Light crank pulley is a useless and aesthetic mod pushed by lazy companies. Use OEM or use a proper piece like a Fluidampr pulley.

Technically, lighter pulleys, drive shaft, flywheel, and wheels all contribute to lower inertia and hence faster acceleration. In terms of effect on the angular inertia, per lb in weight reduction, the order of significance (from large to small) is:

(1) flywheel; (2) wheel; (3) pulley; and (4) driveshaft.

Also, light weight lug nut will also help (ever so slightly).

The incremental improvement of adding each of these light weight parts may not be so apparent. But the opposite is true: ie the result of replacing these light weight parts with their oem, heavier parts, is VERY apparent. It feels like adding a 100lb sack of potato to the trunk.

Please remember none of these light weight part adds power, per se. They only reduce inertia of the drive train, and hence better acceleration (and deceleration). The effect is applicable at all times at any rpm.

The effect may be vey tiny at all RPMs when the car is out of gear. As soon as the car is in gear and powering the driveline then any difference is so slight that is would not even be measurable muchless noticeable. It does not make any difference if you saved 2 ounces on a pulley once the tranny becomes engaged. The engine speed is now restricted by the gearing not the weight of some outlying minor components. The theory and the reality are two radically different things in this case.

I generally avoid buying anything from those manufacturer brands which have such useless, and often overpriced, parts among their products.

Which company is exactly lazy and overpriced? A company like the following one?

http://i64.tinypic.com/dfgm15.jpg

Yes, they have also lightweight pulleys and driveshafts. Because they are simpler mods and not anyone wants or willing to open the engine. Our ignorance, doesn't mean that they are useless.


@OP: I like your mods. Unfortunately, the faster drop of RPMs requires faster gear changes which is not always optimal on a street car. Personally, I would choose as next mod the thicker rear axles.

https://www.sti.jp/parts/subarubrz_z.../ST28421AS100/

Enlighten the ignorant, then. I am ready to listen. You can start with presenting the data for fly wheel upgrade and drive shaft, for example. How much improvement in power and acceleration? Give the numbers.

Why would I start a discussion by giving names of manufacturers that I don't care about. I can give recommendations, though. How about my highest recommendation for Jackson Racing that increased my power to 300hp. Your turn. But no unsupported crap please.

See post 11. I didn't calculate pulleys because I was lazy, and I wasn't expecting more than 1hp return based on the other stuff. Was thinking of fixing up my drive line inertia calculator to make it easier to use and posting it. I just did a rough calculation once because I was curious.

Cars are complex systems with many parameters and a physical model is an over-simplification. We cannot know the engine's potential, until we measure the effect of a specific kit.

Here are the gains of a pulley kit with a small under-drive on the alternator. The measurement was made on 4th gear by Toda:

http://i67.tinypic.com/118gggh.png

The gains are between 3-10 hp in the entire RPM range. You asked about numbers and you got it.


I won't start a discussion of supercharger kits here. It is irrelevant to OPs topic.

^ Graphs that say power increases with lightweight pulleys and Fluidampr ones that say it decreases. This is getting fun.

Fluidampr is a heavier pulley comparing to stock and has an entirely different function. I've seen respected Japanese tuners to use it on supercharged or turbo 86/BRZ cars for increased engine reliability. It is a good option if you are going with FI. On a NA car they are saying that it is not really needed.

Anything in real world data that can be related to actually driving the car, and not just the engine on an engine dyno, where there's absolutely zero drivetrain loss? Or are you just going to prove that you're just a huge sucker for marketing material once again?

You can see my car's modification journal and the majority of the changes are from Subaru / STI. Even the Toda's bigger throttle body is a slightly bored factory part. Reason going with them is because STI never touched the engine. Not to install a turbo, but to make some refinements the way they did on handling. So, it is funny to be accused that I am huge sucker of Toda's marketing material, when I am using basically factory parts.

If you or other people can't get over of what they bought and searching about huge improvements it is not my problem. It is your problem.

I asked Perrin if installing an ACT SB7 with Streetlite clutch, with a lightweight driveshaft, and with Perrin's three lightweight pulleys would damage the engine. Here's their response.https://uploads.tapatalk-cdn.com/201...5795a5b5f0.jpg

Thoughts?

Yes in some older Subaru engines, if you were combing a lightweight driveshaft with a lightweight pulley you could get a CEL miss-fire code. It was known to happen if you were going lower than a specific weight. It wasn't known if there was an actual miss-fire or just the ECU was throwing a code. I've not heard something similar in our engines.


A final remark concerning different lightweight pulley kits. There are some cheap ones and some quite expensive. The difference is not related with the marketing department of each company, but the used material. You replace a steel pulley with an aluminum one and it is important to not have a failure. It is known that 7075 aluminum material is much better than the cheap aluminum, with a strength comparable to many steels. However, it is more expensive. So, you get what you pay ...