What type of ignition distributor in a 1978 SC US

cfeste · 06-10-2009, 10:20 AM

Hi!

I had problems with the distributor on my 1978 SC, and had it replaced with a rebuilt unit, from a not-to-be-said-here-company in the US. My mechanic here in Norway now tells me that the distributor I got is from a much newer car (89 or so), and that it will never work 100% in my car. Does anyone have any experience in this area? The one I had had only one vacuum plug, and the new one has two, but the seller told me to ignore the second one, just plug in the first one (yhe bottom one) as on my old unit, and assured me that it would work perfectly.

If I need a correct distributor, is it possible to rebuild and modify a newer unit to fit the 78?

Any help appreciated!

GaryR · GaryR's Garage

I have one out of a 65K mile 78 SC I bought as a race doner (engine in a box) that I may be interested in selling. Looks like a rebuilt is $1200 (80-83) from our host and 78-79 is NLA. PM me if interested.

RonDent · 06-10-2009, 10:58 AM

Do a search because I could be wrong. I'll hear about it if I am. But I think the SC distributors turned the other direction. Any help here guys?
Also, if the new distributor is from a new car, you may not be able to set the timing with the distributor. The new models were bolted in place and could not be turned.

cfeste · 06-10-2009, 11:25 AM

You're right, the SC has a distributor turning counter clock wise, and so does the one I have now. But is it made for doing that?? I guess a clockwise-turning one would not work at all in a counter-clockwise car, if that's how it works. Confused...

I could be wrong about the year of the one I have now, but it can be adjusted, so it's not bolted straight on. I will try to read the part number from it

RonDent · 06-10-2009, 11:51 AM

Is it just the matter of the vacuum advance having two ports that bothers you, or is there something more that I'm overlooking?

cfeste · 06-10-2009, 12:03 PM

I guess I forgot one major thing: The car runs really bad.....

Idle seems fine, and cruising at 3000 or higher RPMs is fine, but accellerating is jerky, and driving on lower RPMs as well. Carefully inceasing throttle while accellerating works kind of fine, but stepping on it doesnt go well at all. I guess it summarizes as odd, jerky behaviour.

The car has been checked well for other faults.

RonDent · 06-10-2009, 12:18 PM

I don't know if the two vacuum ports are connected to the same side of the diaphragm on the advance. Have you tried swapping the hose to the other port. It sounds like the timing isn't advancing or is advancing to slowly.

You could try to add a few degrees of advance to the timing and see if things are better.

cfeste · 06-10-2009, 12:40 PM

Thanks for the ideas! I do think the mechanic said the distributor isn't advancing enough, and that he has adjusted it as well as he can.

I would think vacuum is the issue, since it runs well on high RPMs while cruising, but that added throttle requires more advance, and the distributor is not responding.

But the main thing I need to know is if I can run "any" 911 1978-1989 distributor on my car, or if I need that specific part number which is stock for the 911 SC 1978.

RonDent · 06-10-2009, 01:40 PM

Sorry, I would have to say no. They are not all the same. I don't know what the differences are, I do know the drive gear is different.

psalt · 06-10-2009, 02:57 PM

cfeste,

You cannot have an 89 distributor, only a 1978-83 SC distributor will work. You need to put a timing light on it and see what is actually happening. The difference between the early and late SC distributors is that the late distributor has vacuum retard and vacuum advance and about 5 degrees less mechanical advance. The later engine has higher compression and the max advance needed to be reduced. The early distributor only has vacuum advance. On the late distributor, the advance is connected to the outside of the cannister and the retard to the backside. Vacuum advance uses ported vacuum (no vacuum at idle), the retard uses manifold vacuum. My advice is to disconnect and plug the vacuum line, set the timing to 26 degrees BTDC @ 6000 rpm and note the idle timing at 950 rpm. Test drive the car with the vacuum disconnected. Then check to see that the line is hooked up to the correct ported source, reconnect it to the outside of the vacuum cannister and note the change in timing with the light. You should be able to make a late distributor run fine on an early engine.

cfeste · 06-11-2009, 01:10 AM

Hi! Thanks for the tip on how to set the timing with the newer distributor. I will check if the mechanic tried this way, and if not, I will try it myself.

Rana1 · 06-11-2009, 04:19 AM

cfeste... if you distributor was other than SC model it would be a bigger problem than vacuum advance.

If you have a distributor other than 78-83 it's made for clockwise turning only. Vacuum advance is just a part of the problem and could be easily solved by disconnecting it. Early SC, euro at least, do not have vacuum advance and work nicely.
A distributor has inertial advance wich is the main adjustement to rpm advance needed. If your distributor is other than 0237301007, 0237303003 or 0237301009 instead of advance you would have retard as revs go up wich would make it difficult if not impossible to rev the engine much wich is not the case.

Can we see a picture of the distributor? Does it have 1 or 2 vacuum hoses? They might be reversed...

For cruising it's ok. When you accelerate "hard" you need less advance than when cruising for the same revs as richer mixture burns faster .

MBruns · 06-11-2009, 04:46 AM

We currently build a 12 pin distributor for 911 engines 2.0 - 3.8 all gear sizes and rotations, we are getting ready to build a 6 pin distributor to replace the troublesome SC and earlier units, it will have a magnetic trigger like the 12 pin setup that will work with the 6 pin bosch or MSD boxes It will have an adjustable advance system to limit some or all of the range of advance easily. It will not have a vacuum advance/retard. The price range should be in the 700.00 outright with cap,rotor ready to install. Let me know if this sounds of interest to you.

Mike Bruns JBRacing.com

aadrew10 · aadrew10's Garage

Rana1,

I have an 81 SC and am experiencing similar problems when the engine is under load. I know my distributor is supposed to have vacuum tubes, but the one in my car has no place for tubes. It is model 0 237 303 003. I noticed you referenced this number earlier, would you mind telling me what car this distributor was made for? I'm starting to think the distributor is my problem.

Thanks,
Andrew