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Twin Plug ignition options
Once again I'm going nuts and thinking I can afford this but please humour me. What are the options for installing a twin plug ignition? Keep in mind that I have the engine apart and I can replace anything that needs to be done.
Oh yeah, incase you don't know, its a 78 3.0. Thanks Adam Roseneck ------------------ 1978 911SC 3.0 roseneck@cyberbeach.net |
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03-09-2001, 12:38 PM
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If you are going higher compression, say 11:1 or are going to pack more air in and are worried about detonition, go for it. Are you going to replace the distributor or go for a crank fired device? That's the expensive part. Do you do your own machining? It doesn't look that tough. Does anyone know about the downside as far as cooling is concerned?
Diverdan |
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03-09-2001, 12:59 PM
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Thats what i'm really curious about. I would probably go with 11:1 compression and the machine work I can get done for about $200 (over and above $500 for the auto-x vavle work). I'm looking for options for the actual ingition. I have heard of electomotive, and the dirstibutor method. But is there any other way? ANy feed back anyone has would help. Like I said, the case is open so if i have to do anything with the dist. gears, now is the time.
Adam Roseneck ------------------ 1978 911SC 3.0 roseneck@cyberbeach.net |
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03-09-2001, 03:22 PM
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Andial use to sell a splitter for the DME equipped cars(84-89)which allowed for twin ignition. I know you don't have DME but perhaps the idea could be adapted to your car. The devil is in the details of the implementation. sometimes its better to bite the bullit and spend the $ for a preengineered system
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03-09-2001, 03:30 PM
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Steve Weiner (porsche@rennsportsystems.com) twin-plugged my heads when I converted the engine from 3.0 to 3.4 liters and went to PMO carburetors. He match-flowed the heads and converted my existing SC distributor to a 12-plug distributor wearing what I believe is an RSR cap, and the the energy comes from two MSD systems with Blaster coils that I installed. Steve's your man if you want truly expert, experienced advice on this subject. He's done lots of these conversions.
Stephan |
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03-10-2001, 12:09 PM
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Quote:
As to 11:1 CR that is also being discussed isn't that a little high? I've always heard that 9.8:1 is pretty much the limit on pump gas, with most people saying that 9.5:1 is the best to run, since it makes allowances for bad gas, etc. Dual plugging the heads is reputedly good for another full point of CR, so maybe 10.5:1. I've heard that a crankfire setup is also good for a allowing a little more CR, but I don't know the specifics, and what crankfire combined with dual plug will allow. Anyone have a good rule of thumb with these mods? I've been looking into the same sort of mods for a while, as I've suspected all winter I'd have to do at least a top end rebuild. So I'm interested too, is anyone running above 10.5:1 CR on pump gas with success for any decent length of time? Thanks, Adam |
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03-10-2001, 01:22 PM
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I haven't actaully decided on the 11 or 10.5:1 compression ratio. Either way, the new 993s are 11.3:1 but they have the electronics to help with knock and all. I'll talk to the person who was reccomended in the previous reply.
Adam Roseneck |
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03-10-2001, 03:18 PM
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Twin plug and pump gas is limited to 10:1 or 10.25:1 if you want to run West coast pump gas and not have to worry about pinging.
Cutting the holes in the heads is the easy part, as said above the spark is the expensive part. What I did was use a 964 dual plug distributor, put the guts from my SC distributor in it for advance curve,some extra machine work and I have a dual plug distributor that I can go buy a pair of caps and rotors for at just about any auto parts store around. Walk into any auto parts store and ask for a cap and rotor for any Porsche cap with 12 holes. RSR caps and rotors are $1800 new, a pair of 964 caps and rotors are around $100. If I vent the drive belt everything works great. An intresting note. A friend just dynoed his race car motor. 3.0 ltr. 50mm PMO's, big tall cams, headers, 11:1, all the racy stuff. The motor makes 300HP with single plug, and 20HP more with dual plug. In SCCA he cannot run dual plug and I think PCA he can. Anyway same motor,carbs,cams, everything but change the lower valve covers,remove 6 plugs, add 6 spark plugs, a new distributor and you get 20 HP. Kinda cool huh! He also has the same distributor as mine, in fact he cut ignition wire for both his and mine at the same time. Randy Jones 1971 911 |
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03-10-2001, 04:23 PM
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How much do you want to make me a distributor like yours. I can send you all the parts you need or you can pick them up and I'll just send money. The other options are running somewhere around $1400 to $2000 and thats a little heavy for me on my $5.50/hour wages
 Adam Roseneck ------------------ 1978 911SC 3.0 roseneck@cyberbeach.net |
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03-10-2001, 04:58 PM
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I forgot to ask, what about CDI and coils, how do you set those up and what did you use Randy.
Adam Roseneck |
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03-10-2001, 05:01 PM
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