So, how much weight is one HP??

Meaning...If I remove XXX lbs its the same as gaining YY HP

Rich

Not sure if this is what you are looking for or not.

Pretty cool website though.
http://www.ajdesigner.com/phphorsepower/ho...eight_ratio.php

Your question is very parallel to the old LBJ:

Q: How many Surrealists does it take to change a lightbulb?
A: FIIIIIIIISH!


The only way you can convert lbs to HP is by throwing in length (feet) and time (minutes). Divide the weight in lbs by the length in feet and by the time in minutes. Throw in a term for revolution as well, and you have HP. Re-arrange it, and you get:

HP = lbs/ft * R/min [ * 5252 to get the units right]


Which is an obnoxious way of saying that your question has no real answer. Too many other factors for any one number to be "correct". For instance, take 100 lbs off of a BMW 7-series. Not much diff, huh? Now take it off of a motorcycle. Big big diff!!

Also, lighter weight means less force required to accelerate, or decelerate, or turn. More HP does nothing for braking or turning, so at an autoX light weight is even more important than at the drag strip, for instance.

--DD

i have heard losing 10lb is like adding 1 hp. or 1/100th of a sec. in drag racing..but that is just hearsay....

It's not a straight x=y equation... you have to do power to weight ratios. Removing 10 lbs from a 4000 lb car is obviously not the same as removing 10 lbs from a 2000 lb car...

Assuming a fairly normal weight 914 and a nice 2056:

2100lbs/125hp=2000lbs/119hp, so dropping 100 lbs gives you 6hp.

I can't show you the math right now, 'cause I had too much beer

Here is the formula I am using for my project.
Keep in mind that this formula is different for every car.
Plug in your numbers and give it a try!

Here is how things worked out for my car:

The original weight was 2300 pounds and it had 320 BHP.

Since the car now weighs 1875 pounds and still has 320 BHP:

1875/320 = 5.86

So if the car still weighed 2300 pounds it would need 392 BHP to be as fast as it is now:

2300/392 = 5.86

If we divide the weight lost by the theoretical BHP gained:

425/72 = 5.9

This means that for every 5.9 pounds the car drops it gains an equivalent of 1 horsepower.
The beauty of this is that the lighter your car gets the less poundage it takes to gain a HP! Yay!
So there you go, bored yet?

It also means that the less horsepower your car has, the more weight you have to drop to gain a HP...

I made an excel program that automatically calculates this but can't figure out if its possible to post it...

And sometimes the best weight to lose is behind the wheel

and there's all kinds of weight...

rotating mass (e.g. roadwheel) very bad weight - rotating plus unsprung.

fixed, unsprung - not as bad, still bad.

high above the roll center - sub-great.

below the roll center, offset to your turn bias requirement - as good as you're going to get. If it's gotta be somewhere, that's a good place. (unless your roll center is below ground, which happens, in which case, anchors are bad...)

a pound on the wheels will hurt you more than a pound in the chassis. A pound on the crankshaft is a lot...

but in case of confusion, F = mA, or F = mV-squared

Depends on how you want to define horsepower... Or better to say 'where'...

Horsepower = 550 ft*pounds/second

(velocity in ft/second * weight of load)/550 can be considered the horsepower of the car...

EX: Say your car can top out at 115 mph with 600 of people plus cargo....
115mph-> ft/sec~169
soo... (169*600)/550 ~184 hp by that definition....
Hmm... I must have a bad conversion somewhere... Easier when dealing with something spinning due to the nice torque units in there...

the 550 constant agrees with dave's equation... google agrees with my conversion sheet....Where am I going wrong? Am I wrong? Is system horsepower generally higher than rotational horsepower... Shouldn't it be less due to more parasitic loss? Am I going insane!!!

Anyway reducing the weight of your car will increase the carried load at a given speed meaning a net gain in system horsepower... Basically think of your car as producing the power and not the wheel or engine...

I was just looking for a ballpark....

I thought I had heard 10 lbs equates to 1 HP...I guess I was mistaken.

What if I fold time along the Y axis, would that reduce my CD enough to get a baseline number of three...three is the number and the number shall be three.

Time for Pizza
Rich

I've heard that too, in drag racing circles, and I'd bet it is fairly close if you're starting with a RWD 4,000 lb American V-8.

What none of this considers, though, is that the real difference is not so much in how many horsepower or lbs you gain or lose, but what the percentage is. Gaining 10hp in a 914/4 would be akin to gaining 40hp in a Corvette.

Lets see...my 75 with a 1.8 and early bumpers I believe was around 2200?????pounds. Now with a 300 hp chevy it weighs top and all 2360, which I thought would be heavier. So I added 160 pounds and gained 200 hp...that's a good deal, not to say all the hp is usuable.
When I get the motor broken in I would like to find a dyno in my area that I could run both my stock 74 2.0 and 75 chevy 914 through and see how they compare. It wil be interesting to see if the chevy motor is really putting out the poinies that it was built for and how the torque curves look. I love my 2ltr, but it's hard not to smile when you mash the pedal on the v-8 and it roars to life.

What Rich has written is true, simply put, all weight is bad but some is worse than others. Weight reduction can be free or expensive....the easy stuff is free, the hard stuff is expensive, but sometimes the necessary stuff is a toss up pricewise but light or heavy.

Fer instance, a buddy had me transport his tires & wheels to an event.....they are still in my shop, so I got to checking weights. His rears are Fiske 17 inchers with 275 X 35 A6 Hoosiers.....44 lbs each. Mine are Monocoque 16 inchers with 22 X 10 Hoosier slicks @ 32lbs. There is 24 lbs of rotational unsprung weight. The fronts are a bit less of a difference...22 lbs ....and his cost more.

An Optima battery is 38 lbs (give or take). An Odyssey PC680 is 12lbs with similar costs.....but you need a battery.

The Hp/weight loss deal is moot (IMO). You want as light as possible regardless of HP....as long as stuff don't break. Lightness works all the time, HP works only when you're OTG.

As always, you pays your monies & you takes your chances.

I don't think anyone mentioned where the weight loss is most important. off the rotating parts of the motor.
My crank, rods and pistons are considerably lighter. fan has every other fin removed, flywheel is 10 pounds (Thanks Kevin).

Wheels and tire assemblies are 30 pounds each new rubber.

So all that is really good weight that would in my non-engineering mind is worth more HP than an all fiberglass trunk lid.

The other thing to note in taking weight off is how it effects your handling.. If you have a nose heavy car and you take weight off the rear of the car, you will have worse handling/balance per say..

FOr instance my Audi needs to have weight taken off the front or I am even considering putting weight on the rear.. Finding that weight can be a problem..