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First of all, I have to hand it to all you guys for your tenacity and focus on the subject of the lightweight crank pulley for all that time. There was quite a lot of things to be learned. Not to fuel the fire, but I got my pulley way back when somebody said there was no harmonic balancer - and i like it so far.

Anyway, my question is along the lines of the crank pulley thread where some of you argued Physics and Inertia and such - but in terms of STi mass vs. aceleration: How much weight would have to be removed from the base weight of 3260 lb to drop its 0-60 mph time 1 second at the same base HP?

Not that I would necessarily be able to go down that low, but it would be nice to have a reference point.

Thanks in advance
Olappa
 

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I'm just gonna *guess* somewhere around 400-500 pounds.

That's just a guess, and I haven't tried to do any kind of calculations or anything, so don't hold me to it....


You're gonna have a hard time getting good numbers for this one though - the crank pulley argument was one of theory, which it is easy to discuss and determine, eventually, what is true and what is not.

In this case, we all know that lighter = faster, but you're asking for specific numbers, and its hard to calculate that quantatively. I would imagine that some people with a good ammount of experience at the drag strip can give you a better or at least more accurate answer to that than I can though.
 

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well since F=ma, we can derive that a=f/m. The force is constant, you have a desired acceleration, and the mass is what will be varied. This will be pretty basic but should be somewhat accurate. Using R&Ts numbers 0-60 in 4.9, you get an acceleration of 12.24 mph/s(5.48m/s/s). You want about 3.9 or 15.38 mph/s(6.89m/s/s). We can also calculate force. The test weight of the car was 3430 in R&T. For the stock numbers, we get an average force of 8543.82 Newtons. Here is our biggest problem, this doesn't take shifts into account, but the numbers should be relatively close. With the same force, 8543.82, you want the Mass needed for an acceleration of 6.89m/s/s. This comes out to be 2728.1 pounds, (or 1240kg for those who picked up that I was not mentioning some converting). 3430-2728=702lbs, quite a weight. Thats a 20% decrease in weight. The numbers desired, ignoring variables, could also be achieved by a 20% increase in horespower, probably a little more due to traction limitations, but this would have to be accross the board.

For those who didn't read through, roughly 700 pounds would have to be removed to drop the 0-60mph time one second.
 

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Discussion Starter #5
BOV

For those who didn't read through, roughly 700 pounds would have to be removed to drop the 0-60mph time one second.
Hmmmmmmmm... first order of business: Remove Engine. :cry:

Seriously though, you can lose about 180 lbs by:
Lightweight Crank Pulley 5 lbs
AC removal 45 lbs
Lightweight Battery 20 lbs
Lightweight Subframe 30 lbs
Lightweight Bumper Beam 25 lbs
Empty IC Spray Tank 10 lbs (?)
Sparcos in front 45 lbs

Total: 180 lbs (Estimated weights used)

This said, the car is still functional as a daily driver, with spare tire included - if you can live w/out AC and stereo. Also, these mods are relatively affordable for its gains. This weight is the equivalent of a tank and a half of gas, or one beefy passenger. And a lot more agility. After this point (I believe) youll have to go on expensive CF parts and gutting the car - at a lot more money per pound....not for my STi.

Sorry the numbers arent exact - just ballpark figures with a generous bias.
Olappa
 

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You can also take out the spare, and the passenger seat, and a lot of other stuff.

A lightweight FLYWHEEL not only drops significant weight, but like the lightweight pulley, it ACTS as if you're dropping much more weight. Dropping 10 pounds of flywheel can SIMULATE dropping 200 pounds (or more... 200 is just an example - this is based on your gear ratios), because of where and how the weight is involved in the mechanical operation of the car. Again, a light pulley does the same kind of thing.
 

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Well that would be a hard question to answer. 1st of all the position of the weigth loss would be a signifigant factor. Also due to the mass/momentum vs rotating weight the engine is almost always your best bang for your buck. If you can remove lets say 10 lbs from an engine then you are not just removing 10 lbs from the car but your HP goes up and your total rotating assembly goes down. thus as rpms increase the advantage also increases exponentialy based on R. R being radius of weight from the centerline of the crank. So unfortunatly the questins is way more complicated than one might anticipate. But 550-680 or so static punds evenly distibuted might be the most tagible way of going about it. Does anyone have a scale layout for the sti? Ie weight distribution for each wheel so we know where to add and subtract weigth from?
 

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Again be wary of blanket statements. We cannot say that 100 lbs will be 1/10 or anything of the sort because it truly matter where you take it from. yes HP/LBS is important but if that were all that mattered then top fuel dragsters would be very small. Weight is only one of 100's of factors in how well a car does in the 1/4. Yes lightening our cars would be benificial, but only if we take time to learn where and why, to remove weight.
 

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Oh boy....

well since F=ma, we can derive that a=f/m. The force is constant, you have a desired acceleration, and the mass is what will be varied. This will be pretty basic but should be somewhat accurate. Using R&Ts numbers 0-60 in 4.9, you get an acceleration of 12.24....
No the force is not constant. The tq of the engine changes as the turbo begins to add compression.

It would be a sweet sweet day when we can get a constant tq from and engine at all rpm speeds.
 

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roadrnr37 said:
Again be wary of blanket statements. We cannot say that 100 lbs will be 1/10 or anything of the sort because it truly matter where you take it from. yes HP/LBS is important but if that were all that mattered then top fuel dragsters would be very small. Weight is only one of 100's of factors in how well a car does in the 1/4. Yes lightening our cars would be benificial, but only if we take time to learn where and why, to remove weight.
I totally agree, however, for the average joe I think my statement stands. Give or take, a tenth.
 

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I'm saying the force would not change by removing the weight, the AVERAGE force therefore is constant. I know that torque is not a constant that's why we have dyno graphs.
 

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When you remove weight you also decrease the car's maximum traction. So if you spin off the line, for instance, with more weight you wouldn't.... or at least wouldn't as much.

It's all relative and dynamic. Any change you make affects the car in more than one way.
 

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Some other factors to consider are the increased acceleration would mean more force used by the engine to accelerate the rotating assembly, and the additional weight transfer would change the traction for good or bad, and the gears are not taken into account so the two gearchanges would mean even more weight needed to be removed. I was just doing this for an estimate.
 
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