100 pound loss = how much HP gain???

-
318willrun

318willrun

Utube channel 318willrun
FABO Gold Member
Joined
Sep 13, 2013
Messages
21,514
Reaction score
27,853
Location
I'm here
Some say for every 100 lbs you lose, it's the same as adding 6 hp to your engine before weight loss. Some say 10 hp before weight loss. Is there an accurate way of figure? I know hp to weight is key. I know the rule of thumb is every 100 lbs is a tenth in the 1/4. I think it makes a difference of the torque of the engine. I think a 100 lbs is more than a tenth to a 318, and not quite a tenth to a 440. But the question is, for every 100 lbs loss is the equivalent to how much hp gained??
 
A hundred pounds is a tenth at the strip. That's all I have ever heard.
 
toolmanmike said:
A hundred pounds is a tenth at the strip. That's all I have ever heard.
Click to expand...

I have always heard that as well, but only to a point. Once the car gets into the 11 second range, it is harder to see that type of gains. That maybe where the 10 pounds equals 6 HP number comes into play. Always seemed logical to me anyway.
 
I'm going to say there is no way to really equate the 100 lbs to the hp.
ET yes.
It's like the Direct Connection Hp, MPH & ET estimators.
If I recall correctly, they correlate Hp and mile per hour, then look at the ET relative to those, the weight, and what different levels of chassis prep should accomplish.
 
toolmanmike said:
A hundred pounds is a tenth at the strip. That's all I have ever heard.
Click to expand...

DrEamer said:
I have always heard that as well, but only to a point. Once the car gets into the 11 second range, it is harder to see that type of gains. That maybe where the 10 pounds equals 6 HP number comes into play. Always seemed logical to me anyway.
Click to expand...
Exactly... a lot of it is rule of thumb. No way no how a 100 pounds is the same to a 408 stroker as a 273. We all know that weight effects engines with less low end torque more than an engine with gobs of low end torque. And as stated above, the faster you go, the harder it is to knock that tenth off.... that is why I'd like to convert it to 100 lbs = X hp
 
318willrun said:
Exactly... a lot of it is rule of thumb. No way no how a 100 pounds is the same to a 408 stroker as a 273. We all know that weight effects engines with less low end torque more than an engine with gobs of low end torque. And as stated above, the faster you go, the harder it is to knock that tenth off.... that is why I'd like to convert it to 100 lbs = X hp
Click to expand...
Wallace Racing HP Calculator For 1/4 Mile
 
Lets say your car weighs 3000lbs and the engine has 400hp ..........and 100 lbs loss = 6hp gain, then if you lost 3000 lbs you would gain 180hp. Which means that a car that weighs "nothing" and has 580 hp would do the 1/4 mile in about .2 second????:realcrazy:
 
Treblig said:
Lets say your car weighs 3000lbs and the engine has 400hp ..........and 100 lbs loss = 6hp gain, then if you lost 3000 lbs you would gain 180hp. Which means that a car that weighs "nothing" and has 580 hp would do the 1/4 mile in about .2 second????:realcrazy:
Click to expand...
Well, in theory you cannot lose the weight of the motor, tranny, rear end and tires. So the max you could go down to would be 3000 to about 1000. LOL
 
318willrun said:
Well, in theory you cannot lose the weight of the motor, tranny, rear end and tires. So the max you could go down to would be 3000 to about 1000. LOL
Click to expand...
Yes but I forgot to tell you that the race track surface was covered in super magnetic material and the engine, trans and rear end were cast iron.....in this case they would be weightless!!! Some trains run on these super magnets!!
 
318willrun said:
I was playing with that, kind of gives a general idea. But the HP is always different when comparing ET vs MPH.
Click to expand...
That HP difference shows you that your car needs work either hp or chassis. As I dialed in my car the difference got closer and closer. I'm within 5 hp but still down on mph. I believe it's because I drive an aerodynamic brick.
This one helps you find the weak areas:
60' to 1/4 Mile Calculator - Wallace Racing
 
Losing weight doesn't add horse power. It allows the engine to work easier by pushing less weight around. "I THINK" the old adage was for every 100 pounds, you knock 1/10 off your ET.
 
mderoy340 said:
That HP difference shows you that your car needs work either hp or chassis. As I dialed in my car the difference got closer and closer. I'm within 5 hp but still down on mph. I believe it's because I drive an aerodynamic brick.
This one helps you find the weak areas:
60' to 1/4 Mile Calculator - Wallace Racing
Click to expand...
I finally got my Duster to run the ET to match the mph. 13.3's at 99 mph. Very hard to do in a street car. Dividing the 1320 by mph car actually ran. All of my cars have ran a better mph than ET. Again, that's do to with street suspension, traction, etc.
 
RustyRatRod said:
Losing weight doesn't add horse power. It allows the engine to work easier by pushing less weight around. "I THINK" the old adage was for every 100 pounds, you knock 1/10 off your ET.
Click to expand...
So you should make your car as heavy as possible so that you can remove as much weight as possible?????:realcrazy:
 
I think another interesting question is shifting location of the weight.
That clearly wouldn't relate to the maximum hp unless it was on the rotating mass - then it might.
I think David Vizard had some tests in Popular Hot Rodding where it showed no measurable power gains by taking weight off the driveshaft, but measurable gains when other components were lightened. My friend had the issue - I remember unsuccessfully looking for it in the stores but was sold out.

