[2008_Dinan335i]

So I was just wondering why there aren't any underdrive pulley systems available for our cars yet? I know they are a popular mod on many cars and are available for the E90/92 M3...why not our cars? Personally I think this would be a great way to get a few extra horsepower by decreasing the parasitic power losses from the accessories ("free" horsepower!!!).

Is there any special reason why we can't do this mod on the 335? If not then I'm voting for someone to come up with a nice setup for this, as I'm sure that it would be a very popular mod if priced well. Any thoughts?

Here is the system for the M3 that I'm talking about:

http://www.evosport.com/product/prod...VO.PER.B92.P01

[cu_north]

+1 to all of this!

When I had my 350Z, the underdrive pulley (specifically crank pulley) was exactly the same size as stock, just lighter. It really freed up HP. When you went Turbo, some rather large gains could be had. It is very surprising these are not available for the 335 yet. Although, different motors, etc who knows, maybe the pulley is already the best it can be

[SfValley335i]

Ive read that Force induction and underdrive pulleys dont mix... as to why i'll let someone more knowledge answer that.

[SoQuick]

I wouldnt want to underdrive my 335i, unless I was only using it at the track...

[gotturbo]

Well it's probably a fair enough question, but my experience with my mustang tells me that I wouldn't want them. Everything that is underdriven is, in a way, partially compromised. I would rather stick to what BMW engineered to be sufficient. Especially for the meager gains that they seem to make. They might make sense if that's all you were gonna do, but when you start adding other things to the equation, you start to kind of need full accessory capabilities more than ever. Just my take.

[2008_Dinan335i]

Def all good points you guys are making! Are there any tuners out there that would like to comment as to why this would be a good or bad idea?

[iPodAddict]

STi's crank are internally harmonic balanced, so underdrive pulleys and crank pulleys for them is not a problem.

[Hunter399]

I know a guy here who is local to me who is making these pulleys

They are harmonic balanced as well

[tom @ eas]

Originally Posted by venemous

Def all good points you guys are making! Are there any tuners out there that would like to comment as to why this would be a good or bad idea?

Plus you have an electric water pump. Only thing left to underdrive would be power steering.

Gains would be minimal, if any.

[sambonator]

Originally Posted by tom @ eas

Plus you have an electric water pump. Only thing left to underdrive would be power steering.

Gains would be minimal, if any.

Power steering, alternator, and AC Compressor would be it... wouldn't change HP output a bit...

[noro]

alternators nowdays are pretty efficient. The parasitic drag is minimal. AC is the same way, when not used the drag on the engine is almost negligent. As others said the water pump is out of equation.

I guess it simply comes down to the fact that with the 335i you can get 20-30HP with $100, while the $300 pulley set will give you some minuscule 5HP gain.

[Mr. 5]

Originally Posted by SfValley335i

Ive read that Force induction and underdrive pulleys dont mix... as to why i'll let someone more knowledge answer that.

I would agree with this.
It seems as though they are common with NA engines but then again, I just thought about the undeerdrive pulley that I had on my VW 2.0T.
It was the pulley for the crankshaft though.

I honestly don't think we need it.

[cu_north]

I seem to remember the crank pulley for the 350z was near 16 pounds and you could get a identical crank pulley aftermarket that was 8-ish pounds. This freed up nearly 10hp stock and nearing 20 hp turbo'd. Disclaimer: I be could waaay off on the respective weights but I know an aftermarket pulley was half the weight of stock.

[Black Chili]

The mechanical advantage under drive pulleys provide is the same on boosted and non-boosted cars, provided your not screwing with the pulleys tied to a blower.

What is relevant is the application. IMO I wouldn't play with underdrive pulleys on a 335 as it just doesn't make sense from a gain/cost perspective. Typically you change the water pump (which is electric on the 335), the crank and the alternator (which I believe will unload itself during hard acceleration to provide more power).

Plus, Gotturbo is correct- you're removing some engineering buffer. Imagine a 335 that was just jump-started from a completely dead battery; then turn on every power-drawing option to max while idling at a stoplight at night. I would expect some reserve past worst-case on a factory car. I just don't see the cost-benefit of this old-school mod on this type of car.

[Mr. 5]

Originally Posted by Graphite Shark

The mechanical advantage under drive pulleys provide is the same on boosted and non-boosted cars, provided your not screwing with the pulleys tied to a blower.

What is relevant is the application. IMO I wouldn't play with underdrive pulleys on a 335 as it just doesn't make sense from a gain/cost perspective. Typically you change the water pump (which is electric on the 335), the crank and the alternator (which I believe will unload itself during hard acceleration to provide more power).

Plus, Gotturbo is correct- you're removing some engineering buffer. Imagine a 335 that was just jump-started from a completely dead battery; then turn on every power-drawing option to max while idling at a stoplight at night. I would expect some reserve past worst-case on a factory car. I just don't see the cost-benefit of this old-school mod on this type of car.

Add a lightweight battery to the mix and you're really screwed.