Esoteric distributor question (sort of long)...

[djs]

I have a '75 2.0 914 which runs great. The motor is completely stock, except for early-style exhaust system. I recently acquired a 2.0 motor (GA series) from a '74, complete with all FI components (including brain).

Thinking I could get a bit more low-end grunt out of my '75, I swapped the throttle body from the '74 motor for mine, as it has the vacuum advance port. It does, in fact, advance my timing faster, and the difference in "seat of the pants" feel is very noticeable. I like it.

However, I also notice that I now "ping" at hi RPM/part-full throttle conditions, which leads me to believe that my total advance (centrifugal + vacuum) is now too much. (91 octane eliminates the pinging, but my car never pinged on 87 octane with the non-advance throttle body, so I'm not sure hi-test gas is the answer)

I also notice that the '74 distributor is a "205B", where my '75 is a "205A".

My questions for the forum:

Should the '74 throttle body be used only with the '74 distributor? Assumption is that the centrifugal advance curve of the '74 dist. is designed for use with vacuum advance, while my '75 distributor is not.

And, are the throttle body, distributor, and less restrictive exhaust the only differences between the GA series and the later GC series? In other words, are the basic engines the same?

Thanks,

Dan Schmitz

[Dave Bell]

From my limitted understanding, most of the 74's did not use the vacuum advance. They came from the factory with a few inches of hose attached to the vacuum advance port of the distributor and the hose went.... well nowhere!... so the 74's ran on centrifical advance only.... so it is surprising to me that the 74 throttle body you have, has both the advance and retard ports... if it only has one port... that port is the retard port and should be hooked up to the retard port of the distributor.... hooking it up to the advance side could result in some interesting running...hmmm...

Check with Dave Darling for a more authoritative opinion.

-Dave

[djs]

No, the throttle body has both a retard and advance port, and I'm currently using them both. It may be from a '73. I haven't verifed the engine number, but I was told it was from a '74 when I bought it.

The engine is quite a bit more responsive, but I'm waiting for Dave's input as to whether I should be running the early distributor with the early throttle body. If so, I will have to take it apart and clean it up, as the advance mechanism sticks.

But, as long as I run Premium 92 octane, pinging is non-existent (as are the dollars in my wallet

Dan

[John Rogers]

If the throttle body has ONE vac port, it gets hooked to the retard side of the distributor, this is to hellp pull the engine back to idle when you let off the throttle. If it has TWO vac ports, the one with vac at idle gets hooked to the retard side and the other side to the advance side of the distributor. Good luck.

[bowlsby]

My very early 1974 2.0 has a throttle body with 2 vacuum ports but...the retard port is soldered shut! I have heard that the 73 throttle bodies have both ports, and the 74's only had one...I speculate that because my car was an early 74 (august 73), that the factory just sealed up one of th ports out of convenience. My distributor has both mech advance and vacuum advance/retard diaphragm...I've been toying with drilling out or swapping out the closed vac retard port to see what happens...

[djs]

Well, my actual question was whether or not the early, dual vacuum port throttle body needed to be used with the early distributor that came with that throttle body due to the advance curve, and I will assume it does, since my '75 continues to ping at high rpm using the early throttle body but later distributor.

As far as I know, all of the 2 liters used a dual vacuum distributor, but only some had a signal to both diaphragms because only some used a dual vaccuum throttle body.

So, it stands to reason that since the distributor numbers changed over the course of 2 liter development, I should keep the throttle body together with its corresponding distributor, to ensure that the advance curve matches the fact that the early throttle body provides for vacuum advance.

Now that we're all confused...

[Joe Bob]

I seem to remember a thread on this over on the Renegade forum site....the dual advance and retard lines on the single ported throttle bodies used to drive the smog techs nuts....there was even an article on it in Panorama.

I had to help out a buddy, 'cause the smog nazi was insisting that both the lines be hooked up...it turned out that only one NEEDED to be hooked up and the other line simply was left to flop around in the engine bay....go figure.

As to pinging on your 75, use the premium...unless a timing change can eliminate it. Pinging will kill your heads...