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under drive pulley

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Old 11-02-2009, 07:59 PM
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dobewillie
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Default under drive pulley

what is involved to install an under drive pulley and what kind of HP gains can I expect on 02 a4 fast92/92 cam heads lth high flow cats stingers and tune thanks for any info
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Old 11-25-2009, 12:35 AM
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C5Natie
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Here is ATI's instructions but they dont tell you all the bs you have to get by or remove like the whole steering rack.
http://www.andersonperformance.net/C...er_Install.pdf
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Old 11-25-2009, 06:42 AM
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Blow Torch
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I would personally NEVER install an underdrive pulley unless I was already in there doing a cam change. There just isn't enough real dyno evidence of rwhp gains to warrant the major PITA of removing the steering rack and pulling the balance (and of course installing new seals etc.)
I have one laying around in my shop that I could put on my wife's car, but wouldn't dream of doing it unless we install a cam
There are a lot more low $$ mods you can do and get proven gains (not gains the vendor claims)
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Old 11-25-2009, 09:42 AM
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Eric D
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Originally Posted by Blow Torch View Post
I would personally NEVER install an underdrive pulley unless I was already in there doing a cam change. There just isn't enough real dyno evidence of rwhp gains to warrant the major PITA of removing the steering rack and pulling the balance (and of course installing new seals etc.)
I have one laying around in my shop that I could put on my wife's car, but wouldn't dream of doing it unless we install a cam
There are a lot more low $$ mods you can do and get proven gains (not gains the vendor claims)
I agree with your thoughts on not installing one unless doing other major changes, like cam or cam drive. I don’t agree with your statement, “just isn’t enough real dyno evidence”. Simple math will show the benefits, no dyno needed.

Engine driven accessories like the alternator, water pump, and power steering pump have a fairly linear curve when it comes to sucking power from the engine. Changing drive ratio is much like shifting to a lower gear allowing faster acceleration. One of the biggest advantages that most people over look is the inertia factor. By using an underdrive pulley, the alternator isn’t spun up as high as with the stock pulley ratio. The alternator is the largest inertia load of all accessories. It plays a major factor on how rapid the engine can rev, much like the inertia of a light versus heavy flywheel. In simple terms it plays a big factor on throttle response. If performance is your game or desire, and you don’t expect to drive your car when it is -40 deg’s outside, then going to an underdrive balancer might be a reasonable choice to gain performance.


Last edited by Eric D; 11-28-2009 at 07:36 PM. Reason: miss spelled word fix..
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Old 11-28-2009, 06:12 PM
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Blow Torch
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I stick to my statement "Show me the money"
I have seen three attempts at dyno "test" on underdrive pulleys and the MOST I have ever seen was 6hp (one showed 1 hp) That is not enough for me to bother with
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Old 12-05-2009, 09:03 AM
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What about ECT's. C6's run 198-205 degrees normally. With less cooling volume what would happen to the water temps?
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Old 12-07-2009, 07:53 PM
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Well, I can't give any dyno comparo, since I also wouldn't think of messing with a pulley swap unless a nice cam went in also. But, I do have experience on the effects of a 25% pulley on the accessories.
- Water temp went up from 183 to 185 when freeway cruising steady-state in 6th gear in 100-degree weather in Texas. No noticeable change in stop-go.
- AC showed no detectable change in the hot Dallas summer.
- Charging circuit unaffected, but I rarely play the radio.
- Steering effort displays a very slight tug when starting off from a rest and turning the wheel sharp - like backing out the drive and heading out down the street. Perfectly acceptable.
- My ASP pulley has absolutely zero wobble, much better than the stock unit.

I feel certain all my accessories, belts, and the infamous idler pulleys will last longer - just seems logical.

One last thing - I did a lot of small mods to my C4 Vette, like exhaust, intake, chip, etc. The only mod I could definitely feel was the underdrive pulley.

DG
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Old 12-08-2009, 03:01 PM
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vetterdstr
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I had one on my car years ago and I believe it was worth 5 RWHP.

Best of luck to you with your future mod decisions.
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Old 12-08-2009, 04:17 PM
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~Josh
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5-9 rwhp on a dyno.

On an F-body it's a good mod even if you're not changing the cam.... on the Corvette it's much more work pulling the steering rack.

Save that mod for when the cam is being changed.
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Old 12-08-2009, 09:08 PM
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marinehacker202
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or just do what I am in the middle of doing. wait for your stock harmonic balancer to go to sh*$. Then since you gotta replace that anyway.. might as well upgrade
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Old 12-08-2009, 11:32 PM
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Originally Posted by marinehacker202 View Post
or just do what I am in the middle of doing. wait for your stock harmonic balancer to go to sh*$. Then since you gotta replace that anyway.. might as well upgrade
be sure and pin the crank too!


should just go ahead and stick in a cam too
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Old 08-14-2017, 11:40 PM
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ZO ZICK
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Too much work for less than 10 HP
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Old 08-16-2017, 12:35 PM
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Originally Posted by vetterdstr View Post
I had one on my car years ago
Ditto, and will never again! The diminished PS assist when needed (parking) had me rueing the decision very quickly.
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