High vs low RPM

[Removed user as requested]

Hi here is something I have received from year one in regards to the choice of engine for a pro-touring (supercar) build.

Like yourself, I am fan of V8 engines over the 10 and 12 cylinder engines used in many supercars. Big-block V8 engines (454 chevy, 429 ford, 440 dodge, 426 hemi) do not have the RPM range to compete with 12 cylinder competitors like the Diablo and some Ferraris. Horsepower and torque are not the only factors to consider

In racing, everything is a compromise. I’ll speak in general terms first. RPM = top end. A low rpm big block engine takes advantage of torque at the bottom end of the power curve and sacrifices horsepower at the top end. For example, the Viper you mentioned can run away from a Ferrari on short straights. Once the engine reaches its peak, the Viper cannot accelerate any more and will only maintain its speed. Meanwhile, the Ferrari has an additional 2~3k RPM with which to continue accelerating. On a short track, the Ferrari may not be able to catch and overtake the Viper.On a long track though, the Ferrari will catch the Viper and will likely handle better in the turns


Can some clarrify this for me? Why exactly would the ferrari be better off with 3k rpm more when the viper could simply 'shift gear' and continue climbing speed?

Is that in the context of when the car reaches its last gear and then the 3k rpm extra makes some difference which probbably wouldnt even be seen when you got 6 gears to go through???

I need some elaboration on why would someone want more RPM for a circuit car vs a massive ci engine with low rpm that makes same power/speed much lower... I dont understand how rpm works and why you would want it.

A: the bigger the engine, the less maintenance.
B: The bigger the engine, the more economical it would be as a cruising car (a small block made with 600hp will be less efficient than a 512ci engine at the same power because the small block has crazy cams etc while the big 512 is sleeping and hence if driven like a grandpa it would be more efficient and thus more streetfriendly)
C: flatter power curve with the BB and thus acceleration will be better and since its at 600hp top speed should be the same given the correct gearing.



Thats my short understanding, how does more rpm act better in a race sense at the same given power when even in this example of a diablo, he would have to change gears just like someone with a 512ci motor would have to change gears with the difference being the 512ci engine reaching higher speeds sooner

hopefully you get what im trying to get cause im confused!

[tazzz25906112]

Wow this one that will certainly get the group in a heated debate ;-) LOL....

Everyone will have their own opinions and many will have fact, some misunderstandings and most will certainly outline preferences...
I personally believe you've hit things pretty much with the understanding of rpm, torque, and their respective rolls..... One thing that isn't in you comments or equation is how are you going to put all of this to the ground???

From experience, I built a car that has what I believe is the maxim compromise available on pump gas only to realize that not enough consideration was given to putting it down (the chassis)...
My motor is a 555ci aluminum engine that has a super light rotating mass that swings up easily in excess of 7,500RPM.... The problem I found was the power & torque is overbearing to the suspension & tires.... I haven't been talented enough or smooth enough to put it down (yet LOL) and the biggest peice of advice I can give you is "balance your effort & build"....

You can always build a car with more power,,, and more rpm for top speed,,, but the costs are going to go up cubically (and that's no joke).... So yes you can have both but it's going to cost a fortune to create a balance between that power and what your putting it in ..

(BTW you're going to want to be a hell of a driver if you chase that goal)

[DartorDemon]

JM unprofessional opinion: i like cars that revv. I think high revvs combined with a manual transmission is heaven.

[ArtosDracon]

Strictly speaking to what year one said, that's utter rubbish. Assuming the cars were geared identically and used the exact same size tires and had the same co-efficient of drag and weighed the same, that would be true. But you can gear your car however you want, and you can even change the gears for the track you're going to be at. I would really enjoy having whoever said that come to try and explain and back-up his statement.

[Bryce]

Just to through this out there: throttle responce makes a huge difference in racing. So how fast does the motor accelerate. A motor with less rotational inertia may rev faster and actually be faster depending on gearing. Hopefully both cars would be geared optimally for that motor.

Example, a jerico 5 speed does not have an overdrive, so you would change your rear gears to accommodate the desired final drive.

[rrunner68]

I would say it's 100% personal preference. I like big block torque, so if nessisary I can "dig" out of a bad turn and or shift, where if you are a revver, you'll have to shift. I also agree to the Aero/gear debate. A healthy big block with 3.23 rear gears and a 1.0-.8 final drive from the trans is perfect for anything below 120-130mph

[79-TA]

Power is a result of force at speed, or in more familiar terms, torque at a given rpm. So what matters most, is the average horsepower over the rev range you intend to use. This varies for each track and ideally, you would customize your gearing accordingly each time. For a race car, this can be taken to the extreme. For a street car, we make compromises for reliability, cost, and flexibility.

