Weight dropping= how much time?

[STINKY NINJA]

How much weight must you drop to get an improvement in quartermile times on a mid to high 14 second car?
Would 50 kg be a tenth?
Ive put on weight since i was last taking my car down the drags regularly(20kg cough cough)

Cheers

[Road Games]

LOL 45kg is generally worth a 1/10th

Unsprung Rotating mass on the other hand x 2

[STINKY NINJA]

haha i can account for around 5/100th then

[prasac]

how heavy is the car?

if it's a 2-ton car will make bugger all difference, if it's lighter car and take 100kg off etc you will find more!

[Giant]

I have seen the spare removal worth a tenth. 25 KG that's on a 1850kg car 163rwkw BA I6.

[noosacuda]

Old rule of thumb was 100 pounds = 1/10th second.

[STINKY NINJA]

Eb ghia v8,papers says it weighs about 1560kg plus me almost 1700kg all up,not sure how accurate license paper weights are,every time ive been at the drags and the scales are turned on theres a race car sitting on them and i cant weigh mine.
Its only run 14.58 at about 96mph so by todays standards its a snail,but i was just curious.
I never race it with the spare tyre in the car,never even have it in the car full stop.

[STINKY NINJA]

Originally Posted by XR6menace

LOL 45kg is generally worth a 1/10th

Unsprung Rotating mass on the other hand x 2

So if i swap my mags for stockies it theoretically should go faster?
Next time i have my wheels off im putting them on the scales!

[Road Games]

Indeed.... Wheels brakes coil overs.... Works for me mate

[STINKY NINJA]

Cheers menace,ive never thought that far into it tbh,excellent info!

[perthfggsute]

from what i have researched every 7 to 8 pounds is worth 1 horsepower......but with all the other variables you would have to drop alot of weight to consistantly drop a couple of tenths in a 1500 too 2000 kg vehicle.
i know we all take the **** out of the yanks but hotrod and other big usa magazines have stripped cars out inline with what you are saying and they didnt pick up much at all.....for all the work involved.cheers dave perth

[Yellow_Festiva]

I remember seeing a YouTube video by Top Gear I think where they track a car several times and measure the improvements, each time stripping weight from it.

They eventually cut most of the body away, looks like a go cart when finished.

And yes, they did make some decent gains!

[FPV GTHO]

Your unsprung weight is different to rotating weight. I believe the gains of less unsprung weight are about twice as much of those of sprung weight, but there's no direct relationship between spring weight and rotating weight as the gains increase the further away from the rotating axis that the weight is removed from.

[prasac]

NA car weight makes more difference compared to turbo car. I've raced full tank vs 1/4 tank made no difference, unless you have a car that you can go out and run the exact same time pass after pass you won't truly know. There is too many variables with the car and driver.

unsprung weight made no difference we put 7kg on each tyre and added 40kg weight car ran 1/100th, this was in a turbo car. Did notice a 1/4-1/2psi more boost because of heavier load.

[Giant]

So many factors, if reducing weight prevents the car from bogging down / loading up on the start line then it's going to have a greater effect. Would have a bigger effect on a under powered street car using stock stally then a race car.

[prasac]

Originally Posted by Giant

So many factors, if reducing weight prevents the car from bogging down / loading up on the start line then it's going to have a greater effect. Would have a bigger effect on a under powered street car using stock stally then a race car.

not really 360rwhp car with 120kg driver went 10.61 with 70kg driven went 10.59 was 3500rpm stall.

Funnily same car same drivers now 870rwhp car still only 2/100ths faster.

130kg driver
http://youtu.be/M0S8EfmLTZk

1 week earlier 80kg driver
http://youtu.be/ek3eoho4n5A

the low boost times show d same was only 1-2/100ths in it. Which is why I say, theres just too many variables, unless you are perfect and you can duplicate times like a pro driver, have a proper setup car that will do pass after pass within 1/100th each pass, your routine is exactly the same,, you will never 100% know if what n how much it's worth. On an NA car weather/elevation etc will affect time more than a little extra weight

[Giant]

Lucky I am a pro driver so I can test these things hahahaha

I agree with your theory.

If you test and keep the data of the weather and weight over a period of 2 years or more and consistently show similar improvement removing the same weight vs running with the weight. You could reasonably average out the gain.

Sure it's not a 100% proven method but it can help you adjust your dial in.

Regarding your theory The other night my mate run 15.2 14.7 15.7. Only change drivers input and a few psi in tyre pressure and weather.

[STINKY NINJA]

From what im reading weight doesnt play much of a factor,im definitely no pro driver and im inconsistent to say the least so not much for me to worry about then.
Thanks for all the info you guys have given me,id still love to hear more!

[comagutsa]

Shannon better lay off Mr G pizza ya tubby haha

[STINKY NINJA]

lol,i just dropped about 1800kg yesterday,my ba is someone elses problem now...
I actually prefer "kenwick pizza"( i expect a discount for this shameless plug!)

[comagutsa]

oh look out you sold it ..dam what you driving now the ED hey

[STINKY NINJA]

Yeah back to cruising in the old eb,ba was using oil...
Got a new awd rig coming on the boat from the land of rice!

