Underdrive Pulley - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

justinc · 06-11-2001, 05:40 PM

Whats the deal with Underdrive Pulley and what do u sacrafice ? Do u need to use premium fuel?

Mr Rose · 06-11-2001, 06:47 PM

A smaller Crank shaft pulley lowers the time spent rotating to maximum revolution. Basically the lighter weight, and smaller diamater of the racing pulley, let the crank rotate and rev faster. Ther is a slight HP increase.
What I truly dislike about the available aftermarket pulleys for 240s, is that they are not harmonic balanced. Basically they are a precise machined metal that has no rubber harmonic dampner on them. This in turn reflects harmonic distortions back into the crank. So there fore the crank is sending out distortion, and the pulley is reflecting it back, and not dampening the harmonic vibrations. Can you say metal fatigue?!
Over a period of time crank failure can occur. Cranks flex and give in a certain range of flex as in design, but the harmonic dampner on the stock pulley compensates for most of that.
I for one have seen what a NON dampend crank pulley can do to a healthy motor. Not pretty. Pieces of crank everywhere.
The gains from a racing crank pulley are minimal, some where in the .1 second, and 1mph gain in the 1/4 mi.
If and only if an aftermarket crank pulley were dampened, then I could recomend you buy it. Other than that, focus on Intake, exhaust, ECU, cams, and various little things that don't mess with your internal combustiion cycle and in a grevious manner.

Mr. Rose: ANTI-PULLEY

justinc · 06-11-2001, 07:23 PM

Thanks man looks like u know ur stuff. My car is pretty much stock the only mode is i took out the y pipe what should i do next for performance?

**West** · 06-11-2001, 09:03 PM

I have a Underdrive pulley and a lightweight flywheel and am prying that nothing happens to my damb KA engine. I have had my UD pulley on my 240 for about 8 month now without any problems, but then like Mr Rose said you will never know till its to late. I had a UD pulley on my Z for 1.7 years without problems too, and the owner now 1 year later has had no problems. I would just stay away from the UD pulley cuz in all honesty is dosent do to much, in fact here is a Dyno of a UD pulley install that you all should be reading about in a up coming Sport Compact Car.

UD Pulley Install Dyno Results (Dyno is on Alex's s13 w/ AEM Prototype Intake and 5Zigen Exhaust)

Mr Rose · 06-11-2001, 09:48 PM

I take my Pulley knowledge from the V-8 world of F-bodies, and Stangs. All I can say is that for a 3 pulley kit on most any Production V-8 that I have ever seen, the pulleys on 281cid and up, only netted about 8hp(flywheel), and about a .15sec., 1.5mpg increase 1/4mile wise
. Besides, you can not run a race pulley with N02, or any kind of forced induction. This set up can and will cause main bearing cap failure. Literally spinning the crank past revolution tolerences.
Most Cranks are run to very pricise balanced tolerences. I would promote NISSAN to be very precisely balanced. However even a world wide automanufacturer adds a harmonic balancer to keep the chances of rotational tolerences in check.
Cranks flex, It's a fact. How much they flex, and what harmonic distortion is given off, is what needs to be in check.
FORD and Chevy both have put out Service bulletins on aftermarket crank pullies: "Block failure in conjunction with aftermarket UNBALANCED/UNDAMPENED crank pulley."

Mr. Rose: ANTI PULLEY
No thanks, stock is fine.

06-11-2001, 10:42 PM

i only know of two manufacturers that make pulleys for the 240, Unorthodox and ASP. I think I saw people comment that the Unorthodox is not balanced, and ASP is. Is this true?

Mr Rose · 06-11-2001, 11:11 PM

I'm sure they are balanced, the point is neither of them have a rubber vibration dampner. That is what makes the stock pulley so heavy. some crank pullies are filled with liquid gel, inside the rubber, like an engine mount.
this amterial absorbs harmonic distortion. bare metal reverbs/reflects the vibrations.

mike240 · 01-15-2002, 12:33 AM

not to get off the subject of UD pulleys but Mr Rose, would a lightweight aftermarket flywheel cause the same probems with balance and all?

idunit · 01-15-2002, 07:53 AM

When you comment about the fluid filled pulley Fluidamper comes to mind...  The flywheel wouldn't matter as it's bolted and there is no rubber bushing or sleeve in the center.

01-15-2002, 08:33 AM

So are you saying that my ASP pulley on my turbo ka is no good at all?

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06-11-2001, 05:40 PM	#1
justinc Leaky Injector Join Date: May 2001 Posts: 119 Trader Rating: (0) Feedback Score: 0 reviews	Whats the deal with Underdrive Pulley and what do u sacrafice ? Do u need to use premium fuel?

