Larry Hargrove

I saw a listing for an underdrive pulley set on ebay promising 10 to 30 h.p. increase, better fuel economy and better acceleration. Does this actually work? Would one need to change to a different length belt?

Whaleman

It slows down the AC Compressor,power steering pump and alternator. I am very leery of 30HP gain. I guess if someone believes this is a good idea they must assume the Chevy engineers are really dumb and did not know how fast the accessories needed to turn at any given RPM. Dan

ctmccloskey

You could end up with a lot of potential problems by going with the pulleys designed to slow down the accessories.

Charging the battery is important on a Electrically Fuel Injected car. Reduce the speed of the alternator and you reduce the output. The water pump speeds are designed to operate within specific speed ranges to keep everything nice and cool. You slow things down and you will probably start seeing higher than normal engine temperatures.

On my C3 I found the difference between a 5.5" pulley and a 6" pulley was a noisy power steering pump and poor responsiveness.

I bought my Corvette because it is a "well-engineered" car, there are a few places to pick up power but that is one that I would not recommend to any Corvette owner.

30 HP gains from slowing down your accessories? I would never believe that unless they had a dyno sheet to prove it with before and after numbers done by a "reputable" independent shop.

There are a lot of gimmicks that people try to sell to Corvette owners in the name of making more power. Some work, most don't.

By the way, yes, you would likely have to use a non-stock size serpentine belt if you change the pulleys. Good Luck!

ddahlgren

If you buy the pulleys an air foil and electric supercharger you could gain 100 hp. easy LOL

Natrlone93

Probably closer to the 10hp and you may end up with battery charging issues among other things. I wouldn't do it.

Cjunkie

Underdrive pulley sets typically replace the crank, water pump, and alternator pulleys. I don’t know where people get their information in above posts.
As a set, depending on application you can see a 6-10 rwhp increase. You may see a low charge or increase temp at idle but I never have and have been using them for over 20 years albeit on Ford products.
They are especially useful when doing gear changes, running at hi rpm, someone wanting to increase fuel economy, or just someone looking for free HP.
Don’t get caught up in the engineers know best. Engineers have to satisfy the company, cost, epa, safety, warranty........may not or doesn’t have to be the BEST.

Natrlone93

Depending on the year C4 the water pump pulley does not apply so the free HP numbers are lower. I did this mod years ago on a 90 5.0 I had and had a low charge issue that's why I mentioned it.

Cjunkie

I only noticed it when i took off the crank pulley that came in the kit and installed the tiny race crank pulley myself. Nothing anyone in the C4 world would do,see,or know about most likely.

383vett

I've used the smaller crank pulley and larger alternator pulley on my car since almost new. Still running the same even though it is now a trailered race car.

Larry Hargrove

Thanks to all of you who offered opinions on this. I'll probably just leave mine stock since I'm not going to be racing it anyway.

Cjunkie

I would unless you want improvements going down the track.

whalepirot

Experimented on a Suburban; sole result was lack of adequate boost when parking... exactly when I needed it. No measureable accel change, timed or SOTP, improvement.

"Free HP"? How, unless parts and labor are free!?