Load-A-Matic Distributor - Did I just get lucky??

[amodel25]

I have a '51 Tudor with a 226 Flathead 6, .060" over, 2x1 Nicson Intake, Knudsen Head, home made split manifold, 3/4 regrind cam. I have a Petronix equipped stock distributor with a relatively new vacumm advance.

When I built this engine, 15 years ago, I had no idea what a Load-A-Matic was or horror stories about running multiple carbs with it, so I did. I started with 2 stock Holley 847's and ran distributor vacumm off of the front carb. Car ran great, good acceleration, 14 mpg, no problems. About 5 years ago, I changed over to Holley 1904 carbs and ran distributor vacumm off of a vacumm plate mounted under the front carb. Again, car runs great, good acceleration, 18 mpg on a recent 3,600 mile road trip at 65-70 mph (added an overdrive before the trip). Initial timing is set at about 4 degree advance.

Did I just get lucky? Is there still vast amounts of untapped power that I should be getting if I had a full mechanical distributor?

Any thoughts?

Randy

[jdl]

I can't understand how a load a matic can work off of manifold vacuum,
(vacuum plate under carb) seems like you would get way to much advance. you might be surprised if you try a combo mech.& vac. advance.
how about a mech advance dist from a later Ford six? I dunno?
I love the look of you engine...very nice.

[BUBBAS IGNITION]

Yep you got lucky ( in a good sort of way), with manifold vacuum applied to the vac diaphram the advance would got to full advance right after start up and stay there !
Many race cars are static timed that way and work very well ( wot most of the time). We do that on a Vertex mag with no mechanical advance , just pull the engine up to 3000 and adjust in xxx amount of degrees and tighten it down.
I personally wouldnt debate the facts of whether you would run better with a smooth mechanical advance curve with low advance at idle progressivily increasing with rpm.
If you dont have any problem with spark knock ( probably not with twin carbs + rich air fuel mix) or overheating ( often caused with retarded timing) then it must be working...
Seems like i have a shelf full of 223 six distributors in for change over from the loadamatic to full centrifigual from folks having problems???????

[Bruce Lancaster]

Now...assuming the thing is working, probably is with new can, it is running on manifold vacuum with NO access to venturi depression...so your curve may well be good at part throttle and cruise, but your vac at full throttle should be close to zero and it is hard to believe you have any advance then.
You cannot test a Loadamatic curve by revving it up in the driveway as that does not come even close to simulating load/vac when it is pulling the car...that will vary almost infinitely under different conditions. On a machine, it can only be tested against arbitrary vac settings provide by machine.
So...I think only practical way is to get a GOOD SENSITIVE vac gauge and Tee it into line to distributor. Record vac at different driving conditions (Hint: First one to look at is full-throttle acceleration), then park the car, apply those vac readings with a hand pump while car idles using SAME gauge and with line plugged off at manifold end and see how much advance results with a timing light. I think you will see about nothing on both vac and advance ubder hard accel or high load like going up a steep hill.
The hotrodders who first got hold of Loadamatic Fords discovered that many would actually go 0--60 faster at part throttle than when floored, because even with proper venturi hookup on a new stocker full throttle advance was very weak. With ZERO vac being applied your advance would work out to...

[amodel25]

Bruce, the car is sidelined right now with a minor clutch issue. I'll try the vacumm gauge thing when its back on the road and report back.
Thanks,
Randy

[BUBBAS IGNITION]

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Originally Posted by Bruce Lancaster

Now...assuming the thing is working, probably is with new can, it is running on manifold vacuum with NO access to venturi depression...so your curve may well be good at part throttle and cruise, but your vac at full throttle should be close to zero and it is hard to believe you have any advance then.
You cannot test a Loadamatic curve by revving it up in the driveway as that does not come even close to simulating load/vac when it is pulling the car...that will vary almost infinitely under different conditions. On a machine, it can only be tested against arbitrary vac settings provide by machine.
So...I think only practical way is to get a GOOD SENSITIVE vac gauge and Tee it into line to distributor. Record vac at different driving conditions (Hint: First one to look at is full-throttle acceleration), then park the car, apply those vac readings with a hand pump while car idles using SAME gauge and with line plugged off at manifold end and see how much advance results with a timing light. I think you will see about nothing on both vac and advance ubder hard accel or high load like going up a steep hill.
The hotrodders who first got hold of Loadamatic Fords discovered that many would actually go 0--60 faster at part throttle than when floored, because even with proper venturi hookup on a new stocker full throttle advance was very weak. With ZERO vac being applied your advance would work out to...

Good point now look at it with the factory loadamatic specs.

0 vac=0 advance
.4 inch of vac= 1-3 degrees
1.4 inchs of vac= 5-6
2.9 inches of vac=2.9 degrees
4.1 inchs of vac= 10-11 degrees

Pretty hard to maintain that low of a vacuum reading ( at least for very long) i think it would just about be full advance when running all the time....

[Kube]

Bruce and Bubba... you two guys amaze me with your knowledge. I always look over what you two write and continue to learn. Keep it coming...

[amodel25]

Bruce and Bubba - The two guys I hoped would respond.

[Ol' Ron]

The problem with people is, if it seems to be running right, then it is so why putz with it. Richard and I have been testing ignition advance curves under driving condition in both power acceleration and cruise. The results conferm that both centrifical and vacuum are necessary for Good total performance. Some distributors like Mallory and MSD with out vacuum, run the centrifugal over the best WOT performance in an effort to improve economy. But with the addition of a vacuum advance a properly tuned engine can produce both power and econmy. The reason is a lean AF in cruise demands more advance and too much centrifugal kills power at WOT.

[Bruce Lancaster]

...and on a flathead cruising without vac advance all the wasted gas is busy cooking off as it passes through the water jackets! A Flathead has to to be worst engine in the world to run retarded under any circumstances.

[Bruce Lancaster]

How the evil Loadamatic Holley thing works, approximately: The port it is supposed to connect to on the Ford carb is drilled into the carb venturi and down into the throttle body to right above throttle plate. The lower connection is normal "ported vacuum", manifold vac that becomes available to distributor when the throttle comes off idle. Vac here is high under low load, cruising, part throttle, most driving. This part works quite well if can is good so car will likely perform correctly in most driving.
At high load, full throttle or close to it, the parted vac drops dead but high airflow through carb brings venturi pressure drop to its highest. This rather weak force is supposed to give the engine its full-throttle advance (which needs to be less than part throttle advance). This portion of the works is very frequently inadequate even on stockers in good condition, as force available is small, and a car with the distributor hooked to manifold vac will of course get about nothing at full throttle or hard pulling.
The distributor has spring adjustment to tune advance, but on a distributor machine the specs used are for vac delivered to certain levels by the machine, and the car especially at full throttle frequently cannot achieve the rated pressure drop in venturi.
Ford and Holley developed this stuff beyond the basic setup used on '49-53 Fords... there were some that had a little shuttle ball between the two passages and heavy trucks that had separate diaphragms for the 2 different sources...I don't think any version was particularly good.