Thread: Calculating Aprox WHP With Injectors

I think I have a way to calculate out your WHP depending on the injector duty cycle. It might not be 100% accurate but should give you a ball park number.

First find out whats your max WHP for your injectors, using this thread.


MAX WHP x Injector Duty Cycle % = Approx WHP


For example, I'm using my setup and what I saw yesterday after driving and using Nissan Data Scan to log.
250whp x 0.91 = 227.5 whp

Which sounds about right, I'm running 370CC injectors and did 230 whp on the dyno. Yesterday was a warmer day and I have some O2 sensor issues so it actually sounds about right.

If you know your max injector duty cycle and injector size there is a real formula to calculate (flywheel) horsepower. Too busy to look it up right now.

Deatschwerks

This sound about right?
Injector Selection Guide

Here's some dyno data for you, peak injector duty cycle and MAF vs whp:

When I dyno'd my turbo car:
71.7% peak injector duty cycle, 4.05v MAF
50lb MSD max 355 * .717 = 254hp

BORNGEARHEAD dyno'd 181whp same dyno, same day.
73.3% duty cycle, 4.38v MAF
370cc max 250 * .733 = 183.3hp

Same day, same dyno, my N/A car, 162.4whp
83.4% peak injector duty cycle, 4.52v MAF
259cc max 175 *.834 = 145.9hp

First two are close, my n/a car results don't make sense though. ???


I also have a spreadsheet that lists MAF volts vs hp for some MAFs.
S13 CA18DET, S13 SR20DET, S14/S15/GTIR SR20DET, Y32 VG30DET & Z32 VG30DETT

My turbo car peaked 4.05v on Z32 MAF on dyno.
The spreadsheet says 238hp, dyno said 246whp.

Not sure which MAF BORNGEARHEAD has, but using the S14 SR20DET MAF values,
the spreadsheet says 184.9hp for 4.38v, dyno said 183.3whp.
I thought he had a maxima MAF, but looks like the S14 SR20DET MAF
is very similar, volt vs hp.

A couple more points, not dyno results though.
My turbo car with O2 induction intake added since dyno.
4.25v MAF, 80% injector:
355 * .80 = 280whp. 4.25v MAF from spreadsheet = 276.6hp

4.27v MAF, 83% injector:
355 * .83 = 294.7whp. 4.27v MAF from spreadsheet = 280.7hp

Note - the scanner I'm using now only displays 2 digits, no decimals for
injector duty cycle, so not quite as accurate as the one I had for the dynos.

^ Is your name Justin? You have the white boosted B13 right?

Josh - w/white B13 turbo

Josh, that's pretty interesting info. So for Turbo it stays pretty close but NA it is a bit off right?

I think mine said 82-84% came out to 243hp. So I'm think it's pretty close. I'd say I'd dyno about 260.

Right! I think I've met you once...? Last fall when we had like 40 people down on east wash. But nvm nvm, I'm done threadjacking.