[dsilvey]

I have read a few different formulas based upon weight versus horsepower. I read one that said decreasing a car's weight by 100 pounds increases 33 hp. Then I read another that said an extra 100 pounds causes one to loose 10 hp. Which is correct or what is the correct conversion of weight to hp???

Thanks, David

[stlwagon]

Here's a good formula I found.

1) Calculate vehicle's current weight(x).

2) Subtract the amount of weight you’re removing.

3) Take this new number(a) and divide it by the horse power of the vehicle (y). The number you come up with (z) will be the amount of lbs. per horse power after the reduction. (Step 1)

4) Then divide 1 by the number of pounds (z) and multiply it by the weight before the reduction(x). This new number (b) will be the new simulated horsepower of the vehicle. (Step 2)

5) Take this number (b) and subtract the horsepower before weight reduction(y) from it. This will be the simulated gain(s/hp (g)). (Step 3)

Step 1: a/y=z
Step 2: (1/z)*x=b
Step 3: b-y=g

[mad4macs]

Originally Posted by stlwagon

Here's a good formula I found.

Step 1: a/y=z
Step 2: (1/z)*x=b
Step 3: b-y=g

Wash your mouth out with soap and go to your room

[dsilvey]

Mark is even more powerful than I thought!

[stlwagon]

The sad thing is I was never very good at math

[tached_out]

well 33hp to 100lbs is not accurate but a good way to explain it.

There is Supported weight and Unsupported weight. Unsupported weight is all the weight that your suspension does not support ie wheels and suspension.

Supported is all the other factors that most of the weight reductions come from.

Other then that there is rotational weight. Which to me makes the biggest difference in how your car performs.

Weight will make the biggest difference in how your car performance and handles. It is fairly easy to knock off a few hundred lbs from your car as well and it will make a huge difference. The best way to test it is to load up your car with people and drive it.

Take out a person and see the difference the car makes and handles.

[GT speeder13]

so it would be better to go on a diet personally and drop 20-40lbs than buying more mods? haha thats awesome, im gonna workout harder next time im at the gym to continue my modding addiction

[dsilvey]

Dang, I have no more weight to lose.... just next time I get a dyno, I'll make sure my 143 pound butt is in the seat rather than that 250 pound mechanic!

[duckbubbles]

It's really simple ratios, like Mark said. Divide the weight of the car by the horsepower.

Say, you have a 4000 lb. car that makes 400 hp. The power to weight ratio is 10 lbs per hp. Got it?

Say you can reduce the weight of the car by 500 lbs. Now your power to weight ratio is 8.75 lbs per hp.

If you kept the car at 4000 lbs, to get the same power to weight ratio, the engine would have to make 457 hp. (Divide the weight by the new pwr/wt ratio.

Using the above example, reducing the weight by 100 lbs, would be equivalent to adding 10 hp. That figure is not constant and will vary according to the power to weight ratio.

I hope this helps.

Frank

[dsilvey]

Yeah, that makes sense!

[tached_out]

Originally Posted by dsilvey

Dang, I have no more weight to lose.... just next time I get a dyno, I'll make sure my 143 pound butt is in the seat rather than that 250 pound mechanic!

it wont change your horse power just free up lost horse power from the weight. Same way if you put a 40lb pack on and run a mile and then take it off and run again. With out the weight its easier and faster but your still just as strong.

It works all most like UDP's do how they free up lost horsepower from being restrictive.

[dsilvey]

Yeah, that's right. The car produces a certain amount of horsepower and by the time in makes it to the rear wheels you lose ~16%. So if you do little things like synthetic oil, UDP's, lightening weight, etc...you are reducing that percentage. Now the hp that makes it to the rear wheels is what will launch you off the line.

[Ragnar]

Originally Posted by stlwagon

Here's a good formula I found.

1) Calculate vehicle's current weight(x).

2) Subtract the amount of weight you’re removing.

3) Take this new number(a) and divide it by the horse power of the vehicle (y). The number you come up with (z) will be the amount of lbs. per horse power after the reduction. (Step 1)

4) Then divide 1 by the number of pounds (z) and multiply it by the weight before the reduction(x). This new number (b) will be the new simulated horsepower of the vehicle. (Step 2)

5) Take this number (b) and subtract the horsepower before weight reduction(y) from it. This will be the simulated gain(s/hp (g)). (Step 3)

Step 1: a/y=z
Step 2: (1/z)*x=b
Step 3: b-y=g

Weight is only an issue when the car is moving. If my car weighs 3500 pounds and I have 300 hp and I then drop 500 pounds I'll bet the dyno will still say 300 hp. What you're really after is the "thrust to weight ratio" as fighter pilots call it. Dropping weight and keeping hp the same will make the car faster. The car may perform as if it had 350 hp. Maybe call we should call this "equivalent hp" or "virtual hp". Maybe simulated hp as stlwagon notes is good too.

[duckbubbles]

Originally Posted by Ragnar

Weight is only an issue when the car is moving. If my car weighs 3500 pounds and I have 300 hp and I then drop 500 pounds I'll bet the dyno will still say 300 hp.

We're not saying that reducing weight actually increases horsepower. Just that it has an effect as if you have more power with the same weight. It all comes down to power to weight ratio (thrust/weight is very similar). Dyno's are a whole different subject.
Also, getting a 4000 lb car moving quickly takes more horsepower than getting a 3000 lb car moving the same- traction being equal. Simple physics.

Frank

[dsilvey]

That is true...So I guess this means weight doesn't matter on Dyno's?!?