Anyone know the stock advance of a 964 distributor?
 

posted on main board

http://forums.pelicanparts.com/showthread.php?threadid=166571

The advance is in the brain
 

The 964 distributor advance mechanism is designed to keep the rotor lined up with the cap electrodes. As the brain ( ecu) inputs advance the rotor changes position to keep the contacts in line . I believe that mechanism has about 12 degrees of movement. That translates to something like 24 degrees of engine advance.
Given a static advance of 5-7 degrees that would give the engine 29-31. I repeat this is not a proper curve. I believe the 964 ECU can put up to 44 degrees of advance in and with the program and knock sensor removes what it doesn't need.

Ok now I'm really confused:

From Henry's reply it looks like I can get about 29-31 degrees of total advance - which should be enough for my application.

Then Chris replied: (in main board thread)
"The 964 distributor doesn't have any advance. Starting with the 3.2, ignition timing was done in software. The 3.2 distributor has some mechanism in there that looks like it responds to RPM but it's not an advance mechanism. 964 distributors may have something similar, I can't remember."

Henry: does the mechanism in the 964 dist'r provide advance in response to RPM increase? If not, then I assume I must put all of the internals of my present dist'r into the primary cap side.

What mods do I need to make to the offset secondary cap side? - which appears to have a bob weight set up as well.

I would like to simply send the thing to Supertec and be done with it - but seeing as I'm in Australia it would be nice to do the mods here and thus be able to fix it in the future should the need arise.

ps: the class rules for my car do not allow any ECU assistance

The dist does advance with RPM but not with an advance curve that is conducive to proper power output. The curve is linear. It is a straight advance with no consideration for engine fuel/ignition needs. If you put a signal generator out of an SC in one half of the distributor it will make spark and it might even run, but with some sense of engineering or anything like optimum output , I think
not.
If I remember correctly some 935 dist had no advance . They just it and forget it. I think at 24 degrees.
It just dawned on me that MSD has a CD box with fully programmable ignition curve. Perhaps that's your solution.

Thanks again Henry,

I see a lot of pics of Historic/Vintage class race cars in the US using 964 dist'rs. I would assume that computers are outlawed in those applications as well - do you know how they get their twin plug motors to run?

Let's see, I guess no one cheats in vintage racing. Using this as a given, I assume they add a signal generator (911SC) and recurve the dist ? Change the weights and change the springs and with some luck, who knows ?

That's pretty much our plan - try to replicate the curve of my 2.7 RS dist'r with similar weight and spring sizes.

Thanks again.

That's correct. Some twin-plug distributors like the ones used on the 935 had no advance mechanism built in.

-Wayne

Although I haven't done it myself, I've heard that you can transplant the guts from a 2.7 distributor into a 964 distributor. Then you have to modify the case to be able to change the static timing...

-Wayne

More than meets the eye
 

I have done this conversion for Chad Seiva when he converted Dennis Aase's 2.5 liter IMSA car to 3.6 MFI engine for club racing. We had one hell of a time getting it to work. The only guts that fit this dist (3.6 twin rotor) were removed from a 1977 3.0 Turbo distributor. The pointless system similar to an SC had to be fabbed in. We used one trigger to operate both CDs. If memory serves me correctly, this was done back in 1987 or 88 so it's not that fresh. If this distributor is to be used on an early car, more than just slotting the hold down plate is needed. You must either change the crank gear to match the dist or the dist. gear must be changed to match the crank gear. The dist. drive gear on the 3.6 dist is not the same as the drive gear on the 2.7 and earlier.

Re: More than meets the eye
 

I think the one I'm thinking of used an Ignitor breakerless ignition.

-Wayne

A mate has already fitted one to his 2.7 - the mechanical bit was easy: fit the new drive gear, grind off the mounting tab, and machine up a clamp with a slot. The slot allows the static timing timing to be set like the original distr.

However, he has wired the internals solid and controls his timing with a little magic black box. My challenge is to get the internals to work. I'm hopeful that the SC bits will fit and then we just play with springs/weights to get the curve right.

Ryan, what about using a converted single plug distributor modified to take the twin (12 lead) cap like the one in the Anderson book? Or is this just too expensive an option? It seems you may have to use something that is closer to the "factory" method in order keep the car period correct.

PS I've seen the cost of a genuine twin plug dizzy.... Ay Currumba!

Hi John,

I initially wanted to go this route but the main downsides are cost (at least AU$1000 for the cap alone) plus you have to custom machine a mounting plate etc. The 964 set up is relatively cheap and all the spares are off the shelf.

Yowza! Good luck....

Steve Weiner at Rennsport Systems does this conversion using the trigger from a SC donor. I don't know what he used for advance, but IIRC mine has about 16° of mechanical advance.

http://forums.pelicanparts.com/uploa...1060054453.jpg

On his conversions, you set the timing by rotating the trigger inside the distributor. It is more of a hassle than simply rotating the dizzy body, but once you set it you don't really need to mess with it again.

Honestly, even if you did make a timing slot around the mounting stud (which BTW needs to be longer than stock), there isn't much room to rotate the distributor body to set the timing. It is pretty tight.

http://forums.pelicanparts.com/uploa...1069134785.jpg

Tom