Underpulleys?
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Joined: Jan 2006
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From: Anoka MN
Underpulleys?
Are underpulleys for a 94 C4 LT1 a good or bad idea? What gains might it get. Where can they be found? Anyone got any? Also looking for some OK used and black seat covers....Any help please...Thx Dan
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Joined: Dec 2002
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From: SCMR Rat Pack'r Charter Member..Great Bend KS
blue,
Go to the C4 Tech/Perf forum.
Click Search This Forum.
Type in "underdrive pulley".
You'll get eight hits.....from which you'll glean all KINDS of good info.
Larry
code5coupe
Go to the C4 Tech/Perf forum.
Click Search This Forum.
Type in "underdrive pulley".
You'll get eight hits.....from which you'll glean all KINDS of good info.
Larry
code5coupe
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
The LT1 doesn't serve to gain as much from a set of underdrive pulleys than does a typical SBC.
The principle is to slow down all of your accessories and therefore reduce the amount of drag that they place on the engine. In a typical SBC this would include the alternator, power steering pump, water pump, and A/C compressor. The gains found by slowing down the A/C compressor may be minimal at best because unless the A/C is running, this functions largely as simply an idler pulley. There may be some gain there, but not a lot.
On the LT1 you can immediately write off some of the gain because the water pump is not driven by the belt to start with. So essentially from a racing standpoint, you're slowing down your alternator and your power steering pump.
Slowing down the alternator can potentially create some charging problems at idle depending on your accessory load. The positive side is that because the alternator is running slower, the bearings should last longer. There is some debate that because the alternator is running slower it also doesn't have as much air flow through it which can shorten its life. To date though I am not aware that anybody has quantified this.
Slowing down the power steering pump is most certainly a good thing. The minimum speed for the power steering pump really isn't that great. Any excessive speed simply results in more wear on the pump. There is absolutely no downside to slowing it down because power steering still works perfectly at idle.
How much power is there to be had with underdrive pulleys on an LT1? I don't know that this has ever really be quantified. There is most certainly some, but you're probably looking at less than 5 to the wheels.
For the LT1 an equally (or possibly more) effective modification is to install an electric water pump. I've written this up before here http://www.wku.edu/~nathan.plemons/htmls/waterpump.html
The principle is to slow down all of your accessories and therefore reduce the amount of drag that they place on the engine. In a typical SBC this would include the alternator, power steering pump, water pump, and A/C compressor. The gains found by slowing down the A/C compressor may be minimal at best because unless the A/C is running, this functions largely as simply an idler pulley. There may be some gain there, but not a lot.
On the LT1 you can immediately write off some of the gain because the water pump is not driven by the belt to start with. So essentially from a racing standpoint, you're slowing down your alternator and your power steering pump.
Slowing down the alternator can potentially create some charging problems at idle depending on your accessory load. The positive side is that because the alternator is running slower, the bearings should last longer. There is some debate that because the alternator is running slower it also doesn't have as much air flow through it which can shorten its life. To date though I am not aware that anybody has quantified this.
Slowing down the power steering pump is most certainly a good thing. The minimum speed for the power steering pump really isn't that great. Any excessive speed simply results in more wear on the pump. There is absolutely no downside to slowing it down because power steering still works perfectly at idle.
How much power is there to be had with underdrive pulleys on an LT1? I don't know that this has ever really be quantified. There is most certainly some, but you're probably looking at less than 5 to the wheels.
For the LT1 an equally (or possibly more) effective modification is to install an electric water pump. I've written this up before here http://www.wku.edu/~nathan.plemons/htmls/waterpump.html
