What is an underpully?
Senior Member
Joined: Jan 2007
Posts: 694
From: Michigan
RE: What is an underpully?
Hi Dale, an underdrive pulley or smaller diameter crankshaft pulley will turn all of the driven items at a slower RPM than stock. This will give a small increase in hp but at a cost of lower output from the driven units. You can choose to underdrive individual items by increasing the size of the driven pulley.
Senior Member
Joined: Mar 2006
Posts: 643
From:
RE: What is an underpully?
You want to know how to build performance on an LT1 the right way? Then go to the link at the bottom of this post. This guy knows what he is doing and he lists whats useless and what works:
http://www.wku.edu/~nathan.plemons/h...rformance.html
http://www.wku.edu/~nathan.plemons/htmls/increase.html
http://www.wku.edu/~nathan.plemons/h...rformance.html
http://www.wku.edu/~nathan.plemons/htmls/increase.html
Underdrive Pulleys - A common bolt on modification is a set of underdrive pulleys. The theory of this modification is to change the pulley sizes in such a way that the accessories are slowed, thereby reducing drag on the engine. This modification is sound in theory but it has some possible drawbacks so I list it in the marginal section. The largest accessory drag on the traditional small block is the water pump, with the LT1 this is not an issue. An underdrive pulley on the the LT1 does effectively slow down the air conditioning compressor, power steering pump, and alternator, which does free up some horsepower. As far as I know the gain has never been quantified so I cannot list it in the proven modifications section.
