Underdrive Pulley
Racer
Joined: Nov 2004
Posts: 298
Likes: 0
The main idea is that if you install a smaller crank pulley, you reduce the torque required to drive all the accessories leaving more for the rear wheels; however, the trade off is that all the accessories are now spinning at less than they were designed for. In some causes such as the alternator, they will simply require more torque and the end result will be the same. In other cases you may get sub-par operation, such as power steering, A/C compressor, cooling system, etc... This would especially be true at idle. IMHO it is a silly thing...even worse than the "performance chips" and other gimmicks....
Drifting
Joined: Sep 2004
Posts: 1,551
Likes: 4
From: Livingston Texas
Originally Posted by G-Z06
Girlfriend just did a pully on her 2003 Z06 earlier this afternoon and she gained 9rwhp.
Drifting
Joined: May 2004
Posts: 1,743
Likes: 0
From: Ohio
Originally Posted by OttoNP
IMHO it is a silly thing...even worse than the "performance chips" and other gimmicks....
Racer
Joined: Sep 2004
Posts: 420
Likes: 0
From: Houston Texas
Originally Posted by Drug Delivery
I think it's well established that a proper "perfomance chip" or programming unit such as what Hypertech offers, are no gimmicks. Particularly when custom tuning is done.
A good friend of mine had one installed and he saw no gain.
On the other hand, a few months later another guy I know got one installed and he saw a gain of 8rwhp.
Is it all based on the tune?
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Racer
Joined: Nov 2004
Posts: 298
Likes: 0
Here's the thing, there is a huge difference between gaining 9 hp over the entire RPM curve versus just gaining it at the peak or a specific RPM. Most people that add modification alway think they feel a difference, but then they measure it scientifically and are disappointed. I'd be interested in seeing the whole HP curve for vehicles with and without, taking over several RPM sweeps. My thoughts are that these aftermarket companies find some RPM with a HP difference and publish that, even though at some RPM there may be no change or even a drop.
Racer
Joined: Jan 2005
Posts: 429
Likes: 0
From: El Segundo CA
I installed an Unorthodox underdrive pulley on my 1995 3000GT when I had it (it was a base model, not the VR4). The power output wasn't a worry as all it did was drop the output from about 15V or so down to just under 13V. This was still plenty of juice to power the features of the car without hindrance.
The biggest difference I noticed with the car was that it was 'perkier'. Meaning with less mass to rotate, the throttle response was improved, crisper, more responsive. What that translated to in actual HP I don't know as I didn't have the car dyno'd or tuned (hardly any I would imagine). But the throttle response was blatantly obvious, which is what I felt the modification was more about anyways
.
As to how much juice a Vette needs and how an underdrive pulley would effect it I don't know. That's something we'll have to wait and see what tuners and others say from their experiences.
The biggest difference I noticed with the car was that it was 'perkier'. Meaning with less mass to rotate, the throttle response was improved, crisper, more responsive. What that translated to in actual HP I don't know as I didn't have the car dyno'd or tuned (hardly any I would imagine). But the throttle response was blatantly obvious, which is what I felt the modification was more about anyways
.As to how much juice a Vette needs and how an underdrive pulley would effect it I don't know. That's something we'll have to wait and see what tuners and others say from their experiences
.
Melting Slicks
Joined: Nov 2004
Posts: 3,064
Likes: 6
From: Pinellas Park Florida
Depends what pulley you underdrive, but yes you will pick up some hp. On the C6 given the electrical load, you may want to pass since the alternator will slow down, in general though, by itself the mod is more work then the results warrant
Race Director
Joined: Oct 2004
Posts: 10,089
Likes: 14
Originally Posted by AutoCutter
Depends what pulley you underdrive, but yes you will pick up some hp. On the C6 given the electrical load, you may want to pass since the alternator will slow down, in general though, by itself the mod is more work then the results warrant
Melting Slicks
Joined: Nov 2004
Posts: 3,064
Likes: 6
From: Pinellas Park Florida
Originally Posted by shopdog
During WOT acceleration, the LS2's ECM is supposed to temporarily shut down the alternator and the A/C compressor. So switching to an underdrive pulley shouldn't offer any performance improvement, except in so far as it reduces rotating inertia. A much more impressive way to do that is to switch to a lighter flywheel.
More or less agree. If I had the engine out I would do an underdrive on the crank and a lighten flywheel as 3hp here, 4hp there it all adds up, but as single mod's-naaa doesn't make $$ sense. Once my electrical snafu's go away I plan on rockers/cam/springs/retainers/headers/flywheel/underdrive crank pully/carbon drive shaft and just do it all at one time.
Race Director
Joined: Oct 2004
Posts: 10,089
Likes: 14
Originally Posted by AutoCutter
More or less agree. If I had the engine out I would do an underdrive on the crank and a lighten flywheel as 3hp here, 4hp there it all adds up, but as single mod's-naaa doesn't make $$ sense. Once my electrical snafu's go away I plan on rockers/cam/springs/retainers/headers/flywheel/underdrive crank pully/carbon drive shaft and just do it all at one time.
Melting Slicks
Joined: Nov 2004
Posts: 3,064
Likes: 6
From: Pinellas Park Florida
Originally Posted by shopdog
A side benefit of the underdrive swap is you can fix the crank bolt problem at the same time, so the labor cost is shared over two objectives.
It is a good solution to the problem and fully justified-no question of that; of course you have to have the problem
