WHP comparisons

Scoobieguy70 · Jan 4, 2016

Pardon my ignorance up front, but I'm not a tech guy. I own a 2015 WRX and live in Calgary, AB at 3,500 feet above sea level. I had my car tuned on Husky94 gas and now have 251 WHP as per Dyno. Stock on 94 octane my car put down 225 WHP, so I gained 26 WHP from the tune. Now I have two questions:

What is my crank HP? A stock WRX on 91 octane has 268HP. I ASSUME 26 WHP is closer to 30 at the crank with about 20 percent drive train loss based on the math, which would mean my car is around 300 crank HP 268 plus 30 after the tune.

My confusion.... a stock 2015 STI on the exact same Dyno here in Calgary put down 231 WHP with 94 octane gas. MY car has 20 more WHP tHan a stock 2015 STI after the stage 1 tune on 94 octane. Since an STI has 305hp at tHe crank, I was curious to know what my crank HP would be. I know there are things that would account for discrepancies, however, it seems odd on the math side that I would have 20 more WHP than a 2015 STI which has 305 crank HP.

Thanks

Darren

EJ257 · Jan 4, 2016

Closest estimate would be a standard algebra equation...
Stock Engine Power / Tuned Engine Power = Stock Wheel Power / Tuned Wheel Power

268 / X = 225 / 251

X = 298.97

Scoobieguy70 · Jan 5, 2016

Thanks for the info.. That makes sense for what I thought my approximate hp would be. What I still don't understand is I thought WHP was the true comparison element between cars as real power. My 2015 WRX has 251 WHP and a 2015 stock STI on the same Dyno has 231, yet is rated at 305 at the crank. So after the tune, I have 20 more WHP than the STI, but 5 less at the crank approx?

Scoobieguy70 · Jan 5, 2016

Thanks for response. It just seemed very odd given the STI was done on the exact same Dyno, same day and city as mine...

zax · Jan 5, 2016

There are a lot of reasons for discrepancies which none of us can claim with complete certainty.

1. STI has more drivetrain loss -- Ever wonder why the 2014 WRX has about 15% better fuel economy than an equivalent STI? Hint: the wing is only a small fraction of the difference.
2. Stock cars aren't created equal. Even in the event of a perfect dyno (which is calibrated to read a TRUE number) operating in PRECISELY the same conditions with the SAME operator, and SAME CF... I'm sure you'll find 10% variance between upper and lower bounds among completely stock cars.
3. The rest of the factors above that are NOT perfect will result in different readings.

It's best not to compare numbers directly. If you want to compare, take both to the drag strip, complete a statistically significant number of runs (complete with R&R study) and THEN compare.

WHP comparisons

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