Went to Test & Tune Day at the Drag Strip and have some questions?

My purpose was to get accurate HP readout as I always seem to dyno way below where I should be.

Made 4 passes. First two - experienced defueling off the line...could not control it..probably pushing to hard! Switched to 2 wheel drive with no power braking. Both were in the 90 MPH range with best at 95.41.

Track was 975', 90.4* OAT, 4 mph tailwind.

My question: Friend gave me a CD from TAG Racing Systems, in which it translates ET or MPH to HP, if you know your weight. I'm at 7450 lbs w/ me and full fuel, which is how I raced (didn't even remove 200 lb tool box in back). This cd says 7450 lb at 95.41 mph in quarter mile = 505 HP!
Is it that simple?
What about corrections for altitude, OAT temps, wind, etc.?
Can I trust the 505 hp?
RJ

 

Those programs are generally pretty accurate.....from what i have seen anyways!!

 

IMO those formulas read a little high for a diesel. They were developed emperically from gasser data (i.e. take a bunch of timeslips and try to make a formula match it), so they're not really accurate for our case. On my old '01 I dynoed several times in the 450-490 area, ran a 12.9 in the 1/4, and the formulas said 575ish on the power.

John

 

What horsepower are we talking? RWHP, BHP, Gross HP, NetHP?

 

use the et,not speed,,subtract about 20%,,and you`ll be getting closer to the actual number......drag slip times are hard to translate into hp numbers,ive dropped 3 tenths and not bought any parts,just tinkered with what i have......just my opinion..............bama

 

975 feet??thats not a quarter anyways,,

 

975' = Altitude of track.

Other than being an interested spectator, I'm pretty ignorant about drag racing. But Using ET's, seems to me, less useful in determining HP than top speed.
In theory I could sit on the line for several seconds and have slow ET but still have the speed & the HP! No?
RJ

 

Actually, no. You could sit at the line for as long as you wanted cause the timers don't start till you leave.

 

the programs are usually taking into account parasitic losses. meaning that it is essentially giving you your SAE net hp

 

Thanks to all!
Not all that hung up on exact HP...just wanted to know I am somewhere near where I would expect to be, based on bombs and other performance indicators. 450 - 500 hp feels about right!
For some reason have always dynoed 10%+/- low. Anyone else ever run into this?
RJ

 

What have you dynoed at?

 

Have not since adding Mach 2's.

Could be much worse...Could dyno well and be a tank to drive!
RJ

 

1/4 mile speed is an indicator or HP. This is why dragracers monitor there speed as a guage for tuning.

There are so many calculators out there and all of them are different. At one time I used about 8 - 10 online calculators and all of them were different. Problem in my eyes is we have huge torque numbers that really throw off the 1/8 mile numbers, but by the time we reach the end of the 1/4, starts to balance out due to poor aerodynamics. I don't think any of them are dead on but some are pretty decent.

I get 439.4 HP for your truck.

A good example, Penny ran a 13.89 in my truck at 98 mph. That calculates out to 441hp and my truck dyno's between 440 - 455 hp depending on the day. She later ran in 2wd and ran a 14.5 at the same speed.

Matt Stuckey dyno'd at the track 699.8, then went out and ran a 11.11 @ 122. That calculated out to 721.7.

Dyno #s are usually corrected. Your drag strip #'s are not. I use them both as tools for tuning.

Congrats on the nice run.

 

Very useful info!
RJ

 

Taken from an online HP Calculator

Horsepower Based On 1/4-Mile E.T.
Your dodge ram which weighs about 7450 pounds should complete the 1/4-Mile in about 14.73 seconds, if you can produce about 460.72 HP at the wheels, or about 598.93 HP at the flywheel.