Under drive pully
Thread Starter
Instructor
Joined: Dec 2003
Posts: 129
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From: Tyler Tx
Under drive pully
I am getting ready to install a cam and maybe under drive pully at the same time. is there any downside of running the smaller pully, from what I have read there is a couple of hp gain running it.
Thanks
Thanks
Drifting
Joined: Jul 2003
Posts: 1,796
Likes: 1
From: Annandale VA
If you are running a lot of aftermarket stereo equipment, you might run a little short on power, especially at idle. Some guys experience that the lights will dim a bit at idle. Main practical difference is that you have to run a non-standard accessory belt. They are also relatively expensive to buy and install, compared to the expected power gains.
In the early days some of the pulleys had some quality control problems, and they were also often back ordered, but I haven't heard many recent complaints.
In the early days some of the pulleys had some quality control problems, and they were also often back ordered, but I haven't heard many recent complaints.
Melting Slicks
Joined: Nov 2002
Posts: 3,398
Likes: 2
From: Allentown PA
Unless you are trying to get every last HP out of your car, it's not worth it. Too many bad thing can happen, although they seldom do, in my opinion its not worth the risk. But if there is ever a time to do it, it's now.
Le Mans Master
Joined: Aug 2004
Posts: 5,259
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From: Monroe Township New Jersey
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16
St. Jude donor in memory of jpee '14
Originally Posted by CYA-Vett
Unless you are trying to get every last HP out of your car, it's not worth it. Too many bad thing can happen, although they seldom do, in my opinion its not worth the risk. But if there is ever a time to do it, it's now.
and that last horse comes in where you won't get to use it very often
Tech Contributor
Joined: Mar 2003
Posts: 12,094
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From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
When the engine is running at off idle rpm's (800-900) then it doesnt matter if the alternator is spinning 10% slower does it? If you are swapping cams and you are increasing the idle from 625 to say 800 then you are again over 10% higher arent you? Now if you left it stock cammed and put on the pulley with a 625 idle, I couldnt answer but...
There has never been a factual problem/complaint on a modded C5 or C6 with stereo equipment or whatever. Just those with theories as to why it might not work. Fact is that its a great mod and worth every penny at 25 bucks/HP. I had a R-Fosgate 700 watt amp in my C5 at one point and had no issues at all with dimming or other supposed issues.
Take advice on mods ONLY from the people that have that mod.
There has never been a factual problem/complaint on a modded C5 or C6 with stereo equipment or whatever. Just those with theories as to why it might not work. Fact is that its a great mod and worth every penny at 25 bucks/HP. I had a R-Fosgate 700 watt amp in my C5 at one point and had no issues at all with dimming or other supposed issues.
Take advice on mods ONLY from the people that have that mod.
Le Mans Master
Joined: Aug 2004
Posts: 5,259
Likes: 16
From: Monroe Township New Jersey
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16
St. Jude donor in memory of jpee '14
Originally Posted by SpinMonster
When the engine is running at off idle rpm's (800-900) then it doesnt matter if the alternator is spinning 10% slower does it? If you are swapping cams and you are increasing the idle from 625 to say 800 then you are again over 10% higher arent you? Now if you left it stock cammed and put on the pulley with a 625 idle, I couldnt answer but...
There has never been a factual problem/complaint on a modded C5 or C6 with stereo equipment or whatever. Just those with theories as to why it might not work. Fact is that its a great mod and worth every penny at 25 bucks/HP. I had a R-Fosgate 700 watt amp in my C5 at one point and had no issues at all with dimming or other supposed issues.
Take advice on mods ONLY from the people that have that mod.
There has never been a factual problem/complaint on a modded C5 or C6 with stereo equipment or whatever. Just those with theories as to why it might not work. Fact is that its a great mod and worth every penny at 25 bucks/HP. I had a R-Fosgate 700 watt amp in my C5 at one point and had no issues at all with dimming or other supposed issues.
Take advice on mods ONLY from the people that have that mod.
Hate to be a pain.......But Yes I have experience. Installed them on my SVT Cobra (the green one in my corvette picture)......very small gain in the upper RPM range in my opinion it was not worth the effort.
There are some of us who know of what we type
otherwise we would not type it. By now you should know where I come from 
Drifting
Joined: Jul 2003
Posts: 1,796
Likes: 1
From: Annandale VA
I had an ASP pulley on my Camaro SS, and experienced the dimming lights at idle. Have to admit I did not have any aftermarket stereo equipment. However, I do know several guys who have experienced various woes from low battery voltage, but not caused by an underdrive pulley.
I have to agree that the gains are limited, and mostly occur at higher RPMs. Pretty low bang for the bucks.
I have to agree that the gains are limited, and mostly occur at higher RPMs. Pretty low bang for the bucks.
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Team Owner
Joined: Feb 2001
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From: Short Hills, NJ
Another possible factor is the water pump...apparently the C6 (and 2004 C5s) water pump doesn't flow quite as well as the pre 2004 C5 water pumps did so adding an underdrive pulley could slow it down too much for it to work as efficiently.
