Best Underdrive Pulley Set?
Thread Starter
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Best Underdrive Pulley Set?
I've never investigated the underdrive pulley situation because of my double sided belt and fear that I would have to get a shorter belt. I am now converting my belt to the newer style single sided version so I thought I would look at the underdrive setup.
All I can find is ASP and at that I can't find any good information. Anybody got any information? What about the belt? How hard is it to get the right length?
All I can find is ASP and at that I can't find any good information. Anybody got any information? What about the belt? How hard is it to get the right length?
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Originally Posted by Nathan Plemons
I've never investigated the underdrive pulley situation because of my double sided belt and fear that I would have to get a shorter belt. I am now converting my belt to the newer style single sided version so I thought I would look at the underdrive setup.
All I can find is ASP and at that I can't find any good information. Anybody got any information? What about the belt? How hard is it to get the right length?
All I can find is ASP and at that I can't find any good information. Anybody got any information? What about the belt? How hard is it to get the right length?
http://store.summitracing.com/egnsea...rdSearch#rstop
Burning Brakes
Joined: Nov 2004
Posts: 1,057
Likes: 0
From: Warren Ohio
ASP is your only option, as far as I know. IIRC, it's a 23% underdrive, available in either a 1pc or 2pc set for ~$140 & $170 respectively. ASP's techs claimed 4HP for it on an LT1 Vette when I spoke with them.
March used to make a set for LT1 Vettes, but subsequently discontinued it a few years ago. I got lucky, and picked up a new 2 pc. set from a forum member last year for $40.
Buy your belt from the store CLOSEST to your house, just in case you need to exchange it for a different size. I did an A/C delete at the same time, and had to make a few trips until I found the right belt.
-Scott
March used to make a set for LT1 Vettes, but subsequently discontinued it a few years ago. I got lucky, and picked up a new 2 pc. set from a forum member last year for $40.
Buy your belt from the store CLOSEST to your house, just in case you need to exchange it for a different size. I did an A/C delete at the same time, and had to make a few trips until I found the right belt.
-Scott
Melting Slicks
Joined: Sep 2003
Posts: 2,270
Likes: 118
From: N. Babylon NY
Originally Posted by 95PoloVert
ASP is your only option, as far as I know. IIRC, it's a 23% underdrive, available in either a 1pc or 2pc set for ~$140 & $170 respectively. ASP's techs claimed 4HP for it on an LT1 Vette when I spoke with them.
March used to make a set for LT1 Vettes, but subsequently discontinued it a few years ago. I got lucky, and picked up a new 2 pc. set from a forum member last year for $40.
Buy your belt from the store CLOSEST to your house, just in case you need to exchange it for a different size. I did an A/C delete at the same time, and had to make a few trips until I found the right belt.
-Scott
March used to make a set for LT1 Vettes, but subsequently discontinued it a few years ago. I got lucky, and picked up a new 2 pc. set from a forum member last year for $40.
Buy your belt from the store CLOSEST to your house, just in case you need to exchange it for a different size. I did an A/C delete at the same time, and had to make a few trips until I found the right belt.
-Scott
I have the ASP on my 1992-not for any HP gains but to slow the power steering pump down at the track. I also have a larger alt. pulley. Getting a smaller belt was no problem.
Steven
Instructor
Joined: Mar 2005
Posts: 178
Likes: 0
From: Thornton CO
Originally Posted by STEVEN13
I have the ASP on my 1992-not for any HP gains but to slow the power steering pump down at the track. I also have a larger alt. pulley. Getting a smaller belt was no problem.
Steven
Stock '92 had the "double sided grove" belt...did you change other pulleys on your motor to accomodate for a "single sided grove" belt system? I'm just wondering if GM made different sized "double sided groved" belts.
Thanks!
Chris
Last edited by stearnman; Apr 4, 2006 at 01:20 PM.
Racer
Joined: Apr 2004
Posts: 487
Likes: 0
From: Huntsville AL
I bought a Jetchip pulley set a few yrs ago. Looking at their site now, they don't mention our LT-1. Maybe their LT-4 set would work fine, I dunno. I'd have to look at my notes at home to confirm the belt size I had to change to.
Thread Starter
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
I have the ASP on my 1992-not for any HP gains but to slow the power steering pump down at the track. I also have a larger alt.
pulley. Getting a smaller belt was no problem.
Steven
pulley. Getting a smaller belt was no problem.
Steven
Anybody know exactly what size the new belt should be? It's not hard to get a different size, if you know what you need. I would like to minimize the number of trips to the parts store. The idiots around here can't just give you a belt, they have to know what it goes on, lord help you if it's not in their computer!
If I knew the sizes of all the pulleys and their orientation to one another I could easily draw it up in solidworks and calculate the length of the new belt.... would be a neat project.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
We don't ever have much talk on this subject for LT-1s
Le Mans Master
Joined: Apr 2005
Posts: 8,077
Likes: 4
From: Scarborough ONTARIO
I bought march pully kit from Lpe i think it was 85 bucks 2 piece and also paid extra 25 bucks for a right belt too, both from Lpe. So give a call to lpe or u may be contact Tpis also their pulley kit comes with belt too. But iam biased if this under drive pully kit will give more free HP as they say, fingers crossed.
