Yes, I have posted this as a response in another topic, but I thought I'd share it with everyone....I cut it from my last post...
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PROOF--Underdrive pulleys free up horse power....
GMHTP July 2003 Vol 9 No. 4 "Project Blue Thunder, 13's or Bust" JET underdrive alt and crank pulley install on an 89 Formula Firebird. 305 TPI. Dyno'd at the SLP plant..
Written by Steve Baur



I took an excerpt from an article in GMHTP.....There were dyno sheets in the article but my scanner is down..

 

This does not apply to LT1 cars because they dont have a belt driven water pump. A pully does help LS1 cars a good bit.

 

This seems like basic physics. I can't see an underdrive not helping. Is this even an argument aside from the argument of 'how much' it helps? All I see up for grabs is variations in how much is gained, not if any is gained.

 

The thing I don't like about LT1 underdrive pulleys is the fact that you are adding a pulley on the crank, and not removing anything. You are actually adding rotating mass, but at the same time spinning the accessories slower.

I think ATI makes a combination damper/underdrive pulley though.

Dan

 

ASP makes a underdrive/dampner set up that I liked. I have a Aeromotive pulley to be put on the 97 but thinking twice b/c of the extra mass that will be turning...

 

No need to guess... this LT1 dyno test has been around for at least 6 years.

http://www.ws6.com/mod-2.htm

I had the ASP 23% integrated damper/pulley, and the ASP 15% alternator pulley, and the only performance difference I was able to measure was a loss of charging voltage at idle with the lights or AC on. The question is whether the gain is worth the aggrevation.

 

That's a valid point that I din't take into concideraton. I suppose that can be concidered with any mod.....Thanx

 

thing w/ these is I had a few friends that had charging problems on there 93 and 94's...For the few hp it free'd up I never though it was worth the possible bs

 

I bought my 95 Hawk with one of these smaller crank pulleys but the thing I dont get is why you have to have the stock pulley over the smaller one?

what will happen if you were to take off the larger pulley and just leave the smaller one?

 

the original is the harmonic balancer, it has to go back on, or the engine will vibrate somewhat.... it's hard on the crank.....if you leave it off,imo

 

I have a friend that had a charging issue at idle after he installed March pulleys

 

I have yet to see a charging problem in mine

 

ya i read that same article. my brother had problems with his on his lt1.

 

Would the installation of the alt pulley correct the difference? Charging problem wise, bring the alt up to the correct speed?

 

There are several different types and sets of U/D pullies made. As far as the alternator pulley, you can get either an underdrive pulley for the alternator (further slows down alternator, producing max HP savings), OR an overdrive pulley for the alternator (speeds alternator back up, increasing charging at low RPM, but gives back some of the not-too-much-anyway HP savings).

As far as the harmonic damper is concerned, you can get a single piece, integrated damper/pulley from ASP, as an alternative to the type that sandwiches behind your stock damper.

I had the ASP integrated 23% U/D damper/pulley, and the 15% U/D alternator pulley, and was not able to measure any power gain. The volt meter would drop into the red when idling in traffic with the lights or A/C on.