With respect to ET, I'm sure on some cars removing weight in the nose or front wheels vs over the axle would have different effects on the 60'.
 
Then there are cars that run .05 faster with 75# MORE weight in the car... LOL

In general on a 3000 pound car vs 3100 pound car it would take about 6-8 more hp for the 3100 car to run the same et. Just a guess

There is the law of diminishing returns in this. There is a reason it take 8K hp to move a fuel car at the et/speeds they go.
 
crackedback said:
Then there are cars that run .05 faster with 75# MORE weight in the car... LOL

In general on a 3000 pound car vs 3100 pound car it would take about 6-8 more hp for the 3100 car to run the same et. Just a guess

There is the law of diminishing returns in this. There is a reason it take 8K hp to move a fuel car at the et/speeds they go.
Click to expand...


Yup. I have added weight to cars and made them quicker.

Also, as mentioned above, once the car is quick enough, and if the chassis is sorted out, a 75 pound reduction can drop a tenth.
 
That’s the whole thing right there cracked.
Diminishing returns!
You can find out how much HP it takes to drop a tenth. As the car goes faster, the return is less.
A tenth at the starting line - 60’ is a huge thing to overcome. You MUST seriously out HP your opponent to overcome for victory.
 
yellow rose said:
Yup. I have added weight to cars and made them quicker.

Also, as mentioned above, once the car is quick enough, and if the chassis is sorted out, a 75 pound reduction can drop a tenth.
Click to expand...
I was going to address that other add weight comment, but you beat me to it. Weight in the wrong area is very very bad.
 
Also, rotating weight as we all know has a greater return. Wheels/tires, driveshaft, fans, and if you loose 3 pounds off the crank, that would be better than loosing 30 pounds from the interior.
 
318willrun said:
Also, rotating weight as we all know has a greater return. Wheels/tires, driveshaft, fans, and if you loose 3 pounds off the crank, that would be better than loosing 30 pounds from the interior.
Click to expand...


Not always. A center counterweighted crank is the perfect example.

If the crank is flexing all over the place (and they do) and you can add center counterweights, you can tighten up the main clearances and the car will be quicker because the crank isn't moving...as much.

That's a perfect example of where to remove weight and where not to. Wrist pins are another place to not skip. I has a BBC on the dyno and after about the 5th pull it started losing power. A couple more pulls and I called it off. Upon tear down, you could see the pins flexing and pulling the Pistons out of shape. Since I made the call on the pins, I got to buy a new set of pins and Pistons.

A lot of hype and BS out there about saving weight. All weight savings are not good weight savings.

One more...the last guy I worked for built himself a super lightweight everything for his circle track car. Conduit sized wrist pins, an ultra light crank that had even more weight removed after he got it (I forget how many slugs of Mallory he used to balance it, but after the experiment he kept all the Mallory out of the crank, and for over 3 years I didn't have to order any Mallory...I used what he had left over!!!) super lite Pistons...all the trick junk. When the car hit the track he said it was like he popped a parachute half way down the straights. The engine didn't have enough internal weight to overcome friction and drag. They played with it for awhile, because on the dyno it made big power and looked good.

I forgot to mention he also had an ultra lightweight clutch in there too.
 
yellow rose said:
Not always. A center counterweighted crank is the perfect example.

If the crank is flexing all over the place (and they do) and you can add center counterweights, you can tighten up the main clearances and the car will be quicker because the crank isn't moving...as much.

That's a perfect example of where to remove weight and where not to. Wrist pins are another place to not skip. I has a BBC on the dyno and after about the 5th pull it started losing power. A couple more pulls and I called it off. Upon tear down, you could see the pins flexing and pulling the Pistons out of shape. Since I made the call on the pins, I got to buy a new set of pins and Pistons.

A lot of hype and BS out there about saving weight. All weight savings are not good weight savings.

One more...the last guy I worked for built himself a super lightweight everything for his circle track car. Conduit sized wrist pins, an ultra light crank that had even more weight removed after he got it (I forget how many slugs of Mallory he used to balance it, but after the experiment he kept all the Mallory out of the crank, and for over 3 years I didn't have to order any Mallory...I used what he had left over!!!) super lite Pistons...all the trick junk. When the car hit the track he said it was like he popped a parachute half way down the straights. The engine didn't have enough internal weight to overcome friction and drag. They played with it for awhile, because on the dyno it made big power and looked good.

I forgot to mention he also had an ultra lightweight clutch in there too.
Click to expand...
I mentioned the "crank weight loss" because I went to a different front crank pulley on my truck and lost 3 lbs in doing so. I guess I was asking the general weight = hp gain (equivalent) assuming the vehicle had traction. In other words, if you removed the front seat for a race seat and lost 100 lbs, how much HP would it take to = the same gain in performance. Not to get twisted sideways.. LOL. But a stock 340 will move a 3000 lbs car faster than a 4500 lbs car. That's pretty safe to assume, considering the same gears, converter, exhaust was used. So how much HP would have to be added to make the same 340 run the same exact ET in a 4500 lbs car as it did in a 3000 lbs car?? Again, don't out think it. Same gears, same transmission, same traction, same converter, same exhaust, same wind resistance, same everything including gas and altitude on the same day at the same track.. LOL. Same Duster, just 1500 lbs of very fat people squished in it. LOL Hope I covered my basis for the question. :D
 
Last edited:
You must log in or register to reply here.
-

Back
Top