Underdrive Pulleys
Thread Starter
Racer
Joined: Sep 2005
Posts: 279
Likes: 1
From: montrose colorado
Underdrive Pulleys
Hi All, would like to get some feed back on installing an underdrive pulley set, worth it or not. Also looks like the install is fairly involved acording to the manual. Last, where to buy from.
Thanks Yall.
Thanks Yall.
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
I have it...no drawbacks. Everyone that I know of that did it got 9-10 rwhp. You move the steering rack out of the way toward the passenger side but you don't have to remove it.
No lights dimming, no start issues, the car runs at 14.2 volts, and you wont know it is there. A/C works fine too. Shop around and get a good deal....tbyrne 10% off the listed price if you order online. One thing: for C6 users; the C5 ac belt is one inch too long. You need a 40 inch not 41 as tbyrne had originally shipped me.
If anyone says this mod isn't a good one or it will give you problems then they don't have it on their car-- and shouldn't be giving you advice. I've noted those guys usually say they had it on their z28 back in 1978 and it made their lights dim. Dated opinion. Different car/different results.
No lights dimming, no start issues, the car runs at 14.2 volts, and you wont know it is there. A/C works fine too. Shop around and get a good deal....tbyrne 10% off the listed price if you order online. One thing: for C6 users; the C5 ac belt is one inch too long. You need a 40 inch not 41 as tbyrne had originally shipped me.
If anyone says this mod isn't a good one or it will give you problems then they don't have it on their car-- and shouldn't be giving you advice. I've noted those guys usually say they had it on their z28 back in 1978 and it made their lights dim. Dated opinion. Different car/different results.
Last edited by SpinMonster; Dec 11, 2005 at 11:04 PM.
Melting Slicks
Joined: Jul 2005
Posts: 2,734
Likes: 0
From: Vacaville California
Originally Posted by SpinMonster
I have it...no drawbacks. Everyone that I know of that did it got 9-10 rwhp. You move the steering rack out of the way toward the passenger side but you don't have to remove it.
No lights dimming, no start issues, the car runs at 14.2 volts, and you wont know it is there. A/C works fine too. Shop around and get a good deal....tbyrne 10% off the listed price if you order online. One thing: for C6 users; the C5 ac belt is one inch too long. You need a 40 inch not 41 as tbyrne had originally shipped me.
If anyone says this mod isn't a good one or it will give you problems then they don't have it on their car-- and shouldn't be giving you advice. I've noted those guys usually say they had it on their z28 back in 1978 and it made their lights dim. Dated opinion. Different car/different results.
No lights dimming, no start issues, the car runs at 14.2 volts, and you wont know it is there. A/C works fine too. Shop around and get a good deal....tbyrne 10% off the listed price if you order online. One thing: for C6 users; the C5 ac belt is one inch too long. You need a 40 inch not 41 as tbyrne had originally shipped me.
If anyone says this mod isn't a good one or it will give you problems then they don't have it on their car-- and shouldn't be giving you advice. I've noted those guys usually say they had it on their z28 back in 1978 and it made their lights dim. Dated opinion. Different car/different results.
Le Mans Master
Joined: Oct 2005
Posts: 5,051
Likes: 889
From: Tampa Florida
For the labor cost, you might as well install a cam also. Could save you some money on the long run. My mechanic wouldn't install the underdrive pulley unless the cam was included. He said just installing the underdrive pulley alone is not worth it. Installation of underdrive pulley and cam, same labor cost as just installing the underdrive pulley.
Last edited by Fore58; Dec 12, 2005 at 07:32 AM.
Advanced
Joined: Oct 2005
Posts: 83
Likes: 0
I did it but frankly I didn't look before I jumped in terms of the install time. I put the ones from LPE in the car, its a pretty big undertaking for the amount of power you gain but I have no drivability issues. They were done in conjunction with the CAI from LPE, all I can say is that the car is night and day from before, not sure though how much of the change could be attributed to the pulleys. Past experiences though have proven that they definitley make the power more "instant" even if the HP increase isn't that big. One caution though is that the belts LPE say's you need to use after the install are WRONG!
I agree, doing the cam at the same time is prudent, if you believe in just doing he cam to begin with. Which is a pretty big decision as your warrranty is pretty much history and without the heads the gains aren't so great, and if you decide to do it all its a big financial expediture even compared to just the labor to put pulley's in.