Burning Brakes
Joined: Nov 2004
Posts: 1,057
Likes: 0
From: Warren Ohio
Originally Posted by Nathan Plemons
Any charging issues at idle? A/C still work alright?
Anybody know exactly what size the new belt should be? It's not hard to get a different size, if you know what you need. I would like to minimize the number of trips to the parts store. The idiots around here can't just give you a belt, they have to know what it goes on, lord help you if it's not in their computer!
If I knew the sizes of all the pulleys and their orientation to one another I could easily draw it up in solidworks and calculate the length of the new belt.... would be a neat project.
Anybody know exactly what size the new belt should be? It's not hard to get a different size, if you know what you need. I would like to minimize the number of trips to the parts store. The idiots around here can't just give you a belt, they have to know what it goes on, lord help you if it's not in their computer!
If I knew the sizes of all the pulleys and their orientation to one another I could easily draw it up in solidworks and calculate the length of the new belt.... would be a neat project.
This info might help RE: the belt issue...most belt manufacturers use a Part # scheme in which the # of ribs and the length of the belt is defined in the Part#. For example, I have a DuraLast in the garage with a Part# of 635K6....this is a 6-rib belt that is 63.5 inches in length. I've used Kelley and several others over the years, but they all seem to use a variation on this theme.
There's a belt guide at www.ASPRacing.com with P/N#'s. They have 2 (?) listings for the LT1 Vette...K060640 Gates and K060637 Gates. Don't know what the difference is between the two pulley sets, but the latter belt is 63.7" and the former is 64".
Oh...one other little issue if you're considering a 2pc set: You may need an impact wrench to swap out the alt pulley. I did with the March set. Unless the ASP alt pulley is larger in diameter, you'll be in the same boat.
-Scott
Drifting
Joined: May 2001
Posts: 1,630
Likes: 0
From: Brandywine, Chester and Ridley Valleys Pennsylvania
Why not just cut the old belt, and route it around the new setup, scribing where the belt overlaps. Then lay the cut belt flat and measure it. From starting point to scribe mark.
The length of a belt in inches (xx.x") is the first 3 #'s of the belt stock # if I remember correctly.
Saves a few trips to the parts store.
The length of a belt in inches (xx.x") is the first 3 #'s of the belt stock # if I remember correctly.
Saves a few trips to the parts store.
Last edited by TrueBlue ChevyDude; Apr 4, 2006 at 04:33 PM.
Burning Brakes
Joined: Nov 2001
Posts: 1,241
Likes: 9
From: Houston TX
nathan, i put the ASP underdrive crank pulley on my '96 LT4. (only the crank pulley.) the belt length they specify for the LT1 worked perfectly on my car as well.
ASP claims that pulley doesn't fit the LT4. i called them to ask why, no one could remember the results from their testing back in the '90s, but they confirmed it wouldn't work. i bought it anyhow.
once in my hands i compared with careful measurements. i couldn't find any reason why it wouldn't work, so i installed it. it works just fine. i suspect when the LT4 first came out they compared their pulley on a pre '96 crank hub to the LT4 pulley on a '96 crank hub, not realizing the crank sensor changed the overall depth, and so it appeared to them as if the LT4 fitment was different.
for the belt, i was worried since the LT1 uses a different size crank pulley than the LT4, yet specifies the same belt length as oem. this made me wonder if some other pulley size or location was different, but the ASP-specified belt length worked on my car. it was tighter than stock, so much so that i don't think it would work had i also done the bigger alternator pulley, so make sure you get the right belt. to reinforce what scott said, it's K060637 for just the crank, and K060640 for both crank and alt swaps.
-michael
ASP claims that pulley doesn't fit the LT4. i called them to ask why, no one could remember the results from their testing back in the '90s, but they confirmed it wouldn't work. i bought it anyhow.
once in my hands i compared with careful measurements. i couldn't find any reason why it wouldn't work, so i installed it. it works just fine. i suspect when the LT4 first came out they compared their pulley on a pre '96 crank hub to the LT4 pulley on a '96 crank hub, not realizing the crank sensor changed the overall depth, and so it appeared to them as if the LT4 fitment was different.
for the belt, i was worried since the LT1 uses a different size crank pulley than the LT4, yet specifies the same belt length as oem. this made me wonder if some other pulley size or location was different, but the ASP-specified belt length worked on my car. it was tighter than stock, so much so that i don't think it would work had i also done the bigger alternator pulley, so make sure you get the right belt. to reinforce what scott said, it's K060637 for just the crank, and K060640 for both crank and alt swaps.
-michael
Melting Slicks
Joined: Sep 2003
Posts: 2,270
Likes: 118
From: N. Babylon NY
Originally Posted by stearnman
Steven,
Stock '92 had the "double sided grove" belt...did you change other pulleys on your motor to accomodate for a "single sided grove" belt system? I'm just wondering if GM made different sized "double sided groved" belts.
