Euro SC distributor questions

[Shuie]

The engine I’ve been in the process of rebuilding was set up for carbs with a euro spec SC distributor. There is no spot for a vacuum line to attach to this thing. How does the advance mechanism work?

I remember reading in BA's book that either the euro SC distributor or the '78-'79 SC distributors were recommended for carbs. How are they different from each other?

Most important to my situation, will I be able to use this distributor if I go from carbs to MFI? My MFI 2.4 has a vacuum line to control the ignition timing advance. Im guessing I could just plug the vacuum orifice on the MFI and use this distributor??

TIA

[BURN-BROS]

Shuie, I think most dizzys are mechanical with vac retard. The euro simply does not have the vac retard which I think is for Idle smog control. Plug the vac port and run it!!!


Please correct if I am wrong.

[Shuie]

Thanks Aaron!

ok, sounds like I was confused on the advance/retard fucntion of the vacuum line . I had a 50/50 chance and still messed it up . That makes sense though since the engine slows down when you hook the line up after timing the engine.


So, whats different about the euro SC vs. '78-'79 distributors? Why are these more desirable for carb'ed engines? Is it strictly becuase of the emissions or are they curved differently?

[emcon5]

I have always wondered about that remark in BA's book. It seems to me that it shouldn't really matter if the dizzy gives you 20° or 30° advance, couldn't you just set the full advance where you want it and let the advance at idle take care of itself?

Granted it may not run clean, but if you are installing carbs you wouldn't really be worried about that anyway, would you?

Tom

[BURN-BROS]

I would imagine that it has a more aggressive advance and/or more total advance.

If the Euro engines had a free flowing exhaust, fuel component differences, compression and intended use then they(Porsche) would alter that advance to take advantage of it.

Lets see if someone will post the two curves and the 73 rs dizzy to see the differences.

[Shuie]

The car is exempt. The engine was already setup for carbs.

I have an outside chance of scoring a complete big bore MFI setup in the near future so Id hope I could still use this freshly rebuilt distributor on the motor if I change the induction. I guess it would be easy enough to sell if I needed to go to a distributor with a vacuum retard device.

[Shuie]

Im game, how would I graph the advance curve?

[BURN-BROS]

Tom, you could run into too much advance at idle resulting in detonation during lower rpm acceleration.

Now you could recurve any dizzy to any curve you would like, such as a sc domestic to a sc euro spec. Ideally you should create your advance using a dyno so that you get the best solution for your specific engine. The curves set at the factory are used to cover all bases for all altitudes,gas, blah,blah,blah.

[BURN-BROS]

Just note advance and rpm every 500 rpm or find the service manual.

[emcon5]

To further muddy the waters:

2.7 RS advance curve:







78 SC advance curves:

[emcon5]

80 SC Advance curves




late SC advance curves:






Note that except the first RS chart the curves are advance at the distributor shaft, and distributor shaft speed, which is half the speed of the crank.

Tom

[RoninLB]

I think you must have the '80+ SC dizzy 'cause the '78-'79 is a counter clockwise dizzy?

The '80+ dizzy may have a radically too steep lower rpm advance curve for carbs. The posted chart is for US '80+ SC's. Not sure if the Euro '80+ SC's were curved differently? The 2.7 Carrera dizzy curve works nice for carbs.

[emcon5]

Originally posted by RoninLB
I think you must have the '80+ SC dizzy 'cause the '78-'79 is a counter clockwise dizzy?

All SCs the distributor turns bass-ackwards compared to all other 911s.

Tom

[BURN-BROS]

Shuie, apparently 1980 they changed to dual vacuum advance/retard. Just for the record.

[Shuie]

I'll get the part number from mine and post it here for reference