Given that there are two basic ways to make power (focus on high torque at low rpm or maintaining torque at high rpm) one must look at what pros and cons are involved with each. Traditionally, focusing on RPM allowed racers to use a smaller engine which equated to weight savings. With tight gearing in a racing situation, the engine could stay in the powerband the entire time and the poor lowend torque would not matter as much. Cars that only make power at high rpm rely on gearing and torque multiplication. Some of the cons of this have already been mentioned in that with more rpm comes more wear and stress. Obviously, if cubic inches and torque were sacrificed, staying in the proper rev range is more critical.


Random other thought. A high revving car might not need an upshift right before the end of a straight, which can save the driver the trouble of shifting. Staying in the lower gear will mean more torque multiplication. On the other hand, a torquier lower revving engine in another scenario might not need to be downshifted in a braking zone allowing momentum to be carried more easily and saving the the driver the act of shifting. It all depends.


Here's a quote from Paul Van Valkenburgh's Race Car Engineering and Mechanics regarding stress and rpm: "Component stresses rise exponentially with the increase in rpm, so an engine might last 100 hours at 6,000 rpm, 10 hours at 7,000 rpm, and 1 hour at 8,000 rpm."




Here are my thoughts on Ferrari vs Viper. Both cars have been tested and you can find actual data for both. The current ACR is an absolute beast that would wipe the floor with most production Ferraris. For instance, the ACR already beat the F430 Scuderia by about 6 seconds around VIR (a long track) in Car and Driver's 2008 Lightning Lap.

But for the theoretical version, it all comes down to how much power each car is putting down. Peak acceleration for any car happens in first gear at peak torque. We'll assume the Viper has the raw torque advantage while the Ferrari has rpm and both have similar peak horsepower. From a standstill, the Viper would have the advantage in raw torque (and better average horsepower within 1st gear.) The Ferrari might compensate with deep rear gearing, but the average horsepower difference might be too much.

At a roadcourse, the cars won't have to dig themselves out from a standstill, so the usable rev range changes and lowend torque is not as much of an issue. The average horsepower in the rev ranges actually used will be very similar, and if the Ferrari's smaller displacement engine allows a smaller and lighter design, it might handle better as well. So yea, it all depends on all kinds of factors.

[H2Ogbodies]

Not to mention the viper is a pig in terms of power to weight ratio when compared to a Ferrari. And being mid engine to boot. Persoanlly, I think if detroit focused on turbocharging instead of raw displacement for max power, you would see big cubic inches disappear. I see turbocharged inline motors as the future.

[406 Q-ship]

What Brett said.

A long track does not necessarily favor a high RPM horsepower engine. I have seen a Z06 Corvette runn away and hide from a Ferrari (can't remember which one) at Laguna Seca, these were street cars on a open track event. It is about gearing, weight, and driver ability when it comes to high RPM vehicles, where a low RPM torque engine is more driver and gear friendly.

[PhillipM]

I think this needs to be moved to the Engine Section...

[rogue]

High RPM is fun but gets tiring winding out everywhere.

13,000 RPM sequential shifting
http://www.youtube.com/watch?v=Ig6yGvS5OkY

6500 RPM BBC TKO600
http://www.youtube.com/watch?v=V_D6HG8BuZk

Both require totally different driving styles. I find myself having trouble switching between cars sometimes they are so different.

I will admit though, NOTHING compares to the sound of a high RPM motor, but nothing compares to the torque of a BBC.

All preference I guess.

[Jim Nilsen]

I have found that the taller the rear gear and the wider ratio 6 speeds give a much wider overlap in the best torque range and higher rpm which gives you the best of both worlds. It made a big difference at the Goodguys autox to be able to go 6500+ rpm in 1st at 35mph, the control with the throttle took out any need for the brakes at all and it was getting better each lap as I was learning what I could really do.

Wide gearing with a lot of torque makes a really nice car to drive all around and I also like being able to wind up to 6500 rpm as long as it is pulling hard and in 1st and 2nd gear the redline comes up so quick even with tall gearing in the rear with the right trans. Going to 7500 rpm would really make even more overlap. With the LSX engines flat and wide torque these days it is really a no brainer to have both !!

[Removed user as requested]

Thanks for the feedback.

So just to make sure I understand correctly...

In theory, 2 identical cars, 2 identical weights, 2 identical drivers, 2 identical HP/Tq (as close as it can be)... so everything is the same other than one car is high RPM and the other low RPM Big Cube...

