Underdrive pulleys
Team Owner
Joined: Sep 2003
Posts: 20,179
Likes: 673
From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
I've got the two pulley set and found that just running the crank pulley is overall the best. Keeps water and alt speeds at their efficent speed. Ran the alt pulley but the speed is too slow for summer nighttime driving. That is pulling up to stop lights with the head lights on. The alt drops offline and your on battery. Do this a coupla times and the batt is now drained. Next time you try to start, dead batt! Not fun. For the track, I run it. But not the street. Just remember you'll need a different size belt for each pulley combination. THat can get expensive...
Drifting
Joined: May 2003
Posts: 1,979
Likes: 48
From: Lakeport CA
March here too, bought the black 3 pully kit, came w/ matching belt. Funny thing though... a few years later I had the engine apart, pulleys off & where the paint had started to crack a little I found... polished alum underneath. Took some paint remover to them & they turned out great. I've also never had a prob. w/ the alt. output? Although I did go to the cooler running rear case (has extra finning) and a higher amp outer winding last year. J-C witless specials....
Le Mans Master
Joined: Mar 2001
Posts: 9,464
Likes: 1
From: Modesto CA
I'm just running the March Crank Pulley and it's only noticeable when you have the headlights on, stereo on, heater on, and it's in reverse, holding the brakes, the dash will show 12.0 volts, but the ACTUAL battery will be at 12.5v+...all other times, it's 14.0v+
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Safety Car
Joined: Jun 2000
Posts: 4,870
Likes: 25
From: Long Island, NY
Originally Posted by L98Corvette
Hi guys, i want to put some underdrive pulleys on my 91, can someone point me to a set of them and how do i determine belt size? Is there anything to be gained with them?
Thanks
Thanks
I run the Crank underdrive pulley only, I ran faster in the 1/4 Mile with it. If I was a Street car only and never raced it at a Track, I would not mess with the pullies.
Vic
Le Mans Master
Joined: May 2000
Posts: 7,033
Likes: 12
Originally Posted by JrRifleCoach
I've got the two pulley set and found that just running the crank pulley is overall the best. Keeps water and alt speeds at their efficent speed. Ran the alt pulley but the speed is too slow for summer nighttime driving. That is pulling up to stop lights with the head lights on. The alt drops offline and your on battery. Do this a coupla times and the batt is now drained. Next time you try to start, dead batt! Not fun.
Burning Brakes
Joined: Nov 2004
Posts: 1,057
Likes: 0
From: Warren Ohio
Originally Posted by 1996man
do they make a kit for the LT4 to free up a little power as well? i was a little confused by their website. anybody here running aftermarket pulleys on their LT4?
March used to make a 23% underdrive unit for LT1s. I have their old 2 pulley "Power and Amp" set, and no problems of any type with them.
Burning Brakes
Joined: Nov 2004
Posts: 1,057
Likes: 0
From: Warren Ohio
Originally Posted by hippy
I'm curious, my March alternator pulley was smaller in diameter then stock which would mean it would spin the alternator at a higher RPM. Correct me if I am wrong but wouldn't the alternator put out more voltage with the 3 piece set vs just putting a crank pulley on and leaving the stock larger diameter alt. pulley?
Melting Slicks
Joined: Dec 2001
Posts: 2,437
Likes: 1
From: Gainesville Fl
Originally Posted by 95PoloVert
March doesn't. I believe ATI makes a 10% underdrive unit, though.
March used to make a 23% underdrive unit for LT1s. I have their old 2 pulley "Power and Amp" set, and no problems of any type with them.
March used to make a 23% underdrive unit for LT1s. I have their old 2 pulley "Power and Amp" set, and no problems of any type with them.
Drifting
Joined: May 2004
Posts: 1,747
Likes: 1
From: Port McNicoll Ontario
No one has answered the second question in the post. How do you determine what size belt you need after swapping pulleys?
Hope I don't sound pushy, I'm curious about the answer as well.
Hope I don't sound pushy, I'm curious about the answer as well.
Team Owner
Joined: Sep 2003
Posts: 20,179
Likes: 673
From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
Originally Posted by 87 rag
How do you determine what size belt you need after swapping pulleys?
What I did is determine the stock belt size. Then bought two belts that were two steps smaller than stock. (kept the receipts) And test fitted until I found the right size. Returned the unused belt.
Race Director
Joined: Sep 2003
Posts: 16,838
Likes: 341
From: Database Error Indiana
Originally Posted by 87 rag
No one has answered the second question in the post. How do you determine what size belt you need after swapping pulleys?
Hope I don't sound pushy, I'm curious about the answer as well.
Hope I don't sound pushy, I'm curious about the answer as well.
