View Full Version : Formula to figure out HP?
09-07-2001, 08:07 PM
I have a question that I am pretty desperate for an answer for. I know there is a mathematical formula to test hp off your MPH off of your traps in the 1/4. Does anyone have this formula? If so could you PLEASE post it?? I really want to know my hp.
09-08-2001, 08:23 AM
The formula for horsepower by using you 1/4 mile times is:
X= Multiply by
SPEED (X ) ACCELERATION (X) WEIGHT OF VEHICLE
WEIGHT OF VEHICLE (X) ACCELERATION AND VELOCITY
Hope this helps.
09-08-2001, 11:50 AM
well yes and no. How do I get my acceleration? Then I can solve it. But thanks!
09-08-2001, 05:53 PM
I got the formula from the G-Tech website. They use the G forces for the acceleration. I guess???? I would buy a G-Tech and let it do the math if I had the extra 140 dollars. It is accurate within 1 horsepower. This is a pretty reliable margin. I got to the G-tech website by going under Google and searching from there. Type in key word "G-Tech".
09-09-2001, 12:48 PM
Guess again my friend,
For all you reading this the Gtech is the worst product I ever bought for my car!!!!!
I purchased a GTech Pro to basically do the math for me and count my HP. I ran 16.7 seconds at 83 mph in my 4 cylinder car with a K&N drop in filter and custom dual exhaust with Cherry Bomb Vortex mufflers. In the meantime I have added a Weapon R Dragon Intake but NOT have had the chance to take it back to the track to test it out again.
My friend has a 1996 Saturn SL2 that runs mid 17sec on a good day and high 18's on a bad day. The last time at the track I took him byt EXACTLY 2 seconds in the 1/4. I always race my buddy and always win. (This is important to know for the next section of this post).
The Gtech was hooked up (YES properly) to my Grand Am and tested for HP count. THe highest number I have ever achieved was 116hp. My car has a 155hp stock!!!!
My friend with the Saturn hit 126 WITH ME IN THE CAR WITH HIM. I was alone when I ran the GTech. His power to weight ration is 144lbs=12 hp. So we calculated his saturn to have approx. 138hp. Which is not bad he has exhaust and Intake upgrades and stock has 124hp.
SO now do you see the problem? I have never lost one race to my friend (counting the 1/4 time and speed). I beat him by 2 seconds most of the time and my car is SUPPOSEABLY pushing 116hp??
And also Stock Grand Am vs Stock Saturn. He has 300lbs LESS weight to pull. Our body weight is very much alike so he is pulling about 300lbs less weight.
This is why I do NOT recommend this product to ANYONE!
Tell me what you think about that!!!!
09-09-2001, 07:59 PM
well Im glad you told me about the product I was in the process of going to purchase one. Only one question though, you said your car came with 155 hp stock and the G-tech registered 116. Could have the manufacturer said 155hp at the flywheel. The G-tech reads only rear wheel horsepower. See you have about a 20-30% margin between flywheel horse and rear wheel, which you probably already know. I was just thinking about the corvette that they tested on the show it was rated about 300 hp from the manufacture but on a actual dyno it only tested about 220 or so. If the Saturn tested to what you thought was close within the horsepower range why do you think your car is so far off? You act like just because a car has more horsepower than another means its faster than another, this is just not true. If my car is running a true 350 horsepower "which is calculated" does it mean I can outrun a new vette or porshe just because I have more horsepower. NO WAY. I have 350hp and only run mid 13's with a 86 firebird.
09-10-2001, 12:17 AM
I understand the differences between having Horsepower available and being able to Utilize it. I know I have a good Top end engine. Whats funny is my friends Saturn has a good top end also. We have all done stupid things in our life so don't act like this is an everyday thing. One day we decided to head to head on a highway and his top end dominted mine. I don't know Torque numbers for either of the cars but as I mentioned the weight makes a diff too and my car weights MORE than the saturn. We are looking into getting a real dyno test done here shortly. I am not sure if the Grand AM is 155 at the wheels but i sure would like to find out. But like I mentioned that would still give my firiend at least a 10hp gain over my car at the wheels. Which still does not make sense. AS for the Gtech. use that 150 dollars to hook up to a real dyno so you can at least get real results. If I would have had to make the choice again. Definetly would go with a TRUE dyno run. Anyway. I will let you know my Dyno results as soon as I get them.
09-10-2001, 08:27 AM
I'd love to see a product like G-tech really work because it is 150 dollars for several dyno runs while a true laptop dyno run cost around 200 a pull. If you know of any other products like G-tech but actually works please let us in on it.
09-10-2001, 09:16 AM
Like I mentioned the only other thing is the real thing. I rather pay for the real dyno. Beleive me you don't want to go through the agrevation and grief I went through with the POS GTech. The real test comes soon once I get the car on a real dyno. I can't wait to see those results then I can be certain.
09-10-2001, 09:22 AM
look at this if you already haven't
09-10-2001, 01:17 PM
yeah thats all great and all but that takes alot of info and its hard to use i think you would find this site much easier to use and alot less confusing. http://www.fantasycars.com/derek/hp.html
09-15-2001, 04:27 PM
The G-Tech is a good product. But to use it right, you have to be running as if you are running a quarter mile. The kid with the Pontiac, you said that the Gtech said you have 116 horsepower when the factory says it has 155. Thats just an estimate AT THE CRANK, not at the wheels, the 116 would be a rough estimate at the wheels. I bet if you go to a good chasis dyno you would see that it is pretty close to that.
09-16-2001, 09:10 AM
Be careful about using the formula quoted above. First of all it's inaccurate because it does not contain the conversion factors necessary to get a correct answer.. e.g. miles per hour (speed) and G's (acceleration) cannot be multiplied without having common units. Speed and acceleration must be converted to feet per sec^2 and feet per second before you can do the multiplication. Similarly weight must be in mass units not weight units. With that said... assume you have a 3000 pound car that does a 1/4 mile in 12 seconds at 100 mile per hour.... then the correct math gives you 152 horsepower. But remember that this result assumes that your acceleration is constant for the entire run and your average speed is 50 mile per hour (you started at 0 mph and ended at 100 mph) both of which are not exactly true. Bottom line is that the equation can give you a decent estimate of you r horsepower but is of very little use in determining horsepower change from minor performance mods..... take it to a dyno.
09-18-2001, 06:10 PM
hey i dont now about all the math but heres a place that i think gets it pretty close. http://www.fantasycars.com/derek then go to hp calculator that seems to get pretty close
09-22-2001, 04:19 PM
Okay i did a lot of calculations and I figured this out. My estimate HP at the Fly is 173hp. This is a Four Cylinder engine. So tell me what you think about that. I'm just curious. It has Exhaust and Intake. About to get a header and High Flow catback. My Extimate at the Wheels is 135hp. Now after I ran the GTech I realized that my tire wear is very poor on my passanger side. I have new tires and checked the alignment. First. I stopped doing burnouts to increase the life of my tires. Second I am going to run the Gtech again as soon as it stops raining and the streets are dry. Also. I know you gotta run the car hard to get the HP for the Gtech the problem is. I don't have a street long enough to run Full Throttle without the Pigs bustin my butt! So I am gonna take my chances tonight or tomorrow and give it another try. I will post results when I get done!
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