HP versus weight? [Archive] - Chevelle Tech

: HP versus weight?


bb489
May 11th, 07, 5:53 PM
Was wondering if there is any formula out there that can calculate (or come close) to figuring out weight reduction as it relates to horsepower. Ie, if I were to take 50 or 100lbs of weight off my car, about how much more hp would the car "seem" like it has? Or maybe a better way of asking is this: Your car weighing 3200 lbs ets at exactly 12.00 secs in the 1/4 mile. Now if that same car, only this time weighing 100 lbs more (3300 lbs)(everything else being equal but the weight) ets at exactly 12.00 secs, how much extra horsepower would you need to make the heavier car et the same as the first? Does lets say an extra 100 lbs make a 400 hp motor perform like maybe a 380 hp motor?

furball8994
May 11th, 07, 6:07 PM
Try here. http://www.slowgt.com/Calc1.htm

novaderrik
May 11th, 07, 7:07 PM
in the magazines, they used to say that 100 pounds is worth a tenth in the 1/4.
of course, 100 pounds is a lot less % weight loss on a 4000 pound car than it is on a 3000 pound car, so will probably be worth a little less at the track. but, either way, 100 pounds is 100 pounds..

540 RAT
May 11th, 07, 7:41 PM
Try here. http://www.slowgt.com/Calc1.htm

I don't know about you guys, but I found the equation there for ET based on weight and hp, to be quite optomistic. In other words, it shows cars being a good bit quicker than they are in the real world.

A couple of years ago, I generated an equation based on 15 to 20 real world sportsman gasoline drag cars. My equation is "the cube root of (weight divided by hp), then all that multiplied by 6.1", which will give you the approximate best ET. Of course it is impossible to be absolutely exact for a specific car, but it does work out to be a fairly close approximation for reference and planning.

If you use that equation, it shows that a 400hp, 3200 lb car should be able to run about 12.2 in the quarter. If the car's weight is reduced to 3100 lbs, the ET should be 12.07, or a .13 second improvement.

furball8994
May 11th, 07, 8:09 PM
I don't know about you guys, but I found the equation there for ET based on weight and hp, to be quite optomistic. In other words, it shows cars being a good bit quicker than they are in the real world.

A couple of years ago, I generated an equation based on 15 to 20 real world sportsman gasoline drag cars. My equation is "the cube root of (weight divided by hp), then all that multiplied by 6.1", which will give you the approximate best ET. Of course it is impossible to be absolutely exact for a specific car, but it does work out to be a fairly close approximation for reference and planning.

If you use that equation, it shows that a 400hp, 3200 lb car should be able to run about 12.2 in the quarter. If the car's weight is reduced to 3100 lbs, the ET should be 12.07, or a .13 second improvement.

I agree its a little optomistic. I think its based on a "perfect" sealevel run.
The interesting thing is, As in "real world" The faster the car, The less gain you see from the 100# loss.

pdq67
May 11th, 07, 8:16 PM
A mag did an article years ago called "Caddy Hack" where they took a DeVille and chop sawed it to see just what loss of weight would show up like on the strip!!

I think they cut on the poor old Cad from 5500+ pounds down to 2800 or so pounds (??) and when I mean cut, chop saw they CUT!!

I wanna say from 17.+ seconds down to 13.+ seconds in the quarter!!

pdq67

JOHN WILSON
May 11th, 07, 8:38 PM
I don't know about you guys, but I found the equation there for ET based on weight and hp, to be quite optomistic.

That depends on the car and how it's setup. The mph is right on for my car and the et is actually ~.2 soft.

rhamm1320
May 11th, 07, 11:45 PM
I don't think its exactly 100 # to 0.1 second. If I remember right is something like to the 1/3 power square root. Here is what I get for going from 3200, to 3100 to 3000#

11.77

11.65 - change of 0.12 per 100#

11.52 - change of 0.13 per additional 100#

http://www.virtualengine2000.com/Calculator.htm

http://www.hotrodink.com/Images/data/546/1bb489.jpg

novaderrik
May 12th, 07, 1:09 AM
A mag did an article years ago called "Caddy Hack" where they took a DeVille and chop sawed it to see just what loss of weight would show up like on the strip!!

I think they cut on the poor old Cad from 5500+ pounds down to 2800 or so pounds (??) and when I mean cut, chop saw they CUT!!

I wanna say from 17.+ seconds down to 13.+ seconds in the quarter!!

pdq67

that was Hot Rod, back in the late 80's.
they started off with a 500 powered luxu cruiser, and ended up with a 500 powered frame with a seat and a steering wheel.
i think they were gonna do it again a couple of years ago, but no track wanted the liability..

novaderrik
May 12th, 07, 1:11 AM
and who can forget the Chevette that Magnante built with a bone stock junkyard Caddie 500/TH400 crammed into it..
i'm thinking it went into the 11's.

10secBu
May 12th, 07, 8:08 AM
Every combination is gonna be different. In my Malibu, I have a 100 lb ballast bar in the rear bumper. I've taken it in and out several times and not seen any difference in ET.

This past winter I did aftermarket disc brakes, lighter front wheels/tires and a smaller fuel cell all of which took 100 lbs off the car with over half of that being unsprung and rotating weight. I saw zero difference on the ET slip.

bracketchev1221
May 12th, 07, 8:14 AM
I think, now this is just my opinion but it seems the faster my car has gone, the theories don't hold. Maybe in the average street car 100 lbs is a tenth, but in my car now 100 won't get me a tenth.