Ahhh, decisions decisions
I agree, doing the cam at the same time is prudent, if you believe in just doing he cam to begin with. Which is a pretty big decision as your warrranty is pretty much history and without the heads the gains aren't so great, and if you decide to do it all its a big financial expediture even compared to just the labor to put pulley's in.
Ahhh, decisions decisions
Racer
Joined: Aug 2005
Posts: 449
Likes: 68
Originally Posted by DONALD HALL
Hi All, would like to get some feed back on installing an underdrive pulley set, worth it or not. Also looks like the install is fairly involved acording to the manual. Last, where to buy from.
Thanks Yall.
Thanks Yall.
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Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Originally Posted by Fore58
For the labor cost, you might as well install a cam also. Could save you some money on the long run. My mechanic wouldn't install the underdrive pulley unless the cam was included. He said just installing the underdrive pulley alone is not worth it. Installation of underdrive pulley and cam, same labor cost as just installing the underdrive pulley.
Remove the coil packs, valve covers, plug wires
Remove the valvetrain; rockers and pushrods
drain all fluids
Remove the air cleaner assembly, air bridge, Maf
remove the TB (just for more room)
remove the water pump
Remove the timing chain cover
Remove the fan
Remover the radiator, its cover, all hoses
remove the oil pump unless you trust that the chain wont come off
Remove cam gear w/o dropping the chain
Remove the cam without destroying the AC lines
Tuning for a cam is a must...add 500 there
The stock valve springs wont work with any new cam worth installing
15-20 hours for a cam change if you're fast
Your mechanic is an idiot. Even if you pay 210 (70 per hour) to install a pulley it is under 500 for 9-10 hp and that is 50 per hp....right in line with any good mod. Find a good mechanic.
Burning Brakes
Joined: Aug 2005
Posts: 767
Likes: 6
From: near Spokane WA
On the LS2 doesn't the underdrive also reduce the water pump speed? On my LT1 I did the mod in about an hour and on that engine it didn't affect the water pump speed because it is not run by the belt. If the water pump speed is slower on the LS2s that would concern me if I'm running a track day. Anyone know for sure?
Le Mans Master
Joined: Oct 2005
Posts: 5,051
Likes: 889
From: Tampa Florida
Originally Posted by SpinMonster
The only thing you need to do in installing this pulley is move the steering rack over (not out). Two bolts hold it in and tie rods. I can install one in 3 hours with a break in there. The cam adds the following to the mix:
Remove the coil packs, valve covers, plug wires
Remove the valvetrain; rockers and pushrods
drain all fluids
Remove the air cleaner assembly, air bridge, Maf
remove the TB (just for more room)
remove the water pump
Remove the timing chain cover
Remove the fan
Remover the radiator, its cover, all hoses
remove the oil pump unless you trust that the chain wont come off
Remove cam gear w/o dropping the chain
Remove the cam without destroying the AC lines
Tuning for a cam is a must...add 500 there
The stock valve springs wont work with any new cam worth installing
15-20 hours for a cam change if you're fast
Your mechanic is an idiot. Even if you pay 210 (70 per hour) to install a pulley it is under 500 for 9-10 hp and that is 50 per hp....right in line with any good mod. Find a good mechanic.
Remove the coil packs, valve covers, plug wires
Remove the valvetrain; rockers and pushrods
drain all fluids
Remove the air cleaner assembly, air bridge, Maf
remove the TB (just for more room)
remove the water pump
Remove the timing chain cover
Remove the fan
Remover the radiator, its cover, all hoses
remove the oil pump unless you trust that the chain wont come off
Remove cam gear w/o dropping the chain
Remove the cam without destroying the AC lines
Tuning for a cam is a must...add 500 there
The stock valve springs wont work with any new cam worth installing
15-20 hours for a cam change if you're fast
Your mechanic is an idiot. Even if you pay 210 (70 per hour) to install a pulley it is under 500 for 9-10 hp and that is 50 per hp....right in line with any good mod. Find a good mechanic.
Thanks for the instructions. This is funny because I'm mechanically inclined in working on motorcycles but not cars. You may had missed my point. It was a suggestion only to install the cam along with the underdrive pulley. It would save me on labor cost if I get both done. That's all.
