r9559

What is the formula to fiqure out HP @ sea level?

Thanks

Bullydawg

iTrader: (7)

The Dyno never Lies!

r9559

My engine ran 358hp on the engine ( Sun chassis Dyno) but runs 14.8's on a gtech. (25 degree temp @ 2500ft with 3650lbs vehicle)

five7kid

iTrader: (14)

358 HP on an engine dyno, can we assume corrected to sea level?

NHRA has correction factors for ET & MPH, but not density altitude correction. http://www.nhra.com/tech_specs/altitude.html They call it "altitude", wish they'd call it elevation. Use the "Stock/Super Stock" chart. You'll have to use somebody's HP calculations from there.

r9559

Dyno was at 2500ft on a MAHA 500 HP Chassis Dyno

ecm.programmer.com

five7kid

iTrader: (14)

But did the dyno print-out give you a local as-tested/where tested HP number, or a corrected-to-sea-level number?

Wait, this was a chassis dyno? If you were given an engine HP #, it's highly suspect.

1989GTATransAm

iTrader: (3)

There are formulas on the internet. I found a couple with a Google search. You will need to know the barometric pressure, temperature and humidity the time the dyno pull was made.

AlkyIROC

Depends what hp number you're starting with. A dyno already give you a corrected HP number. Calculating HP based on 1/4 mile MPH you use this formula. The first part is a simple common formula to calculate just how much HP it takes to move a weight to a specific MPH in 1320 feet. Don't use ET because it gets affected by to many other factors. If a car is set up properly and there's good traction, ET and MPH calculations should be very close.

Altitude Corrected HP = (race weight x (1/4 mile mph/234)^3) x Dyno Correction Formula

The dyno correction formula is the hard one. You need to know the Station press, Vapor Pressure, and air temperature.

Station pressure is the actual uncorrected air pressure taken from a barometer or altimeter. The barometric pressure given in weather forecasts is altitude corrected and won't work. Air temp from a thermometer in Celsius. Vapor Pressure is calculated. The formula for calculating due point from the local weather conditions is longer than what I want to type but can be calculated if you also know the humidity.

VP = (6.11 x 10^(7.5 x Due point/(237.7 + Due point))/10) x 0.2953

DCF = (1.18 x ((29.235/(SP-VP)) x (TempC + 273)/298)^0.5)-0.18)

Clear as mud? How about calculating Density Altitude?
http://www.hardtail.com/techtips/weather.html

These are some of the formulas I use to do my ET predictions. Once I know the corrected HP for the day, I can track how much faster or slower the car should run as the weather conditions change. Of course many things can affect the ET but the number I get is what the car "should" run and theoretically unless some weird thing happens, I should never run quicker than the predicted number.

r9559

Thanks for the info, never thought it would be so confusing

IHI

iTrader: (1)

engine dyno's are notorious for bogus info based on shop it's in, some guys have their parameters for solid real world numbers, while others have their programmed to be very optimistic...just the way it is, and kind of funny when one guys dyno showed 950hp and the car actually runs 900hp numbers, so on and so forth.

Chasis dyno's and automatics...nother joke, take all those numbers with a grain of salt since the convertor messes readings up...my 388 in the sig below, supposedly when adding 20% back to areadings to compensate for drivetrain loss, that motor made 793ftlbs of tq LMFAO!!!!

Dyno's are nothing but a tuning aid, take all the supposeded hp/tq numbers with a grain of salt until you actually run the car down the track and get true life hp numbers.