Twin-plugging options--advice needed.

Steve in SLO · 12-26-2001, 06:15 PM

I am building up a 2.8 engine with 10.3:1 CR, and am well aware that in CA, with 91 octane, this will require twin-plugging to run street gas. I am seeking advice from those experienced in this as to my ignition system options (short of a $2000 Crankfire system). Any ideas as to the best distributor/coil (MDS?) system for this application? FWIW, the car will be mostly a street/DE car. FWIW, I will be using S cams and MFI. Thanks in advance for any advice.
Steve

Early_S_Man · 12-26-2001, 07:03 PM

Steve,

You may want to review the following thread, and then do some further searches on 'twin plug,' 'twin-plug,' 'twin-plugging,' and 'electromotive.'

http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=54091&highlight=twinplug

Formerly Steve Wilkinson · 12-27-2001, 05:56 AM

Get in touch with Steve Weiner, at Rennsport Systems, in Portland, Oregon (porsche@rennsportsystems.com for e-mail or or www.rennsportsystems.com/~porsche/ for a look at stuff he's done. He's a major authority on twin-plugging and other performance enhancements, and he twin-pluged and bench-flowed my '83SC heads. Also modified the stock distributor to utilize the 12-plug cap, and I installed (at his suggestion) dual MSD units and coils. Works splendidly.

Stephan

Tyson Schmidt · 12-27-2001, 11:53 AM

Hey Warren. I missed your reply to my twin-plug thread. I didn't notice it until you posted the link above.

The 964 distributor can be had, used, for around $250. The beauty of it is, that the the caps and rotors are easily attainable, and relatively cheap.

Your points idea is what I thought of doing initially. It would definitely simplify things. I'm also not sure though, if it will work.

The other issue is the advance curve. Since twin-plugging gets the mixture burned in half the time, you only need half the total ignition advance. I'm sure the advance mechanism could be reworked to attain the proper advance curve for a twin-plug motor.

If I get the chance, I'll try to play with some of these ideas to see if they are feasible.

Early_S_Man · 12:22 PM

Tyson,

I believe that if you soldered/brazed up the ends of the 'limit' slots in the advance mechanism, and changed the stiff spring to a soft one, you could end up with an advance curve consisting of essentially the left, or steep half of the 2.4 curve in the following diagram from the service manual. By filing the slot so the distributor advance is limited to about 10°-12° and using an inititial advance of 10° ... would give you a good starting point for further experimentation.

Tyson Schmidt · 12-27-2001, 06:12 PM

Well, now I guess I just need to come up with some donor distributors and commence with the transplant surgery.

Great ideas Warren.

CamB · CamB's Garage

I am sure there is an extremely good reason, so this ought to get a quick reply, but why can't spark plugs be run in parallel, if there was a way to splice the two wires into the distributor? Would one spark more than the other (assuming even length of wires/even impedence)? Would the coil not be up to the task?

I ask because as far as I know the twin plug options use simultaneous firing (as opposed to the modern Alfa system which (from memory) uses two slightly differently timed sparks for optimum combustion).

Thanks!

Cam

Steve in SLO · 12-28-2001, 07:11 AM

Cameron,
Like water, electricity takes the path of least resistance. That being said, unless everything from the distributor cap-->wire-->spark plug-->gap has EXACTLY the same resistance between the two systems (a practical impossibility), current will flow preferentially to one spark plug, leading to no or weak spark at the other, plug fouling being the endpoint. However, it is an attractive idea that instead of spending$$, I could just do it with a pair of wire cutters and a crimper....

BTW, thanks to all for the options and knowledge. I appreciate it.

Steve

rscupper · 12-28-2001, 12:08 PM

Steve, when you can please let me know your final solution for the twin plugging. I'm interested for mine. What do you estimate total parts cost & hours to be? Doesn't the head work get pretty expensive (I know, it's Porsche so it's relative)? Thanks

Steve in SLO · 12-28-2001, 01:59 PM

Brian,
I think about $250-300 for head-tapping not including dis/assembly time for the heads, and, I am hoping, less than $1000 for distributor/MDS/wires should bring me in at between $1000 and $1200. Take this with a large grain of salt, as I haven't yet priced everything out. I will post when I have definitive answers.
Steve

rscupper · 12-28-2001, 05:56 PM

Thanks Steve, I'll look for your post.

BTW - I'm planning on Cambria. I figure a SLO brewery run on the way up and, what the heck, a stop on the way back. Even with my roll cage, I think I can bring back about 10 gallons

Join us for a pint?

CamB · CamB's Garage

Quote:

Originally posted by Steve in SLO
Cameron,
Like water, electricity takes the path of least resistance. That being said, unless everything from the distributor cap-->wire-->spark plug-->gap has EXACTLY the same resistance between the two systems (a practical impossibility), current will flow preferentially to one spark plug, leading to no or weak spark at the other, plug fouling being the endpoint. However, it is an attractive idea that instead of spending$$, I could just do it with a pair of wire cutters and a crimper....

BTW, thanks to all for the options and knowledge. I appreciate it.

Steve

That was the best idea I came up with while thinking on reflection (working on the theory that I had to be wrong 'cause nobody did it), so I am glad to see that my crappy electric knowledge is improving

12-29-2001, 11:43 PM

When I finaly get my Porsche car running I promise to never mention drag racing again.

But there is a company called Jesel that makes belt drives for small and big block chevy's that replace the timing chain.
They also have a belt drive distributor kit that runs off the front of the motor. www.summitracing.com may have a picture.
So you might want to look at what they do to get some ideas.
If I was going to wack up some distributors I would think ford 200cid six early 80's with eecIV duraspark electronic ignition.
Benifits are mag pickup, distributor cap with wide spacing on the secoundary terminals. And you don't get bent on parts pricing.
And MSD has wiring diagrams to hook up to the ford mag pickup.
All ya need is 1 Porsche distributor 2 ford's and a machine shop.
Or go the DIS route.
Just a thought
Chris

Early_S_Man · 12-30-2001, 10:52 AM

Hey, Tyson! This what you had in mind for a 'donor?' A $377 bid didn't make reserve price minimum!

http://cgi.ebay.com/ebaymotors/aw-cgi/eBayISAPI.dll?ViewItem&item=599456340

Tyson Schmidt · 01-02-2002, 06:10 PM

Well Warren, we all know E-bay isn't the best place to find bargains on Porsche parts. Especially not from over-priced So. Cal. wrecking yards.

I have seen 964 distributors advertized from private parties, that needed a rebuild of course, for $250. The rebuild (read: replace broken drive belt) is a piece of cake. And hell, you're going to dissassemble it to do the mods anyway, so a core is all you need.

That E-bay item included the caps, rotors, and wires. If all those were in good condition, (Big if!) it wouldn't be that bad of a deal. ($600 buy-it-now)