I like the rod to stroke ratio for that rpm requirement, 1.72 is solid.
Quote:
Originally Posted by syborg tt
Just curious what is more important on a race / track car. Horsepower or Torque ???
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throw in my .02, worth maybe a penny... and specific to road racing, not drag racing.
keep in mind that HP is a multiplied number with torque the basis of the math and a multiplier of 5252, so it is basically a math measurement - dynos measure torque and then do math to quote a HP number and this is also why HP
always equals torque at 5252 rpm.
HP = Torque x RPM ÷ 5252
Keeping that in mind, you want the most torque you can get
in the power band that you are going to use which tends to start looking like HP since race cars operate at high rpm. So while the torque seems low in an F1 car, the HP is huge because it is multiplied by such a high rpm value - that said, that is the powerband they want to use to get the most overall power out of that engine combo so they are technically maximizing the engine for max torque
in that powerband.
The way I have always tried to do it is have the car make max torque near the bottom of my rpm range -500rpm and max HP at the top rpm. So if I am going to shift at 8500rpm and my rpm drop is 1500 rpm with a race trans, I would want max torque around 6500 rpm with the torque curve as flat as possible up to 8500 rpm with the max HP around 8500. You don't want it to be too peaky of course as there will be turns where it is better to go below the band and "lug" out of the turn than shift and 1 second later shift again.
Point = while a slightly smaller cam might make a higher torque number at 6000 rpm than the bigger cam at 7000 rpm, may be even flat as hell from 4500-6500, and appear to only rob a little HP at 8000-8500 rpm, it does absolutely nothing for me on a road course because I will rarely use the power below 6500 rpm, maybe that one turn that it is easier to lug the engine than to downshift only to upshift a second later.
So, as an example, my current engine combo for my road race car - I wanted to use a tappet cam for longevity which limits the rpm a fair amount, which then adds to component longevity with springs, rods, so forth as higher rpm is higher loads on these parts. I have 7 years on this engine with zero rebuilding and it is just now starting to use oil and puff a little smoke, so I have gotten a lot out of it
Max torque = 5000 rpm with max HP at 7100 rpm. That is a 2100 rpm band. I had a 1500-1700 rpm drop on my shifts, so at 7100 rpm I would drop to 5400-5600 rpm which is peak torque + 500. If I felt like lugging a turn down to 4500 rpm I would, but I don't optimize for that. I could run out to 7500 rpm with no issues if it was required to run deep into a turn, but generally I shifted around 7K and dropped to around 5500 rpm.
That all goes out the window if you demand 2500 rpm drops of the trans, which then requires a much broader powerband from 5500-8500, but a spread that wide on shifts is a bad idea for a number of reasons, not just powerband.
Brian Hobaugh SCCA National Tour June 2014
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