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Please enlighten me

So what does a crank pulley do and does it add Any hp gains?

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Old 03-27-2011, 12:50 PM   #1 (permalink)
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So what does a crank pulley do and does it add Any hp gains?
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Old 03-27-2011, 01:26 PM   #2 (permalink)
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Lighter pulleys help in the unsprung weight on the crank and therefore giving you a small hp gain. There are two types Just a Lighter pulley or A Lighter Undersized pulley with a matching Alternator pulley in which you would also need a smaller belt. NST? Sells this version as a set and also Stillen? Sells the Lighter and Undersized type. You need to decide if its worth the expense and what type would work for you? I've been using the NST lighter undersized type with no problems and I did notice a slight off idle difference.


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Old 03-27-2011, 01:34 PM   #3 (permalink)
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Thanks Triple, on NST site, they say it gains about 7-10 HP ??
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Old 03-27-2011, 01:43 PM   #4 (permalink)
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Seems like the threads I've seen, people were getting less than 4 (iirc)
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Old 03-27-2011, 08:21 PM   #5 (permalink)
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4 is a more realistic number...not 7- 10
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Old 03-27-2011, 08:23 PM   #6 (permalink)
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you gain hp by spinning the accessories at a slower rate due to the undersized pulley.
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Old 03-27-2011, 10:06 PM   #7 (permalink)
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If anything, the biggest reason to install a light weight pulley is to increase engine response as it has less rotating mass to spin up which lets it rev up and down more quickly as well as respond more quickly to throttle input.
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Old 03-27-2011, 10:39 PM   #8 (permalink)
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installed a lightwheight standard size stillen crank pulley last year,definitely revs up quicker,if you can install these pulleys yourself i recommend them
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Old 04-07-2011, 06:07 PM   #9 (permalink)
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Quote:
Originally Posted by Triple's View Post
Lighter pulleys help in the unsprung weight on the crank and therefore giving you a small hp gain. There are two types Just a Lighter pulley or A Lighter Undersized pulley with a matching Alternator pulley in which you would also need a smaller belt. NST? Sells this version as a set and also Stillen? Sells the Lighter and Undersized type. You need to decide if its worth the expense and what type would work for you? I've been using the NST lighter undersized type with no problems and I did notice a slight off idle difference.


NST (NonStopTuning) 370Z VQ37HR Pulley Kit Review w/ Dyno Charts
NST - The Leader In Nissan 370Z Pulley Development



Stillen Underdrive Pulley - Review/Pics/Dyno/Vid
STILLEN : STILLEN Performance Lightweight Pulleys

Thank you sir! NST Pulleys have consistently shown positive gains across all platforms and are very popular here with the 370Z community.

Much more info here... NST (NonStopTuning) 370Z VQ37HR Pulley Kit Review w/ Dyno Charts
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Old 04-08-2011, 11:27 AM   #10 (permalink)
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Quote:
Originally Posted by christian370z View Post
If anything, the biggest reason to install a light weight pulley is to increase engine response as it has less rotating mass to spin up which lets it rev up and down more quickly as well as respond more quickly to throttle input.
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Old 04-08-2011, 12:09 PM   #11 (permalink)
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Quote:
Originally Posted by Triple's View Post
Lighter pulleys help in the unsprung weight on the crank and therefore giving you a small hp gain. There are two types Just a Lighter pulley or A Lighter Undersized pulley with a matching Alternator pulley in which you would also need a smaller belt. NST? Sells this version as a set and also Stillen? Sells the Lighter and Undersized type. You need to decide if its worth the expense and what type would work for you? I've been using the NST lighter undersized type with no problems and I did notice a slight off idle difference.
...
A lightweight crank pulley reduces the rotating mass, but that is not the same as unsprung weight. Much of the unsprung weight also happens to be a rotating mass (wheels/tires/brakes), but the difference is that unpsrung weight also affects handling by changing the inertia that your springs must overcome to keep your tires stuck to the pavement.

But yeah the other advantage of an underdriven crank pulley is that your belt driven accessories(Power steering, A/C, Alternator) sap less power from your engine, at the cost of slightly reduced performance of said accessories.

The NST kit includes an overdriven alternator pulley, so that the net effect of overdrive + underdrive = normally driven alternator, so only the power steering and A/C would be underdriven.

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Old 04-11-2011, 03:22 PM   #12 (permalink)
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just a little point to throw in here is that we've had problems with our bmw customers and a decent amount of others that have broken bearings inside the motor as well lost their motors because they've used different crank pulleys

the rotating assembly is balanced from factory with the stock front pulley so by changing it you essentially "unbalance" the motor...not to sure how this effects the 370s motor because in some cars this doesnt cause any issues for the most part

but just something to keep in mind...
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Old 04-11-2011, 04:33 PM   #13 (permalink)
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^I've heard about that on some cars too, that's why I would probably go for a lighter flywheel which nets the same results and has no effect on the engine internals.
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Old 04-11-2011, 04:38 PM   #14 (permalink)
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what about the long term negative effects of pulley's??? Im worried about putting a pulley on because the engine only has 1500 miles on it. Do you think their long term issues with pulleys?
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Old 04-11-2011, 05:37 PM   #15 (permalink)
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Quote:
Originally Posted by 370Fitment View Post
just a little point to throw in here is that we've had problems with our bmw customers and a decent amount of others that have broken bearings inside the motor as well lost their motors because they've used different crank pulleys

the rotating assembly is balanced from factory with the stock front pulley so by changing it you essentially "unbalance" the motor...not to sure how this effects the 370s motor because in some cars this doesnt cause any issues for the most part

but just something to keep in mind...
What sort of bmw engines? From what I've heard and read, harmonics play a more important role the longer the crank is. If they were I6 that's a big difference from V6.

I'm still curious what the harmonic frequencies of a given crank would be and how those are determined. The hope is that the frequency is high enough for our motors that it's only an issue at a rpm higher than we are using (10k or something)
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