Questions on an underdrive pulley
 

Hey, has anyone used the Motorsports Underdrive pulley set-up? I'm replacing my timing belt on my 94 LS and i thought now would be a great time to order the step up from something stock, plus it comes with belts, i think. Any inputy to the stuation would help.

Works great. I have the underdrive on ne car and the standard size one peice on the other. Doesnt seem to have any effect on performance, though Id imagine if you combined it with other lightweight stuff, in theroy, it could make a slightly noticable diffrence to performance. More or less, it's shiney, and wont seperate like the factory ones sometimes do..plus it makes your mod list 1 longer

If it doesnt come with belts, make sure to get some. The stock size will be too big, I think you need something like 1 or 2 inches smaller

Yes it will work and may look pretty and you may not have any problems.

However, your engine will no longer incorporate any means of torsional vibration dampening and this will impose unwanted stresses on the crankshaft. Accessories will run at a slower speed including the alternator, which could be important if you are running extra electrically powered gear.

To be honest trevor, I don't see the stocker really doing much along the lines of dampening vibrations. I have been running an undersized pulley for my S/C for quite some time now with the only alternator issue being that sometimes it likes to get torn off the car:rolleyes::D Either way... the only upside to an underdrive pulley would be that it is a one piece... Other than that any real performance gains cannot be obtain through such simple means

Tom

Tom, this argument has been well and truly thrashed.:eek:

It can nor be denied that the OEM pulley incorporates a means of, and is a torsional dampening device. The expense of incorporating same will have been taken into account by Subaru.

I agree that the effects or affect can not be seen, are from obvious and lack of same may not directly cause a problem. But is dispensing with a known advantage warranted?:confused: A google will disclose some very interesting facts and detail regarding the technology involved.

All accessories driven via a flexible belt comprise an excellent means of absorbing torsional vibration and a supercharger will add to the affect. I would not suggest such a load should be imposed on the OEM pulley and you have no alternative option.

As a matter of interest I ran up against the lengths designers go to in respect of torsional vibration when I built my first car for competition, over fifty years ago. The Fiat engine had the generator flexibly coupled directly to the front of the crankshaft. The fan was fitted directly to the overhead crankshaft, chain driven at the rear end, via cone clutch sort of slipping hub. This set up was beautifully neat and tidy, but belt drives are superior.

Sincerely, I would love to have the opportunity to talk engine design, etc., etc., Tom/Tom/Trevor, over e beer or two.:D

Cheers, Trevor.

tehn come to the states and we can do this;)

Tom

Thanks Tom.

Invitation much appreciated, noted, recorded and put on hold pending a windfall. ;)

I have emailed dayle about his pullys and he told the the best one to get for your money and proformance would be the stock size pully that is lightened if that helps anyone?

i agree... the stock sized pulley is your best bet for aftermarket pulleys. You can also find them on ebay as they are the same as other subies for the most part. But they are of lesser quality than dayle's

Tom

I have Dayle's lightweight stock pulley and I noticed that the engine cranks over a little easier. Other than that it's pretty much the same.

wouldn't torsional vibration dampening be less important on a H6 than on some other cars like an I4 design, as its already a fairly well-balanced design?

Thanks for the advice
 

I'm not really expecting any more hp from the underdrive pulley, i just thought it would help with lowering the total recipricating mass by alittle. But you all pose so many good points its still hard to decide what to do. I have another question for you all. I've been told that not having enough back-pressure in your exhaust can make you lose power. Now i have always thought the other way, less back-pressure, more power. I know for a fact that i have 0 back-pressure as you can see in the pic i'm posting, but is there a certain amount i should have? there not in the pic, but i have a pair of Thrush glass-paks about 2/3's the way down the straight pipes.
Anywho thanks again.
P.S. if my pic fails to show, check out my cardomain page. www.cardomain.com/ride/2488463

ooooooooops

2.5InchTrueDual
 

My puter didn't like your link.

TomSVX
 

"i agree... the stock sized pulley is your best bet for aftermarket pulleys. You can also find them on ebay as they are the same as other subies for the most part. But they are of lesser quality than dayle's

Tom"


How is Dayle's of better quality? What is it made of? 7075, 6061, 6063? Is it hard anodized? Or does it come with a sticker?
Seriously though, I am curious. What is it that make it better?