okay so just curious can it be done? i realize before anything else said i would think it would be fairly inaccurate and used only as a guide to flywheel hp. anyways i figured assuming your air/fuel is reasonable is their a direct relation between fuel used and power, with say a certain volumetric effeciency? anyways outta money to have the car dynoed but have access to motis scanners and can watch my injector duty. anyways im still on stock 24lb injectors and i was just wondering if i could get close on hp based on what rpm my injectors are at 100% duty cycle. assuming they get there. thanks for the help.

 

This is highly accurate.

 

The only way it could be accurate is if you knew the true AFR.

I know for b-bodies the MAF GPS ends up being fairly close to RWHP, a lighter drivetrain f-body or an M6 car would be higher than the MAF readings due to lesser parasitic lose through the drivetrain. Again though this will require the tuning to at least be close.

 

what is the maf gps? can i read those values off a typical scanner that can data log? how would those values be related to hp. thanks

 

Grams per second.

 

Mass Air Flow sensor readings, yes they are readable with logging or scanning equipment.

How much air an engine moves is the limit to the power it can produce, giving it adequate fuel is comparatively easy so airflow measurements can be a good indicator.

 

okay so now that i know it CAN be done, the question is how. if i just had some equations im sure i could work my way around them. if anyone has a link to this type of information or anymore advice on a method to do such a thing itd be great.

 

I've heard that if you take your GPS and multiply that times 1.1 that gives you an estimate of rwhp.

 

anyone else heard of this? anyother formulas.
*woah i just noticed your from newton. i work about 25 miles from there in Marion.

 

Yeah i'm also friends with Brad Perkins the guy that helped diagnose your car.

 

I once created a program that took an autotap log and gave HP/Torque measurements. The main assumption that has to be made is the BSFC and that can vary wildly based on FI, N/A etc

I'll see if I can dig it up.

 

We have always used the 1.1 from the MAF reading and been really close!

 

IIRC, 1.233 is the derived constant I found for my ATI FI LT1. Obviously things like timing, poor calibration ,overlap etc are not accounted for but it is a good guesstimate. If you have a different targer A/F then the constant will be off

 

sweet so it seems like i can atleast get close with multiplying it by 1.1. this is on the engine in my sig which has a mail order tune, so hopefully itd be close. im really interested to get it on a scanner now!

 

If the car is tuned fairly close you can assume a BSFC of .5 and get it close. Forced induction pump gas cars will likely be closer to .6 . An example

(24lb/hr injectors*90%duty cycle)/.5 BSFC= 43hp per cylinder

This would give ~345 flywheel hp.

Is this close to what you guys see? (I haven't looked at a n/a datalog in a LONG time). It works almost dead nuts on my 4 banger mustang, in it I see:
(52 *.9)/.6=78hp per cylinder, or 312 flywheel hp.

Assuming 15% driveline loss, this would be 265 rwhp.
At the megasquirt dyno day, with pig-rich A/f and crap timing I put down 250. Since then I have added 3 degrees of total timing, and lean it out about 5% MORE. So it should be very close to 265, if not more.