reducing weight=cheap horsepower

[drsimonwong]

A drop in weight will give an equivelant in horsepower rise. Does anyone have an approximate formula?

Simon

[JonT]

I remember 8lbs/hp being used as an approximation.

[Wavey]

That's what I was thinking too, but for the life of me I can't put my hands on the reference. It's the location of the weight loss that's more intangible and harder to formulate, ie: 50 pounds off the roof is better than 50 pounds off the floor pan, at least in terms of handling.

[84CAB]

12LBS. = 1HP I think. Check out rennlight.com for some good info. and comparisons.http://rennlight.com

[jaydubya]

Doesn't it depend on the initial weight of your car?

[Bill Verburg]

There is no one size fits all formula. It all depends on where the weight is. 1# at the tire is more significant than 1# at the wheel, is more significant than 1# at the hub, is more significant than 1# at the CoM.

1# at the front bumper is more significant than 1# at the rear bumper, is more significant than 1# at the CoM

1 g at the piston is more significant than 1g at the crank

a few grams of engine speed reciprocating mass is more significant than 1# at the CoM

Etc Etc Etc.....

[jaydubya]

If we assume as an exercise that the weight is applied at the CoM...

[widebody911]

Check out http://rennlight.com/cgi-bin/hp.cgi

[jaydubya]

Yes, that makes sense.

[Bill Verburg]

Thom that's interesting
and in line w/ figures I have seen elsewhere, the problem is there are lots of fudge factors involved especially at our budget levels

[drsimonwong]

Thanks for the Rennlight connection and all the other variables. Not really that simple is it?

Simon

[widebody911]

Originally posted by drsimonwong
Not really that simple is it?

Nope. The best you can do is get the easy stuff first, and then delve deeper as time and money permit. The last few pounds will be quite expensive. I think I could write up some sort of 'progression' list for weight loss based on mine and other's experiences. For instance, one would start with cleaning out the beer bottles under the seat, rather than with cross-drilled brake lines and synthetic blinker fluid.

I've done some stuff to lighten my car which some might consider extreme, like a fiberglass roof and felt dash, but I've left some low-hanging fruit to pick up later, like removing undercoating and replacing my fenders and quarters with composites. In fact, just last weekend I picked up a set of carbon fiber front fenders, but I can't install them until I get my fuel cell installed, as they don't have a filler flap.

[Mike Metzler]

If the weight/horsepower discussion is only considering acceleration, then it is rather simple for non-rotating parts because it is lbs/hp that really matters. A decrease in weight will give approximately the same improvement in acceleration as a similar fractional increase in power. Going from 3000 lbs to 2800 lbs in a 200 hp car is equivalent to keeping the weight at 3000 lbs and increasing the power to 214 hp.

Of course, it really becomes a bit more complicated than that as the various replies above can attest to, and removing 200 lbs from a 3000 lb car will help cornering and braking, whereas adding 14 hp will not.

[masraum]

check out this thread.

Tell Me About Weight

[Mike Metzler]

Ignore my post above -- it is correct, but has all been said before (probably many times!) This is what I get for being gone for a while and catching posting before checking all the unread posts...

[Bill_Rockoff]

Light weight is only "cheap" horsepower if you're removing stuff you decide you don't want. If you're replacing stuff with lighter stuff, that's usually expensive horsepower. If you're doing it that way, adding horsepower is usually cheaper than adding lightness. (And adding noise is cheaper still.)