Underdrive Pully???
Underdrive Pully??? Ok so I am going to be doing heads and cam on my 99 camaro Z28 M6 here pretty soon. I had a underdrive pully on my previous LS1 car and never had a problem. But I was giving it some thought and cant decide if the power gains is worth it or not. Basically my question is, Is it safe to be underdriving the water pump?? I am sure the GM engineers put alot of time and effort into making the water pump flow just right for the engine, and taking flow away could cause problems IMO. So lets here what you guys think.. 
actually,,since the belts are shorter, and the pully is smaller,,would'nt there be more flow vs less? sorry, thought id throw that out there since this is probably the most valid question ive seen about a UD pulley. 
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It should not be a problem for a couple of reasons. First, if the water pump was designed to flow "just right" for the stock engine, then any performance modification would make the water pump "undersized" for the engine as more H.P. translates into more heat, and then you would have a overheat issue. Second, "just right" for what conditions? It has to be able to handle conditions from the desert at over 120 degrees to sub-zero conditions. So chances are the water pump is oversized for a stock engine in "normal" conditions. With underdrive pulleys only the crank pulley is smaller, the water pump and alternator pulleys would be larger so that they spin slower than stock, thus freeing up the H.P. that would normally be used to drive them at a faster rate.
It should not be a problem for a couple of reasons. First, if the water pump was designed to flow "just right" for the stock engine, then any performance modification would make the water pump "undersized" for the engine as more H.P. translates into more heat, and then you would have a overheat issue. Second, "just right" for what conditions? It has to be able to handle conditions from the desert at over 120 degrees to sub-zero conditions. So chances are the water pump is oversized for a stock engine in "normal" conditions. With underdrive pulleys only the crank pulley is smaller, the water pump and alternator pulleys would be larger so that they spin slower than stock, thus freeing up the H.P. that would normally be used to drive them at a faster rate.
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i agree, the hp gain isnt worth the risk. couple threads about UD pulleys breaking timing chains tuned me off them for good. you can definitely make up for the approx 10rwhp with a good driver mod 
fibblesteaks.
fibblesteaks.
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From: Alpharetta, Ga
Me. ASP UD Pulley. Upon tearing everything down and checking the install, everything was perfect. There was no cam walk, all tq specs were dead on, red locktite was on everything, valve spring pressures were tested and came back perfect, pushrod length was re-measured and re-verified, and tune was dead on via my hard mounted w/b 02 guage along with the full HP tuning suite.
TC broke at 4000rpm. Was it the pulley's fault, a faulty chain, or both? Who knows...
TC broke at 4000rpm. Was it the pulley's fault, a faulty chain, or both? Who knows...
Last edited by 1.8t; Feb 17, 2009 at 09:51 AM.
I feel the UD is worth it. I felt a big increase.
If your worried about the engine getting to hot, whoever tunes it for you, tell them to have the fans turn on sooner. Or get a cooler thermostat. Either way I don't think you'll have any problems with cooling
If your worried about the engine getting to hot, whoever tunes it for you, tell them to have the fans turn on sooner. Or get a cooler thermostat. Either way I don't think you'll have any problems with cooling
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I do not see how a underdrive pulley can break a timing chain. Just not possible. If the underdrive pulley (crank) was installed incorrectly, then maybe.......but not likely. I would venture to say it was a defective timing chain. What did the crank gear look like? What did the locating key and keyway look like? The torque of the bolt holding the crank pulley on is what also clamps the crank gear in place so that the key and keyway do not have any load on them while driving the valvetrain. If the crank bolt was not torqued properly then it is possible to have the crank gear shear the key and cause a failure that way, which could cause the cam timing to change resulting in piston to valve clearance issues. This is a extreme example of what could happen, but not likely.
Anyway, the underdrive crank pulley is only underdriving the water pump by what, 15%? That should not be a issue even with H/C/I ect. I know in the Mustang 5.0/4.6 world underdrives are never an issue. (cooling wise) It is usually a undersize radiator that is the real issue. Of the several LS engine I have had delt with, a underdrive pulley has never been an issue. Even on highly modded engines. I say take the 10+ whp with confidence.
Anyway, the underdrive crank pulley is only underdriving the water pump by what, 15%? That should not be a issue even with H/C/I ect. I know in the Mustang 5.0/4.6 world underdrives are never an issue. (cooling wise) It is usually a undersize radiator that is the real issue. Of the several LS engine I have had delt with, a underdrive pulley has never been an issue. Even on highly modded engines. I say take the 10+ whp with confidence.
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No one says TC failure can be a direct result of a UDP, but there is a lot of theory that it can play a key role.
What? Who broke a timing chain with an under drive pulley?
I would say that at least a 1/3 of the people on this board have an under drive pulley and very few have had problems. Truth be told the problems they had were probably not entirely the UDPs fault.
That's not to mention the millions of other cars out there that have UDPs and belt driven water pumps that have few problems.
They're worth a tenth in the 1/4. If that's not worth it to you, then so be it.
I would say that at least a 1/3 of the people on this board have an under drive pulley and very few have had problems. Truth be told the problems they had were probably not entirely the UDPs fault.
That's not to mention the millions of other cars out there that have UDPs and belt driven water pumps that have few problems.
They're worth a tenth in the 1/4. If that's not worth it to you, then so be it.
I think the damper diameter and design play a key role in their effectiveness. 25% under drive is too small to adequately control crankshaft harmonics on an LSx engine. The problem manifests itself as a broken timing chain due to the lack of adequate crankshaft harmonics control.
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Then I would think that it would be a ASP issue with their underdrive pulley as opposed to ALL underdrive pulleys "causing" this problem. I personally have not seen it with other underdrive pulleys. And I have not used a ASP underdrive pulley in this application. I have used their pulleys in other applications with no problems. So maybe they need a little more R&D for the LS market to resolve this issue. Has anyone asked them about this issue?
Last edited by Bullitt347; Feb 17, 2009 at 11:49 AM. Reason: spelling
Then I would think that it would be a ASP issue with their unerdrive pulley as opposed to ALL underdrive pulleys "causing" this problem. I personally have not seen it with other underdrive pulleys. And I have not used a ASP underdrive pulley in this application. I have used their pulleys in other applications with no problems. So maybe they need a little more R&D for the LS market to resolve this issue. Has anyone asked them about this issue?
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So is this timing chain breaking issue only with the stock chain, or does it happen with a dual roller t-chain as well? Has anyone checked to see if this is happening only to higher milage stock chains, or does it not matter? Just curious......
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So I will go back to what I previously said, installation issue. The proper way to tighten the new balancer is to use the old balancer bolt, tighten to 240 ft/lb, remove old bolt, install new bolt, tighten to 37 ft/lb, then tighten an additional 140 degrees. Last time I did this, engine was out of the car and it took two people, one to hold the flexplate and me with a big cheater bar on the front crank bolt to get the 140 degrees rotation on the bolt when final tightening. I would bet that the average installer is NOT following proceedure when installing underdrive crank pulley. Just a guess..........
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From: Alpharetta, Ga
My balancer was installed correctly. Additionally, it is generally accepted that if you can 100deg on the bolt during reinstall, your fine. All of that tq is necessary to keep the bolt from backing out....it doesn't have anything to do with the balancer as of that point.
Read through this thread -> https://ls1tech.com/forums/generatio...n-failure.html
No one says TC failure can be a direct result of a UDP, but there is a lot of theory that it can play a key role.
No one says TC failure can be a direct result of a UDP, but there is a lot of theory that it can play a key role.