Another vote for under drive pulley
 

Installed Pedro's 4" underdrive pulley. Wow, could definitely tell a difference! I recommend it, seems to have only benefits with no downside.

I had trouble getting pulley stud out so had mechanic use air gun, he removed it with no problem. Filling down the boss is easy and does not take away it's functionality. I will keep the original pulley in case engine ever needs to be locked TDC.

What that do Exactly ?

An underdrive pulley slows the speed that the accessories turn at therefore reducing engine rotational drag which free's up HP.

I sure do like mine. The old butt dyno said, "THIS THING'S GOT MORE POWER NOW!!!"

It's a great mod.

+1
The UD pulley was the fix to the constant power steering issues (fluid spills) during autoX events.

Holy crap!!!

Instant HP off the line, right where you want more.

I can't believe they don't come this way. Lots of power.

Can't wait to do cat deletes. They should be in any day!!

How much more HP are we talking?

Not sure, but very, very noticeable. An absolute must for a simple bolt on mod that gives so much. Can't imaging all that new power to the wheels still being absorbed by the engine components.

In this thread (fourth post), engine builder Jake Raby says that he has measured +5HP at the rear wheels when using a UDP.

http://986forum.com/forums/general-discussions/37563-underdrive-pulley-questions.html

none? hmm.. seems to go counter to racing logic.

How exactly is this part improved over stock?

New pulley is 4". Stock is 6" diameter.

http://i868.photobucket.com/albums/a...pse4d96115.jpg

I didn't feel it did that much.

We see this number over and over again with the 4" pulley. The UDP is THE best bolt on for net gains available.

Does it have any more/less impact on the 2.5/2.7 motors vs. the 3.2 motors, or is it a flat 5HP due the common ancillary components used on all engines?

What's the second best? :D


p.s.
While you are(n't) endorsing products, do you mind sharing the make of the UDP that you use in your testing? :D

I just ordered the pulley from Pedro. He said I should get it in the next few days. I'm looking forward to a couple of more horses.
Question for the class: I the bolt reverse thread or normal thread?

Its not commercially available.

RHT. (Normal)

Should come with a new bolt. If. 4" you need a shorter belt.

Okay I'm sold on the Udp. But whats this about shaving down the boss? Can someone explain? This sounds like a must do for my Fall projects.

The boss sticks out far enough to almost touch the back side of the pulley. The belt surface just wraps around it on orig pulley.

The UD pulley will rub into the boss. It's belt surface is dead even with the boss. So I used a sawzall and cut mine off. It would take a while to file down. Cut off flush or slightly proud.

I do not suggest you use a sawzall unless you are skilled with one. I've been using them for many years.

http://i868.photobucket.com/albums/a...pse4e58e4c.jpg