Distributor Advice

[rcnagel]

I am restoring a 68' soft window targa. The smog pump was missing and I have no intention of putting it back the smog stuff. So now I'm vacillating back and forth with whether I'll put the original distributor with the vacuum advance or use the earlier type without. I'm just wondering if I'm going to run into problems finding replacement vacuum parts? Is there a performance advantage running with or without vacuum advance. For originality, would it be better to use the vacuum advance?

[cmcfaul]

once you deviate from original its almost impossible to go back. Porsche designed it that way for a reason. No reason to change it.

Chris

73 911 E

[304065]

Casey, here is what the factory had to say about it:


"This way, a more combustible fuel/air mixture is prepared, with a resulting reduction of the unburned,
poisonous air pollutants in the exhaust gases. In addition, the ignition distributor is equipped with a vacuum
control unit which retards the ignition timing at idle speed.

The vacuum line connection is attached at a point below the throttle so that the negative pressure can be
effective only at idle speeds. The retarded ignition timing permits a slightly wider opening of the throttle
valves at idle speeds. This results in better cylinder breathing at idle speeds and a more combustible
mixture on deceleration."

So this is an emissions thing. However, it's a 68 thing. 68s are hard to restore to perfection because they need all the smog equipment. If you're doing it, and you actually have the uber-rare cast iron with vacuum retard, I vote to put everything back to original.

[edmayo]

The retard goes away as soon as you open the throttle, it's not costing you any performance, leave it! Not worth worrying about.

[rcnagel]

Okay now I'm getting some information. I thought the 68' vacuum distributor was aluminum and not cast iron. See attached image below. So this short wheel base soft window targa will be a driver car now that my 65' coupe has gone crazy.

I have a lead on a cast iron vacuum advance I think, but I could go the route of a 911L spec. I'm not going in for smog equipment. Ill put in a box for a future owner. This is the car for long driving trips, vacations etc...

I'll do vacuum advance if it works. Thanks for the help. Let me know if this attached image is not a 68' vacuum distributor.

Thanks

Casey

[Brad Davis]

Hi Casey,

Here is my 68 911 distributor before and after restoration. I kept the vacume advance in place.

[rcnagel]

Brad,

We are hitting close to home, we work a mile away. It looks more aluminum? Is it plated? It looks so different from earlier cast iron dizzies? You must have one of those "ultra rare vacuum distributors".

Casey

[ibmiked]

If Porsche really believed in the advantages of vacuum advance on the '68 cars, why leave it off the ROW ones? (Genuinely asking)

-Mike

[304065]

If Porsche really believed in the advantages of vacuum advance on the '68 cars, why leave it off the ROW ones? (Genuinely asking)

-Mike

It's just for emissions. Retarding the spark allowed them to have the throttle plates open further at idle, presumably to help emissions. In the old days, the European emissions standards were less restrictive than the USA.

[304065]

Hi Casey,

Here is my 68 911 distributor before and after restoration. I kept the vacume advance in place.

Brad, what is the date code on your Bosch distributor? (tiny three letters stamped into the body somewhere)