Hp question

[efnfast]

So Chevy advertised my my90 as 375 hp. Is that flywheel hp or rear wheel hp? Mine dynoed at 311.

[efnfast]

So my math says about 357 flywheel hp. Acceptable?

[XfireZ51]

Originally Posted by efnfast

So my math says about 357 flywheel hp. Acceptable?

311/.85 = 366chp. Car is 20+ years old along w not knowing what has transpired or the state of tune the motor is in. Finally, you have the variability of dynos.

[efnfast]

Thanks guys. Xfire, I like your math better. I did 311 X 1.15 to get my 15% loss. 366 sounds pretty good. Now if I can just squeez another buck and half out of it.

Steve

[mike100]

My guess (which I mentioned on your other thread) was that you are losing 10-15 hp from exhaust restriction (your catalysts might be partially plugged)- or maybe from your intake boot collapsing. What rpm was your peak hp at?

There is always the possibility of loss from mileage, but I don't recall what you said about the condition of your car or the compression on the engine etc...

I'm sure different dynos will vary 10 hp or so. I've heard you will get a different number in 3rd and a higher reading in 4th gear. Certainly if you are at a higher elevation, that could also explain a few percent loss...like about 3% per 1000ft elevation.

[efnfast]

Mike, new exhaust is pending. Can't wait.
Peak hp at about 6k. Hood was open, never bothered to check the boot.
Car has 39,000 miles.
Dyno'd in 4th gear.
I would expect elevation around 750'.
This all started 'cause I stopped to look at a Vette and the sales guys said all hp since 75 or so is advertised as RWHP.
I'm happy.

[A1990]

Originally Posted by efnfast

Mike, new exhaust is pending. Can't wait.
Peak hp at about 6k. Hood was open, never bothered to check the boot.
Car has 39,000 miles.
Dyno'd in 4th gear.
I would expect elevation around 750'.
This all started 'cause I stopped to look at a Vette and the sales guys said all hp since 75 or so is advertised as RWHP.
I'm happy.

He was thinking Gross HP vs Net HP. after 1971, the engines had to have the accessories installed before the dyno pulls.

[mike100]

well 2% loss (about 700 ft elevation) is about 367hp (from 375hp) at standard elevation and temps. of course the temp and atm pressure are usually measured and corrected on the dyno calc. There might be a correction number on the dyno plot.

[efnfast]

Correction number was .96 as I remember. To convert to SAE.
He mentioned NH correction numbers are usually low.

[A1990]

SAE is corrected, whereas STD is uncorrected.