Thread Starter
Racer
Joined: Sep 2005
Posts: 279
Likes: 1
From: montrose colorado
Hi SPINMONSTER,
Another question, the manual says to mark the pulley/balancer
before removal so you can reinstall in same spot. How do you do this when installing a different pulley/balancer. One vendor told me to install it in any position.
Thanks
Another question, the manual says to mark the pulley/balancer
before removal so you can reinstall in same spot. How do you do this when installing a different pulley/balancer. One vendor told me to install it in any position.
Thanks
Racer
Joined: Dec 2005
Posts: 363
Likes: 13
From: Dallas TX
Hey guys, I'm somewhat new here at Corvette forums. I've come from a long line of buying foreign (Japanese) sports cars, namely the 300ZX Twin Turbo. On that car, more power can be "uncovered" by swapping out the very heavy underdrive pulley (12 lbs) for one that is slightly smaller and weights about 4 lbs. However, a lot of concern grew over doing so because the engine journals/crankshaft is balanced with the factory pulley, and changing it could cause unbalance over time leading to serious engine damage. I just wondered if that was a concern in the LS motors?
I've since long sold that 300ZX and am looking at a Corvette in the near future. Always enjoy reading the forums here!
I've since long sold that 300ZX and am looking at a Corvette in the near future. Always enjoy reading the forums here!
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Originally Posted by DONALD HALL
Hi SPINMONSTER,
Another question, the manual says to mark the pulley/balancer
before removal so you can reinstall in same spot. How do you do this when installing a different pulley/balancer. One vendor told me to install it in any position.
Thanks
Another question, the manual says to mark the pulley/balancer
before removal so you can reinstall in same spot. How do you do this when installing a different pulley/balancer. One vendor told me to install it in any position.
Thanks
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Originally Posted by Fore58
Spinmonster,
Thanks for the instructions. This is funny because I'm mechanically inclined in working on motorcycles but not cars. You may had missed my point. It was a suggestion only to install the cam along with the underdrive pulley. It would save me on labor cost if I get both done. That's all.
Thanks for the instructions. This is funny because I'm mechanically inclined in working on motorcycles but not cars. You may had missed my point. It was a suggestion only to install the cam along with the underdrive pulley. It would save me on labor cost if I get both done. That's all.
Anyway, its a great mod even staying with the stock cam.
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Originally Posted by normlunt
On the LS2 doesn't the underdrive also reduce the water pump speed? On my LT1 I did the mod in about an hour and on that engine it didn't affect the water pump speed because it is not run by the belt. If the water pump speed is slower on the LS2s that would concern me if I'm running a track day. Anyone know for sure?
A lot of track guys run an electric water pump so they can keep the pump going with the car off still cooling.
Last edited by SpinMonster; Dec 13, 2005 at 02:14 PM.
Racer
Joined: Nov 2004
Posts: 298
Likes: 0
In my opinion they are bad idea, the gain is not worth the cost/effort/risk....
I'd like to some dyno charts to see where in the RPM range the gain is achieved.
Also, note that basically with a smaller drive pulley you are spinning all the pulleys slower, which I think everyone knows, but let's look at the effects on some of the systems, in all cases I would think that GM tries to spin them at the min speed to save on fuel economy.
power steering:
spinning this pully slower should have positive effect in power, but may result in increased power steering effort at idle. It may not be apparent at first, but may appear over time. Basically the pressure of the flud will be less and over time effort may increase.
water pump:
cooling flow is reduced, this should also have a positive effect in power, but may result in over heating. The flow rate will be less so overheating is a possibility;however, since you have a gauge to monitor this, it would be the least of my concern.
a/c:
could reduce a/c performance at idle, but you can always turn of a/c, no real gains here....
alternator:
may or may not get any benefit, since the alternator is regulated, it may increase the torque when the speed is lower, resulting in same power requirement since torque*RPM=Power. If you measure the output of the alternator before and after and it is the same, you got no benefit from alternator.
reduced mass:
win win situation
balanced crankshaft:
could be worrysome for the long term durability of engine, this will probaby vary in a case by case basis depending on how well balance the end crankshaft/pully combo is. You may think it ok because of a lack of vibration/noise, but the engine is pretty isolated and holding the crank tight, the stresses around the crankshaft bearings would be increased.
I'd like to some dyno charts to see where in the RPM range the gain is achieved.
