Vacuum advance w/ solenoid

[tak419]

All good reading..
So what is the purpose of the single wire solenoid that advances the timing 6.5. I wouldn't think you'd want to advance timing on a heat soaked engine when starting it..and the single wire is only energized on start.

 

[72RoadrunnerGTX]

 

[Ron H]

Interesting...any quick comments on how this impacts the extent more or less of off the line launch?

 

[383man]

Mopar used a solenoid at the vacuum advance to do both retard and advance the timing at certain times. Some used the retard solenoid that was grounded by the idle screw so it retarded timing some at idle. Some also had the advance solenoid that was hooked to the starter relay and only advance the timing some during cranking. And that was because they were retarding timing a lot during the emission years so this advanced the timing a bit for better starts. Ron

 

[RJRENTON]

The retard spec for that solenoid is 5 and half degrees (Service Procedures, page 9A-5, ’70 FSM). For ’70-71, the retard solenoid was a federal application, not just California spec cars. There were other add-on systems specifically targeting NOX for California spec cars that restricted vacuum advance under certain conditions, starting in ‘71.


View attachment 758837

YES.....YOU ARE 100% CORRECT IN THE OPERATION. Post #19 says its purpose (retard device) is to reduce NOx emissions. Its purpose is increase combustion chamber temperatures to reduce Carbon Monoxide and unburned Hydrocarbons at idle and low speed operation . The formation of NOx occurs at ~ 1200°F, then exhaust gas recirculation (EGR) is added to the incoming fuel charge to moderate combustion chamber temp to inhibit NOx formation. EGR cripples performance but helps (?) the atmosphere. Isn't modern technology (of the day) wonderful.....stumbling, hard hot starting, poor fuel mileage, dieseling on shutdown, etc.... Just my opinion of course.
Bob Renton

 

[Dibbons]

Was this "system" used on any small block motors?

 

[HALIFAXHOPS]

Not that I have seen yet but did not look into it I know the 340-6 has the solenoid and bracket. Big block it retards at start on the HP motors for easier start, most of the others it advances it at start. Hard to keep track of. I go by the box color if it was not changed. White/tan advances, black retards that's the two wire ones then the single wire no box is off the starter circuit and advances off the starter circuit. Real pain in the *** for me at least. That thread I linked covered most of what we are posting now.

 

[HALIFAXHOPS]

Any idea if that whole system is just a Mopar thing? Just curious. I know the idle solenoids are on all.

 

[RJRENTON]

I've worked on Chevy, Pontiac, OLDS, Ford. GM liked "auto thermac system - AIR air injection reactor systems, which additional air was injected as the exhaust exited the cylinder...the premise was to after burn any unburned Hydrocarbons....in reality it just DILUTED the exhaust gas to make it pass emissions, much external plumbing . Ford used both vacuum advance AND vacuum retard on the same distributor controlled by thermal vacuum switches.....very confusing operation. Some used air pumps also Mopar used this vacuum advance/electric retard mechanism on both LA, B, RB engines except the HP engines, but configured for LAs CW rotation. The Hemi auto trans (?) used a vacuum device to advance the distributor during coast down to conttol HC & CO emissions. Mopar started using air pumps in the middle 70's. Then came the catalytic converter in 1975....all makes and models ....and the rest is history
Bob Renton

 

[tak419]

I have an NOS with tan two wire box and it retards the timing.

 

[HALIFAXHOPS]

There goes that theory! Thanks for the info. Back to part numbers.

 

[pjm8047]

I replaced the original holley 4160 on my 71 rr with an edlebrock carb awhile back and the distributor solenoid wires are just hanging out there from distributor advance unit. Would that effect the function of the vaccum advance?

 

[HALIFAXHOPS]

Will work just like a normal vac advance. Man this got a boost

 

[pjm8047]

What should the timing be set on a stock 383 auto? The 71 manual says 2.5btc but thats with the solenoid hooked up.

 

[Ron H]

With this setup you're running mechanical vs vacuum advance. There are pros & cons and will get some varying opinions. It's not advised to run this way for street use as it impacts gas mileage and emissions, which are ahh not a biggy with muscle cars. Some say this affects engine temperature from running a richer mix of fuel. An improperly adjusted vac advance or out of curve, can cause miss-firing at various RPM's. I'm running without it for now and have for sometime as my engine runs better until such time I replace my advance module (the adjuster isn't working).

 

[HALIFAXHOPS]

I was just going to post near the same. Lots of different info out there on them. The original intent of it was anti dieseling on shutoff. I really don't get it, the ignition is off I do get that the solenoid on the carb retracts for it. I prob have thrown out 20 of them either the solenoid is bad or the vacuum side is bad. NOS are a crap shoot also one side or the other is bad sometimes. As for your timing I would set it where it starts and runs best, probably no rea documented answer on that.

 

[72RoadrunnerGTX]

The '71 distributor retard solenoid has nothing to do anti-dieseling, the Idle speed solenoid addresses that. The retard solenoid was strictly to lower tail pipe emissions at hot idle to meet the emissions requirements of the day, nothing to do with performance. Do yourself a favor and disable the retard solenoid function or replace the retard/vacuum advance unit with a straight vacuum advance unit and tune the timing to the what the motor wants for best overall performance.

 

[RJRENTON]

The '71 distributor retard solenoid has nothing to do anti-dieseling, the Idle speed solenoid addresses that. The retard solenoid was strictly to lower tail pipe emissions at hot idle to meet the emissions requirements of the day, nothing to do with performance. Due yourself a favor and disable the retard solenoid function or replace the retard/vacuum advance unit with a straight vacuum advance unit and tune the timing to the what the motor wants for best overall performance.
View attachment 935516

EXCELLENT EXPLANATION AND ATTACHMENT.....WELL PRESENTED. Easy to disable..... As I recall, Ford used a vacuum retard AND vacuum advance diaphragm on some engine combinations. The system was controlled by a forrest of vacuum hoses, thermal vacuum valves and the vacuum delay devices....a real PITA.
Just my opinion of course.
BOB RENTON

 

[Dibbons]

My vacuum advance on a 1000 mile road trip was defective and my four-barrel (AFB) 318 burned a lot fuel because of that problem (found out after I arrived home)>

 

[HALIFAXHOPS]

EXCELLENT EXPLANATION AND ATTACHMENT.....WELL PRESENTED. Easy to disable..... As I recall, Ford used a vacuum retard AND vacuum advance diaphragm on some engine combinations. The system was controlled by a forrest of vacuum hoses, thermal vacuum valves and the vacuum delay devices....a real PITA.
Just my opinion of course.
BOB RENTON

Did one of them for a friend, One of the reasons I only do Mopar's!