? etc..., but those don't sound like anything that can't be done to bigger displacement engines. Can't big blocks use the same technology as smaller one?


Also, how do F1 engines get such high revs? And why do they keep such low displacement?

The reason I'm asking is because I've always heard the saying
"There's no replacement for displacement!", but that doesn't seem to hold ground in today's automotive world.

I know the general HP formula [HP=TQ*RPM/5252], and everyone seems to be getting their cars faster by increasing TQ [FI, NO2, etc]. However wouldn't it be possible to take a high displacement/low rev, high torque engine and double the peak RPM's, hence the same effect as doubling the torque.
Ex. '04 Viper 8.3L 525TQ @ 4200RPM = 420HP @ peak TQ with peak HP @ 5600RPM pushing and estimated 500HP. Imagine keeping that TQ but with RPM #'s like an RSX (peak TQ @ 6000RPM and peak HP @ 7200RPM). At peak TQ you'd have around 600HP. Not to mention what you would get when HP peaks @ 7200RPM!!!
That's a pure theoretical examplle, but you guys get where i'm goin with this. If someone could point me in the right direction i would be very appreciative.

PS. Also if anyone knows any good books on topics like this I will check them out. Thanks in advance to all who help.

[curtis73]

Originally Posted by nubtuner

Before anybody flames me I looked through the forums, but I did not see anything particularly useful to my question, which is.....What generally prohibits High displacement engines from making high revs? I say generally because I know it won't be just one engine part, but a combination of things. I've heard of things like weight of parts? Position of the block? etc..., but those don't sound like anything that can't be done to bigger displacement engines. Can't big blocks use the same technology as smaller one?

In general, it is weight that is the big issue. I won't post numbers, but inertia and acceleration are exponential figures. Adding a few ounces to a piston at 5000 rpms is like adding several tons of inertial weight. Certain engines are more suited to high RPMs than others; for instance: The Buick 455 has a 4.313" bore and 3.9" stroke. Contrast that with the Olds 455 at 4.126" and 4.25". The shorter stroke lends itself to higher RPMs three ways; 1) bigger bores allow for larger unshrouded valves which in general promotes better breathing, 2) the inertia created from a 3.9" stroke is much less than that of a 4.25" stroke., 3) The bore/stroke ratio and corresponding rod/stroke ratio that can be acheived allows longer piston dwell. This allows for more of the combustion pressure to act on the piston at its best points in the stroke.

Also, how do F1 engines get such high revs? And why do they keep such low displacement?

Those two go hand in hand. HP is achieved with RPMs. They have the luxury of using small, light engines spinning very fast to make power. They are also geared so that they can stay in that RPM band all the time. F1 engines make such high revs (this will sound sarcastic but its just the truth) because they have $6million to spend on R&D and $100,000 to spend on each engine. They use some pretty exotic metals, designs, and techniques to make an engine that will rev to 15,000 rpms. You also have to keep in mind that they rev that fast for 500 miles and then they are rebuilt or scrapped. A Buick 455 would probably rev to 8000 with the proper breathing and cam, but it might only last 500 miles as well.

The reason I'm asking is because I've always heard the saying
"There's no replacement for displacement!", but that doesn't seem to hold ground in today's automotive world.

You are right. In today's world, its easier to take a small engine that is easy on emissions and fuel usage, and make it spin to 7000 so that you can advertise big HP numbers to the public. Take a look at the Honda S2000. Some people like them as daily street vehicles, but I"m not a big fan of them. I got tired of the constant struggle to get enough RPMs to make power. The automakers have fleeced the general public into thinking that HP is the number they want, when its actually torque that is the "drivability" part of the equation.

I know the general HP formula [HP=TQ*RPM/5252], and everyone seems to be getting their cars faster by increasing TQ [FI, NO2, etc]. However wouldn't it be possible to take a high displacement/low rev, high torque engine and double the peak RPM's, hence the same effect as doubling the torque.
Ex. '04 Viper 8.3L 525TQ @ 4200RPM = 420HP @ peak TQ with peak HP @ 5600RPM pushing and estimated 500HP. Imagine keeping that TQ but with RPM #'s like an RSX (peak TQ @ 6000RPM and peak HP @ 7200RPM). At peak TQ you'd have around 600HP. Not to mention what you would get when HP peaks @ 7200RPM!!!
That's a pure theoretical examplle, but you guys get where i'm goin with this. If someone could point me in the right direction i would be very appreciative.

I like how you think, but there is a problem with the theory. Taking your example; the Viper engine makes 525 tq at 4200. If you spun it (in its current configuration) to 7200 rpms, you would have almost zero net torque. You almost certainly wouldn't even have enough to spin the engine anymore. If you notice the current torque curve on the viper 8.3 starts falling and is slim to nill at 7200. Your math is however correct. If you could get a viper to make 525 tq at 6000, you would have a real hp monster. The problem is to get that, you would need extreme intake port flow on the heads, a massive cam, and you would lose the 525 you used to have at 4200. You have then made monster HP, but you'd have to gear it so that achieving that HP can happen. You've basically killed low RPM torque, so you have to lower the rear end ratio to multiply the torque you have remaining. Then, once you get up to the RPM where power is being made, you're in for one heckuva ride. Basically, you've taken a streetable engine and made it a race-only engine.

