edz968s

Looking at the pic of your engine.
I would say the by-pass valve is fitted wrong way round, the tube on the bottom, should be on the other pipe as the inlet and the side tube the outlet going back towards the head unit. In that configuration as is, it will be bleeding boost off.
It`s not a dump valve a such, but a recurculating valve and won`t dump air pressure to atmosphere.

Jfrahm

Interesting, I had similar results earlier in the thread with my double sided belt setup. I could run smaller pulleys and get more boost lower down but hit a limit around 5 psi with whatever pulley I ran on the SC. I got sidetracked and have not worked on it for a few months. My assumption was that the drive required at around 5 psi hit a point where I was getting slip at the crank or the SC still. That did not make a lot of sense as it seemed like I'd reduced the grip I'd had with some of the other options when I thought I'd have increased it.

My double sided setup was annoying to work with as it reduced the effective travel of the belt adjuster and made belt installation and adjustment a chore. It's possible my setup also causes the belt to whip and slip due to the turnaround right before the crank pulley and that was reducing grip. If it worked I thought it was a good setup as it increased crank wrap as well as allowed a double sided belt to be used. The missing piece was an easier belt length adjustment (which I have solved on paper) and of course I just never got the boost that I got with the old Stage 2 standard drive.

What does this mean? My feeling was that I'd increased the contact patch at the crank and had a double sided belt so my setup is similar to the larger crank pulley in that regard, and I also had a double sided belt, and I also am stuck at 5-ish PSI. so I am interested in how this goes.

I have been able to get a Euro Phaeton V6 belt which will be easier to work with and perhaps better, the reports are that it works very well indeed so that is encouraging.

-Joel.

pudjnr69

The feedback from Tim at Raptor is that with the pulley set-up I am running, I should have 11psi prior to the intercooler. So we will measure it and see what we are getting.
It is hard to see how 11psi at the intercooler equates to a drop of 6psi across it and with the double sided 6-rib belt, there should not be any slip.

Carl Fausett

Check the boost pressure before and after your intercooler. Have a fella watch it while you are on the dyno, and see if the restriction doesnt become compounded at high flow volumes.

The change you made in CR for 11:1 to 8.5"1 is not insiginificant, and you cannot compare the boost pressure before-and-after that modification. That compleel;y changed your volumetric efficiency.

Concentrate on HP produced, and not what the boost gauge says.

Your engine is now less restrictive. It shows me that the the SC is producing higher volumes, but the engine is inhaling nicely. I bet your output has gone up sweetly.

I disagree with Tim that it should produce 11 psi - I think that would be right for a stock 968 with stock internals, but not with your cylinder volume.

From our website:

Carl Fausett

One last consideration: it is possible to spin the supercharger too fast - where you are now operating it outside of the sweet spot on the compressor map.

When this happens, the adiabatic efficiency drops off. You are producine more air, but it hotter air now, and hot air is less dense.

In this case, it is better to slow the SC down to operate it in the core of its compressor map. There is less parasitic drag, less heat, less stress on the parts, and only a little less HP.

Carl Fausett

Our 968 is here and we've begun work on it. First order of business was placing the DFU (Direct Fire Unit) and ordering the custom ignition wires to length.

Carl Fausett

Some pics from the end of this week. The engine management is in and wired. The parts for the extended belt are made, but not installed in these photos. It all comes together next week.

RajDatta

Looks good. You might finally have a well sorted, high performing kit. Good luck.

pudjnr69

Carl,

Is there a specific engine management kit that is required for the ignition system, or can any use it? Also, if this free's up room in the engine bay, will the belt arrangement change?

Have you looked at putting the bigger Raptor unit in there as it seems that the smaller Raptor unit canot make big boost numbers?

pudjnr69

I asked TIm from Raptor if the bigger unit would make any difference, his reply was that it would not. The issue to be dealt with is the power that the belt can provide and therefore belt wrap and tension. So some work to be done to get some more wrap and to install an auto-tensioner. Hopefully the 10psi or so of boost will come.

Carl Fausett

I'll be adding more belt-wrap, and as you know, a 6-rib double-sided pulley.

You can use any EMS you like - I prefer the Electromotive system, but a Haltronic, Motronic, or other comparable would work very well also.

pudjnr69

Carl - what length belt (I am assuming it is the 1710mm version)? Can you add the tensioner as an after-market fitment (I already have the belts). If I don't have to re-engineer this I will be happy.

Any lead-in on the solution and timing?

Carl Fausett

Cant tell you what the final length of the belt we will be using is just yet. I will as soon as I know. I am trying to build around the belts I can actually easilly get first, to make it easier for me and my customers to get replacement belts anywhere.

I will go to a custom-made belt only if I have to.

We will be able to control both the ignition advance, the boost retard, and the injection events.

Carl Fausett

A couple progress pics from this morning.

The belt drive is completed and the belt is tight. The electromotive installation is very near complete, we should be keying the car over soon.

Not finished, need to check belt tracking and belt slip yet, but getting close.

Carl Fausett

With the induction tubing in place. Note the absence of the Blow-Off Valve re-circulation and the MAF sensor, no longer needed.