Dave_B

Yes, but keep in mind that if you remove weight from the flywheel, you're going to remove stored energy therefore your car will be a pain to launch without bogging. It's very common for the car to result in slower 60 foots and that has a hugely detrimental effect on the elapsed. Lightened flywheels are great for cars that used for road racing because it allows the driver to execute easier rev matching on downshifts.

I hate cars

Agreed. And drag cars with an auto. It was a nightmare to just drive my friend's 951 with aluminum flywheel and a 3 puck clutch.

Mr Marco

supra98

Lost me at...

"Here goes...."

haha, ok so, Is it worth getting an aftermarket pulley? or is it a waste of $$?

TheChamp531

iTrader: (3)

It's up for you to decide, but I think it is worth it.

Aman

Noob alert.

One question about your calculations regarding the pulley, Cross-hair (Or anyone who can answer).

You used 2 seconds as your elapsed time for the engine to accelerate from 1500rpm-6500rpm both with the stock pulley and the lightweight one. But so far nobody's doubted the UR's ability to let the engine rev quicker. Wouldn't this decrease the elapsed time needed to rev for an engine equipped with a lightweight pulley? Or would this be applicable only to an engine with no load on it? How would you calculate any decrease in time?

This sort of leads me to my next question about lightweight flywheels. I hope it doesn't count as OT.

Is the only benefit of a lightweight flywheel a quicker revving engine? Does it help with acceleration at all (negligible benefits or no)? I can understand the engine bogging at the strip if you're doing a high-rpm launch, or going up a hill. In layman's terms, is it because a lighter object spinning at the same speed has less momentum? That's the only explanation I can think of.

Shouldn't it help in acceleration though? My theory is that it's less rotational mass for the engine to accelerate, less "drag" if you will.


DISCLAIMER: I am stupid and don't really have a clue what I'm talking about.

TL Luver

iTrader: (2)

Man yall must have alot of time on yalls hands to write all that!!! and thanks!!!

"but im gonna keep it short; so here I go"

"I'm happy with mine!"

realfresh

awesome post.


but thanks for taking the time crosshair, interesting theoretical read

jr27

damn i just read all this stuff but im still not sure if im gonna buy one. all i wish to have answered is this.

will my car move faster off the line?

thanks guys i am about to do my 105k tune up and have everything bought so i will basically get this installed for free if i throw it in there at the time of installing my belts and tensioner, so i want to know if i should buy it or not.

I hate cars

Basically it will make a very small difference with the largest difference being in 1st gear and fading with each gear. I doubt you could measure a difference in 3rd. In theory it will have the largest effect in neutral lol. If you're looking mostly for off the line improvements, it's probably a good idea especially since you would be getting free labor.

jr27

cool, thanks man, you or inaccurate always come through for me... lol. i will order it now. i am getting the stock diameter because i have two 12 inch jl audio subs i plan to put in my car very soon aswell so i think the underdrive will be a problem. what do you think i believe my amp is 1200 watts rockford. and i have a epicenter and a capacitor too.

lumyeinjun

iTrader: (1)

I'm sorry brother, but I think a more affordable route to make your car move faster off the line would be losing some weight in that fat ass (referring to your trunk ). 100lbs of equipment deleted would serve as a far greater benefit in performance than the addition of a lightweight pulley.
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And sorry for reviving an old thread but I think Crosshair's thread is full of invaluable information and I would hate to see this thread fade into forgotten history. We have a great discussion going on here and I believe anyone thinking about a lightweight pulley should read this and at least try to understand it.

If you aren't familiar with physics here is the short answer:

Will your car benefit from a lightweight pulley? YES
Are the benefits significant? Statistically: yes; real world: miniscule
Will you feel the benefit from a lightwight pulley? Probably not.

With that said; I've had my underdrive pulley on for four years and I don't regret it. Saving 7lbs at the nose of the car is saving 7lbs, and with a $39,000 car I'm not losing any sleep missing $200

Majofo

Is that a flux capacitor?

