I just got am underdrive pully and claims 10-13hp increase. What can i expect from this mod?

 

at normal operating i would guess 5 to 7 hp

 

And your alternator putting out less power (read possibly marginal) at idle.

 

Yeah, I would really assume maybe 1-3 HP on a stock engine.

 

What was the percentage of the UD pulley? I know there is a 10% and a 25% one. You can run an overdrive alternator belt to help compensate for some of the loss that comes with a UD pulley.

 

If he runs are overdrive alt pulley with an underdrive crank pulley it's really almost the stock setup then.

 

That defeats the whole purpose. The underdrive pulley setups are for slowing down all the belt driven accessories. The alternator spinning under a load is the biggest drag of them all, so you'd just be adding it right back making the investment and time spent not worth it. Unless you're mostly after the "ooh" factor of having billet pulleys.

 

I've read of quite a few people on ls1tech running a UD crank pulley and an OD alternator pulley, and still have improvements over stock. Some also claim certain brands/kits provide you with a OD alternator pulley.

Doing some more reading on ls1tech, I see a lot people claiming gains of around 8rwhp with a 25% UD pulley. Don't know how truthful some of their statements are, but oh well. Let us know when you install it if you have any issues with it.

 

Do i need a new belt to to fit, since the pulleys are different sizes? Or will the tensioner take care of that?

 

Amd im not sure on the percent, this was the only one i could find on summitracing on mods for a 3.4 are hard to come by so i was just happy i found this one. And idk if this will make a difference but my engine isnt completely stock, ive CAI and 180* stat.