Carl Fausett

The engineering on the new crank pulley for the 968 kit is finished, and I have my manufacturing bids.

If I order 5 of the crank pulleys, I can get them at $393.00 each. If I order 10 of them, I can get them for $315.00 each.

The new crank pulley is 6.125" in diameter, which will turn the impeller at 46,838 rpm at 6500 crank, when using a 2.55" SC pulley. There will be no belt slip in this combination.

Currently, 928MS Kit owners are running a 5.11" crank pulley and a 2.35" SC pulley to spin the impeller 42,402 rpm at 6500. Most report 5 psi of boost from this setup.

Experience with the 968 has shown us that an increase of 922 impeller rpm translates to 1 psi.

My best estimate of the boost made from the new Stage II crank pulley and a 2.55 SC pulley is 9-10 psi on an otherwise unmodified 968.

Be advised that I am certain the stock fuel system, even with our FMU installed, will not be able to fuel a 10 psi boost kit. Larger injectors will be needed, and quite possibly a larger pump or modern engine management system.

My question for the forum is: now that we know the price of the new crank pulley, how many want one?

Jfrahm

Thanks Carl.

I am intrigued but wonder what-all is involved.

Do you run without belt guards and AC? What is done to replace the AC Compressor?

Cheers,
-Joel.

Carl Fausett

There is only one plastic belt cover, near the bottom, that needs to be removed to run a larger crank pulley. The AC, Power steering, and alternator will work as they do now, albeit they will be spinning faster. Thats why I dodnt "go nuts" with a 7" crank pulley (even though there is room for it) because I did not want to over-clock the accessories.

Mark944na86

That's good to hear. I remember trying to find the factory spec for the alt belt tension, and the FSM only had it it as a 9201 reading. So, like you, I just did the "tighten until it doesn't slip" method -- but I was under the impression I ended up at about 60lbs on the Krikit. So 100lbs sounded high to me -- but maybe not, from what you're saying.

One of the things that gave me pause from time to time about using the alt belt for the SC (rather than a separate dedicated belt and pulley) was the possibility that the belt tension would have to be set significantly higher than normal to prevent SC slip, and that might have a negative impact on the life of the alt and a/c compressor bearings. It's actually been a question I've been meaning to ask for some time.

Lemming

Power steering will not be affected by the larger crank pulley. Alternator can be fixed by getting one of Carl's overdrive pulleys. AC will be colder at idle, that's a good thing!

Additionally, using the larger crank pulley will allow you to run a larger SC pulley, that means you don't have to run the belt as tight to keep it from slipping.

edz968s

So what do I need now?
I have the composite head gasket fitted, the set of larger injectors that I already have from the S2 buy, I need to confirm with you that will be the correct set, an upgraded fuel pump and possibly a live re-map.
So more $$$

Carl Fausett

Mark - You have mentioned the idea of a separate pulley just for the supercharger.... we would have loved to do that, but there wasnt room. Have a close look - if you add a separate belt sheeve to the existing pulley, you move the supercharger forward by that amount also - and right into the radiator.

Check it out.

Carl Fausett

Ed - as I said in my email to you I am not certain exactly what you will need to fuel 8-10 psi of boost once you get it. You have heard of the "cutting edge" of technology? This is the "bleeding edge".

This new pulley has just past design stage and is stopped at manufacturing stage pending interest.

It hasn't even been made yet. It doesn't exist. I don't KNOW what you will need to provide enough fuel for the increase in boost, not yet. I can only guess. And i guess a 968 with this pulley producing 8-10 psi will need larger injectors (perhaps larger still than the ones we supplied with the "old" Stage II kit, and a larger fuel pump). I would start there. If that doesnt do it, it may require an modern Engine Management System, like our Electromotive kit.

mikey_audiogeek

Love that teminology!

Mike

ninefourfourt

Speed costs....How fast do you want to go?
It is a darn shame that speed is so addicting. I went down this same road with my 951. And I wouldn't have changed a thing if I had to do it again.

mikey_audiogeek

I thought the quote went:

"Speed costs - how fast do you want to spend?"

edz968s

Had another good weekend out in the car, no probs, well not quite. Getting a good 1 Psi from 4000 then up to 4-5 to the red-line and pulls well.
Still getting a bit of belt dust and after a few hundred miles boost drops off to 3-4. The new fully knurled pulley is a good step up, but the problem of belt slip is still evident. The smooth side of the belt that runs over the knurled pulley is wearing away, that you can see the white/grey fibres of the construction showing, so a short belt life is now the sacrifice for a good Psi showing.
Is there anyway that on the rear face of the head unit plate a small pulley could be installed to get more wrap from the idler to the impeller pulley belt run, space is at a premium, but something could be fabricated: maybe.
Other than that and changing belts often, or could be my driving syle, on/off with the gas pedal, car is now running nicely.
Have a dyno due soon, so see if I we can better the 230 RWHP from last time.

savvas944

It appears that the solution is a bigger pulley for the crank together with a bigger smooth
pulley for the s/c similar to the water pump ,keeping the same ratio ,which can both be obtained from Carl.

Lemming

Did you tighten the belt during the weekend?

Carl Fausett

That is what I have designed. But when I posted it here with the price for the larger crank pulley, only had 1 taker. I cant justify making 5 or 10 crank pulleys to sell 1 and stay in business long.

What we need are more 968 owners to "sign up" and I will put them in manufacturing. They are all designed and ready.