Aman

But it's a good thead.

T Ho

It's already been covered, but if you did a before and after dyno in 1st gear, it probably would have shown up (assuming you could isolate results for weight and negate the converter design benefits). Lightweight stuff shows up when you increase the dyno climb rate from 250 to 3000rpm/sec.

On my old Camaro, I have an under drive pulley (25% under the factory) that consistently showed me a tenth and 1-1.5mph (consistency is not my strong suit...) in the 1/4. It drives a clutch fan, but slowing the acceleration of the accessories should help as well.

Cross-Hair

Hey guys, it's been a little while since posting much, but I thought I'd follow-up. Since my original post (uh 2 years ago already I guess), I had not purchased a lightweight pulley. Personally I thought that it's a fairly steep price and install effort to get this thing on.

Now however, I'm about to reach my 105k service, and thought it was time to look into it again (since "install" would basically be taken care of anyway). I decided to look at the details again...

I thought I'd go and do an actual test of my assumption of ~2s to go from 1500rpm to 6500rpm, which is a main driver for these results. And here's what I got (tonight):

Temperature: 77degF
Dew Point: 44degF
Humidity: 38%
Pressure: 29inHg
Elevation: ~5300ft (biggest factor)

Under these conditions, I tried a few runs from 0mph through the first gear shift. My very "scientific" approach consisted to mashing the pedal at the same time as starting my stopwatch on my phone (~700rpm), and then clicking stop as I hit 6500rpm (initiating the shift to second). A few things to note is that the car has an ever-so-slight delay between me pressing the gas pedal and the car starting to rev. Additionally, my front tires are almost absolutely bald and I haven't put on my new set yet... this led to a good amount of tire spin.

That said... my results were an unimpressive ~4.5s between several runs, with trying to keep things constant. To approximate a better number by excluding the throttle delay, wheel spin, dropping out the 700-1500rpm and my fat-fingering the timing on the start/stop timer... I'm going to use 4.0s as a best case for me for a rough approximation (plus it's convenient with the calcs).

If you take a look at my original calcs, you'll see that I did everything assuming linear relationships, which is good enough for average values. The nice thing with this, is it makes determining your actual power a lot easier by a quick scaling factor. In short, I can take my original calculated values and scale them by 2s(theoretical)/4s(actual) to get my personal values.

This brings my effective results to the following approximate values (ft*lbs and hp):

1st gear:
Torque gain - 4.75
Power gain - 4.5

2nd gear:
Torque gain - 2.85
Power gain - 2.7

3rd gear:
Torque gain - 1.9
Power gain - 1.8

4th gear:
Torque gain - 1.7
Power gain - 1.65

5th gear:
Torque gain - 0.85
Power gain - 0.8

Please, please keep in mind that this is still part theory and part actual results. This is not the exact number that everyone gets. However, I feel very confident in saying that these are a pretty solid +/-20% estimation (assuming you use your own rev-time).

(As a side-note, please keep in mind that you sea-level guys get about 25% more power than what's listed in this post due to the significant impact that elevation plays in general.)

Now, back to it: 4.5hp for ~$200 sounds decent, but when I look at it percentage-wise, it's only an additional 1.5% (of my 286hp TL-S). To put that in perspective, do you think you'd be able to visually recognize the difference between 200 pennies and 197 pennies? Now how about by weight...? Probably not... Same applies to feeling horsepower. 1.5% is 1.5%...

Also keep in mind that this is in 1st gear only, and drops off significantly with each additional gear.

Hopefully the tone of my post has already made it clear, but I will not be purchasing a light weight crank pulley and would probably only seriously consider it if it were in the sub-$100 range. That's not to say it's not a good mod... it's just not for me.

I believe that spending the extra cash to get an nice J-pipe (potentially with cat-deletes) should be a priority as you'll not only get more bang-for-the-buck, but be able to feel it consistently in each gear.

Anyhow, I hope this helps some people make a decision. Good luck!

Aman

Thanks again for posting this.