PS. Also if anyone knows any good books on topics like this I will check them out. Thanks in advance to all who help.

A subscription to Hot Rod, Car Craft, or similar mags will help immensely, but only after conscious reading for several months. I suggest listening to others who reply here, since I can't get my point across without five long paragraphs.

Basically, high RPM engines need tons of flow. Low RPM engines need velocity. Adding flow typically slows velocity. If no one else replies with a concise answer, I'll give you my long answer but lets see first .....

[benchtest]

Curtis hit most of the reasons quite well. Weight is #1. You're throwing a lot of mass around in there. You can build a light-weight set-up and rev it higher, but longevitiy is lost. A 1/4 mile engine can turn 9000, but it only has to do it for 9 seconds or less. Also consider that burn-time is fairly fixed. As you rev higher, you have less and less time for the flame to travel across the cylinder. Big engines have big bores, and long flame travel. We're talking milliseconds here. It boils down to the horsepower formula...torque and horsepower are going to cross at 5252. Horsepower will win after that. Does that help you at all?

[Alastor187]

Originally Posted by nubtuner

Also, how do F1 engines get such high revs? And why do they keep such low displacement?

The primary driving force of engine configuration in any F1 car is the rules and regulations. Currently F1 engines are limited to 3.0 liters but next year this will drop to 2.4 liters. Also, they are prevented from using forced induction. So their solution to get large amounts of power from a small displacement naturally aspirated engine was "higher rpms".

As was already stated that there are any number of issues with extremely high revving engines. I would also like to add that friction will increase non-linearly with engine speed, not only reducing the net power output but also increasing internal temperatures.

Also, the issue with flow rate and flow velocity stem from the inertia of the air/fuel mixture. Because the mixture has inertia at higher rpms the mechanical response of the valves actually becomes better than the fluid response of the mixture. So a different cam profile is needed to overcome the high rpm fluid response time. Negatively, a high rpm cam tends to reduce low rpm performance and vice-versa.

[RandomTask]

Guys! You forgot to flame him! Excellent question nubtuner . I just have to post some basic things here before curtis's intelligence makes me crawl under my desk and start sucking my thumb...
Vipers redline at 5500/6K RPM.
Formula cars rev up to 20K RPM.
Alastor, are you sure they're going to 2.4liters next year? I heard BMW just finished designing their motor for next season and its a 3.0Liter? I could be wrong .

Just to emphasize this on curtis's explanation: A Suzuki GSXR 600CC (0.6Liters) comes stock with 105 HP but only 45ft/lbs of torque. However the motor gets this HP at 13,500+RPM.

[clawhammer]

^Don't be so hard on him. He's just trying to learn. There are no stupid questions. It's among the easiest ways of learning.

[Kven]

formula 1 cars can rev high also due to their bore size; most of them are v10's; so each cylinder displaces about 300cc...Honda's B16 displaces 400cc per cylinder.

[RandomTask]

claw, sarcasm? I thought it to be an excellent question, if you read the post .

Kven, are you trying to compare a Honda B16 block to Formula Racing?--Lets do math here:

1000HP/10 cylinders=100hp per cylinder
where as
140HP/4 Cylinder= 35 hp per cylinder

Better yet;
1000hp/3000cc=0.333hp/cc
140hp/1600cc=0.0875hp/cc

I still don't understand the relavance of your comparison

[drdisque]

F1 engines also have no camshafts, the valves are opened and closed electronically.

[Kven]

no im not comparing power; im comparing that small cylinders rev faster; like the puny glow engines used in rc cars, they rev up to like 21,000rpm super easy and pretty quick.

[Alastor187]

Originally Posted by RandomTask

Alastor, are you sure they're going to 2.4liters next year? I heard BMW just finished designing their motor for next season and its a 3.0Liter? I could be wrong

You are right, the 2.4L V-8 restriction wont be active until January 1st, 2006. As well, there will be an exception through 2006 and 2007 for 3.0L V-10 with limited peak rpms.

[curtis73]

Originally Posted by clawhammer

There are no stupid questions. It's among the easiest ways of learning.

Before you say that, read this one I got caught in...
http://www.automotiveforums.com/vbul...d.php?t=314378

The guy wants to check his float level and keeps begging for his info or he'll be "in deep sh--". I asked him make, model, year, and engine, and he told me its either a Toyota, Ford, Mitsubishi, or Mazda but he can't tell. Its an engaging read. I know he just wants his info, but he won't tell me what I need to know.

I'm sure he's a fine gentleman, but...

[Reed]

i may be wrong but i thought that one of the main reasons that formula one engines have such high revs because of their extremely short strokes but are able to produce such high hp because of the large bore and high revs. if i am wrong please correct me and fell free to add anything if i am right because i have been trying to find info and specs on f1 engines.

[CBFryman]

also, F1 engines make 0-nil torque at say 3,000-4,000RPM... its like rotaries. i love 'em but in daily driving when passing (i dont onwn one but i have driven a few FC's and FD's) you have to bring revs up to 4,000 to make good power on the NA 13B's. roataries are able to make such high RPM's because the piston never has to stop and change directions. it just goes around and around and around in a eliptical motion.... stock redline of like 9,500. able to make a streetable 13,000RPM monster...

[Kven]

f1 cars make their hp mainly through revs; they make only about 250-300lbs of torque. the large bore is so they can have the displacement they want but retain the small stroke.