Process Driveline Loss Assumptions

[DavidM]

I wasn't aware that rear wheel or front wheel hp even figured into the process. As far as I knew it was based on a IT gain and target hp/weight for the class. I've never even heard wheel results come into it. Just basing this on my involvement with the ITR discussions.

The 240SX as well as I believe the CRX and Integra in ITA were weighted based upon reported wheel HP numbers during the grand re-weighting.

HOWEVER, having RWD at 18% instead of 15% is actually an advantage when back-calculating for the purposes of the "what we know" adjusters. Example: assuming your 1.8L Miata puts out 130 whp on a Dynapack; if we were to assume 15% then we'd back-calc that to an assumed 152.9 crank hp (130 divided by 0.85). However, if we assumed 18% instead then we'd back-calc that 130 to 158.5 crank hp (130 divided by 0.82) and adjust your process weight accordingly higher.

So, regardless of the 15/18% thing is accurate or not, using 18% instead of 15% for your RWD is yet ANOTHER advantage for you...so, honestly, I'm not clear as to what your concern is (from a personal level).

I think I'm missing something. Using the 18% results in a higher back-calc'ed HP and thus a higher weight. Using 15% results in a lower HP number and weight. How is more weight an advantage?

Edit: Greg clarified himself already.

David

 

[tnord]

Scratch that whole paragraph from above; I'm even confusing myself here...

18% is actually a DISADVANTAGE within the IT process for RWD. What you (Travis, and all other RWD'ers) want is to have everyone at 15%, that way when ACTUAL whp is back-calculated to chp, the numbers - and thus the percentage above Process - come out lower.

Example: 140 stock crank hp (chp) car. Standard process says the car "should" get 140*1.25 = 175 chp after IT mods. Car is dyno'd on a Dynapack; actual measured whp is 150.

Using 15%, calculated chp is 150/0.85= 176.5 = 100.8% of process = no "what we know" adder.

Using 18%, calculated chp is 150/0.82 = 183 = 104.5% of process = +5% "what we know" adder.

So, is there actually a difference in drivetrain losses between FWD and RWD? If so, as that percentage-number-used grows the disadvantage (in terms of The Process) for RWD'ers grows. On the other hand, if there truly is a larger disparity than what we're actually using (spnkzss mentions 15/20% for drag racing, another number I've heard tossed around) then the larger the actual disadvantage for FWD cars.

I'll toss in the simplicity bone and contend that there is no significant difference in drivetrain loss between FWD and RWD, and thus 15% should be used for all cars in IT.

Did I get it right this time...? - GA

i was going to correct you.....but i'm trying to get work done.

yes, i think you've got it this time. i'd bet donuts to dollars that the 15/20 numbers are no more of an actual calculation with legitmate math and reasoning behind it than the 15/18 POOMA number.

the problem here is that very small discrepancies in our estimates and "data" (3% driveline loss difference, 5whp) result in very real and significant changes to the minimum weight (100lbs).

i don't like it, and i'm afraid these beliefs rooted in just about nothing but time will point the ITAC to a conclusion at the detriment to any RWD car somebody feels needs a second look.