Calculating HP at the crank

babbagandu

Im just curious about whether there is any reason why this method isn't accurate.


Let's say you do a baseline dyno and get 270 at the wheels. The crank hp that Nissan claims for the Z is 332. So that means the crankhp/whp ratio for your car is 332/270 = 1.23

Then after all your mods let's say you dyno at 310.

Would it then be accurate to assume your new crank hp is 310x1.23 = 381.3 ?

Rui Z

It would not be accurate, but it would be a good estimate.

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kromberg

Most manual transmission loose about 12% through drive train loss and automatics about 18% to 22% depending on the converter stall.

The type of dyno also plays a role. Mustang dynos have always reported 'lower' numbers then Dynojets because of the method it uses to calculate BHP.

SS_Firehawk

I think it would be a very good ballpark figure so long as the dyno runs were in similar conditions on the same dyno. Crunching the numbers (my baseline was 270 as well), the shop told me my car was putting down around 360-370 at the crank and it was in line with the calculation.

I kind of like this guesstimate method because it takes out dyno queen and heart breaker numbers and illustrates a more accurate representation.

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Spikuh

I would think as long as the 332 number from Nissan is pretty accurate for all the engines across the board, then backing into crank hp this way should be fairly accurate. This is of course assuming you do not change dynos, weather conditions are the same/similar, etc. If you swap to a different dyno, then this method will not work at all.

LafitteZ

yea nissan is getting an average number, probably inflating it a tad and throwing it out there. The best way to tell is on a stock manual is about 12 to 15 percent drivetrain loss. Now wheels, tires, pulleys etc make it change thats why only car manufactures use that number because your average joe will never truly know unless they pull the engine and put it on an engine dyno which I dont think I know one person whos done that.

Dwnshift

Just from what we have seen in our program....the hp loss through the Z's drivetrain is on t higher end.

Jordo!

Going by (SAE corrected) dynojet numbers, which have very little variance from shop to shop, and data I've acquired from half a dozen VQ37HR's...

***Dynojet derived whp and drivetrain loss***

Average power for 370Z or G37: 273 +/-5

Average power for Nismo version: 290 +/-5

Drive train losses for both AT and MT appear to be between 16.5% and 17.5%

So... if you want to get a good (SAE corrected, dnyojet based) estimate, take what your car puts down (on a dynojet) and divide by either .835 or .825.

So, if you make 300 whp on a dynojet with SAE correction, it makes (probably) somewhere around 359 - 363 bhp.

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Dwnshift

Bingo