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DC Crew
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Discussion Starter · #1 ·
Does anyone have opinions on this mod? Is there a noticable advantage to this or is it something done more on modded motors? My car car is basically stock and I have engine plans in the future but for now I was looking for a little more punch.
Thanks for the advise.
 

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65Z01 on the cf had some good info on that a while back, you might try searching the archives over there. But I'll bet grumpyvette will also have info on that.:)
 

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i will keep an eye on this thread as i am contemplating,i remember someone saying the steering rack has to come off:huh: i clean my engine once a week and i keep forgetting to look at the pulleys and rack:D
 

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We mod our cars because the mods usually are an improvement over factory engineering.

I think the pulley ratio's are something to leave alone. You have to consider what happens under load and at idle. Will the slower alternator, water pump, power steering, a/c, whatever...perform acceptably or not?

I knew a guy with a 351 Mustang that installed a full set of underdrive pulleys. He had to step his idle rpm to 950 from 700 so the alternator could keep up, and at highway speeds he ran hotter.
 

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i agree with alot of what you said,my only concern is the alternator.i have a 160* t-stat and a fan switch,my car now never gets above 195*.i thought the three piece system had a pulley on the alternator to compinsate.but i never really researched any further.
 

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DC Crew
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Discussion Starter · #6 ·
When you buy the pulleys don't they come with the approiate pulleys to correct the speeds of your acc.?
 

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raidmagic said:
When you buy the pulleys don't they come with the approiate pulleys to correct the speeds of your acc.?
I never really looked closely at them. But wouldn't the correct speed be not correct because of under drive?

If OEM drives the alternator at say 6 rpm for every crankshaft R, then underdrive may be 4 or 5 rpm per crankshaft R. How are you going to correct that?
 

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biltogo said:
I never really looked closely at them. But wouldn't the correct speed be not correct because of under drive?

If OEM drives the alternator at say 6 rpm for every crankshaft R, then underdrive may be 4 or 5 rpm per crankshaft R. How are you going to correct that?
well the a/c and alternator dont care how many times the crank turns,so the theory is a larger crank pulley,and smaller than stock a/c and alternator pulleys(or whatever size combination they use to get the final ratio) to keep those spinning close to stock.the one piece(crank only) kit is the one that will slow everything down,im more concerned with the power steering spinning slower and somehow affecting the pressures in the steering hydrolics,i never put a magnet on my pulleys,im assuming there steel,if so it seems most of the horse power gain would be the change from steel to aluminum.less weight for the motor to turn.i do know someone putting a 3piece set on an L98 next week.guess i'll wait and see how it turns out.
 

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The theory (or fact) behind underdrive pulleys is---

One-The Underdrive pulley replaces the main crankshaft pulley. It spins the accessories slower. Since less engine power is used to run the accessories, the freed up power is now available to move the car. More power, faster car.

Two-Larger diameter accessory pulleys acheive the same ratios as above, but leave the crankshaft pulley original.
 

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i just looked at a summit catalog and they have under driven pulleys with alternator and water pump pulleys,claiming the water pump can spin at a couple different speeds depending which pulley size you go with and an alternator pulley to spin that near stock speed and these are suppost to work with the under driven crank pulley and still achieve a 25% under drive.im real concerned about the power steering rack pressure change,its probably a mod you do and can't tell if it made a difference or not.so i will pass on it.i would like to get those ugly stock pulleys off of there.:D oh well good times.
 

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biltogo said:
Todd, read from some of this. http://www.google.com/search?hl=en&ie=ISO-8859-1&q=underdrive+pulley&btnG=Google+Search

There are a couple of links that talk of measuring the results. I still don't believe that underdrive pulleys are worth the change out.
ya,i dont really think its worth it either.i'll probably just change to some billet stock size pulleys.my friend is still gonna try the 3 piece set,as a matter of fact hes probably putting them on right know.its good to toss theories around and then see if they work in practical terms.alot of times they dont.thanks for the reply.
 

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I use the system from March Pulleys. The Amp setup.
My vette voltage at idle is 14.7, and it runs cool.
Don't know if it actually frees up any HP, But they sure look good.
On an '84 vette.
Just my thoughts. Go for it.
tony

:cheers:
 

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oldace84 said:
I use the system from March Pulleys. The Amp setup.
My vette voltage at idle is 14.7, and it runs cool.
Don't know if it actually frees up any HP, But they sure look good.
On an '84 vette.
Just my thoughts. Go for it.
tony

:cheers:
right on-i new someone had to have them.i kinda fiqured it was one of those mods that dont do a heck of a lot.even if they did give you 10hp,thats really hard to feel"in the seat of the pants",might help the motor rev a little faster?they do look killer.i'll probably just get the stock sizes in billet:cool: thanks for checkin in.:cool:
 

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DC Crew
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Discussion Starter · #17 ·
Hawaii, did your buddy get his on yet?
Thanks for the info Old Ace glad to see you over here.
 

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my buddy was picking his buddy up from the airport,the guy was bringing them from L.A.the guy forgot to bring them,bummer,he will ship them to Da Punch when he gets back to L.A.probably a week or so.i was looking forward to the results myself.i'll let ya know.
 

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Once again, "Hawaiian Punch"
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hawaii-5-lo said:
my buddy was picking his buddy up from the airport,the guy was bringing them from L.A.the guy forgot to bring them,bummer,he will ship them to Da Punch when he gets back to L.A.probably a week or so.i was looking forward to the results myself.i'll let ya know.
Not a related subject. Todd, check out what I did for you.
 

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damn Kalani,your getting pretty good making pictures.that looks good,i would copy it and use for signature,might be a little to tall.were did you find the picture of my car?
 
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