Underdriven Pulleys

[AYW550]

so the next upgrade i want to do is a lightweight pulley kit, some of the kits available are underdriven, by like 10 and 30 percent for the water pump and alternator

obviously these underdriven kits are for high reving motors , like drift cars right, slowing down how fast the water pump pumps and the charging rate of the alternator... so would an underdriven kit be a bad thing for a motor that isnt commonly in a higher rev range?? although sumday i am planning to drive it as a weekend track car...

Edited August 13, 2009 by AYW550

[G0DZLR]

for a daily i think itd be best to keep the stock pulley arrangement. nothing worse than having a flat battery every second morning cos the alternator isnt charging as much as it could. plus youd get no real benefit unless you hit the rev limiter every time you do the groceries

[mad082]

yeah as was said, unless you are chasing every last possible pony from your motor and have done everything else, don't bother. spend the money on something more worth while that will give you better gains.

[Pal]

as far as i know, your alternator puts out maximum voltage at fairly low rpms. it doesn't charge any more at 2000rpm compared to 6000rmp. same as your water pump. alot of the v8 boys are putting in under driven pulleys with good results.

[AYW550]

yeah as was said, unless you are chasing every last possible pony from your motor and have done everything else, don't bother. spend the money on something more worth while that will give you better gains.

hmmm, well i am chasing every possible bit of power i can from my motor, and have now done most of the NA upgrades possible to my r34 without cracking the motor open, the light weight pulley kits advertise 4-7kw more from the motor plus making it more responsive...but a good number of the kits are under driven and was wondering about the side effects

[AYW550]

also, does any one know the dimensions of a rb25de crank shaft and crank pulley? im looking for a single belt crank pully set up, im hoping to greatly reduce the rotating mass of the crank pulley as i have removed my AC system and am planning to replace the stock belt driven fan with an electric fan but havent seen any kits with a single belt crank pulley, anyone know of any? could a crank pulley for a different type motor fit on ? id like to avoid the price of the custom route...

[mad082]

just out of curiousity, what mods do you currently have?

[AYW550]

just out of curiousity, what mods do you currently have?

well,,,ive done

-wheels and suspension

-romoved entire AC system (to reduce some weight and gain a bit of power)

-battery moved to the boot (improved handling)

-full 2.5 inch exhaust system with high flow cat, high flow exhaust and coby extractors

-POD filter with heat shield and CAI

will do brakes some other day and replace them with slotted ones when the stock discs wear out, but for now they stop me plenty good

that about it really as far as performance mods are concerned....about to put in new coils and plugs, and soon after that swap out stock radiator fan for an electric one as i mentioned above

so, what do you think?

[R34 -_-]

you should dyno your car and get a tune, would be interested to see wha kind of power an na r34 makes

[AYW550]

you should dyno your car and get a tune, would be interested to see wha kind of power an na r34 makes

yeah im keen as to get it dyno tested and tuned, after i get my coils in and the probably the pulley kit ill do it for sure, its also a manual but is 4wd, ive tried to remove as much weight from her as possible too...

[mad082]

i would be looking at cams over the pulley set. even without an ecu you are going to see decent gains throughout the rev range. look up prices for a set of poncams

[BASHO]

hmmm, well i am chasing every possible bit of power i can from my motor, and have now done most of the NA upgrades possible to my r34 without cracking the motor open, the light weight pulley kits advertise 4-7kw more from the motor plus making it more responsive...but a good number of the kits are under driven and was wondering about the side effects

4-7 kw gain, what was that that just flew past my window --why it was a pig--honest .

It'll look good if you get the anodised ones and red will deffinately give the biggest gains, ah-hem .

[AYW550]

4-7 kw gain, what was that that just flew past my window --why it was a pig--honest .

It'll look good if you get the anodised ones and red will deffinately give the biggest gains, ah-hem .

have you experinced cases where light weight pullies made no difference?? reducing the rotating mass of a motor would decrease its work load, requiring less power to turn its self, they say its a similar effect to that of a light weight flywheel, im not saying i believe their claims hands down, but it makes sense to me...

Edited August 15, 2009 by AYW550

[AYW550]

i would be looking at cams over the pulley set. even without an ecu you are going to see decent gains throughout the rev range. look up prices for a set of poncams

ok ill look into that, i had just assumed cams would be expensive

[AYW550]

cams are expensive!

[mad082]

but they are garanteed to give you decent gains. pulleys, not so much.

[AYW550]

<br />but they are garanteed to give you decent gains. pulleys, not so much.<br />

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yeah true, ill deffinately look into it, i know sumday ill be opening the motor up and i think cams will be the first thing i do,,,would a power fc computer go well with a cam?

Edited August 17, 2009 by AYW550

[BASHO]

have you experinced cases where light weight pullies made no difference?? reducing the rotating mass of a motor would decrease its work load, requiring less power to turn its self, they say its a similar effect to that of a light weight flywheel, im not saying i believe their claims hands down, but it makes sense to me...

Mate , I'm probably being a bit silly there so sorry but yes to you're question , my last but one 00 WRX, had a reasonable amount of mods so was on and of the dyno a fair bit, it had 178kws at all 4 put on a set of lightwieght pulleys just prior to a ECUtech customtune and it read exactly the same as the previous reading with stock ones.

[Chrispy]

They have a pretty good effect on VG30DE's, normally good for 10-15hp on one of them. Standard pulley weighs around 7kg!

I always thought that non harmonic balanced pulleys where no good on RB's, they have trouble due to the long cranks, it reaches a natural frequency that fatigues the crank then it snaps. Only what I have heard

[AYW550]

<br />They have a pretty good effect on VG30DE's, normally good for 10-15hp on one of them. Standard pulley weighs around 7kg! <br /><br />I always thought that non harmonic balanced pulleys where no good on RB's, they have trouble due to the long cranks, it reaches a natural frequency that fatigues the crank then it snaps. Only what I have heard <img src="http://www.skylinesaustralia.com/forums/style_emoticons/default/wink.gif" style="vertical-align:middle" emoid="" border="0" alt="wink.gif" /><br />

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hmmm, well i dont like the sound of that...no pun intended!