3liter6

On aforementioned monster motor, I will be going with a twin plug setup (machining already done) as necessitated by both bore (100mm) and CR (~10.3-10.5:1). So, I'm looking at my options for distributing the spark to my now 12 plugs.

#1 is the tried and true RSR dist cap and rotor machined onto distributor of my choice. My mechanic is recommending that if I go this route I use a euro curved (Euro 'S' or whatnot) distributor as a basis. I have found a Euro SC one that seems to fit the bill.
Drawbacks: Cap & Rotor pricey as all get out, and possible limited avail. in future.

#2 is the 964 distributor setup, which my mechanic is unfamiliar with and a little wary of. This is the one that I have the most questions about. Questions are:

Drawbacks: Fitment? Belt-breakage?

#3 is a prototype crankfire ignition setup with ignition programmable down to a 1/2 degree (or some sort of highly precise timing arrangement)
Drawbacks: May not be ready in time for fitment to motor, prototype nature.

Any comments, suggestions, solicitations to sell me needed parts? I was thinking that a further description of the motor might be of some merit as well.

3.3 SC (100x70.4), "S" cams (actually Web-Cam variant, but close enough), 3.2 heads, Weber 46 IDA's.

Thanks
Adam

[ 06-19-2001: Message edited by: 3liter6 ]

Bill Verburg

Steve Wilkinson recently completed a similar project. I believe that he had Steve Weiner at Rennsport adapt a 12 wire distributor cap to his oem dist. He seemed quite happy. You might want to contact Steve W. at
Rennsport Systems

Steve Weiner-Rennsport Systems

Hi Adam:

We did indeed, do the work on Stephan's distributor to accept the RSR cap and rotor. This is our preferred method of choice for twin-ignition conversions.

We have every reason to believe that Bosch Motorsports will continue to make the RSR caps and rotors available, albeit not cheaply. I've never need to buy replacements unless I dropped it on the floor,......
I've never even worn a set out.

Recently, we converted a 964 dual-distributor to use in a 3.2 carbureted, "S" cammed engine and used the internals from an SC distributor for its trigger and advance mechanism. You must use an SC crank gear since the SC advance mechanism rotates CC. With the factory vent kit, belt life problems should not be an issue but I would always recommend installing a new belt (very cheap) every 40-50K miles or so. We do this routinely!

I'm no fan of the current crop of crank-triggered inductively fired DIS igntions due their less than adequate coil saturation times and 12V operating voltages. Fact is, the engines that are equipped with carburetors or MFI require a somewhat mixture for good idle and transition and these DIS ignitions are prone to plug fouling under such conditions due to insufficient output. Further, they are incapable of firing the wide plug gaps necessary for best idle and best power and they will NOT clear fouled plugs.

We really like using MSD-6AL's and MSD HVC coils with either an RSR-converted distributor or the 964 unit, so modified. These will fire plug gaps up to .065 without strain. We run our 911 engines at .040 and this make a nice idle, best peak HP, and will NOT foul plugs with extended idling.

I hope this answers your questions.

Thom Fitzpatrick

So what does one of those cap and rotor setups run?

Also, are the wires sequential in the cap, ie plug 1 then plug two of a given cylinder, then on to the next one?

JPIII

To Steve W.

I read with interest your comments on using the MSD ignition set up. I am having a hell of a time keeping my lugs from fouling at idle and low rpms. I'm presently using a permatune CD and a Pertronix replacement for my points. The engine is a 2.7L with Solex cams, 9.7:1 pistons and Webers set on the rich side. I don't really want to lean it out as I feel that I'm at the upper limit(compressionwise) for street gas.
It is a major problem while sitting in the staging lanes at autoX(and embarassing at stoplights). It starts dropping out cyls and the only thing that will clear it is a hard blast(or 2) under load.


If I go with the MSD set up, what do I about points. I have read that the MSD unit will fry the Pertronics. I hate to go back to mechanical points......What'cha think?

DonNewton

JP,
I'm using a 7AL2 with Pertronix (for just about 2 years now) with absolutely no issues! I also have a 2.7, but with GE-60 cams and Webers. Don't think you're anywhere near frying your system.

JPIII

Thanks, Don.

Just shows to go ya.....ah.. that one can't believe *everything* one hears. I've been waiting for my POS Pertronics to puke for about 2 years, myself. Sounds like there's an MSD in my future.

Steve Weiner-Rennsport Systems

Hi JP:

I understand very well about what you are experiencing and this is quite common with Weber'd and MFI'ed cars using Bosch CDI & Permatunes. You will not have troubles with using a Pertronix to trigger MSD's. They do not really care what triggers them, points or Hall sensors,......

The root cause is a fuel quality/formulation issue in this country caused by the reduction in evaporative emissions from gasolines. In short, they are simply tougher to get "started" than they used to be and if you notice, they do NOT evaporate very well.

Once the plugs get kinda wet from prolonged idling or rich idle mixtures, they STAY wet until they are removed and cleaned.

At this point, the cure is a 2-part solution:

1) You must use wide plug gaps to get the fire burning better and hotter. In technoterms, this is called using a larger flame kernel to get the fuel burning easier. There are also measurable power increases using plug gaps between .040 and .045. Plus, you get MUCH smoother idle quality.

2) The above solution really requires better ignition hardware than any OEM Porsche stuff.
Factory ignitions will simply misfire when attempting to use such wide gaps since the Bosch or Permatunes cannot supply the voltage and current required when using wide plug gaps and any reasonable compression ratios.

We have had excellent luck using MSD 6 series CD boxes with MSD coils to aleviate these problems. Using the plug gaps mentioned above, these systems work quite well and will clear a fuel-fouled plug.

Hope this helps,