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Underdrive Pulleys do they work

4244 Views 15 Replies 10 Participants Last post by  Idahoan T-Bird
I'm really interested in unlocking 10-12hp with the underdrive pulleys but I don't want to end up buying them to gain nothing. For all that has used them, do they really work like they say they do? Is there a noticable gain in the hp or really no change?

SCP 2 Piece Accessory Underdrive Pulley Set $105
Includes a new alternator, and crankshaft pulley.
An easy bolt on that yields 10 to 12 HP. Less parasitic drag from your accessories means more power can go to the rear wheels. These are no gimmick...they work like a charm!
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of course they work. dont expect the 10-12 hp on your N/A 3.8 though, be happy if you can manage 7
Just the Crank pulley was dyno tested at 8.6rwhp on an automatic 3.8L mustang, thats a 10-11hp gain at the flywheel.......... Very well worth the money, IMO its the BEST bang for the BUCK mod on a 3.8L. You only need the 1 pulley set unless you have a huge stereo system. Check out for a good price! (I've done business with them and they are great)
Thanks for the help!

Hey you guys really helped me out a lot! Hopefully someday I will be turning the ponies you guys turn. I take it I will need to get a new belt for this mod correct?

Thanks a lot for all the help.
Yes a 96" belt, stock is 98.5"
I agree the easiest, best bang for the buck.

Also, it is an easy mod for a beginner. There is not much to taking off the old belt, putting on the pullies and then on with the new belt. I did it in an hour or so on my 5.0.
What are the best U/D pulleys for my 3.8 lx?

I heard Steeda U/D pulleys were the best to get, but I'm not sure if that's only for V8s.. do they offer them for the 3.8 V6? if so, can someone give me a link on where to find them. I looked in the tccoa most wanted parts.... that led to summit racing.. but i couldnt find it anyway..


Any help would be great.. cuz i really wanna get these in my car... and if not steeda, what else?

Thanks guys!:D
I've got the ASP pulleys on mine. I know MAC made a set, not sure if anyone else does. Follow the link that RancherLee gave you, they have them.

i went to but could only find 3 "ASP Underdrive Crank Pulley" for the V6 3.8..... but they were for the "94-98 3.8 mustang," "99-00 3.8 Mustang," and the "01-02 3.8 Mustang"...

i have a '93.... so are any of these for me?
94-98 mustang one is the one you want.
go with the 94-98 like rancher said...I got mine, installed it in like 15 minutes! Easy mod to do...I feel my car pick-up better, not A LOT but some...I manily feel it at 35-45 mph is good for a first-time mod, but not too good with my stereo system...oops... :D

Is the 94-98 stang set gonna fit on my 1990 NA 3.8?
Also, anyone know where to get three piece sets cheap?
Also do they make 4 pc sets for the 3.8's (water, steer, alt, crank?)
Also in the one piece sets, is the crank pulley smaller than in a 2 or 3 piece set or is it the same.
Yup! The Mustang set will work. There is only a 2 piece set for the 3.8.


but not too good with my stereo system...oops...
What do u mean?
What I meant by my stereo system is that since the crank is smaller, the car needs to be at about 950 rpm for alt to put out a full charge and with my system playing at a stop light or something, the battery dont charge to well...I need a bigger alt put on...Other than that fact, I like the pulley...

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