99 Trans Am

It was in GMHTP several months ago. The formula for finding out horsepower from your weight and 1/4-mile time, or something like that. I need it for physics today. Thanks!

Rob98Z

here ya go <img src="images/icons/wink.gif" border="0">

hp = weight / (ET / 5.825)3

You can also do it using speed

hp = weight * (speed / 234)3

[ November 14, 2001: Message edited by: Rob98Z ]</p>

2quick4u

Guys, these formulas that determine peak Hp from 1/4 mile times are empirical relationships. That is they are derived from test data and are not derived from physical laws or relationships. As such there are MANY formulas for this and each is accurate for only a small range of HP and ET. The best you can do theoritcally using the laws of physics is to determine an average Hp expended over the length of the 1/4 mile. From there you have to use empirical relationships to convert average hp to a peak hp. Really though, peak hp is unimportant. Average hp over the 1/4 mile is the important number.

Bettering your ET at the track revolves around increasing your average hp production put to the ground over the 1/4 mile. You can increase your average, and reduce your ET, without ever increasing your peak Hp. The easiest way to do this is gear your car, add a high stall converter, and/or adjust the shiftpoints so that your engine spends more time in the rev range that produces near peak hp levels. Because of this, for a quick street car in the 1/4 mile it is more important to have a fairly broad and flat hp plateau than a sharp peak. If you run the car all the way down the track in this hp plateau rpm region then you will produce the most average hp and get a quicker ET than an engine with a peaky hp curve with a sharp dropoff even though that engine might produce more peak hp.

One formula that I derived to compute average flywheel hp from 1/4 mile times is:

Av. fwhp = (wt x V)/9.1(ET)^2

and for peak fwhp:

Peak fwhp = (wt x V)/7(ET)^2

An important thing to remember when using these formulas is, since you can only accurately determine an average hp, the emirically deriven peak hp number can be way off if you have a car that has a high stall converter or a N2O shot. Why? Because a converter flashes off the line and gives extremely high torque to the ground for a very short period. This helps to accelerate the car quickly, but is not representative of engine power output since this momentary torque mulitiplication is caused by the converter and not the engine. This is why A4 cars with high stall converters run so damn well with so little peak engine hp.

Same with nitrous. When it first comes on there is a huge momentary torque spike that is not representative of a peak hp number that would show up on a dyno pull.

[ November 14, 2001: Message edited by: 2quick4u ]</p>

Crazyquik

Horsepower = torque x rpm divided by 5250 <img src="images/icons/wink.gif" border="0">

J.

RyanJ

theres lots of cool forulas like that one here: http://www.prestage.com/carmath

2quick4u

ttt

DriveATransAm

alright! I have 386.98 hp!

hmmm, is that at the crank <img src="images/icons/grin.gif" border="0">

Toxic Texan

If you know your RWHP you can use these to find out engine HP
M6
RWHP/.88
A4
RWHP/.82

Hope that helps! <img src="images/icons/grin.gif" border="0">

Crazyquik

I used one of those mph-hp calculators and it told me 315 rwhp, I dynoed at 312....

JaSSon00

it takes 1 hp to raise a 550 lb weight up 1 foot in 1 second, so to measure u need to know force (in lbs) and velocity (in feet per second).

Force= Mass X Acceleration

This is how dynojet determines it.

2quick4u

[quote]Originally posted by DriveATransAm:
<strong>alright! I have 386.98 hp!

hmmm, is that at the crank <img src="images/icons/grin.gif" border="0"> </strong><hr></blockquote>

If you used one of the formulas on this page, yes, that is crank or flywheel horsepower.

TrahnZam WS6

:waits for ChrisB to post:

<img src="images/icons/grin.gif" border="0">

McRat

Horsepower is calculated by one NIST (National Institute of Standards and Technology) standard horse.

Horses from all over the country compete in the Miss USA Mare pageant to vie for this honor. The Lucky Winner tours all the Dyno shops in the USA to help calibrate their equipment.

Sorry... Hadta do it...

2quick4u

Here are two more equations I have used that seem to be pretty accurate:

Net FWHP = (.0043 x V)^3 x Wt

(.0043 x 115.19 mph)^3 x 3,450 lbs = 419 hp

Best possible ET = 176/V x (Wt)^.25

176/115.19 mph x (3450 lbs)^.25 = 11.71 sec.

Check out my best ET in sig. <img src="images/icons/smile.gif" border="0">