[Giant]

Originally Posted by prasac

NA car weight makes more difference compared to turbo car. I've raced full tank vs 1/4 tank made no difference, unless you have a car that you can go out and run the exact same time pass after pass you won't truly know. There is too many variables with the car and driver.

unsprung weight made no difference we put 7kg on each tyre and added 40kg weight car ran 1/100th, this was in a turbo car. Did notice a 1/4-1/2psi more boost because of heavier load.

How much more power and torque does the 1/4 to 1/2 more psi produce?

[prasac]

Originally Posted by Giant

How much more power and torque does the 1/4 to 1/2 more psi produce?

not enough to affect times that much, running slower 10rwhp/10rwtq might net you 1/10th, at the times thr Capri runs 10rwhp would be a couple hundredths if that. To go from 8.2 to 7.8 car needs to find another 300-350hp lol

[nelsonian101]

Don't know about BA/BF but in FG, the rear seats are very easy to remove. The base weighs nothing but the 2 split back rests are surprisingly heavy.

Quick disconnection of negative battery terminal to stop an airbag blowing up in your face, and the front passenger seat is a quick removel job too with an electric drill and torx socket adapter.

Dry cell or lithium battery if you have the $.

Some light cast rims like RPF01's or any forged alloys save a heap of unsprung weight. 2 piece front brake rotors.

Lots of Fibreglass bonnets around now on the market to choose from.

With a sorted anti-surge fuel supply set up, low tank levels can be used safely at the track.

Lay off the junk food and beer for a fortnight....but let's not get that serious hey.....

All this adds up to a substantial and noticeable weight saving. Not each component by itself, but the whole weight saving package does.

It's all about getting personal pb's, even if it is a tenth or 2, it's still a pb.

If you are at your own personal limit for times, I'm all for a good diet.

[ebv8]

search youtube for the roadkill episode they stripped a corvette with a reciprocating saw

i am putting my track car (2002 VX commodore) on a diet now to make it faster, the carpet weighed about 20kg as it was foam backed and some parts 80mm deep. removed everything out of my rear doors so windows will be 3mm perspex and the door trim will cover the total removal of inner skin, and for good measure i got the hole saw to every other part of the rear doors. went from a 25kg door to under 10kg.
i removed the bumper reo bars and these had no effect on supporting the bars and weighted about 5kg each.
i am hoping to get the weight down to about 1350kg with me in it so i may be looking for more ways soon including putting myself on a diet.

[Shonky.]

Originally Posted by ebv8

door trim will cover the total removal of inner skin, and for good measure i got the hole saw to every other part of the rear doors. went from a 25kg door to under 10kg

Be careful you don't end up hurting yourself if you end up in a wall mate

[ebv8]

Originally Posted by Shonky.

Be careful you don't end up hurting yourself if you end up in a wall mate

just the rear doors, front doors will be stock just with acrylic windows. rear doors still have anti intrusion bars too, no way i'd do it to a street car though this is a track only car so i don't car much for how it looks plus i made sure i have spare stock doors.

[Quadcams]

For our heavy street cars, roughly every 100kg take off a tenth.

[2242100]

Originally Posted by STINKY NINJA

How much weight must you drop to get an improvement in quartermile times on a mid to high 14 second car?
Would 50 kg be a tenth?
Ive put on weight since i was last taking my car down the drags regularly(20kg cough cough)

Cheers

I think the effect is around a tenth for a 2.5% weight variation. That would be around 45 kg's for an 1800 kg car and driver combination.

One point I'd like to make though, is that making comparisons between 1/4 mile times with different weights on board can often be very misleading, and I say that even if the car delivers the best possible performance on both runs.
Why so? Well because of the varying amounts of rollout that a car can get at a Dragstrip.

If a driver shallow stages a car with Commodore/Falcon sized wheels as much as possible, it can get up to nearly 16 inches of rollout before the 1/4 mile time count starts, and that will commonly give between a 2 and 4 tenth faster timeslip than if the car was deep staged. I can say that with some confidence because I've got the same accurate GPS based test gear that MOTOR and other magazines have been using, and it's possible to accurately check times to any point in a run.
So even with exactly identical performances on two runs, a car could get timeslips that are up to 4 tenths different, and of course the 60 foot and other times would vary by the same amount.

But what about the average trap speeds that are printed on Dragstrip time slips?
Well, the timing systems are very accurate, so you could normally expect the time slip speeds to be very accurate as well. However they can be wrong when a speed traps first and second beams are broken by different parts of a car (these beams are only 66 feet apart).
They are normally set at around 5 inches above the track and unfortunately some car spoilers are at around the same height. That caused a problem for my standard XR6 T when I last went to a Dragstrip. On the last (and by far the slowest) run of the night, the car hit the Rev Limiter in 3rd at around the start of the 1/4 mile speed trap. The nose dropped and the time slip showed around a 4 kmh higher speed than the car can possibly reach in 3rd and it showed the fastest speed of the night.
I was initially puzzled, but later I took some measurements under the front of the car and it became clear that although the first beam was broken by the front wheels (as it should have been), the final beam was broken by the spoiler in front of the wheels. So the car hadn't actually covered the full 66 feet when the timing system assumed that it had.
Hence the time slip's incorrect 4 kmh higher speed.
Actually if the nosed had dropped enough for the second beam to be broken by the front bumper, I believe the speed could have been about 6-7 kmh too high.

So it seems clear to me that braking, easing off, or gear changes near the end of a 1/4 mile run, can sometimes cause time slips to show incorrect speeds.