Questions on an underdrive pulley

2.5InchTrueDual · #1 09-19-2007, 02:17 PM

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.

It's Just Eric · #2 09-19-2007, 02:23 PM

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

Trevor · #3 09-19-2007, 04:44 PM

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.

TomsSVX · #4 09-19-2007, 05:00 PM

Quote:

Originally Posted by Trevor

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

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

Trevor · #5 09-19-2007, 05:48 PM

Quote:

Originally Posted by TomsSVX

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

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.

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?

A

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.

Cheers, Trevor.

TomsSVX · #6 09-19-2007, 06:13 PM

tehn come to the states and we can do this

Tom

2.5InchTrueDual · #7 09-20-2007, 05:33 PM

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

YourConfused · #8 09-20-2007, 07:36 PM

ooooooooops

YourConfused · #9 09-20-2007, 07:36 PM

My puter didn't like your link.

YourConfused · #10 09-20-2007, 07:43 PM

"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?

TomsSVX · #11 09-20-2007, 09:13 PM

Quote:

Originally Posted by YourConfused

"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?

Not sure... But I haven't heard of any issues with his... The cheap Ebay ones have had a couple break into pieces causes major damage to engine components like the timing belt etc.

Tom

YourConfused · #12 09-20-2007, 09:36 PM

that sounds crazy, weird, scary and expensive.
Is it true though?
I bought one of those cheap ebay ones fyi.
thanks for the reply though.

p.s.
Oh, $24.95 was too good to pass up. Haven't seen one of those on there since. Machine quality was tip top, and had laser etched logo (OBX). Some work went into that part, but i am sure it wasn't heat treated. Rockwell is low as per tester at work said, like 47ish. Don't remember actually, could be offf on the spec, as it was a while ago.
Well whatever. I guess it's like a flywhel that is great until it blows and cuts your toes off. (met a guy who had that happen in his shoe box w/ a 283 sbc hittin 9.8K rpm) Anderjesky has passed, but i am glad I got to meet him. So I may loose a hood, rad. and plastic timing covers? (I love your car btw)