:tup:

O.K. Two questions:

1. DD - you responed to one of my questions on this earlier regarding HFCs. While the HFCs will not make that car THAT much louder, you noted they would change the tone. If I was running an Amuse R1 Titanium catback and Y pipe, would HFCs make the Z louder? I am not sure if that can truly be answered, but I appreiciate any thoughts.
2. The Nismo flywheel and clutch that shaves 20 pounds is very cool, but how much would that affect the already noticiable shifter vibration??

Any thoughts/experiences/comments are greatly apprecieated guys!!

Yes they would make it louder. The stock cats restrict more noise than high flow cats do no matter what setup you have for the rest of your exhaust.

Just use moment of inertia calculations to determine how much you will save off the rotational mass change. I can do it later - too many ppl watching me @ work lol

Oh my - looks like he did my calculations for me!!

Please do, I'd love more information on how to calculate the effects of changing the rotational masses (as in lighter wheels and brake rotors), but I'm not really familiar with the math/physics involved.

ok if we assume the wheel is a uniform disc... of weight M then the moment of inertia of that wheel is 1/2 * M * R^2 ... so... with a 19'' wheel - lets say it weighs 25lbs the moment of inertia is about - 1/2 * 25lbs * 19 * 19 = 4512 lb*inch^2

now lets say the new wheel weighs about - 24 lbs so a 1lb saving... moment of inertia = 1/2 * 19 * 19 * 24 = 4332 lb*inch^2

ratio of difference = 4% less moment of I w/ 1lb diff in wheel

so ... what that tells us is... roughly - shaving 1 lb off per wheel - makes it 4% easier to spin that wheel ... hope that makes sense :p

EDIT: for more info: http://hyperphysics.phy-astr.gsu.edu/Hbase/tdisc.html

Nice. I have some followup questions though:

1) Does it make any difference whether the weight is being dropped from the driven (rear) or rolling (front) wheels? I'm inclined to think it doesn't matter, as the engine is pushing both rotationally, assuming no appreciable tire slip being factored in for a simple case.

2) How do we apply this to the car as a whole in order to determine how much effective % difference in acceleration a weight drop at the wheels makes? Let's say I run the numbers for the whole wheel/tire package at all 4 corners, using the combined weights of the tire+wheel at each corner and the radius of the tire+wheel. Let's say I shaved off 4% per corner. That doesn't really mean the same in terms of overall acceleration numbers as, say, a 4% drop in car body weight does it?

I would imagine one would have to calculate moment of inertia stuff for all rotating masses (so the hubs, rotors, wheels, tires, etc, plus the driveshaft, the rear axle, the rear diff, the transmission, the flywheel, the engine itself, etc??? it's a long list), and then somehow combine that and the static weight of the car into some final number for how much force has to be applied to move the car a foot, and then see what % that number drops from removing weight at just the wheel as a percentage of the whole, right?

Very interesting discussion going on here.. check this out.. kinda funny and really shows the effects of saving weight on performance.

SCC Technical Assistance Program

so i see what your saying......all i need to do is chop off 1,000 lbs of crap off my car, render it useless, but, ill have a 12 second ride at least:icon18:

great link BTW

Chop SHop Race Car?
 

Alternatively, buy a car design to for the race track if that what's your after.

DUDE!!!! That was Freaking Hilarious!!!! basically ur left with wheels an engine 1 seat and a floor board! :roflpuke2::roflpuke2::roflpuke2: And the funny things is... They are still slow!:bowrofl::stirthepot::inoutroflpuke:

That formula assumes a 1984 lb car also known as a lotus. It's just a power to weight formula. It seems a little off too should be something like

equivalent horsepower= (hp*original weight)/(original weight - amount removed)

or say Ehp=(332*3232)/(3232-100)

Ehp=1073024/3132 Ehp=342.6 so a 100lb savings = 10.6 horsepower

But you aren't making more horsepower it just means you now have the same power to weight as the guy with the stillen exhaust

^^ :icon14:

:iagree: this looks like the euro thread.