Also, note that basically with a smaller drive pulley you are spinning all the pulleys slower, which I think everyone knows, but let's look at the effects on some of the systems, in all cases I would think that GM tries to spin them at the min speed to save on fuel economy.
power steering:
spinning this pully slower should have positive effect in power, but may result in increased power steering effort at idle. It may not be apparent at first, but may appear over time. Basically the pressure of the flud will be less and over time effort may increase.
water pump:
cooling flow is reduced, this should also have a positive effect in power, but may result in over heating. The flow rate will be less so overheating is a possibility;however, since you have a gauge to monitor this, it would be the least of my concern.
a/c:
could reduce a/c performance at idle, but you can always turn of a/c, no real gains here....
alternator:
may or may not get any benefit, since the alternator is regulated, it may increase the torque when the speed is lower, resulting in same power requirement since torque*RPM=Power. If you measure the output of the alternator before and after and it is the same, you got no benefit from alternator.
reduced mass:
win win situation
balanced crankshaft:
could be worrysome for the long term durability of engine, this will probaby vary in a case by case basis depending on how well balance the end crankshaft/pully combo is. You may think it ok because of a lack of vibration/noise, but the engine is pretty isolated and holding the crank tight, the stresses around the crankshaft bearings would be increased.
Le Mans Master
Joined: Oct 2005
Posts: 5,051
Likes: 889
From: Tampa Florida
Originally Posted by SpinMonster
Yes it saves you 3 hours labor by getting the pulley in there for free but if you don't have 1500-2000 for a cam change/spring change/tune I fail to see the point of a mechanic not taking a 3-hour labor job. He makes it seem like it is 'almost in there' and it isn't even 1/10th of the job.
Anyway, its a great mod even staying with the stock cam.
Anyway, its a great mod even staying with the stock cam.
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Originally Posted by OttoNP
In my opinion they are bad idea, the gain is not worth the cost/effort/risk....
I'd like to some dyno charts to see where in the RPM range the gain is achieved.
Also, note that basically with a smaller drive pulley you are spinning all the pulleys slower, which I think everyone knows, but let's look at the effects on some of the systems, in all cases I would think that GM tries to spin them at the min speed to save on fuel economy.
power steering:
spinning this pully slower should have positive effect in power, but may result in increased power steering effort at idle. It may not be apparent at first, but may appear over time. Basically the pressure of the flud will be less and over time effort may increase.
water pump:
cooling flow is reduced, this should also have a positive effect in power, but may result in over heating. The flow rate will be less so overheating is a possibility;however, since you have a gauge to monitor this, it would be the least of my concern.
a/c:
could reduce a/c performance at idle, but you can always turn of a/c, no real gains here....
alternator:
may or may not get any benefit, since the alternator is regulated, it may increase the torque when the speed is lower, resulting in same power requirement since torque*RPM=Power. If you measure the output of the alternator before and after and it is the same, you got no benefit from alternator.
reduced mass:
win win situation
balanced crankshaft:
could be worrysome for the long term durability of engine, this will probaby vary in a case by case basis depending on how well balance the end crankshaft/pully combo is. You may think it ok because of a lack of vibration/noise, but the engine is pretty isolated and holding the crank tight, the stresses around the crankshaft bearings would be increased.
I'd like to some dyno charts to see where in the RPM range the gain is achieved.
Also, note that basically with a smaller drive pulley you are spinning all the pulleys slower, which I think everyone knows, but let's look at the effects on some of the systems, in all cases I would think that GM tries to spin them at the min speed to save on fuel economy.
power steering:
spinning this pully slower should have positive effect in power, but may result in increased power steering effort at idle. It may not be apparent at first, but may appear over time. Basically the pressure of the flud will be less and over time effort may increase.
water pump:
cooling flow is reduced, this should also have a positive effect in power, but may result in over heating. The flow rate will be less so overheating is a possibility;however, since you have a gauge to monitor this, it would be the least of my concern.
a/c:
could reduce a/c performance at idle, but you can always turn of a/c, no real gains here....
alternator:
may or may not get any benefit, since the alternator is regulated, it may increase the torque when the speed is lower, resulting in same power requirement since torque*RPM=Power. If you measure the output of the alternator before and after and it is the same, you got no benefit from alternator.
reduced mass:
win win situation
balanced crankshaft:
could be worrysome for the long term durability of engine, this will probaby vary in a case by case basis depending on how well balance the end crankshaft/pully combo is. You may think it ok because of a lack of vibration/noise, but the engine is pretty isolated and holding the crank tight, the stresses around the crankshaft bearings would be increased.
