Over a year go I caught a thread comparing the 8 and the z. The poster was analyzing the weight difference between the cars, and that since the 8 is x amount of lbs lighter than the z, it would have the effect of such and such horsepower.

he provided the formula and i've been trying to find it. so far, every search i've made both here and on google have returned just hp to weight ratios or torque to hp relationships.

anybody know what i'm talking about?

 

I read in someones signature once on an elise forum that 10 lbs is equivalent to 1 hp. Don't know if it was right or not, but there was a big formula and it seemed legit. I think that was approximate though, based on the weight of the car. A heavier car would have slightly less impact. So the elise weight approx 2000 lbs, a 3000 lb car might be 12 lbs = 1 hp or something.

 

yeah, 12 lbs = 1 hp is right for the 8, I figured it out for another thread. I didn't explain the math though, and I don't remember. It will change slightly as the weight goes down, but not much.

 

1hp = the ability to move 660lbs by 1 foot per second

:D

 

are you looking for lbs per hp?

that's just weight of car / hp

doubt that's what you're looking for, but meh :o

 

I think he is wondering what the equivalent horsepower of the weight difference is. Which was 1 hp per 12 lbs. so So a 200 lb difference would be equivalent to approx 17 hp

 

Yep. That was pretty much what I was lookin for. Thanks, man.. I appreciate it.

 

I think that must be what he's looking for -- comparing the power to weight ratio of 2 different cars.

There's no formula to convert pounds to horsepower. The pound is a measure of mass. Horsepower is a measure of power.

 

you can find the effective horsepower gains of losing or gaining weight though.

 

where do people learn this stuff? hp is the measure of the amount of work done specifically the amount of lbs you can move a certain distance ina specific time-

HORSEPOWER
A measurement of the amount of work; one horsepower is the amount of work necessary to lift 33,000 lbs.one foot in one minute

http://auto.howstuffworks.com/horsepower1.htm

so you can absolutely figure how much hp is being used up by pulling the extra weight of the other vehicle.

 

The basic formula is reduced_weight / (normal_weight / hp) = equivalent_hp in the reduced weight car.

The lighter the car is, the greater the effect of removing a certain amount of weight. Basically 10 lbs off a 2000 lbs car is like adding 1.2 hp while the same 10 lbs off a 4000 lbs car is like adding 0.6 hp. (for a 238 hp car)

Of course instead of looking at equivalent hp gains for weight reduction, you could always look at changes in power to weight ratios, which are comparable between cars.

 

yep power to weight ratio is a much "cleaner" comparison.

 

similar to what I put, but my infor was from the discovery channel

 

 

The Italians have gutted out RX-8s, and it came to a curb weight of 2600 lbs.

 

Sure, but there's no static equation to say 1lb = X horsepower. It depends on the starting weights and the desired acceleration so we get back to power to weight ratios. Pounds don't convert directly to horsepower without involving other terms, that's all I was saying.

 

oh cool okay. sorry if i was harsh

 

they're both the same thing.

It's like calling something a rectangle with 4 equal sides
vs.
calling something a square

Same thing, just one is inherently more confusing.

 

I believe 1hp is defined as the ability to move 550lb at a rate of 1foot per second.

I could be wrong but I hope I learned something in engineering.

 

you are correct

 

The adding and loosing of weight does not affect acceleration linearly, so you can NOT just say, loosing so many pounds is equivilant to gaining so much horsepower. Two completely different terms.