Have problems understanding relationships of Weight vs HP/TQ as to 1/4 mile time

[Qikbbstang]

If you have a 400HP 3,2000lb car that runs 13sec.

   Lets say you remove 200lbs from that 3,200lbs..............Is there any kind of formula's that could predict how much faster the  400HP 3,0000lb car will run?


Accordingly if you have the above mentioned car:  400HP 3,2000lb car that runs 13sec. how much additional power will it require to run as fast as the car lightened down to 3,000lbs?

[jayb]

Try playing around with this calculator to get the idea:

http://www.race-cars.net/calculators/et_calculator.html

[Joe-JDC]

From personal experience, I picked up about .015 second et. for each 100 pound less car weight with sbf.  If the gear ratio is correct for crossing the line at maximum rpm of the engine, there may not be as much difference.  There are more things to take into consideration at the 400hp level, like wind resistance, tire pressures, alignment, frontal area, head winds, weather, etc. Joe-JDC

[Posi67]

If your 400 HP 3200 lb car only runs 13's then you either don't have 400 HP or need to do a lot of work elsewhere. The standard rule of someone's thumb is 100 lb reduction should get you a tenth. Poor traction, bad driving or just a lousy tune up will affect everything.

[CaptCobrajet]

Like Dale said......100 lbs = approx .10 in ET.  It takes +/- 20 hp to get the same .10...........both assume equal conditions, good traction, repeatable situation.  Slower than 12.00s it takes less of either to get .10 reduction.  Faster than 9.50, it takes more of either to get .10 reduction.  Pretty linear......

[Ford428CJ]

The Moroso slide rule works very well... And you can take it everywhere with you. P/N 89650

[machoneman]

Wallace Racing has about 100 really useful formulas, so many you can get crazy with them in one day!

http://www.wallaceracing.com/Calculators.htm

[rcodecj]

I've had a few mustangs that I've removed weight on and they pretty much reduced et by a tenth for every 100 lbs.
50 lbs was half a tenth, etc

[shady]

about 12 tears ago I dropped 50#s. While complaining to my doc about how hard it is to do, she said, look at the bright side, for every 10 lbs you lose, you gain a half inch of penis back. To which I said, oh great, I need to get down to 60lbs to finally have the penis I always wanted. The galaxie didn't feel any faster, but could have been the hunger pains.

[Falcon67]

As the above - rule of thumb has always been a tenth per 100 lbs dead weight.  Note that another engineering rule of thumb says that reducing rotating weight is as much as 5 times more effective in freeing up power than removing dead weight.  Hence the people running aluminum drive shafts, lightened gears, gun drilled axles, light wheels, tires, brake disks, etc.

I still want to make a run, then take all 4 doors off the Falcon and make a pass - just to see. 

YMMV of course. 

[Qikbbstang]

One thing I always remember was feeling the car simply not pull as hard when taking two-friends for a ride. Skip the out of the hole comparo, but the hard-pull in third gear was noticeably slower.... One passenger no difference, but that marginal 150 lbs of a third person poked things down.

[machoneman]

As the above - rule of thumb has always been a tenth per 100 lbs dead weight.  Note that another engineering rule of thumb says that reducing rotating weight is as much as 5 times more effective in freeing up power than removing dead weight.  Hence the people running aluminum drive shafts, lightened gears, gun drilled axles, light wheels, tires, brake disks, etc.

I still want to make a run, then take all 4 doors off the Falcon and make a pass - just to see. 

YMMV of course.

Hey Chris! Car Craft or Hot Rod (think it was CC) actually did that some years ago on a door slammer but they went all the way! Between every drag strip run, they took more and more off until honest the car was literally just a frame! I wish I knew the month/year but it was pretty fascinating science experiment in my book as yes, the car went quicker and faster each time.

Btw, on last test run....I don't think they'd get ANY track today to let them take it down the strip!

Here's a good article too but it's not the same one as above:

http://www.hotrod.com/how-to/paint-body/ccrp-0911-chevelle-weight-reduction/

[Hemi Joel]

Hey Chris! Car Craft or Hot Rod (think it was CC) actually did that some years ago on a door slammer but they went all the way! Between every drag strip run, they took more and more off until honest the car was literally just a frame! I wish I knew the month/year but it was pretty fascinating science experiment in my book as yes, the car went quicker and faster each time.

"Caddy Hack" in the Feb. '87 issue

[Rory428]

The Moroso slide rule works very well... And you can take it everywhere with you. P/N 89650

I agree, I have found the trusty old Moroso Power Speed Calculator to be more accurate than any of the computer simulators that I have even tried. At least on a fairly well sorted out combination, otherwise it at least shows what type of 1/4 mile potential a car of  certain weight CAN have if setup properly. A good calculation for determining optimum ET for a given MPH is to simply divide 1320 by your cars MPH in the 1/4 mile. Again, if your ET is considerably slower, it shows the potential. I don`t know how this factor works with "power adder" cars, or at the extreme ends of slow or fast race cars, but it works very well with good working cars in the 9 to 14 second cars, and likely others faster and slower.

[machoneman]

Hey Chris! Car Craft or Hot Rod (think it was CC) actually did that some years ago on a door slammer but they went all the way! Between every drag strip run, they took more and more off until honest the car was literally just a frame! I wish I knew the month/year but it was pretty fascinating science experiment in my book as yes, the car went quicker and faster each time.

"Caddy Hack" in the Feb. '87 issue

Thanks Joel that's the one! hah!