Vacuum advance removal, is it possible?

[pishta]

Vacuum advance works great on resorations, ie. STOCK cam cars with STOCK carbs set for minimum NOx ans CO emissions, and STOCK intakes and log manifolds...no place on a performance or mild build. youll be fighting the cam, carb, EGR dohickeys, vacuum water temp fitting, etc. Dump it if you have a somewhat modded motor.

 

[oldkimmer]

................Now u see how easy that was, thats what i told u 2 do from the begining........good job........kim.............

 

[604]

Yep,
Just took a while to get brave enough to do it. LOL

I think I will get a new lean bun pick up plate assembly. I figure it might be a little weak as it is an original 1978 one. Found new ones are really cheep.

................Now u see how easy that was, thats what i told u 2 do from the begining........good job........kim.............

 

[twofosho]

Quality control and stability issues aside, a working vacuum advance negates the need for a high initial (static) timing setting (less starter bucking, easier starting) and gives the tuner another tool to select the proper timing for any combination of load and RPM.

If you really want to add fuel to the fire (pun intended), you can get into dual pickups for stretching dwell, and reworked Ford reluctors with grooved timing veins for multiple coil discharge. You can also machine multiple roll pin grooves in the reluctor for phasing in unison with the rotor, and use an old MSD Adapt-A-Cap (Ford cap) to prevent crossfiring.

 

[67Dart273]

.................... a working vacuum advance negates the need for a high initial (static) timing setting (less starter bucking, easier starting

Uh..........................!!!NO!!!

 

[RLF Cuda]

The following was posted by Rick Ehrneberg of Mopar Action:
Tech Question
bob santarsieri, schaumburg, IL, 71 plymouth road runner 440

I have a msd pro billet distributor and msd 6al box. What would be the best setting for the distributor? Right now it is set at 2 heavy silver springs and silver bushing per the instructions. It starts to advance at 1400 and goes to 5500rpm then levels off. What would you suggest. 440ci, 0.040" overbore, 0.474" purple shaft cam, Hedman headers and 3.23 gears. Just street driven. Thanks for your help.

Bob, assuming sufficient octane vs. C.R., you need a curve something close to this:

Under 1400RPM - no advance - set initial at 15 degrees BTDC
2000 - 10 dergees mech (25 total)
2500 - 20 degrees mech (35 total) - all in.

Plus, at LEAST 15 degrees of vacuum advance under light throttle (50 deg. total, 52-55 better).

If it currently doesn't go to full advance until 5500, you're giving up lots of power.

If it currently has less (or no) vacuum advance), you're giving up LOTS of fuel economy and fouling plugs.

Rick

http://www.moparaction.com/Tech/quest/SLOW_CURVE.html

As a fuels chemist and having worked in the fuels and lubricants areas for 30 years, I can say that Rick is exactly correct. Vacuum advance on any engine is necessary for proper operation under light throttle.

Here are the issues that can help people with problems:

If the distributor is not in a good location, move the oil pump drive gear a notch or two, but the factory position works for most people.

If you have irratic spark timing, get a new distributor. Vacuum advance doesn't impact this.

Always use ported vacuum. Never hook the vacuum line to the manifold or the carb port that has vacuum at idle. This will pull the vacuum unit on instantly and cause too much advance at idle and very low speeds, leading to detonation and poor operation.

Use timing tape to KNOW what you advance looks like, and verify the TDC mark on the ballancer. This is critical in older motors as the ring can rotate on the hub making all marks useless.

Set total timing to 36 degrees for most stock and mildly modified motors. Power tune at the track for optimum MPH (carefully, to avoid detonation). If timing needed for best power approaches 40 degrees, look at the entire system for issues.

I run a 30 year old electronic ignition with a Chrome box and the timing is steady using a timing light (+/- 1 degree). This should be OK for most mild engines. more accuracy requires a high end distributor with roller bearings for movement and shaft alignment.

Good Luck,
Bob

 

[RedFish]

""If the distributor is not in a good location, move the oil pump drive gear a notch or two""

What difference could that make other than where the wires are placed on the cap ?

 

[67Dart273]

...............If you have irratic spark timing, get a new distributor. Vacuum advance doesn't impact this.............

This is the second time in this thread that someone has claimed this, and...............

IT IS NOT TRUE when speaking of a high performance engine running a fair amount of RPM (5-8K) with either a single point or breakerless Mopar distributor.

THIS IS a well documented weak point in these distributors. I no longer have the tons of rod mags I used to, but anyone who has ever done much work with a distributor machine knows just how poor these distributors are when compared to a dual point or decent aftermarket unit. "Been there, done that."

In fact, the entire Mopar V8 dist. drive system is a "little weak" when compared to the traditional GM designs.

If you look back through the years of Mopar racing, there are all kinds of experiments with stuff like rubber timing belt driven distributors, etc, all trying to solve the poor design of the original "stuff." This of course was back in the days before crank triggers came along

 

[805moparkid]

Quality control and stability issues aside, a working vacuum advance negates the need for a high initial (static) timing setting (less starter bucking, easier starting) and gives the tuner another tool to select the proper timing for any combination of load and RPM.

If you really want to add fuel to the fire (pun intended), you can get into dual pickups for stretching dwell, and reworked Ford reluctors with grooved timing veins for multiple coil discharge. You can also machine multiple roll pin grooves in the reluctor for phasing in unison with the rotor, and use an old MSD Adapt-A-Cap (Ford cap) to prevent crossfiring.

my motor likes 30 locked... no kick backs or anything, hot or cold...

 

[FISHBREATH]

A bit off topic, but I seem to remember that "back in the day," racers used dual-point distributors, but with the points wired separately with a manual switch. One set of points was set at a higher advance than the other and the driver would "switch" them at some point down the track.