Both cars should reach the finish line after 20-30 laps at the same time, its just how you drive it?

See, Im going to take my 68 Charger down to prodrive to do a supercar suspension on it (probbably looking at 40 000 or so for suspension fabrication), The power will be put down to the ground, going to run 335s out back unless I find 345s possibly and likely to run 265/275 front.

All I want to get my head around is...

A Lamborghini Diablo for example to me is a street car. I can hop in it... it goes hard, it definatelly handles awesome, feels racey on the road but not 'hard like a rock such as a dedicated race car'. So to me its something you can go in a nice cruise in but also take it out to a race course and have some serious fun with it.

Now... considering its a street car, 5mpg cruising means I cant really use it for anything and therefor defeats the purpose. I know a engine builder that is able to pull out 565hp out of a 440 stroked to 512ci, running on a proform 850cfm 4 barrel carb and gets 20mpg (if you feather the accelerator and drive like grandma)

If I build a small block at 600hp vs a 528ci engine at 600hp, which one will be definatelly the more 'street' engine... and if taken to the track (say 2 identical chargers built identically one with the small block at 600 and one with the 528 at 600) which one would be the leading car? Or would performance be the same just requires a different way of driving it?

I mean, vipers as example can go to 300kmh, so can ferraris... so how the heck does the extra revs help when they both got the same top speed.

Which style would be best for me and can CI be gotten with the RPM? (roller motors etc with reliability)?

Last thought... they also told me the 440 would run circles around the hemi because it can make the same if not 'more' power than a Hemi and the 440 would be alot more reliable while the Hemi was designed for drag race and designed to be pretty much rebuilt after every race. Obviously speaking in the context of a lambo, its a car that would be fun to cruise in, handles awesome, can be taken to the racetrack for fun and wont need a 20 000 dollar engine rebuild at the end of the race... so obviously I need a durable engine style build as this is a street car with fun at the track (context of the lambo which to me is a street car)

[HUSTLESTUFF]

For what you are looking for, you may want to look at XV motorsports and a twin turbo new Hemi and 6 spd. XV http://www.xvmotorsports.com/ has done all of the homework for the early Mopars, but did so with the new Hemi in mind. Get the Level II Suspension (probably what prodrive would come up with), stiffen up the car, get brakes to match and stuff in a TT 6.1 and you'll get 20+ mpg unless you're WOT. I'd guess you'd be in below $40,000 for motor and suspension. Mike

[MonzaRacer]

