How do we get to HP = weight / (ET / 5.825)^3 - Team Camaro Tech
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post #1 of 9 (permalink) Old Sep 11th, 02, 08:24 AM Thread Starter
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HP = weight / (ET / 5.825)^3

I've looked and can't seem to find a derivation of this calculation? I know work is force*distance and power is a time rate of work... and 550 (ft*lb)/sec = 1HP. What am I missing? Point me in the right direction. I thought I could just do the weight of the car times 1320' divide by ET and convert to HP by dividing by 550....

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1968 Coupe, 327/210hp project in process. PS/PB, Factory AC, adding camelhumps and a cam
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post #2 of 9 (permalink) Old Sep 11th, 02, 03:14 PM
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Not related but I was looking for a HP calculator and found this... it relates to using NOS and jet sizes. http://www.robietherobot.com/NitrousJetCalculator.htm

Does this help? http://www.revsearch.com/dynamometer...orsepower.html


[This message has been edited by HwyStarJoe (edited 09-11-2002).]
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post #3 of 9 (permalink) Old Sep 11th, 02, 06:14 PM
 
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This site has multiple calculators. http://users.erols.com/srweiss/#jcalc then click on to the interactive javascript calculators on the left side of the main page. Ronnie

[This message has been edited by JUNKPIECE200 (edited 09-11-2002).]
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post #4 of 9 (permalink) Old Sep 11th, 02, 08:56 PM Thread Starter
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I'VE SEEN A THOUSAND ON-LINE CALCULATORS!!!
I need to know the real math behind them! I need engineers and mathematicians!


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1968 Coupe, 327/210hp project in process. PS/PB, Factory AC, adding camelhumps and a cam
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post #5 of 9 (permalink) Old Sep 12th, 02, 04:39 AM
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There are other factors involved, also. How much energy is stored in the rotating mass prior to the coupling of the engine to the driveline? How much is the rolling friction? How about the aerodynamics of the car?
If you go to the smokemup.com or prestage.com calculators and calculate the power of a 3100# car that runs 11.12 in the quarter, you get estimates of 450+ rwhp and 500+ fwhp. If you go to http://www.motortecmag.com/archives/...JUN010201.html you'll find a 3100# car that runs 11.12 with 404 dynoed flywheel horsepower.
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post #6 of 9 (permalink) Old Sep 12th, 02, 04:43 AM Thread Starter
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Yeah... that's only because they might be using different equations. Does anyone know if the above equation is from experimental data only?

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1968 Coupe, 327/210hp project in process. PS/PB, Factory AC, adding camelhumps and a cam
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post #7 of 9 (permalink) Old Sep 12th, 02, 06:13 AM
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There are plenty of variables used to calculate HP.

Some of those are frontal area, accelleration, because its not constant, coefficient of friction between the tires and pavement, air friction, humidity, dry & wet bulb temperature, altitude, atmoshere pressure, heat losses from the engine, mass, weight, convertor slippage, cam specs, co;umetric efficiency of the engine, and all the other items mentioned earlier by others here. As you can see, it is an involved calculation.

However, there is an out. I use the formula to calculate HP using the car's speed through the traps at the top end of a 1/4 mile track, i.e., speed lights.

The formula is as follows: HP = weight times the quantity cubed 0.00426 times MPH, HP=weight X (.00426XMPH)^3. This formula is supposedly accurate to +/-5%.

You need to know MPH as HP makes MPH, Torque makes ET.

Just my two cents worth....I'm sure others will have comments, I could be wrong, ask my wife.....



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post #8 of 9 (permalink) Old Sep 12th, 02, 08:15 AM
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<BLOCKQUOTE>quote:</font><HR>Originally posted by JIM68:
I'VE SEEN A THOUSAND ON-LINE CALCULATORS!!!
I need to know the real math behind them! I need engineers and mathematicians!
<HR></BLOCKQUOTE>
<A HREF="http://www.amazon.com/exec/obidos/tg/detail/-/1557880204/qid=1031854432/sr=1-1/ref=sr_1_1/103-3138713-8605443?v=glance&s=books" TARGET=_blank>
http://www.amazon.com/exec/obidos/tg/detail/-/1557880204/qid=1031854432/sr=1-1/ref=sr_1_1/103-3138713-8605443?v=glance&s=books[/url]
http://www.amazon.com/exec/obidos/tg/detail/-/07 60306966/qid=1031854432/sr=1-2/ref=sr_1_2/103-3138713-8605443?v=glance&s=books

I have a book also, but apparently my son borrowed it and never brought it back...

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David
Camaro - '68 327 Coupe, '86 Z-28 IROC 305 TPI
Corvette - '73 Mako Shark II, '82 Cross-fire, '01 Coupe

[This message has been edited by djunod (edited 09-12-2002).]
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post #9 of 9 (permalink) Old Sep 13th, 02, 05:32 PM
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Jim68, how could et have anything to do with calculating hp? What if the tires are smoking all the way down the track? I think et has to do with how well the car uses the available hp, i.e. friction, wind resistance etcetera. I would say that the formula you quoted is an empirical formula that someone derived by using lots of data given to them.

Gary

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