Underdrive Pulley - The 1947 - Present Chevrolet & GMC Truck Message Board Network

GMC1967 · 10-02-2002, 03:43 PM

What do you think about using a smaller diameter pulley. The idea behind this is that the smaller crank pulley slows down accesories and thus giving more power to the wheels. Anyone done this?

68 with 350 TPI · 10-02-2002, 05:51 PM

I have put some on a few of the imports I work on.
It does help with peak HP just a bit on the dyno but never enough to really feel.

I dont think that its worth the $$$ but it does give a few extra hp.

The most I have ever seen a set of 3 UDP's give was 14 hp on a dyno and that was for a camaro and even then the "A$$-O-Meter couldent tell they were on the car on a before and after test.

Like I said it helps out at peak HP so it will be in the upper revs before you even get the few hp it gives you.

So if your just doing the crank I wouldent expect much of a gain but maby 4-5 hp at peak.

Keep in mind that some of the cheaper companys go too far of a underdrive and it can drain you battery at idle.
Dosent happen often but it can happen.

10-02-2002, 03:43 PM	#1
GMC1967 Registered User Join Date: Jan 2002 Location: South Deerfield, MA Posts: 162	Underdrive Pulley What do you think about using a smaller diameter pulley. The idea behind this is that the smaller crank pulley slows down accesories and thus giving more power to the wheels. Anyone done this?

10-02-2002, 05:51 PM	#2
68 with 350 TPI Registered User Join Date: May 2002 Location: Wingate NC Posts: 456	I have put some on a few of the imports I work on. It does help with peak HP just a bit on the dyno but never enough to really feel. I dont think that its worth the $$$ but it does give a few extra hp. The most I have ever seen a set of 3 UDP's give was 14 hp on a dyno and that was for a camaro and even then the "A$$-O-Meter couldent tell they were on the car on a before and after test. Like I said it helps out at peak HP so it will be in the upper revs before you even get the few hp it gives you. So if your just doing the crank I wouldent expect much of a gain but maby 4-5 hp at peak. Keep in mind that some of the cheaper companys go too far of a underdrive and it can drain you battery at idle. Dosent happen often but it can happen. __________________ Life is good with a 6-71 supercharged 355 in a 72 camaro



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