[Mk2] [Turbo] Unorthodox Underdrive pulleys and belt sizes- just a quicky

[megatart]

As my car is currently having a rebuild, i'm wondering if its worth getting a nice light underdrive pulley. As I'm getting the whole crank balanced with the individual parts attached(fly, clutch, pulley) I'm not too bothered about the balance being affected.As the pulley is smaller than stock, I am just wondering if the stock size belts will still fit, or if they need specially making.
Anyone got an underdrive pulley fitted? cheers

[karammander]

depending how much smaller the pulley is you may just be able to adjust the alternator, or just go to a factors with measurements and find one on the shelf

cheers karam

[dai21t]

deleted

[simmo490]

will a smaller pully not affect the alternator.

not too good with sums but if you have a smalled main pully it will make the alternator spin faster thus making the regulator work harder and fail quicker????

jsut a question??

[cantfindausername]

I'd be very worried if something was out of balance. - Effectively kissing good by to your new engine.

The UR pulleys are nice, but get it all balanced together.

Once on, get a bit of string around the crank and alt pulleys and measure it, take that to a motor factor and get a belt to match, I think its a 4groove belt. My part number was 4PK770, and cost £4.94.

If the crank pulley is smaller, it will underdrive the alternator. People say this reduces the output voltage, but thats b0ll0cks. I've never had dipped lights or anything. ok maybe if you're running a killer stereo it might have an affect, but come on, how many of us are in these?

[megatart]

Excellent. Cheers for replies. I wont worry too much about it then as it is gonna get balanced into the crank shaft. Also i'm not running a big bad stereo so wont worry too much about a volt dip. think i'll get one then.
May as well get the bottom end light whilst its being built.

[cantfindausername]

Good man. The UR Pullleys are lovely. So light too!

This is mine with belt...



and on the engine...

[Harry]

http://www.unorthodoxracing.com/

Fitted this unit all good seem to recall Issues with an air con belt but can't remember If It was related or just a basic Issue that this belt was not In stock at the shop at the time etc.

Standard Belt Layout (Underdrive)

Our Tuner Series crank pulleys provide HP & Torque gains across the entire RPM range. Power gains come from the reduction of weight. An average of 2.7 HP is gained from every pound lost off the crank shaft. 80-85% of our gains are from weight loss.

Additional power gains, between 15-20%, can be seen from underdriving all the accessories. We do not push the percentage of underdrivie to high for two main reasons. First it is important to keep charging systems, air conditioning, power steering, and water pumps moving fast enough for every day driving. Second not much horsepower is gained from extreme underdriving. We always keep our underdrive percentage under 20% which allows us to maintain factory spoecified output for all of the accessories. Our testing has shown that for most vehicles you can upgrade to a stereo of up to 600 watts (RMS) without any charging problems.

[Harry]

Layout (Underdrive)

Our pulley sets provide most of the power gains through weight loss (80-85%). The remaining part of the gains from these pulleys comes from underdriving of all the accessories (15-20%).

However, we do not push underdriving for two main reasons. First, it is important to keep charging systems, air conditioning, power steering, and water pumps moving fast enough for every day driving. Second, not much horsepower is gained from extreme underdriving.

In most applications all of our underdriving is done with the crank pulley, not the accessory pulleys. This is done so maximum weight loss can be achieved at the crank where most of the horsepower gains are found.

Our underdrive pulley sets are available in polished finish only

[cantfindausername]

Some people do think that because you're removing the harmonic balancer that your engine will fail catastrophically, but i'm yet to see proof and be convinced of this.

[Harry]

Interestingly they mention around 2.7 hp gain per pound need to weigh my old unit. It must be at least a pound or two any one measured one at all? Going to have to dig out the old one!

I suppose In the great scheme of things the factory build the car for It's life duration and the usual compromise between economy and performance and are more conservative here.

[cantfindausername]

yeah definately, and I doubt the factory balance it to the extent that a fully built engine should be done.

I know the stock one is bloody heavy. I think the UR site has the stock weight on it doesn't it?

[megatart]

Well after having difficulty getting hold of an Unorthodox underdrive, i have cancelled the order, and bought a stock size lightweight ali pulley instead from Chris.F over on the MR2OC. Not sure if he's a member on here but his work looks good. All balanced and well cnc'd. And for only £75 delivered who can complain. Only weighs 0.8kg as opposed to the stock 2.2kg. Excellent.
His site is www.cdfracing.co.uk if anyones interested. He does other bits too, cam gears etc.

[Harry]

Sounds good.