Underdrive Pulley Questions
Thread Starter
Safety Car
Joined: Apr 2010
Posts: 4,231
Likes: 451
From: Maryland
Underdrive Pulley Questions
I have used them on others cars but not the vette. I have a 2010 LS3.
1) What is the percentage of underdrive and are there different percentages offered for the vette.
2) Average HP gain; any dyno or track results from just adding a pulley.
3) Does it affect the cooling or charging system, if so how much.
4) Best brand to use and price range.
If I do one, I would like to get the right one. Thanks
1) What is the percentage of underdrive and are there different percentages offered for the vette.
2) Average HP gain; any dyno or track results from just adding a pulley.
3) Does it affect the cooling or charging system, if so how much.
4) Best brand to use and price range.
If I do one, I would like to get the right one. Thanks
Advanced
Joined: Mar 2012
Posts: 56
Likes: 0
From: DALLAS TX
I have used them on others cars but not the vette. I have a 2010 LS3.
1) What is the percentage of underdrive and are there different percentages offered for the vette.
2) Average HP gain; any dyno or track results from just adding a pulley.
3) Does it affect the cooling or charging system, if so how much.
4) Best brand to use and price range.
If I do one, I would like to get the right one. Thanks
1) What is the percentage of underdrive and are there different percentages offered for the vette.
2) Average HP gain; any dyno or track results from just adding a pulley.
3) Does it affect the cooling or charging system, if so how much.
4) Best brand to use and price range.
If I do one, I would like to get the right one. Thanks
Racer
Joined: Sep 2007
Posts: 418
Likes: 3
From: Fallsington PA
I have used them on others cars but not the vette. I have a 2010 LS3.
1) What is the percentage of underdrive and are there different percentages offered for the vette.
2) Average HP gain; any dyno or track results from just adding a pulley.
3) Does it affect the cooling or charging system, if so how much.
4) Best brand to use and price range.
If I do one, I would like to get the right one. Thanks
1) What is the percentage of underdrive and are there different percentages offered for the vette.
2) Average HP gain; any dyno or track results from just adding a pulley.
3) Does it affect the cooling or charging system, if so how much.
4) Best brand to use and price range.
If I do one, I would like to get the right one. Thanks
Le Mans Master
Joined: May 2011
Posts: 5,022
Likes: 18
From: Tampa FL (formerly Justinjor)
Tech Contributor
St. Jude Donor '11-'12-'13-'14
I have used them on others cars but not the vette. I have a 2010 LS3.
1) What is the percentage of underdrive and are there different percentages offered for the vette.
10% and 25% are your 2 choices
2) Average HP gain; any dyno or track results from just adding a pulley.
I don't know of anyone who has done a back to back test, but 7-10whp is the norm for a 25% UDP. The car doesn't make any extra power, but power is freed up as a result of the slower spinning accessories.
3) Does it affect the cooling or charging system, if so how much.
This is a highly debated topic when it comes to an UDP. Some people have issues, but from the research I did before buying one myself, the increased idle speed makes up for the slower spinning alternator at idle and no adverse effects are present. I have a 25% UDP in my car and also a tiny 17lb motorcycle battery in my car and have yet to experience any issues with charging or starting after the car has sat for over a week. I do not use a trickle charger. The deka battery just plain works.
4) Best brand to use and price range.
After reading of multiple people snapping timing chains with a particular UDP, I would go with either a Powerbond or ATI. I have a good buddy(taken19) who road races often and snapped a C5R timing chain within a year. There have been a few different threads about this and road race+that brand of UDP=bad harmonics and a broken timing chain.
If I do one, I would like to get the right one. Thanks
1) What is the percentage of underdrive and are there different percentages offered for the vette.
10% and 25% are your 2 choices
2) Average HP gain; any dyno or track results from just adding a pulley.
I don't know of anyone who has done a back to back test, but 7-10whp is the norm for a 25% UDP. The car doesn't make any extra power, but power is freed up as a result of the slower spinning accessories.
3) Does it affect the cooling or charging system, if so how much.
This is a highly debated topic when it comes to an UDP. Some people have issues, but from the research I did before buying one myself, the increased idle speed makes up for the slower spinning alternator at idle and no adverse effects are present. I have a 25% UDP in my car and also a tiny 17lb motorcycle battery in my car and have yet to experience any issues with charging or starting after the car has sat for over a week. I do not use a trickle charger. The deka battery just plain works.
4) Best brand to use and price range.