06-11-2001, 06:47 PM	#2
Mr Rose Join Date: Jun 2001 Posts: 47 Trader Rating: (0) Feedback Score: 0 reviews	A smaller Crank shaft pulley lowers the time spent rotating to maximum revolution. Basically the lighter weight, and smaller diamater of the racing pulley, let the crank rotate and rev faster. Ther is a slight HP increase. What I truly dislike about the available aftermarket pulleys for 240s, is that they are not harmonic balanced. Basically they are a precise machined metal that has no rubber harmonic dampner on them. This in turn reflects harmonic distortions back into the crank. So there fore the crank is sending out distortion, and the pulley is reflecting it back, and not dampening the harmonic vibrations. Can you say metal fatigue?! Over a period of time crank failure can occur. Cranks flex and give in a certain range of flex as in design, but the harmonic dampner on the stock pulley compensates for most of that. I for one have seen what a NON dampend crank pulley can do to a healthy motor. Not pretty. Pieces of crank everywhere. The gains from a racing crank pulley are minimal, some where in the .1 second, and 1mph gain in the 1/4 mi. If and only if an aftermarket crank pulley were dampened, then I could recomend you buy it. Other than that, focus on Intake, exhaust, ECU, cams, and various little things that don't mess with your internal combustiion cycle and in a grevious manner. Mr. Rose: ANTI-PULLEY

06-11-2001, 07:23 PM	#3
justinc Leaky Injector Join Date: May 2001 Posts: 119 Trader Rating: (0) Feedback Score: 0 reviews	Thanks man looks like u know ur stuff. My car is pretty much stock the only mode is i took out the y pipe what should i do next for performance?

06-11-2001, 09:03 PM	#4
West OMNOMNOMNOM Join Date: Dec 2000 Location: Denver, CO Age: 44 Posts: 6,456 Trader Rating: (0) Rides Gallery: West Feedback Score: 0 reviews	I have a Underdrive pulley and a lightweight flywheel and am prying that nothing happens to my damb KA engine. I have had my UD pulley on my 240 for about 8 month now without any problems, but then like Mr Rose said you will never know till its to late. I had a UD pulley on my Z for 1.7 years without problems too, and the owner now 1 year later has had no problems. I would just stay away from the UD pulley cuz in all honesty is dosent do to much, in fact here is a Dyno of a UD pulley install that you all should be reading about in a up coming Sport Compact Car. UD Pulley Install Dyno Results (Dyno is on Alex's s13 w/ AEM Prototype Intake and 5Zigen Exhaust)

06-11-2001, 09:48 PM	#5
Mr Rose Join Date: Jun 2001 Posts: 47 Trader Rating: (0) Feedback Score: 0 reviews	I take my Pulley knowledge from the V-8 world of F-bodies, and Stangs. All I can say is that for a 3 pulley kit on most any Production V-8 that I have ever seen, the pulleys on 281cid and up, only netted about 8hp(flywheel), and about a .15sec., 1.5mpg increase 1/4mile wise . Besides, you can not run a race pulley with N02, or any kind of forced induction. This set up can and will cause main bearing cap failure. Literally spinning the crank past revolution tolerences. Most Cranks are run to very pricise balanced tolerences. I would promote NISSAN to be very precisely balanced. However even a world wide automanufacturer adds a harmonic balancer to keep the chances of rotational tolerences in check. Cranks flex, It's a fact. How much they flex, and what harmonic distortion is given off, is what needs to be in check. FORD and Chevy both have put out Service bulletins on aftermarket crank pullies: "Block failure in conjunction with aftermarket UNBALANCED/UNDAMPENED crank pulley." Mr. Rose: ANTI PULLEY No thanks, stock is fine.

06-11-2001, 10:42 PM	#6
Guest Posts: n/a	i only know of two manufacturers that make pulleys for the 240, Unorthodox and ASP. I think I saw people comment that the Unorthodox is not balanced, and ASP is. Is this true?

06-11-2001, 11:11 PM	#7
Mr Rose Join Date: Jun 2001 Posts: 47 Trader Rating: (0) Feedback Score: 0 reviews	I'm sure they are balanced, the point is neither of them have a rubber vibration dampner. That is what makes the stock pulley so heavy. some crank pullies are filled with liquid gel, inside the rubber, like an engine mount. this amterial absorbs harmonic distortion. bare metal reverbs/reflects the vibrations.

01-15-2002, 12:33 AM	#8
mike240 Leaky Injector Join Date: Jan 2002 Posts: 86 Trader Rating: (0) Feedback Score: 0 reviews	not to get off the subject of UD pulleys but Mr Rose, would a lightweight aftermarket flywheel cause the same probems with balance and all?

01-15-2002, 07:53 AM	#9
idunit Zilvia Member Join Date: Dec 2001 Posts: 164 Trader Rating: (0) Feedback Score: 0 reviews	When you comment about the fluid filled pulley Fluidamper comes to mind...  The flywheel wouldn't matter as it's bolted and there is no rubber bushing or sleeve in the center.

01-15-2002, 08:33 AM	#10
Guest Posts: n/a	So are you saying that my ASP pulley on my turbo ka is no good at all?