Underdrive Pulley: Useless?

conquistador · 12-17-2014, 12:47 AM

I was chatting with my father (a long time Porsche tech) about my next mod--which was UD Stillen pulley-- and he said it didn't free up any power. He said it was completely useless to underdrive the accessories because 1. when you're going in a straight line or dyno'ing you're not putting the power steering under a load, 2. when you're battery is fully charged there is very little load on the alternator, and 3. if you're A/C if off you don't have the AC clutch engaged and the pump is under little to no load.

These accessories are basically free spinning and drain very little power from the system so why waste money on an UD pulley?

Got me thinking...

DEpointfive0 · 12-17-2014, 12:49 AM

... Holy crap...

It lowers rotational mass... And why spin the accessories when you don't need to?

Trips · 12-17-2014, 12:58 AM

Underdrive pulleys usually are a performance enhancing item that increases the torque and horsepower output of an engine by reducing drag caused by belt-driven accessories.

Horsepower gains from underdrive pulleys alone are usually around 4-7 hp.

Jordo! · 12-17-2014, 02:12 AM

^^^Although most of that is from the crank pulley...

BGTV8 · 12-17-2014, 04:53 AM

Was debated here ................

Stillen U.D. pulleys help.

IMHO opinion, the benefits are outweighed by the drawbacks, and since I am an old f4rt, I agree with your father

njobe89 · 12-17-2014, 10:12 AM

learn something new every day

Zoren 370 · 12-17-2014, 11:21 AM

I thought a Porsche Tech would know any better.
But it wont harm if you do listen to a fathers advise!

I would in certain circumstances

BC416 · 12-17-2014, 12:03 PM

Honestly, when factoring the risk vs. reward, a couple HP isn't worth it to me to install pulleys.

1st · 12-17-2014, 12:37 PM

I believe sombody on here tested it after the install and got like 5 hp.

Rusty · 12-17-2014, 01:04 PM

My 2 cent on this. Why take a chance with the underdrive pulley. It's well known that our our oil pump isn't the greatest. And any new induced harmonics on the end of the crank will have some affect on it. For a DD, it may take awhile. But for a trackday car......tick..tick...tick...tick...tick....

I've seen a couple of V8s with broken cranks. All had an underdrive pulleys. So from what I've seen. I don't what to take that risk for a couple hp.

Jordo! · 12-17-2014, 02:01 PM

I think the OP is talking about things like the oversized (to under drive) alternator pulleys and such -- I don't know about the difference they make, but a lighter crank pulley will definitely make a few extra ponies.

Of course, you are putting faith in the presumption that all automotive engineers are dampening the harmonics produced by their crank pulleys because they have nothing better to do...

abm89 · 12-17-2014, 02:24 PM

Quote:

Originally Posted by BC416

Honestly, when factoring the risk vs. reward, a couple HP isn't worth it to me to install pulleys.

I agree with this statement 100%. Which is why I will never install them.

Dreadnaught · 12-17-2014, 03:36 PM

^Agreed.

7419sundat · 12-17-2014, 03:48 PM

Dude your engine will come unraveled within a thousand miles lol

conquistador · 12-23-2014, 02:32 PM

I went against my ole man's recommendation and bought UD Stillen from Elmo370z

Stillen U.D. Crank pulley

I hope my harmonics aren't affected

12-17-2014, 12:47 AM	#1 (permalink)
conquistador Base Member Join Date: Sep 2014 Location: CA Posts: 46 Drives: G37 Sedan Rep Power: 10	Underdrive Pulley: Useless? I was chatting with my father (a long time Porsche tech) about my next mod--which was UD Stillen pulley-- and he said it didn't free up any power. He said it was completely useless to underdrive the accessories because 1. when you're going in a straight line or dyno'ing you're not putting the power steering under a load, 2. when you're battery is fully charged there is very little load on the alternator, and 3. if you're A/C if off you don't have the AC clutch engaged and the pump is under little to no load. These accessories are basically free spinning and drain very little power from the system so why waste money on an UD pulley? Got me thinking...

12-17-2014, 12:49 AM	#2 (permalink)
DEpointfive0 Premium Member Bitches Join Date: Jan 2012 Location: SoCal Posts: 14,824 Drives: a lot Rep Power: 17151	... Holy crap... It lowers rotational mass... And why spin the accessories when you don't need to? Trips and FLUJOKE like this. __________________ Do YOU want to know what/where I got my username from? ( Click to show/hide ) NSFW due to language:

12-17-2014, 12:58 AM	#3 (permalink)
Trips Administrator Join Date: May 2009 Location: Disneyland, Ca Posts: 8,728 Drives: 🔰 Rep Power: 10	Underdrive pulleys usually are a performance enhancing item that increases the torque and horsepower output of an engine by reducing drag caused by belt-driven accessories. Horsepower gains from underdrive pulleys alone are usually around 4-7 hp. FLUJOKE likes this. __________________

12-17-2014, 02:12 AM	#4 (permalink)
Jordo! A True Z Fanatic Join Date: May 2010 Location: nirvana Posts: 6,394 Drives: 2023 NATM Rep Power: 417	^^^Although most of that is from the crank pulley... __________________ Enjoy it. Destroy it.

