Mopar Performance Distributor

[Houle #382]

Anyone running the Mopar Performance Distributor with the adjustable vacuum ? My nephew bought a 70 Cuda with a 440 and it has this distributor in it and he's been having issues with the car surging at cruising speed. It did have the vacuum hose hooked up and I had him unplug it and put a plug on the carb and that cured the surging but not sure where to set his timing or how by the vacuum canister adjuster. Do we put the vacuum hose back on I don't know, I never messed with a distributor with a adjustable vacuum like this.

 

[dla4567]

I use that distributor but don’t use vacuum advance.

 

[Houle #382]

Yeah once I told him to pull the hose off the carb and put a plug on it she ran much better. What do you have your initial timing set at and total timing. His 440 has the shitty heads so he can't go to crazy but he is running a aggressive Comp Xtreme Energy hydraulic roller cam # 23-712-9.

 

[dla4567]

Yeah once I told him to pull the hose off the carb and put a plug on it she ran much better. What do you have your initial timing set at and total timing. His 440 has the shitty heads so he can't go to crazy but he is running a aggressive Comp Xtreme Energy hydraulic roller cam # 23-712-9.

22* initial, 38* all in at 2200 rpm.
906 heads, high compression, 110 octane.

 

[Nacho-RT74]

The adjustable vacuum doesn't adjust the advance really, but the spring pressure over the diaphragm. Of course at the end it affects the advance at certain vacuum rate, but is not an straight adjustment.

The use of the vacuum is allways a debate.

 

[HALIFAXHOPS]

The adjustable vacuum doesn't adjust the advance really, but the spring pressure over the diaphragm. Of course at the end it affects the advance at certain vacuum, but is not an straight adjustment.

The use of the vacuum is allways a debate.

Adjustable Vacuum Advance | For A Bodies Only Mopar Forum

 

[440beep]

Pretty simple explanation link below. To dial mine in, I started by turning that internal hex nut counterclockwise a 1/2 turn, reconnect vacuum hose, go for a steady drive, if still surging, readjust another 1/2 turn. Keep adjusting until the surging stops, but remember to reconnect the vacuum hose each time.

http://www.cuda-challenger.com/cc/index.php?topic=37404.0

 

[Dragon Slayer]

Test the vacuum can with a vacuum pump/gauge. You may have a vacuum leak causing the surge. I have seen slow leaks that will pull the arm, but slowly bleed off.

 

[AR67GTX]

I’ve had the highway surging issue on a BB Corvette I own and ended up fashioning a stop to limit the amount of advance arm travel on the vacuum can to limit total vacuum advance to 8 deg. Pretty easy on a GM distributor but haven’t tried to do the same on a Mopar. I would look at the vacuum can and see if you can figure out some sort of stop that will bottom out on the bracket/housing to limit its travel. Maybe a small screw drilled into the arm or a collar with set screw over the arm. Adjustable is nice but if it just becomes guess work - with 38 degrees timing, and if your vacuum advance is pulling in 20 degrees or more on top, I would shoot for cutting travel in half IMO.

 

[AR67GTX]

Here is what I came up with on my GM distributor.

I don't know if it is just coincidental but several years after I did this and posted it on the Corvette Forum someone actually started fabricating a nearly identical bracket (a bit smoother and better quality) and selling them for a nominal price. Not sure if he got the idea from mine or just great minds (ha ha) think alike. Didn't matter, it's helped a bunch of guys out.

 

[Dragon Slayer]

The Perf Vacuum I have seen have been lower overall values. See what is stamped on the arm, if 8, that would be 16 total at high vacuum. If the spring pressure has not been set to keep it from reaching maximum given the engine vacuum.

 

[HALIFAXHOPS]

The vac advance on all mopar vac advances ony adjust the rate at which it gets to total vacuum, does not llimit total amount of advance, posted the expination link above.

 

[Dragon Slayer]

Understood Ray, but can't it put such a high force that the motor vacuum can't compress it fully? Some of the prestolite cans had arm values higher than max advance. The spring and spacers created a higher force for slower rate but also prevented full extension. I have not actually played with the mopar can much.

 

[HALIFAXHOPS]

Understood Ray, but can't it put such a high force that the motor vacuum can't compress it fully? Some of the prestolite cans had arm values higher than max advance. The spring and spacers created a higher force for slower rate but also prevented full extension. I have not actually played with the mopar can much.

kind of shows it all G You can crank it full ccw and it will barely move. Realy depends what the vaccum is. Really starts the advance when it goes to the min set then the highest say 15 it is full in always when testing them. I get what you mean though. But to set it like a mechanical stop no. I am working on that have a prototype I need to get made. and aso the pattent.

 

[Dragon Slayer]

Got it.

 

[HALIFAXHOPS]

Pics are great! Thats why the army made maintenace comic books!

 

[moparedtn]

Thanks for that pic, Ray. I've always wondered what was inside one of those.
BTW, I've always used the Direct Connection/Mopar Performance distributors on my 440 cars.
Fred has one on him right now, albeit with the vacuum advance plugged off - I haven't
gone through the process of dialing it in yet and he does surge at steady highway, so I reckon
it's allen wrench time.

 

[HALIFAXHOPS]

The MP's work ok just a reg distributor with light springs in it. you have to watch they have a realy fast curve to full mechanica advance.