After reading of multiple people snapping timing chains with a particular UDP, I would go with either a Powerbond or ATI. I have a good buddy(taken19) who road races often and snapped a C5R timing chain within a year. There have been a few different threads about this and road race+that brand of UDP=bad harmonics and a broken timing chain.
If I do one, I would like to get the right one. Thanks
Thread Starter
Safety Car
Joined: Apr 2010
Posts: 4,231
Likes: 451
From: Maryland
Thanks for the replies. 
Sounds like I might as well do a cam and pulley at the same time along with drilling the crank for a pin if or when I do this.
Justin approx. what would the new idle speed be to cover just a pulley change? and which brand of pulley would be your choice at this time?
Sounds like I might as well do a cam and pulley at the same time along with drilling the crank for a pin if or when I do this.Justin approx. what would the new idle speed be to cover just a pulley change? and which brand of pulley would be your choice at this time?
Le Mans Master
Joined: May 2011
Posts: 5,022
Likes: 18
From: Tampa FL (formerly Justinjor)
Tech Contributor
St. Jude Donor '11-'12-'13-'14
I had a 750 idle for months and had 0 issues with starting, voltage, a/c blowing cold, etc. The car ran perfectly. Considering that's a 25% idle speed increase from stock and I had a 25% underdrive pulley, I think it was a wash.
I haven't heard anything negative about the Powerbond brand of UDP but if I had to do it all over again, I'd go with an ATI I think. It's possible the notion of snapping a timing chain is very rare but even still, the extra $300 would be worth the peace of mind to me. The only reason I didn't buy one to begin with was because I was misinformed and thought ATI did not come in a 25% version.
I haven't heard anything negative about the Powerbond brand of UDP but if I had to do it all over again, I'd go with an ATI I think. It's possible the notion of snapping a timing chain is very rare but even still, the extra $300 would be worth the peace of mind to me. The only reason I didn't buy one to begin with was because I was misinformed and thought ATI did not come in a 25% version.
Track Junky
Joined: Jun 2007
Posts: 4,074
Likes: 36
From: Orlando Area
Tech Contributor
Do not buy ASP, that's what most likely caused my timing chain to break. In a discussion with Jason Katech, he told me that ASP pulleys have been responsible for at least 12 timing chain failures that he seen. As Justin mentioned, ATI or Powerbond appear to be the 2 best out there. Don't make a $10k mistake like I did using an inferior brand...
Sean
Sean
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Will work for HPDE time.
Joined: May 1999
Posts: 2,560
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From: Orlando FL
Pro
Joined: Jul 2011
Posts: 515
Likes: 1
From: Boca ARton FL
Just remember if your Grand sport is a Manual and then has the dry sump your crank snout length will be different as well as the bolt and the regular LS# pulley won't work, haven't done all the research yet but I am looking (will call ATI) and think the ZO6 pulley might be the way we'll have to go...
Last edited by Kerrdogg; May 23, 2012 at 02:36 PM.
Drifting
Joined: Oct 2004
Posts: 1,790
Likes: 29
From: STL MO
St. Jude Donor '09-'10
I went with a Powebond 10% UD pulley and have had it on for a little over a year with no issues. I ordered the ATI and they were on back order for a while at the time so after much research switched my order to the PB. I think it is a very nice piece and would buy another without hesitation.
Hey Sean,
What valve spring were you running?
Do not buy ASP, that's what most likely caused my timing chain to break. In a discussion with Jason Katech, he told me that ASP pulleys have been responsible for at least 12 timing chain failures that he seen. As Justin mentioned, ATI or Powerbond appear to be the 2 best out there. Don't make a $10k mistake like I did using an inferior brand...
Sean
Sean
What valve spring were you running?
Team Owner
Joined: May 2001
Posts: 36,836
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From: Dear Karma, I have a list of people you missed.
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15-'16
Agree on the PB. I've had the 25% for a few years and no issues. Pin your crank snout when you install one. Easy to do.
Drifting
Joined: Oct 2004
Posts: 1,790
Likes: 29
From: STL MO
St. Jude Donor '09-'10
In tracking the broken timing chain threads there were two pieces coming up often, the ASP was the more predominate but there was a certain spring in probably 75% or more of the reported failures..probably more of a coincidence as they were pretty popular throughout the timeline.
Thread Starter
Safety Car
Joined: Apr 2010
Posts: 4,231
Likes: 451
From: Maryland
In tracking the broken timing chain threads there were two pieces coming up often, the ASP was the more predominate but there was a certain spring in probably 75% or more of the reported failures..probably more of a coincidence as they were pretty popular throughout the timeline.
