So I take it you can't throw on a RSR cap and rotor and make a 930 a twin plug machine? Doing the wires, twin plug the heads, etc. of course....

 

Why would you want the dist when you can buy good reliable crank sensor stuff, and you can map the spark? Are you looking for reliability, or simplicity, or authenticity? And at what price...

 

Agreed, I have one of these dated systems on a car that came in and it is missing most of its piston above the second ring. Needless to say the engine builder has missed something. The system will be replace with a more reliable digital setup. They RSR are pricey and not accurate compared to today’s technology. In fact aside from the dist wearing, the cap being expensive and almost non-existent the brass gear to the dist often wears and can vary timing up to 10 degrees at any given time. That compared to the digital systems that stay accurate within a 1/4 of a degree and have no moving parts to fail make it almost a no brainer. Don't forget you can tune your own ignition curve then retard based on a real live map sensor. Technology is grand.

 

Distributors are pretty reliable. Porsche used them long after crankfire was available... but then maybe they just didn't understand the advantages of it.

 

They got pretty close with the 965/993TT on out. Of course now everything is. We know the Germans typically aren't in a hurry to change things

 

There's a lot put on the new stuff to. In some case too much. I have seen some Crank fire Ignitions where the Timing accuracy is no better or worse than with a Distributor. The problem with distributors is getting the repair parts. There were a lot of engines running RSR type Distributored Ignitions and I'm sure some blew up and some did not. Shame to "throw the baby out with the bath water" here. Yes the parts are very expensive, but when looked after they will last a long time and work very well. There are some advantages to the latest type of ignitions, but sadly some have this technology but cannot back it up with accuracy or reliability. Take a look into the engine bays of many club racing cars and see how many are carrying an extra sensor. Don't see many carrying an extra Distributor.

 

True some units are junk and some are not. Bottom line is the parts are hard to find and 6-800 for a cap will almost buy a whole crank fire system. As mentioned some systems are better than others and it will pay to do some research here.

On the early systems with the smaller pick up they were prone to failure due to the design. The epoxy would drop out of the center and cause the sensor to come apart. Most now are using a larger sealed design that isn't prone to the failure of the earlier versions. It could be compared to that of the 944 type sensor. The issue will always remain on the wear of the dist and gears. On most of these motors when something happens you will know when a hole is in it. If you invest in a crankfire system there are no moving parts, period. Yes, failure sometimes occurs and most of the time not. The parts of the older technology are on a timer, they are being used up every time you start the car. I have run crank fire on at least 5 of the 33 Porsches I have owned and the only thing that ever failed was the Bosch relay running them.

FWIW the cap that is on the car we are rebuilding has less than a year of running time. It has already started to show spidering. The quality has either become less or the engine builder did not sell him a new cap. It is on the rebuild receipt so I have to assume it new and just isn't holding up.

 

Your right about the cost. These replacement parts are making it impossible to keep anything original. I have a Distributor on my Black engine with the RSR Cap and Rotor arm. I wanted to keep things simple and be sequential. 1 CDI single Channel unit makes the total cost even with the Cap and rotor a little more acceptable. There are not many Ignition systems out there where you can be sequential without the expense of multi channel CDI units. I suppose you can use inductive, but then how many of these Ignition systems can control the dwell? I was a little early in my build, as there is nowparts available to use a 2nd distributor for 911 and 930's driven off the Camshaft. This uses an inexpensive 911 Cap and Rotor. For the 930 application it comes with a new pump gear for driving the Rotor arm. Simple and effective.

 

Hmmmm, I wonder if that is my cap the Doc is refering to??

Ralph

 

Stephen,
So to go twinplug, which route would you recommend which is value for money?

 

Even on a stock 930, I would still opt for the crankfire for flexibility in timing. The ability to advance timing early and back it off as boost comes up is valuable in performance tuning. Couple this with EFI and you can map it exactly to engine load and rpm. Add twin plug and I think it strengthens the argument. In addition, you can keep the cost down with an inductive system with twin plug and a good ECU. No doubt, distributors work. I simply prefer the technologies.

 

I agree with DonE...the crankfire provides the best flexibility in timing, not to mention accuracy. Ideally, the ignition control unit should provide MAP input so the ignition can be programmed to adjust for vacuum/boost conditions. The twin-plug Electromotive HPV-1 unit I have doesn't provide for MAP which is really lacking, IMHO.

Dave
'85 Factory 930S

 

Dave,
That market has changed a ton. In fact the new units are far from the original HPV1s. We have seen three more model changes since then. They now have moved the igniters into its own box that is mounted in the car and the DFUs are separate and upgradeable. The HPV1 is a collector piece now

 

Stephen,
Does that mean you'll swap an HPV-1 even up for an XDI?


Dave
'85 Factory 930S