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post #1 of (permalink) Old 02-25-2002, 12:35 PM
SPAMurai
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Underdrive Pulley?

Someone once recommended an underdrive pulley for a few extra HP. Any comments on this? Is there one that's easily swapped in? Where can you get one? Thanks,

Steve O'

'87 4-Runner, 31's, Downey headers & 2.5" cat-back, Flowmaster, 3" lift, and locked.
'87 SPAMurai, 30's, 2" lift, to be locked soon.
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post #2 of (permalink) Old 02-25-2002, 01:34 PM
Alfie
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Re: Underdrive Pulley?

Haven't tried one, want one tho'.
RRO, Asian Autos's Northcoast etc. etc.
Don't expect HUGE gains. With this stuff it's a little here and a little there.
Add an adjustable cam sprocket, roller rocker arms, etc.
Cam and carb of course.
I can honestly say the adjustable cam sprocket and cam grind opened my eyes up to what a 1.3 can be like.
Some guys on this board have over 100 Hp on tap from an 8v 1300.
That's where i'm headed, i hope.
Jus my thoughts, don't mean to preach.
Alfie

post #3 of (permalink) Old 02-25-2002, 02:00 PM
IMC2112
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Re: Underdrive Pulley?

I make several billet aluminum "under-drive" pulleys for Samurai's and Sidekicks. Can't promise you 20h.p. gain but like Alfie said every little bit helps. Roadless Gear, Rocky Road and Asian Auto carry them.

Philip
Rotational Dynamics

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post #4 of (permalink) Old 02-25-2002, 02:42 PM
 
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Re: Underdrive Pulley?

Who makes roller rockers? Are they stock ratio?

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post #5 of (permalink) Old 02-25-2002, 03:13 PM
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Re: Underdrive Pulley?

Can you explain the concepts of underdrive pulleys, adjustable cam sprockets, and rocker ratios? I'm not clear on the potential benefits.... Thanks...

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Crow

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post #6 of (permalink) Old 02-25-2002, 08:08 PM
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Re: Underdrive Pulley?

Ok, I'll give it a shot, Crow. Underdrive pulleys do just that, in effect they "gear down" the engine accessories. This results in less drag on the motor, and frees up a few hp. Unfortunately, they do have some drawbacks. Your alternator won't be able to generate many amps since it will turn slower, mostly noticeable at idle, and engines sometimes have a problem with running hot at low speed since the water pump isn't turning fast enough. Philip's pulley is designed as 18% underdrive, not really enough to hurt a Zuk's accessories. Adjustable cam sprockets will allow you to tune the cam according to the engine. No two engines are alike, two identical ones will always run different. Once you start modifying a motor, many things change beyond what you have done. If you mill the head, you change the effective ratio of the timing belt, and changing cams will also effect valve timing. Sometimes, you get lucky, and everything works together, most of the time, it don't. Rocker ratios are nothing more than forcing the valve train to read the cam as bigger, longer duration and such. Stock rocker arm ratios on Zuks is 1.6, by increasing this geometry, you increase the lift and duration. On some cams, it helps quite a bit, on other cams it will actually hurt. Using modified rockers takes a lot of caution, as an aftermarket cam that is designed to maximize valve lift can cause the valves and pistons to hit each other, destoying a lot of money in the process. It's like Philip said, every little bit helps.
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post #7 of (permalink) Old 02-25-2002, 09:06 PM
 
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Re: Underdrive Pulley?

Would it be possible to add an overdrive pulley (or underdrive...which ever makes it spin faster) to just the alternator (or even the PS pump) to increase it's output?


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post #8 of (permalink) Old 02-25-2002, 11:19 PM
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Re: Underdrive Pulley?

Thanks Sarge, Couldn't have expained it any better myself. I've made over-drive pulleys for Glenn at Rocky Road for his p/s kit. Over-drove the p/s belt by 20%

Philip
Rotationl Dynamics

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post #9 of (permalink) Old 02-25-2002, 11:24 PM
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Re: Underdrive Pulley?

I was 1 of the first to run Bergs underdrive pulley still running it today wouldnt change it for anything! and of course have his adj cam sproket cover , waiting on rollerrockers, and spacer for tbi which buy the phillip should be there wensday .

<font color=red>And yes if you dont no it buy now i cant spell LOL!</font color=red>
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post #10 of (permalink) Old 02-26-2002, 01:11 AM
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Re: Underdrive Pulley?

what benefit do you get from overdrive pulley? yyes.... Over-Drive....

JKing
Suzuki Samurai (a.k.a. Jimny SJ413 in Asia)
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