high rpm engines

[Duckhnter83]

Why do people build these motors for nods and the like to run such high rpms? Wouldn't you rather spin lower rpm with the same HP /torque? I'm just asking for my knowledge.

[perfconn]

What do you consider high rpm?

[Duckhnter83]

I was talking to a guy who builds motors for several a mods and he was saying they are always wanting more rpm out of there motors. So that had me thinking why. If I can build a motor with same HP with less rpm what's the advantage

[sj valley dave]

In a general sense higher HP engines will be higher RPM engines. The cam shafts and cylinder heads that make big HP depend on a lot of RPM. Big ports and cam lobes won't work at 6,500 rpm for the most part. I know that this is a simple answer to a more complex question, but that is the basic answer...

[Krooser]

Big blocks can make big power @ lower RPM's but they are outlawed in most places. I guess the option of letting some guys run an extra 150# of front end weight is intimidating to some guys...

[perfconn]

Because someone else wants to do it doesn't mean you have to.What rpm an engine needs depends on the combination.For instance if the rules require a 23* head and you build a 415ci and try to turn it 9000 rpm then youwill never win.Several reasons why.First of all there is not a 23* head on the market that will flow enough to feed that ci at that rpm.Second,you will be missing a lot of races because your engine is blown up.
OK, so you insist on turning 9000 rpm with a 23* head.Then that means you got to build a smaller engine.Now you get into the discussion of which will run best,a small ci at 9000 rpm or a large ci at 7800.It can never be answered in black and white.Some drivers have good enough throttle control to drive a large motor on 8 inch tires and some don't.
I had a driver win back to back championships in SRRS late models with one of my big bore short stroke 362ci Southern All Star SPEC engines.He raced every weekend against 430ci all aluminum 13*-18* engines.How did he do it? It wasn't by turning 9200rpm.It was because he was a hellova driver and never turned the engine over 8100.

[QQQQ]

if the rules require a 23* head and you build a 415ci and try to turn it 9000 rpm then youwill never win.Several reasons why.First of all there is not a 23* head on the market that will flow enough to feed that ci at that rpm.Second,you will be missing a lot of races because your engine is blown up.

I'm sure the guys at Mullins Race Engines would not agree with that!

[perfconn]

Mullins isn't the only engine builder that has ever won races.

[LateModel B23]

Chad Mullins builds some good motors, alot of them USMTS/USRA spec head motors. They have to run a 8000 chip and are also choked by the spec head.

[Krooser]

Engine builders and parts retailers are the racers worst enemies… they just love to pick our pockets.

[perfconn]

I rate racers as being their own worst enemy.If an engine builder tells you he will build you a 23*- 415ci that you need to race at 9000rpm then its not him making you go broke for listening to him.Sure Nascar does it but not with 23* heads and not on a weekly racers budget.

[Krooser]

We are pretty much in agreement.

I don't hate the engine shops… nobody puts a gun to an owners head forcing him to buy. But the prices on so many of these engines is out of sight… but not all shops are expensive.

My son and I just picked up his b-mod engine… I had a tough time trying to get my motor guy to install lighter pistons, low tension rings, etc. Ultimately he won… he's old school and has winning engines running good, but less expensive, stuff. I guess you can't argue with what works. I did supply the cam/lifters… he voted for off the shelf stuff but I got a custom ground number. All in… long block, carb/adaptor, oil pan and other bolt ons we were $1800.00 cheaper than the 'big shop' down the road. And $2500.00 less than the 'brand name' out of town guys.

We'll see how this deal works out...

[let-r-eat]

>rpm requires < operating rpm window.

[speedbuggy]

Curious why nobody mentions that the rear gear also comes into play here. More rpm enables use of more gear which means more torque multiplication to the rear wheels. Which would accelerate harder...a car with a 5.43 rear gear or a car with a 6.50?

As let-r-eat says above, for this to work, your usable power band has to be wider with more gear though. Engine still has to be pulling from turn exit to the time you let off on entry. If the motor noses over at the flagstand, more gear/rpm might not be faster.

[perfconn]

But the answer for more power is not more rpm.You have to turn the rpm the engine is designed to make power at.The contact patch on the tire will only take so much power before it starts to slip and you spin the tires.If you get passed at the flagstand the answer is not more rpm or necessarily more power.If you can't get through the corner you will get passed on the straights by a better handling car that may have less power.

[avenger1]

Higher rpm cars are easier to stay hooked up, you don't see any USMTS cars turning low rpms

[let-r-eat]

I agree with avenger1 to a certain degree but it makes everything else more critical. A piss poor driver getting the thing out of the rpm window is death as is ill handling, bobbling, etc. Stop at a red light and let someone roll through at 10 mph and try to catch him............He will make you look like your setting on jackstands. LOLCorner speed is critical to overall performance as perfconn mentioned.

[Krooser]

All I know is building a good 9,000 RPM motor costs a hell of a lot more than I can afford.

[Brian Gray]

Its more about power curves and control. Way back when we could turn them up our NASCAR program required the higher rpm to produce the power we wanted through a specific rpm range with the small ci your allowed. Now days its more about keeping the power at your foot. Most engine builders right now are forced by drivers to keep the power available and with what we have to work with it requires the rpm to be up all the time. That's why I believe the sb2 is becoming so popular again. We hated having to carry that extra weight but the drivability factor is starting to outweigh The downside. The thing to know is every engine has a power range knowing what that is and applying that knowledge will help your driver use its available power. Big HP and rpm won't Chang your program if your driver is a poor traction manager.

[Brian Gray]

To answer the last question if we could get the same power curve at a lower rpm I do think we would opt for less rpm. But that's not the case right now. Yes you can get the numbers but the rpm ranges aren't there yet.