If I had an older C5 I would certainly consider an UD pulley but I will likely not be installing one on my C6 unless I go to a more efficient or even electric water pump which is highly unlikely LOL.
I do have one (ASP) on my bolt on Z28 and it has been fine with a full size battery but when running a lightweight (save 22 pounds of the nose) battery it really dimmed the lights even though the idle was bumped up another 50rpm.
If I had an older C5 I would certainly consider an UD pulley but I will likely not be installing one on my C6 unless I go to a more efficient or even electric water pump which is highly unlikely LOL.
I do have one (ASP) on my bolt on Z28 and it has been fine with a full size battery but when running a lightweight (save 22 pounds of the nose) battery it really dimmed the lights even though the idle was bumped up another 50rpm.
Safety Car
Joined: Jan 2005
Posts: 3,675
Likes: 58
From: Hayward (Bay Area) CA
Im thinking of buying a UD pulley. My car is a 99, A4.......ALL stock. Will I benefit from this, or rather have a negative affect? 
I'm planning on doing H/C, but not anytime soon though...
I'm planning on doing H/C, but not anytime soon though...
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Yes, 9rwhp just like everyone else who had one installed on a corvette.
Tommy, cobras are not corvettes and I never saw a corvette owner complain. If your lights dim, raise the idle 10% then its spinning at the same speed as it was before the pulley was installed. So the stock people runinng 625rpm can go 700 with no issues cant you?
Tommy, cobras are not corvettes and I never saw a corvette owner complain. If your lights dim, raise the idle 10% then its spinning at the same speed as it was before the pulley was installed. So the stock people runinng 625rpm can go 700 with no issues cant you?
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Originally Posted by Tommy D
Hate to be a pain.......But Yes I have experience. Installed them on my SVT Cobra (the green one in my corvette picture)......very small gain in the upper RPM range in my opinion it was not worth the effort.
There are some of us who know of what we type otherwise we would not type it. By now you should know where I come from
There are some of us who know of what we type
otherwise we would not type it. By now you should know where I come from 
Safety Car
Joined: Jan 2005
Posts: 3,675
Likes: 58
From: Hayward (Bay Area) CA
Originally Posted by SpinMonster
Oh come on, a Cobra??? I had one on my 1979 trans am and had issues so I raised the idle back then. Same fix today.
IF I put on a UD Pulley on my Stock A4, C5 - does that mean I'll have to raise the RPM in idle? And is it true that the lights will dim and overall I'll loose current?... I don't know the basics of this how it works. But it seems like a cheap mod, for a 8-10 rwhp gain... Somenone plz educate me...Thanks...
Le Mans Master
Joined: Aug 2004
Posts: 5,259
Likes: 16
From: Monroe Township New Jersey
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16
St. Jude donor in memory of jpee '14
Originally Posted by SpinMonster
Yes, 9rwhp just like everyone else who had one installed on a corvette.
Tommy, cobras are not corvettes and I never saw a corvette owner complain. If your lights dim, raise the idle 10% then its spinning at the same speed as it was before the pulley was installed. So the stock people runinng 625rpm can go 700 with no issues cant you?
Tommy, cobras are not corvettes and I never saw a corvette owner complain. If your lights dim, raise the idle 10% then its spinning at the same speed as it was before the pulley was installed. So the stock people runinng 625rpm can go 700 with no issues cant you?
Now if you run the car at the track a lot and want every bit of horse power you can get.......... Hey that is a different story. It is a whole bunch more work on a Vette than the Cobra but you need every little bit of horsepower at the track
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Originally Posted by Vette_Fan
I am not understanding this.... IF I put on a UD Pulley on my Stock A4, C5 - does that mean I'll have to raise the RPM in idle? And is it true that the lights will dim and overall I'll loose current?... I don't know the basics of this how it works. But it seems like a cheap mod, for a 8-10 rwhp gain... Somenone plz educate me...
Thanks...
IF I put on a UD Pulley on my Stock A4, C5 - does that mean I'll have to raise the RPM in idle? And is it true that the lights will dim and overall I'll loose current?... I don't know the basics of this how it works. But it seems like a cheap mod, for a 8-10 rwhp gain... Somenone plz educate me...Thanks...
Only take advice on a mod by a person who has that mod ---themselves---on a corvette---that is the same year.
Le Mans Master
Joined: Aug 2004
Posts: 5,259
Likes: 16
From: Monroe Township New Jersey
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16
St. Jude donor in memory of jpee '14
Originally Posted by SpinMonster
Take advice on mods ONLY from the people that have that mod.
................. & I know I came from the dark side ........ those Ford guys, think they know what they are doing
Le Mans Master
Joined: Aug 2004
Posts: 5,259
Likes: 16
From: Monroe Township New Jersey
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16
St. Jude donor in memory of jpee '14
Originally Posted by SpinMonster
Yeah but your vote doesnt count because your car is junky and you should give it to me and take mine.
Tech Contributor
Joined: Mar 2003
Posts: 12,094
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From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Originally Posted by Tommy D
That is just because you need a slave cylinder bleeder extension which isn't in production yet......... Ford makes other things fun like installing Long tubes on a Cobra %~"**^$
What is so hard about cobra longtubes?