23% under drive pully
i couldnt tell you mine still is up in the air. But i can tell you you will want to get the bigger alt pully as well. If you dont with the smaller crank pully you will overclock your alt and make it produce more amp's. Causing to over charge the bat or burn up the alt.
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Joined: Jun 2007
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From: centerville, ohio
It might only be 1 or 2HP, but it's still 1 or 2HP. If you want every ounce of power out of your setup, go for it.
That being said, it would be the LAST bolt-on that I'd ever do as you can likely better spend your money elsewhere.
That being said, it would be the LAST bolt-on that I'd ever do as you can likely better spend your money elsewhere.
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i couldnt tell you mine still is up in the air. But i can tell you you will want to get the bigger alt pully as well. If you dont with the smaller crank pully you will overclock your alt and make it produce more amp's. Causing to over charge the bat or burn up the alt.
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Verdad Gallardo for a more reliable install an alternator pulley is recommended. but i have a pretty tiny pulley on mine without an alternator pulley and its been working great for at least 6 months (i forget when i put it on) LT1s come with a huge alternator. i wouldnt bother with the second pulley unless i started having problems later
i have a 23% one on mine. if u want all the bolt on's then do it. my car is bolt ons to the max and the valvetrain is even ready for a cam. ima dyno it mid may before the ltxshootout so i can compare what ill make after i do the cam swap 
i put buses on a exhaust only 04 cobra from a dig 
23% works great in a cammed car since idle is usually already raised a little.
With a stock idle, that much underdrive often required an overdrive Alt pulley.
I had one on my LE H/C 350 LT1
It really did improve throttle response. It's much lighter than the stock pulley.
I picked it up used at a good price, so no complaints.
Once thing to note is that it wasn't perfectly neutral from the factory, I had a local shop fix that for me for $20.
I run a 10% underdrive ATI harmonic balancer on my 383 to handle the RPM.
Same deal there, much lighter than stock.
With a stock idle, that much underdrive often required an overdrive Alt pulley.
I had one on my LE H/C 350 LT1
It really did improve throttle response. It's much lighter than the stock pulley.
I picked it up used at a good price, so no complaints.
Once thing to note is that it wasn't perfectly neutral from the factory, I had a local shop fix that for me for $20.
I run a 10% underdrive ATI harmonic balancer on my 383 to handle the RPM.
Same deal there, much lighter than stock.
LMAO funny guy here 
Great to see you're contributing a lot to this forum. Do the Mustang forums suck that much? Or are you just that bored? Or option C...you are getting owned by LSx's so you have to troll through the LTx subforum?
Exactly! Im deleting my other post because I hate **** talkin, but this cobra guy is a douche!!