Question about Underdrive puleys

Silveradoguy04 · October 23, 2005

Hey guys, I was looking at summitracing.com today and found a underdrive pulley kit for my truck (Silverado with a 4.8L) I was wondering what you guys thought about them. Pro and Cons

facn8me · October 23, 2005

Con's Reduced water pump speed bad in hot weather. Slower A/C speed= Less cooling inside. Slower Alt speed= lights dimming at night at idle. Can't see any Pro's with the Con's involved.

99Silver6.0 · October 23, 2005

ASP makes the best for the trucks. To solve the Alt issue, you can get an overdrive pulley for that. But do keep in minf you are under driving the water pump too. I made a no BS 12HP with my ASP crank pulley alone. Took it off cause my truck started running hot.

Silveradoguy04 · October 24, 2005

Con's Reduced water pump speed bad in hot weather. Slower A/C speed= Less cooling inside. Slower Alt speed= lights dimming at night at idle. Can't see any Pro's with the Con's involved.

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Thanks guys for your input.

badbrown427 · December 14, 2006

sorry this is an old thread but seriously there have to be more pros to the pulleys.....

DayUSeX · December 14, 2006

well the pros to any underdrive pully is less rotating mass.

Less rotating mass means the engine is moving less weight per cycle.

So you get more MPG and horsepower (more oculd even be .001 its still more).

You are not adding, so much as you are freeing up.

Some say they gain 10 horsepower (ls1's)

Some say they gain 8 (focus svt)

where I have seen alot of 4 cylinder domestics, not gain jack s**t from crank other than the negatives.

As for ls1's I have actually seen some decent gains (8 being the highest).

Cheers!

badbrown427 · December 14, 2006

well that is good to hear. i dont have a huge stereo or big offroadlights or a winch so i dont see why this isnt the perfect upgrade to me.

thanks DayUSeX for the input. it seems around here everyone is 50/50 split about it. However is the overheating issues are for real then it makes me very very skeptical about it.

thanks again

MyFirstV8 · December 15, 2006

My advice is to avoid ASP and anything that they make. I've had issues with them where they did not stand behind their products.

I've used a JET underdrive pulley on the 4.3 V6 and gotten really good results. Gained 2 mpg, which was a 10% increase. Thing is that was an older design of engine. I think that with a newer design engine you will not be able to improve as much.

DayUSeX · December 19, 2006

Hey myfirstv8 can you tell me how the install went. I want to do this. What size belt did you need to get. Some people said there is ltos of cutting and griding, is this true??

And when looking at my stock underdrive pully i thought HOLY HELL. That thign is massive and must weigh a tone.

I wish that a company made lightend pullys for us 4.3 people =(

MyFirstV8 · December 20, 2006

The install for the 4.3 was pretty easy. Just pull off the old pulley and bolt up the new one. I had to figure out the belt size myself since I did not use the alt pulley. A piece of string around the pulleys gives that #.

On the 4.8 I have no pulley experience. I'm betting that there is no pulley offered because the stock one is not a problem. I've got a 285 horse 4.8 and I still get over 19 mpg in my crew cab. The better the engineering that goes into a vehicle, the less room for improvement there is by the owner.

TheClassic · February 15, 2007

This is an old thread, but I thought I'd give a little input here. The running hot issue could be solved by an electric water pump. That would be even better for power. Granted it would make this project a lot more expensive, but it's a very good option. As for the lights dimming, go with the above mentioned overdrive pulley for the alt. That should cover any problems. Power steering might be a little tougher, but that's probably not too bad.