Thanks!
Chris
Stock '92 had the "double sided grove" belt...did you change other pulleys on your motor to accomodate for a "single sided grove" belt system? I'm just wondering if GM made different sized "double sided groved" belts.
Thanks!
Chris
Steven
Last edited by STEVEN13; Apr 6, 2006 at 06:21 PM.
Melting Slicks
Joined: Sep 2003
Posts: 2,270
Likes: 118
From: N. Babylon NY
Originally Posted by Nathan Plemons
Any charging issues at idle? A/C still work alright?
Anybody know exactly what size the new belt should be? It's not hard to get a different size, if you know what you need. I would like to minimize the number of trips to the parts store. The idiots around here can't just give you a belt, they have to know what it goes on, lord help you if it's not in their computer!
If I knew the sizes of all the pulleys and their orientation to one another I could easily draw it up in solidworks and calculate the length of the new belt.... would be a neat project.
Anybody know exactly what size the new belt should be? It's not hard to get a different size, if you know what you need. I would like to minimize the number of trips to the parts store. The idiots around here can't just give you a belt, they have to know what it goes on, lord help you if it's not in their computer!
If I knew the sizes of all the pulleys and their orientation to one another I could easily draw it up in solidworks and calculate the length of the new belt.... would be a neat project.
Steven
Melting Slicks
Joined: Mar 2003
Posts: 2,472
Likes: 0
From: Toronto ONTARIO
I had 2 March sets when i first had the car. the first one the rubber dampener part seperated from the balancer. I ended up getting a 2nd set from March and guess what.. yeah it seperated again. i ended up putting a stock balancer on from GM until i found out about ASP. With the current build i am using a ATI non underdrive pulley so i have the asp lying around. I probably used for about 500 km. i was throwing money at the car tryng to fix things and since nothing worked i eventually tore it down and decided to upgrade the entire car
Im not sure if its underdrive or not.. i need to measure it. Look for it in the c4 parts for sale section soon 
Im not sure if its underdrive or not.. i need to measure it. Look for it in the c4 parts for sale section soon
Thread Starter
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Hey guys, the information on this thread has been great. I had looked on Google for ASP's website but I couldn't find it.
The fact that they list part numbers for belts is awesome and ensures that it would never be a problem.
ONE question though that doesn't make sense to me, I'm curious if they have their numbers backwards.
For the 1 piece kit they list 22% crank and list full charge at 800 RPM.
for the 2 piece kity they list 22% crank and 15% alternator and list full charge at 900 RPM
Now I was under the impression that the two piece kit was used to overdrive the alternator and thus speed it back up, which should then LOWER the full charge RPM?
Am I just confused about their terminology?
The fact that they list part numbers for belts is awesome and ensures that it would never be a problem.
ONE question though that doesn't make sense to me, I'm curious if they have their numbers backwards.
For the 1 piece kit they list 22% crank and list full charge at 800 RPM.
for the 2 piece kity they list 22% crank and 15% alternator and list full charge at 900 RPM
Now I was under the impression that the two piece kit was used to overdrive the alternator and thus speed it back up, which should then LOWER the full charge RPM?
Am I just confused about their terminology?
Melting Slicks
Joined: Mar 2003
Posts: 2,472
Likes: 0
From: Toronto ONTARIO
Originally Posted by Nathan Plemons
Hey guys, the information on this thread has been great. I had looked on Google for ASP's website but I couldn't find it.
The fact that they list part numbers for belts is awesome and ensures that it would never be a problem.
ONE question though that doesn't make sense to me, I'm curious if they have their numbers backwards.
For the 1 piece kit they list 22% crank and list full charge at 800 RPM.
for the 2 piece kity they list 22% crank and 15% alternator and list full charge at 900 RPM
Now I was under the impression that the two piece kit was used to overdrive the alternator and thus speed it back up, which should then LOWER the full charge RPM?
Am I just confused about their terminology?
The fact that they list part numbers for belts is awesome and ensures that it would never be a problem.
ONE question though that doesn't make sense to me, I'm curious if they have their numbers backwards.
For the 1 piece kit they list 22% crank and list full charge at 800 RPM.
for the 2 piece kity they list 22% crank and 15% alternator and list full charge at 900 RPM
Now I was under the impression that the two piece kit was used to overdrive the alternator and thus speed it back up, which should then LOWER the full charge RPM?
Am I just confused about their terminology?
Melting Slicks
Joined: Sep 2003
Posts: 2,270
Likes: 118
From: N. Babylon NY
Hi,
I would also like to add that when I ordered the pulleys from ASP I also ordered it with the belt-HOWEVER, they sent me the wrong belt-to big.
Steven
I would also like to add that when I ordered the pulleys from ASP I also ordered it with the belt-HOWEVER, they sent me the wrong belt-to big.
Steven
Last edited by STEVEN13; Apr 6, 2006 at 06:22 PM.