I know that the UR Underdrive Pulley is supposed to lighten the load as you rev and such . . . is this good/bad/doesn't matter for a Twin Turbo car? My friend told me that it should help my revs and throttle response and that I should replace my pullies with lightweight ones.

What else is available for replacement besides the underdrive pulley?

Thanks as I'm not too familiar in this area.

-Miluo

 

I'm not big into underdriving my accessories. I say it's not worth it even for an NA car, much less a car with twins.

 

+1 on not underdriving. It just means your AC and alternator get less juice and less cold air all for 2 hp that you won't feel

if anything get a stock diameter lightweight crank pulley, but since you run a turbo I probably wouldn't bother at all. It'll help your throttle response, but it'll make you "outrun" your boost build up by a couple hundred rpms or so since a turbo is load dependent. That'll end up negating a lot of the gains, but you'll overall accellerate just slightly faster - but probably not really noticable

For NA or supercharger, a lightweight crank pulley will serve more of a complete benefit since the amount of boost for a given rpm isn't a variable, but the risk is still up to you if you want to risk your crankshaft over it

 

I've already killed my AC and removed it. No AC all summer . . . I'm used to it.

So you're saying that if I go and underdrive everything that I won't boost as quickly because there is less load?

 

well kinda in a way

here's two examples:


-stock crank pulley
start at 3000 rpms, floor it, at 4000 rpms you have 8 psi
this whole process takes around let's say .8 seconds


-lightweight crank pulley
start at 3000 rpms, floor it, at 4000 rpms, you have 7 psi
this whole process takes around .6 seconds

if you waited .8 seconds the same as the first scenerio, maybe you'll be at 4200 rpms and reach 8 psi then




It's the same concept running a turbo in a low gear vs a high gear.
With a turbo you'll build boost at a way earlier rpm when in a higher gear than in a lower gear where there's less time for a turbo to spool before shifting

you'll be a little faster overall, but because you're "outrunning" the boost pressure build up by a little, you're giving the turbos less time to do their thing before you have to shift at redline so you're not going to get a complete benefit like the NA or supercharge people do where the name of the game is to get to redline ASAP and the SC's boost is either constant (stillen SC) or tied consistently to the engine rpms (vortechATI/HKS SC)

 

https://my350z.com/forum/forced-induction/298701-almost-back-on-the-road-new-and-improved.html

read this post by Zivman . Might change your mind on using a light Wt. pulley