[QUOTE=Simply_the_best;1320955The BuddyClub set is an underdrive style. So the crank pulley is actually a bit smaller than the factory one. A downside to that is that it changes the charging voltage of the alternator but BuddyClub did their homework with this pulley set and actually made the alternator pulley a bit bigger to make up for the crank pulley being smaller. So the battery still charges normally with zero issues, maybe even a little better. :party0030:[/QUOTE]

I would think that if the crank pulley were smaller, and the alternator pulley were bigger, the alternator would spin even slower...but maybe basic geometry is different in Japan. Dunno....well, enjoy!

A larger diameter will spin faster, smaller = slower. Basic "anywhere" in the world. Think of a 5,10,21 speed bicycle in this regards and how that works. Now depending on what that ratio "overall" is depicts the speed of each item, ie: alternator, H20 pump etc....

Zooki I know where you are going with that but we do not know his ratio and how that was sized..

That's what I think as well. Smaller crank pulley drives the belt slower, bigger alternator pulley spins the alternator even slower.

I don't see how this would change the alternator's voltage, other than if you never rev the engine at all. An underdriven alternator on an engine that gets driven aggressively (higher rpm's) will see basically the same rpm's as normal and create the same voltage.

The voltage regulator is what determines the voltage regardless of alternator rpm's.

It would mainly affect charging at idle. On some vehicles anyway. I remember back in the 5.0 mustang days some of the kits were a little too under driven for street vehicles, especially if you had a stereo system. With the radio up it would discharge at idle. I'm sure they've ironed the kinks out by now. Lord, it's been 20 years since I was building 5.0's...LOL

350matt's post #7 on this thread explains it perfectly.

For those that were not paying attention, my entire explanation is that IF you are counting on just reducing the rotational inertia of the engine by changing the pulley, then the difference is negligible.

Of COURSE if you change the pulley diameter (to smaller), then you underdrive the Alt, AC, & water pump. That is physics too and you WILL notice a difference, but at what cost?


Here's an idea to shed some weight from the car: take off the balance weights from your wheels! That is probably 2 lbs of unsprung weight....

Now that sir is funny :lol:

I still like my idea of making the cam chain drive sprocket half as big which would underdrive the cam chains. OOOH think of the gains in Powah!

must say I think you were a bit harsh on your early posts....and i woke up grumpy this morning....you have grabbed my attention with these latest set of numbers. assuming they are real this time?

my quoting privileges seem to have been revoked?!?

I read through the thread because honestly i had been considering picking up a set of pulleys down the road...figured it would be an easy first step before the flywheel.

Would a flywheel let the engine wind down faster? I see people selling stock flywheels cheap...been thinking about picking one up and having a local shop lighten and rebalance it. I'm suddenly convinced this could be much more effective and possibly cheaper than the pulleys. I've been a bit worried about the aftermarket full on race flywheels because they are super light + the vibrations and stuff you guys mentioned. Again, i dont really care about reving up....I want the engine rpms to drop quicker when shifting....lighter factory flywheel still a bad idea?

My background is general mechanics, not performance

There are many companies selling lightweight flywheels as part of their clutch packages.

Not sure how much it would cost to lathe down a stock flywheel, but ACT and Excedy both sell clutch/flywheel combos for $4-600.

I don't know if those flywheels work with the OEM clutch either, but there might be a lightweight flywheel available that works with the OEM clutch if you didn't want to upgrade. Usually not necessary unless you're going FI.

Yes, going to a lightened flywheel will make a huge difference compared to the pulley swap, and probably for less $$ than one pulley. It will help both revving up, and down.

ACT sells their Race-lite (10.5 pounds) and their street-lite (11.8 pounds) and others are in the 11-12 pound range.

People have reported needing to raise the idle a little to keep from stalling, and it's a little easier to stall the car when taking off from a stop.

That's it in a nutshell unless I've missed something.

Also, a tune will go a long ways towards revving down more quickly.

Stock tune is not very responsive and has the engine revving down and dropping to idle pretty slow.

thought I was being "funny" until told (by someone that probably knows nothing) that I know nothing...

No the "flywheel calculations" are not real in that I made up numbers close to reality to make the calculations simple.
Flywheels are about that big and weigh about that much... I didnt pull any from my stash to measure and weigh them.
The ones I have are for a Porsche, so I would get my ass chewed for not being exact anyway.

For a true rotational inertia calculation you pretty much need the solid model or at least a blueprint. If someone posted me the dimensions & weight of the: Pulley, flywheel, pressure plate, clutch plate, & crank I could give you a better approximation, but I am not that bored (maybe my 17yr old son/pit crew....)

You understand perfectly.
Lighten the flywheel = Get faster throttle response. At risk is bad harmonic resonance and less momentum when shifting.
Regardless of what anyone on this thread "feels", faster throttle response does NOT always equal faster lap times.

Clearly your background retains your common sense as well as a firm grasp of basic physics :burnrubber:

:offtopic:

I've got an ACT streetlite flywheel, heavy duty pressure plate, and their performance street clutch on my STI. The car revs a lot faster, bogs less, and clamps better. The stock clutch would get some bad shuddering from time-to-time. It's a worthwhile upgrade when the stock clutch is done, probably overkill on an NA BRZ. The flywheel would make a big difference for revs, though.

So I will ask this question again: When the engineers were trying to squeeze every last hp out of this engine to reach the rated "200hp" mark why didnt THEY just change the size of the pulleys?

Seems simple right?

If you want a drag car why not just bypass the alternator & AC entirely with a belt that only drives the water pump?
ON TOPIC enough?