Carl Fausett

Dubai944 is correct, the limiting factor on boost has been the very small size of the 968 crank pulley... it forces us to us very small supercharger pulleys, and then we have almost no tractive force left between belt and pulley.

A larger crank nose pulley would allow use of larger supercharger drive pulleys, less belt slip, and more boost.

On other kits where we have to make crankshaft pulleys and provide them (Porsche 928 and Ferrari 308, for example) expect the kit price to go up significantly because of the pulley, and the installation gets more difficult (many do-it-yourselfers do not have the proper tools to remove and replace a crank nose pulley).

In Dubai's case (above) he not only changed the crank pulley but has also had to have made a complete set of matching auxillary pulleys to match. How many 968 owners are willing to put up the $$ for that?

There is one other limitation - if you look at the block and oil pan below the crank pulley, you will see that moving to a larger nose pulley isnt easy... there are interference points with other parts that will quickly become an issue.

Going back to our original design objectives (this thread, page 1) where low cost and ease of installation were key - these are reasons why our kit did not include or require a crank pulley swap.

Carl Fausett

Back to the current design - as we watch these kits in the field and get more and more hours and miles on them, I think I may have under-shot the pulley sizes a wee bit.

The Stage 1 pulley performs much better with nowhere near the belt slip issue, and the Stage 2 pulley continues to give racers (and some street drivers) fits with belt tension and slippage. I am recommending that racers use our Stage 1 (larger) pulley and have been moving each one to that as the opportunity provides.

I think we will retool, and the current 2.25" Stage II pulley will be phased out. The current Stage I pulley (2.30") will become the Stage II pulley, and a more moderate 2.40" pulley will become the new Stage I pulley.

This will go a long way towards our goal of customer satisfaction with long service intervals and zero maintenance on street-driven vehicles.

Carl Fausett

If anyone has a spare 968 nose crank pulley off the car, I'd like to see it so I can contemplate making a pulley upgrade kit. It would be an optional accesory that we could offer....

Reading the number of fellas that have broken their belt tensioners on NA motors just trying to reduce belt slip at the alternator and AC compressor - it seems that the crank pulley has been too small for a while now.

This accesory kit (crank pulley with auxillary drive pulleys) would address this.

Lemming

Carl, can you tell us the PSI that each pulley will produce.

Carl Fausett

No. PSI is a measure of engine back-pressure and restriction, not a measure of supercharger output.

Car 1 has stock exhaust, stock everything and will see more "boost" on his psi gauge as his engine is more restricted than Car 2, who has removed his Cat, re-timed his camshafts, done some head work, etc. His "boost" will be lower, and he will have more HP than Car 1.

The supercharger output between Car 1 and Car 2 will be the same, but the psi readings will be different.

That being said, it seems as though the stock 968 will see a peak of about 5 psi with our Stage 1 kit and 6 psi with our Stage II kit.
On average. Dont quote me. :-)

Lemming

Understood, but you do say on your website that the stage 1 is under 5 psi and the stage 2 is 5 psi. So, on the same car, with nothing changed, what would you expect the difference in PSI between the 2.4 and 2.3 pulleys.

lsinlv

carl...have you thought of going to a stacked crank pulley to drive the SC alone??? I know fittment/clearance issues are a concern? this is the solution I went to to drive higher boost with less slip on my VR6.

just curious.

edz968s

Ok, a bigger pulley again for racing/track use and also deleting the injector upgrade, less power, but longevity with the belt at sustained throttle openings.
Would it be possible to knurl the entire face, side to side of the pulley, so as to eliminate the central wear issue of the belt.
I have had my kit for nearly a year now and not really been able to fulfill it`s day to day running potential. Ok I had no a/c to start with, but have retro-fitted an a/c compressor for belt tension, but with belt stretch on track it`s a constant re-tightening senario, less on street usage.
Would some sort of extra pulley similar to the alternator belt wrap set up be feasible to get more belt wrap on the drive pulley, perhaps a positive spring tension wheel set up.
Sure, this is in field R and D with great input from Carl and the users, but suppose myself and Tim are pushing the boundries for this street kit, though I`m sure solutions are always around the corner

Lemming

Some video from the enduro on Saturday. My radio screwed up and the flag was thrown when I was at pit in, hence the crappy start. Also notice how much I am fighting the car under hard braking, too much back brake that I could not dial out with the cabin adjuster. Fixed for Sunday with some less aggressive rear pads.

http://www.vimeo.com/16905135

edz968s

Absolutely brilliant. Superb footage. Some driver
Makes my in car track day videos look like a Sunday stroll.
Nice one

ninefourfourt

Wow! Excellent video and fantastic driving. It looks like Carls kit is putting out great power on your setup! You were reeling in some fast cars on the straits.

Carl Fausett

Yes, when I re-order pulleys they will be knurled by the manufacturer and I am confident we can get them knurled all the way across the face.

The pulleys you have were knurled by us in-house, and our knurling bridge only fits in the center of the pulley. This knurling was done experimentally to see if it helps. It seems to, so the next bacth will be ordered fully knurled.

Carl Fausett

Damn nice driving, Tim. Good video!

For those that are not sure why racing would be "different" than street driving a supercharger kit, they should listen to this video. Yes, LISTEN. Note how the Rev's are up AND STAY UP almost all the time. This demands the utmost from bearings, bearing lubricants, and the belt in the supercharger.

Lemming

Thanks guys, but to be honest, I felt a bit rusty out there since I have not raced since early May, when I totaled my car! Add to that a number of issues with the car (expected given the fact that this was the 1st real shakedown) and my times were not what I had hoped for. In fact, I'm a second off my track record set last year in Franky I, when I had significantly less power

The good news is that it was just as fun as I remember it being

odurandina

great video Tim !!



btw, your car sounds EXACTLY like my car sounded before adding the 2.5"/4" hollow chamber resonator.