OK so a lot of people will spread misconceptions on which is better. Small blocks were built to make small ,compact, fuel efficient and easily maintained power plant at a reasonable price.
Now in small block terms after a point they ran out of power potential in design and materials stand point.
So fast forward nearly 60 years from the development of the small block chevy and if properly well built the engine can make literally unknown amounts of power. now go back, why did we build big blocks, they were developed heavy truck, industrial use. As the Hemi was but because if its success in industrial use it was put in cars, so never say a hemi wont last, it just doesnt last in stock form at high rpm.
You must decide, which engine suits the application, could a 409 fit into NASCAR now,, most likely not due to a compromise design, can it be done ,sure, with enough cash but a clean sheet design gets the nod over an adaptation.
Now do you need torque to get you there in quicker acceleration or do you need your power up on top end.
There where CanAm 305 big blocks running super light rotating assemblies, and turned some serious rpms and were competitive.
Make the engine larger displacement and you blow the design idea of the nearly $5million dollar program of making a BBC rpm and make power. From what I got those FI engien would spin up to 11,000 and make well over 600hp, but no torque.
Take a 454 sbc and spin it 11000 rpm and you wont own it long with out NASA spec/price parts.
Any engine IS and always will be a compromise by the designer to fit the application/use.
Why is it that NASCAR engines are big bore short stroke? Because it was the best design, now can you drag one, yes but its no a smooth match. Now take a 434/454 sbc it will be a better drag engine,,,and cheaper as it isnt required to spend ridiculous sums of cash to build over the NASCAR unit.
Trying to say that one engine suits everything is a misnomer and shouldnt be believed.
I have always been a believer in smaller engines, in some respect. the best of both worlds, I have a 77 Monza, the 355 I built for the yellow car in my avatar was simply the best performing engine for the least amount of parts and time and cash I ever built.
BUT its bottom end torque was BRUTAL in the car. So now I am going to do something slightly different, less stroke/CU in. a slightly better cam head combo to kill low end torque, thne to build upper end torque I am going to turbo it.
The 355 wouldnt pass in turbo form but the number do play out for my 302 sbc idea.
Match torque production in a flat curve for moderate weight cars, with a faster acceleration ramp, ie it makes torque but accelerates faster will , if match with proper gearing , be better engine.
Peaky torque curve with slow or fast acceleration ramps will need crutches to live in same environment.
Like probably one of the best seat of the pants engineers ,Smokey Yunick (sp) , mentioned in an article I read, his theory was build as much torque as quickly as your chassis can apply, and your in the right ball park.
The more power you can build , faster will out accelerate the engine that takes time to build power, and less crutching you have to do with gearing and suspension.
Too much torque and you use less effective gearing, , not enough and you have to over gear it.
In drag racing if your final drive gearing stays in the 10to 1 range in low your nearly golden if your power is right. Proven numbers.
Most guys and gals are running 4,5 and 6 speed in Auto cross but are using what 2nd and 3rd? , maybe 1st?
But if they have a decent power curve that accelerates at sufficiently enough speed/torque you do less shifting(modifying) of the gearing as is.
Take Jim Nielsons (sp) Cormaro, his first engien was a compromise, in many ways. It was good deal but want really built for the use.
He, from what I read had a better suited design/matching of parts and now has a better car for it.
So would a properly tuned V12 work better in a dump truck, yes but it would be over kill and over engineering. A big low speed V8/V10 lumbering along works fine. try to patcha small block for heavy use and it wont live.
So saying one is better than another is a misnomer or in actuality WRONG. Each engine has it purpose.
Put a 305 BBC CanAm engine in place of a 502 and you might not even move the truck.
Its design of the package.
The hemi of 1950s has barely a resemblance to the Hemi in a Top fueler of today, but share history and maybe some basic design influences yet the Hemi started life as an industrial engine and thats a fact.
Why did it get hot rodded, because it was bigger, had heavierduty parts that would hold up to being beat on, remember a 331 Firedome was a very large engine at time, did have a very solid head design and made great torgue over a 265 or 283 SBC.
Torque accelerates you faster , horsepower just gives you speed.
Look at Bonneville land speed cars 1500 hp but very little low end torque and compromised gearing, thye cant even take off from standing start most times yet make ludicrous speed!
Now take tazzz and his engine build same light weight engine decrease the stroke to take bottom end edge off and it power to weight ratio might be more suited. too much of a good thing like torque CAN be a bad thing per application.
If it was say 505 with less stroke, would it suit his use more, maybe if its matched properly, would it be worth packing into my 3000lb Monza, nope. too much torque for chassis/driveline, put it into a car with more room for mods and tada a better package.
One engine design will fit a one car design better, but must be matched.
How is it LSx engines work so well, because a designers took 60+ years of ideas, new design technologies and new materials and made it a near perfect power plant, light, strong, powerful. BUT is it for ,say my car, nope I cant even afford to delve into LSx ignition.
Heck I am even working on something for SBC engine, well any engine actually , just for my project but would work on LSx too.
Because Iliek to design and swap and modify and make odd parts work.
Ever car I have built has almost always been a compromise of power,performance and money.
I have gotten cars to a point in every build, mainly because I work in automotive field and get to pick up some cool toys from tool truck, but just enough to get me one step closer to being able to build a quality car.
Oh and most of my stuff winds up off of someone scrap pile most times!
So. NEVER stick any one engine into the perfect box. Right now the LSx is top dog, 50 yrs ago the sbc was, and before that a Flat head Ford V8.
Give me or one of the others who noodle out power packages on this forum, a price application and frame you need it in, and most of us can make something extraordinary. Give me $1000 and and moderate weight car to drive and race and Ill got back to the same 355 design I bragged about from the old Monza, Give me $10,000 and I can do a pretty good sbc,bbc or LSx. Give me $100,000 and ill design the dog gone engien to fit if need be. Give me a $1,000,000 and I can build you a near car from ground up and make it look like what ever.

[Zachalanche]

Remember that torque HP and RPM are all related (HP = (torque*RPM)/5252). on the low end torque is easy to come by without having a lot of horspower (diesels are a good example of this) on the high end it takes an exponential amount of horsepower to maintain the same amount of torque (for example my yamaha R6 has to spin at 17,000 RPMs and makes 100+ HP just to make 40 ft*lbs of torque).

HP is a work rate and Torque is simply a force. A deisel truck can apply a massive amount of force to the ground which allows it to move a lot of mass but it lacks aceleration due to its inability to do a lot of work in a small amount of time. Conversely a streetbike cant move a lot of mass, but it can move a small amount of mass very quickly.