12-17-2014, 04:53 AM	#5 (permalink)
BGTV8 A True Z Fanatic Join Date: Dec 2009 Location: 03350 Australia Posts: 1,503 Drives: 09 Nissan 370Z M6 Rep Power: 29907	Was debated here ................ Stillen U.D. pulleys help. IMHO opinion, the benefits are outweighed by the drawbacks, and since I am an old f4rt, I agree with your father Trips, Jordo! and Rusty like this. Last edited by BGTV8; 12-17-2014 at 04:57 AM.

12-17-2014, 10:12 AM	#6 (permalink)
njobe89 A True Z Fanatic Join Date: May 2014 Location: Atlanta, GA Posts: 5,227 Drives: 2013 370z BS 6MT Rep Power: 174283	learn something new every day __________________ 2 plus 2 times 2 = ? ... hint, it's not 8 Stillen CBE, Stillen Gen 3, TP's, Uprev tuned - 324whp/264tq

12-17-2014, 11:21 AM	#7 (permalink)
Zoren 370 A True Z Fanatic Join Date: Mar 2012 Location: FL Posts: 11,018 Drives: 11 Nissan 370 M6 Rep Power: 1913653	I thought a Porsche Tech would know any better. But it wont harm if you do listen to a fathers advise! I would in certain circumstances

12-17-2014, 12:03 PM	#8 (permalink)
BC416 Track Member Join Date: Jun 2014 Location: NJ Age: 37 Posts: 718 Drives: 2012 KAD 6MT Rep Power: 591	Honestly, when factoring the risk vs. reward, a couple HP isn't worth it to me to install pulleys. Jordo!, NoirG and abm89 like this. __________________ F.I. / K&N / 180 / Forgestar

12-17-2014, 12:37 PM	#9 (permalink)
1st A True Z Fanatic Join Date: Jul 2012 Location: I 80 Biz U.S. 50 Posts: 1,708 Drives: Platinum Z Rep Power: 1615	I believe sombody on here tested it after the install and got like 5 hp. Joker_J likes this.

12-17-2014, 01:04 PM	#10 (permalink)
Rusty Ronin Samurai - Assassin Join Date: Dec 2011 Location: Fayettenam,Pennsyltucky Age: 68 Posts: 34,854 Drives: 2011 Nismo GM 6M Rep Power: 2684436	My 2 cent on this. Why take a chance with the underdrive pulley. It's well known that our our oil pump isn't the greatest. And any new induced harmonics on the end of the crank will have some affect on it. For a DD, it may take awhile. But for a trackday car......tick..tick...tick...tick...tick.... I've seen a couple of V8s with broken cranks. All had an underdrive pulleys. So from what I've seen. I don't what to take that risk for a couple hp. Streetlife, BGTV8 and Super Werty like this. __________________ 浪人 - 殺し屋 "The Difficult Anytime, The Impossible By Appointment Only" http://www.the370z.com/members-370z-...o-journal.html Last edited by Rusty; 12-17-2014 at 01:07 PM.

12-17-2014, 02:01 PM	#11 (permalink)
Jordo! A True Z Fanatic Join Date: May 2010 Location: nirvana Posts: 6,394 Drives: 2023 NATM Rep Power: 417	I think the OP is talking about things like the oversized (to under drive) alternator pulleys and such -- I don't know about the difference they make, but a lighter crank pulley will definitely make a few extra ponies. Of course, you are putting faith in the presumption that all automotive engineers are dampening the harmonics produced by their crank pulleys because they have nothing better to do... conquistador likes this. __________________ Enjoy it. Destroy it. Last edited by Jordo!; 12-17-2014 at 02:18 PM.

12-17-2014, 03:36 PM	#13 (permalink)
Dreadnaught Track Member Join Date: Dec 2009 Location: Farmington, Utah Posts: 582 Drives: 14 SR 370z 6MT Rep Power: 10139	^Agreed. __________________ Ford Diesel and Heavy Line Technician at your service.

12-17-2014, 03:48 PM	#14 (permalink)
7419sundat Base Member Join Date: Aug 2011 Location: colorado Posts: 145 Drives: 09 370z Gtm TT 2 Rep Power: 13	Dude your engine will come unraveled within a thousand miles lol

12-23-2014, 02:32 PM	#15 (permalink)
conquistador Base Member Join Date: Sep 2014 Location: CA Posts: 46 Drives: G37 Sedan Rep Power: 10	I went against my ole man's recommendation and bought UD Stillen from Elmo370z Stillen U.D. Crank pulley I hope my harmonics aren't affected

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