Like I said, the only people who knock this mod are the people that don't have it. Here we have a man that went through all that opinion and as previously stated...NONE of those theories hold true in practice. The car runs better, same running temp, same power steering assist, same voltage, same freezing ac, and no vibration since the engine is internally balanced with a zero balanced pulley from the factory.
HP can be verified at www.ls1howto.com 9-rwhp
Sorry everyone doesn't reinvent the wheel everytime a doubting thomas comes along and needs proof. Everyone that has it, has the gain and none of the downsides you theorized.
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Originally Posted by OttoNP
In my opinion they are bad idea, the gain is not worth the cost/effort/risk....
I'd like to some dyno charts to see where in the RPM range the gain is achieved.
Also, note that basically with a smaller drive pulley you are spinning all the pulleys slower, which I think everyone knows, but let's look at the effects on some of the systems, in all cases I would think that GM tries to spin them at the min speed to save on fuel economy.
power steering:
spinning this pully slower should have positive effect in power, but may result in increased power steering effort at idle. It may not be apparent at first, but may appear over time. Basically the pressure of the flud will be less and over time effort may increase.
50 bucks per HP isnt worth it?...thats 25 per HP if you install it yourself. Thats is as good as it gets on the 'worth it' scale.
water pump:
cooling flow is reduced, this should also have a positive effect in power, but may result in over heating. The flow rate will be less so overheating is a possibility;however, since you have a gauge to monitor this, it would be the least of my concern.
a/c:
could reduce a/c performance at idle, but you can always turn of a/c, no real gains here....
alternator:
may or may not get any benefit, since the alternator is regulated, it may increase the torque when the speed is lower, resulting in same power requirement since torque*RPM=Power. If you measure the output of the alternator before and after and it is the same, you got no benefit from alternator.
reduced mass:
win win situation
balanced crankshaft:
could be worrysome for the long term durability of engine, this will probaby vary in a case by case basis depending on how well balance the end crankshaft/pully combo is. You may think it ok because of a lack of vibration/noise, but the engine is pretty isolated and holding the crank tight, the stresses around the crankshaft bearings would be increased.
I'd like to some dyno charts to see where in the RPM range the gain is achieved.
Also, note that basically with a smaller drive pulley you are spinning all the pulleys slower, which I think everyone knows, but let's look at the effects on some of the systems, in all cases I would think that GM tries to spin them at the min speed to save on fuel economy.
power steering:
spinning this pully slower should have positive effect in power, but may result in increased power steering effort at idle. It may not be apparent at first, but may appear over time. Basically the pressure of the flud will be less and over time effort may increase.
50 bucks per HP isnt worth it?...thats 25 per HP if you install it yourself. Thats is as good as it gets on the 'worth it' scale.
water pump:
cooling flow is reduced, this should also have a positive effect in power, but may result in over heating. The flow rate will be less so overheating is a possibility;however, since you have a gauge to monitor this, it would be the least of my concern.
a/c:
could reduce a/c performance at idle, but you can always turn of a/c, no real gains here....
alternator:
may or may not get any benefit, since the alternator is regulated, it may increase the torque when the speed is lower, resulting in same power requirement since torque*RPM=Power. If you measure the output of the alternator before and after and it is the same, you got no benefit from alternator.
reduced mass:
win win situation
balanced crankshaft:
could be worrysome for the long term durability of engine, this will probaby vary in a case by case basis depending on how well balance the end crankshaft/pully combo is. You may think it ok because of a lack of vibration/noise, but the engine is pretty isolated and holding the crank tight, the stresses around the crankshaft bearings would be increased.
Like I said, the only people who knock this mod are the people that don't have it. Here we have a man that went through all that opinion and as previously stated...NONE of those theories hold true in practice. The car runs better, same running temp, same power steering assist, same voltage, same freezing ac, and no vibration since the engine is internally balanced with a zero balanced pulley from the factory.
Sorry everyone doesn't reinvent the wheel everytime a doubting thomas comes along and needs proof. Everyone that has it, has the gain and none of the downsides you theorized.