Limiting factor for RPMs?

[TC]

How about if you put some numbers on it? Do you know how to calculate the moment of inertia of a crankshaft?

Not off the top of my head.... But I could learn........

[The Outsider]

"My subject is racing engines, not street motors"

I guess if you're racing, then you have to do what it takes to win that class.

I'm with Bob, I can't afford high RPM

For most racers in classes with minimal rules (e.g. bracket racing), a cheap, relatively low-reving engine of modest displacement with a cheap, consistent, tractable power adder tends to yield the most "bang for the buck." Huge increases in size or r.p.m. in common 2-valve OHV engines tend to cost a lot.

In restricted classes, high r.p.m. is often necessary to win.

[Brian Lohnes]

Well, I guess I'm weird. I want the lowest "revving" engine that will get me to my goals.

I don't make enough money to want to rev the wee out of an engine.

Bob, I know you're a Ford man, but the fine engineers at General Motors agree with you. In discussions with the ALMS team mechanics today, they said that the little 336ci motor in the (hairy ass, freaking awesome) race Corvette makes peak HP at a measly 5,800RPM and peak torque at 4,500 RPM (or thereabouts...specific details weren't flying around like skittles as you can imagine).

The bore being, "a little over 4-inches" and the stroke being, "a little over 3-inches"

[Dynoroom]

The above reminds me of the multi-time LeMans winning Dodge Vipers. 6200 rpm max IIRC, 'course if was an endurance race.

[Bob Holmes]

Interesting, that's almost exactly the range I have on my turbo-4 endurance engine, I hit peak horsepower at exactly the same rpm. They must have read the same SAE paper on LeMans racing engines that I did. (Said firmly with tongue in check, LOL)

Anytime I hear that someone's goal is X boost, or X rpm, I figure they can't find their ass with either hand. Those are means to an end, not the end.

[BKBridges]

Not that Ive got the cash, but this thread started me looking for R5 parts on ebay. Lots of good stuff out there for lowish bucks,
at least when compared to new.

[TC]

We're just trying to figure out the moment of inertia of the crankshaft, first....

So we're talking about the moment when push goes to shove??, which I guess would be a degree of crankshaft rotation??..

[Dynoroom]

Not that Ive got the cash, but this thread started me looking for R5 parts on ebay. Lots of good stuff out there for lowish bucks,
at least when compared to new.

Yep, that's one reason we've got one between the frame rails of my race car.

By the way, El Mirage next weekend! Bring the Jensen

[Bob Holmes]

Reher-Morrison has a different view.......

http://www.rehermorrison.com/blog/?p=220

Nothing I said is inconsistent with their views.

[Bob Holmes]

For most racers in classes with minimal rules (e.g. bracket racing), a cheap, relatively low-reving engine of modest displacement with a cheap, consistent, tractable power adder tends to yield the most "bang for the buck." Huge increases in size or r.p.m. in common 2-valve OHV engines tend to cost a lot.

In restricted classes, high r.p.m. is often necessary to win.

Bingo.