Underdrive Pulley and Supercharged Engine

[Makahveli]

Does an Underdrive pulley defeat itself when being used on a supercharged engine? It makes sense to me since it would cause the pulley on the supercharger to turn slower, and since I heard that smaller pulleys decreases a superchargers life. On the other had a smaller pulley bringing it back to normal speed, is worth or a waste of money getting that whole pulley setup?

I mean an underdrive pulley, alternator pulley, and supercharger smaller pulley?

 

[rocket 5979]

Does an Underdrive pulley defeat itself when being used on a supercharged engine? It makes sense to me since it would cause the pulley on the supercharger to turn slower, and since I heard that smaller pulleys decreases a superchargers life. On the other had a smaller pulley bringing it back to normal speed, is worth or a waste of money getting that whole pulley setup?

I mean an underdrive pulley, alternator pulley, and supercharger smaller pulley?

In short, not it is not worth it. Keep reading if you want an explanation as to why....

The problem is that when running a supercharger it is putting one heck of allot more parasitic loss on the crankshaft than the difference an underdrive pulley will make. Another big problem is that you will want plenty of belt wrap on the supercharger pulley itself so as to prevent belt slip. Belt slip equals less boost and in turn less power. This can even happen on setups running low boost. So it would be bad to go with a smaller crank pulley. However, it would still be beneficial to go with any other UD pullies besides one for the crank. You will see gains from those even in a SC'ed application. It is just my personal opinion that if you are running FI that there are better places to put your money than into one or two UD pullies that will net minimal gains.

 

[justin146]

In short, not it is not worth it. Keep reading if you want an explanation as to why....

The problem is that when running a supercharger it is putting one heck of allot more parasitic loss on the crankshaft than the difference an underdrive pulley will make. Another big problem is that you will want plenty of belt wrap on the supercharger pulley itself so as to prevent belt slip. Belt slip equals less boost and in turn less power. This can even happen on setups running low boost. So it would be bad to go with a smaller crank pulley. However, it would still be beneficial to go with any other UD pullies besides one for the crank. You will see gains from those even in a SC'ed application. It is just my personal opinion that if you are running FI that there are better places to put your money than into one or two UD pullies that will net minimal gains.

The way I look at it- it is alot easier to put on a smaller supercharger pulley

 

[Makahveli]

Good info for me then, I'm currently swapping my cam and was wondering while the pulley for the crank was already off if changing the pulleys would be a good idea. But thanks now I'll just skip that thought and put the original back on.

 

[rocket 5979]

The way I look at it- it is alot easier to put on a smaller supercharger pulley

To a point. However, there is a reason why my crankshaft pulley is larger than most full sized dinner plates. Belt slip can be a nasty demon once encountered.

 

[Jakee]

To a point. However, there is a reason why my crankshaft pulley is larger than most full sized dinner plates. Belt slip can be a nasty demon once encountered.

That should also make that thing on top of your engine turn faster, right?

 

[rocket 5979]

That should also make that thing on top of your engine turn faster, right?

Yep, my extra alternator (big black box) does spin faster with the larger crank pulley. Jake, don't make me break my crapton of boost theory out again.