[DaveN]

What is the amount of play for the drive belt? I have have about 2 cm of deflection from a good strong push up to a good pull down on the underside by the AC compressor. It has probably stretched since install but it seemed pretty tight from the topside during the summer; this is the first time feeling the play from underneath.

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[flash]

it only needs to be tight enough not to slip. if you have a boost gauge, you'll see the boost fall off. if not, you should hear it, though it might be drowned out by the venturi squeal.



basically, it wants to be tight enough so that you can move it about 1/2" either way with a pretty good push. 2cm may be a little bit loose, but not a lot. i'd give it a couple of turns. they do tend to stretch a bit. do it cold though, and don't over-tighten it. the adjuster should rotate by hand. the flats are there only so that you can tighten the locknuts, not so you can put a wrench on it for adjustment.

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[DaveN]

Tks. I never did tighten it after I left your place in May as it felt ok. I have never noticed any loss of acceleration but your right, there is a lot of screaming excitement under the hood when you tromp it so it would be hard to hear the belt. I'll give it a few turns cold and call it a day.

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[rxter]

"...lots of screaming excitement under the hood... " reminds me of my younger days...

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[Dubai944]

I recommend using a proper belt tension gauge. I use one similar to below. The benefits are no guessing on the amount of belt tension, the ability to set tension exactly where you want it once you work out the optimum tension level for your particular setup, and the ability to see how much the belt is stretching over time. Surprising the difference in quality I have found between belt brands.

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[flash]

to use a gauge, you would need to know the spec you were trying to measure. there is no spec for this belt on this car, and it does not need to be as tight as it did in OEM configuration. there is also only one belt for this kit. i suppose it could still be a useful thing though, once you determine what tension is correct, as you would be able to repeat it, but since due to its design this kit does not have any belt slip problems, it would really be overkill.

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[jfrahm]

The 9201 can be used on this belt also. I did some measurements with a krikit and a 9201 on the serpentine belt and was surprised at how tight the factory spec is. Factory spec, for AC equipped cars you set the belt to 9,5 +/- 0.3 on the 9201 on the run between the AC and the crank, and then add one full turn of the jackscrew., which is a tension of about 100 on the Krikit. Tighter than I think is sensible but this car has issues with alternator slip when cold if the belt is not very tight. Some SC kits improve the alternator belt wrap so it might be possible to reduce this somewhat as long as the belt does not slip.



You cannot really hear SC belt slip but if you have a boost gauge you can see the boost flatten out. On my SC you do not even notice the power rolloff if you do not rev the hell out of it, and the car still seems very fast.



-Joel.

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[flash]

yeah - it's not a problem with this kit.



the design allows for less belt tension, and provides better traction. it's a combination of things that makes it work, including improved angular wrap on the alternator, maximizing angular wrap on the supercharger, minimal distance between pulleys (adding idlers to facilitate this), a double sided belt, and the most important is grooved pulleys in all key areas. all together it makes for a better design that keeps the belt together. we could easily run this up to over 7lbs without slip. already done it.



we haven't had one with a slipping problem yet. it looks like we'll get at least 10k miles from a belt, and likely 20k or 3 years, pretty much the same as the rest of the belts.

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[Dubai944]

Yes different application,10K from a belt on a road car! I run a new belt every race weekend for insurance and running to 7500rpm and 10lbs needs a bit more attention to belt tension <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" /> For me the tension tool is pretty useful.

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[flash]

yeah - i can imagine that.



if the kit isn't designed well, the belt will need attention. fortunately, this one doesn't need that. i've only tested it up to 7psi, but there is no reason to expect that it would be any different at higher boost levels. i've seen 16psi on other kits using this unit, and using the same design features, at higher rpm levels, and no unusual attention to the belt required.

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[Dubai944]

Out of interest how long is the belt in your kit?

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[Lear35A]

[quote name='Dubai944' timestamp='1324402101' post='119364']

Out of interest how long is the belt in your kit?

[/quote]

1741mm OC according to Gates

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[Lear35A]

My belt was very tight on initial installation. After a call with Flash, I was able to get it on, but it took some "encouragement." The tensioner is at its shortest, i.e. belt loosest, position. The belt now has about 75 miles on it. I measured the tension with my 9201 tool on the belt between the A/C and crank pulleys. I got a reading of 13. That seems quite high, but it's the lowest I'll be able to get unless the belt stretches some with use.

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[flash]

yeah - it will be pretty tight for the first 500 miles or so, then it will be closer to the right tension. there wasn't any way around that, if i wanted to have any adjustment later.

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[Eric_Oz_S2]

[quote name='jfrahm' timestamp='1324388685' post='119356']

The 9201 can be used on this belt also. I did some measurements with a krikit and a 9201 on the serpentine belt and was surprised at how tight the factory spec is. Factory spec, for AC equipped cars you set the belt to 9,5 +/- 0.3 on the 9201 on the run between the AC and the crank, and then add one full turn of the jackscrew., which is a tension of about 100 on the Krikit. Tighter than I think is sensible but this car has issues with alternator slip when cold if the belt is not very tight. Some SC kits improve the alternator belt wrap so it might be possible to reduce this somewhat as long as the belt does not slip.



You cannot really hear SC belt slip but if you have a boost gauge you can see the boost flatten out. On my SC you do not even notice the power rolloff if you do not rev the hell out of it, and the car still seems very fast.



-Joel.

[/quote]



Joel,



What tension did the Krikit show? Mine is showing around 15kg using - though I am not using Flash's kit and am not running AC. It is hard to adjust tighter as there is not much adjustment with the way the SC is mounted and the overall geometry. The alternator tensioner is maxed out with the 1045mm belt I am running and a 1040mm is a little bit tight (I would need to install the idler roller after the belt goes over the other pulleys to get it on). I'll see how this goes with slip (using a 100mm pulley with almost 180 degree belt wrap). It is probably the alternator that will slip more as it only has about 90 degree wrap.



In any case, I'll probably fit a smaller pulley once the tuning is about right in terms of driveability.



I'm curious to see how tight others run...

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[DaveN]

Here is another clue as to whether your belt needs adjusting. I just cleaned my belt guard and noticed the underneath had belt scrubbing.

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[flash]

which reminds me.......i need to get made and send out new and improved replacement belt covers. i've seen the tabs on two of them break.

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[jfrahm]

Eric I was getting 100lbs on the Krikit, which is under 50kg, I doubt you were only running 15kg. 100 is about 10 on a 9201 and is about stock, which IMO is a bit tight but alternator slip is common on a stock 968 without high belt tension.



The larger crank pulley is interesting as it would resolve several problems and suggests the possibility of some impressive boost. I may try it someday after I try again to run big midrange boost and top end boost limiting and see how I like that.



Another thing I plan to try is to put an eccentric on the reversing idler to allow easier belt tension setting from above. This would also solve the issue I have created with my extra crank wrap pulley, which was that I lost about half my belt tension adjustment range and made for a miserable belt tension setting procedure. I was tempted to move this pulley to run between the alternator and AC and get my adjustment back, but then I lose my crank wrap.



At any rate on the kit I am running there is room, I believe, to adjust the belt at the reversing idler particularly if you tie back the ignition wires and gain a couple cm of clearance. I might mock up an eccentric out of wood to check the clearances for the SC bracket, etc. If it worked one could adjust the belt tension from above easily with a couple wrenches in a minute or two. If the swing is a problem (as it might be) one could use a linear tensioner in the same spot but it would not be as elegant.

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