Ultimately it comes down to power to weight ratio. Heavier vehicles will require more foce to make them move, but thats not all, not only does it take a lot of force it takes a lot of work to keep that car accellerating if you want to accelerate a heavy car in a short amount of time it requires a very high work rate (HP) which is easier to come across at high RPMs. Thus torque is more useful (for going fast) if applied at high RPMs, but if you refer to the formula, that would require a lot of power.

Lots of torque at low RPMs requires less power. so, the extreme example here (if you limit power) is a car that does a nasty burnout because it is trying to apply too much force to the ground, but once it gets moving there is not enough HP to keep the torque up resulting in poor acceleration. yes gearing up would help optimize this setup, but would not make up for lack of necessary HP.

As with everything there are always compromises, but for performance Higher RPM operation is more desirable. And big displacement that can reliably run high RPMs - that would be having your cake and eating it too.

feel free to rip into me for missing any info or misstating anything. I have a hard time explaning this sometimes.

[79-TA]

. . . on the high end it takes an exponential amount of horsepower to maintain the same amount of torque (for example my yamaha R6 has to spin at 17,000 RPMs and makes 100+ HP just to make 40 ft*lbs of torque).

The relationship would be linear, not exponential. Constant torque with twice as much rpm would result in twice as much horsepower. Now, in a real situation, the torque curve begins to drop at high rpm, so the engine will have to spin much faster, which is what I think you were getting at.

[Charley Lillard]

I have a 66 Shelby GT350 vintage race car with a 289 making 480 hp that I can rev to 8000 with no problems. I have found that those extra rpms really come in handy when you are closing on someone right before a turn etc and upshifting would just screw everything up since you are about to be decelerating. It's just nice to have that little something extra.

[ratman67]

one of the car mags a few years back built a 406sbc and a 402 bbc ran em back to back in the came car at the same track, same day. the bbc always one and pulled a little more mph. look at the oppen road races like the the one the big red camaro ran, that 540 crushed everything in the field including all the high strung exotics. lol my 540 bbc make 800 ponies just like the big red camaro...but on pump gas. i look at mark stielows red devil build. he is running a cast iron block ls series motor then added a blower and all the other stuff needed to run the blower i bet my alum headed bbc weighs about what his sbc does with the blower and all the other stuff he had to add to run the blower, inter cooler, plumbing, etc.. i saw where he said he has to slip the clutch to hook it up in 1st gear and slip it some more at the 1-2 shift. he is making over 800 ft of tq at 3500 rpms, im making 680, i would be willing to bet i would out accelerate him as i think i can hook my power up without feathering the clutch as he does. i watched the grumpy jenkins tribute camaro run an autocross and he boiled the hides trying to get off the line with that 572 he is running 1/4 more stroke than my 540. i have seen several pro touring cars running turbos and they can't hook em up at 50 mph, and they are always out of control. i think around 700 foot lbs is the most you can hook up with a 335 rear tire. just my .02, rm

[Removed user as requested]

Thanks guys.

Being honest I still dont trully get the whole High vs Low RPM thing... it just doesnt seem to go into my head *argh*. I guess its because my brain is still saying "why make 600hp at 8000rpm when you can make it down at 4000rpm" (speed would be the same wouldnt it cause its 500hp????) and 6 gears to use to play with... I dont see how the SB would keep up.

Whether its high or low rpm, big or small block, I only plan to run 600-650HP with 650-700ft/lbs torque.

If BB can be gotten to have RPMs I know my heart is set on a Hemi 528 alloy block, heads, etc. But I got told that motor wont last long...

So If a built a small block 360 or something outputting 600hp... wild camshaft to do it (fuel economy out the door) reving its head off... that will last longer than a 528 thats sleeping at 3000rpm making 500+ ft/lbs up to 6000rpm...

Some reason something tells me the BB would be the winner and the more street friendly motor at the same time and probbably the economical version of the 2 (even though both are not economical). I dont want to run any power adders, whether big or small both will be made to make 600hp naturally aspirated. I also am not going to Auto-X this car. I will only run it at the Bathurst raceway course in Australia or Eastern Creek Raceway down in sydney as a circuit car (primarily street car).

O yeah, others suggested I put a v10 viper engine in charger as I get new technology, reliability, high power (more than Hemi they said - uhm... i doubt it) and RPMs. However... I hate the sound of the 10. I like v8s and why cant a v8 be made to make the power Im after 600-650 with reliability and gearing to get enough top speed to run with the best of them and probbably out accelerate them out of corners.

DUnno but my heads spinning.