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By DANIEL TINDER - 18 Years Ago
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While the 'hot rodders" might consider this question mere "mental masturbation", those of us married to the original, obsolete system might be interested:
Recently, someone mentioned that a longer duration camshaft would reduce manifold vaccum, and implied a resulting loss of spark advance on a Loadomatic distributor/carb combo. If the signal to the diaphram is a mixture of manifold/venturi vaccum, then the more important performance factor (acceleration) would depend on the venturi signal, as manifold vaccum would seem inconsequential at WOT. In fact, one of the problems with the LOADOMATIC system when initial advance is set by ear is too much advance at cruising (no load). If an early distributor was "race tuned" on a SUN machine (weaker springs), wouldn't the reduction in manifold vaccum actually cure the rough-running-at-cruise problem without affecting the enhanced, venturi-driven performance curve?
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By 46yblock - 18 Years Ago
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Arent WE getting a little deep ? Seems like the pre 57 performance distributors had either larger diaphragms, or double diaphragms to compensate for the lower manifold/venturi pressures.
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By pcmenten - 18 Years Ago
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Dan, the early distributors don't have springs. As Mike mentioned, they had two diaphragms. I'll bet the dual diaphragm design worked beautifully in a new, stock engine, but the advance rate was not tunable the way the centrifugal advance system is.
As I'm sure you know, the centrifugal system used weights, springs, and slots to adjust the timing, rate, and limit of spark advance. This tuning was further modified by ported manifold vacuum to a diaphragm that could add advance under light loads.
I've never studied the dual-diaphragm system, but I'd guess it can be tweaked. Is somebody supplying new dual-diaphragms for the early distributor? I have some early distributors but the diaphragms leak.
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By Hoosier Hurricane - 18 Years Ago
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I have read the installation instructions for the installation of the '56 dual four kit supplied by Ford. It included instructions for installing the different vacuum advance and return springs, so obviously the system can be tweaked. I would guess the new diaphragm had at least one bigger chamber and the springs weaker to compensate for the reduced vacuum signal. Also, they connected one diaphragm to the front carb and the other to the rear carb. John
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By DANIEL TINDER - 18 Years Ago
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I guess I should study the '56 dual-diaphragm Loadomatic system for a clue to the relationship between manifold vaccum and advance. It could have been Ford's attempt to correct the rough-running at low-load limitations and improve the drivability of a performance-tuned pre-56 single setup? (The increasing availability of high-octane gas and demands of T-bird/police customers must have tempted Ford mechanics to crank-up the ultra-conservative factory initial advance settings). Also, I don't think the '56 312 camshaft duration changed from my late '55's 292.
FYI: The '55 distributor DOES have springs. The tension is adjustable by turning eccentric attaching posts. I believe one spring is weaker than the other, which allows fine tuning. A performance advance curve would require a considerable reduction in tension from new springs, but weaker ones only MIGHT be required (depending on the adjustment range). As the ONLY other variable in the factory Loadomatic setup, the delicate ballance between manifold and venturi vaccum would have been critical in dialing in an RPM advance CURVE (inscrutable). I assume mid-50s shade-tree rodders installed some sort of stop-screw to limit total advance.
Easy to see why Mallory centrifical distributors were so popular back then.
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By DANIEL TINDER - 18 Years Ago
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Rather than me coughing up $30 for a '56 service manual (my car is a '55), maybe someone out there who has one would scan & email me (dantinh62@kconline.com) the page(s) that explain the operation of the dual diaphragm advance mechanism? Or, if you know that the '56 Holley teapot manual supplement (CM56) has the info, let me know and I will send for it. Apparently, there is no '56 supplement available for my '55 Holley distributor manual.
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By 46yblock - 18 Years Ago
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I think you are right Daniel, regarding the mechanical stop used by 50's guys. It has been suggested I solder in a mechanical stop on my 57 and later distributor, so that the amount of vacuum advance is reduced.
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By DANIEL TINDER - 18 Years Ago
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46yblock,
I MIGHT have an old HRM article (with photos) with details on how to do that. I'll look for it.
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By 46yblock - 18 Years Ago
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Daniel I would appreciate it. When Bill the Super Mechanic was helping me with my distributor problem the other day, he felt the vacuum advance was going to far. Mike
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By pegleg - 18 Years Ago
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Mike, You can (or could) get different cams that had differing amounts of travel. they simply install in the distributor over the pins. Something in the range of 8 -12 deg initial with a total in the mid thirties seems to work out best.
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By 46yblock - 18 Years Ago
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pegleg (7/25/2007)
Mike, You can (or could) get different cams that had differing amounts of travel. they simply install in the distributor over the pins. Something in the range of 8 -12 deg initial with a total in the mid thirties seems to work out best. Hmm. Me not comprehend. Cam as in the vacuum mechanism? If so, these are the same vacuum units (post 57) that were used in post Y years arent they? And if so, seems they should be available. Mike P.S. Daniel sorry about the hijack. I guess you werent gettin deep at all . Thanks for starting the thread and I will shut up.
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By Hoosier Hurricane - 18 Years Ago
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46yblock: Why don't you want to upgrade to a later distributor, you can dial in the advance curve you want for performance, and let the vacuum advance help your fuel mileage? John
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By pegleg - 18 Years Ago
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Mike, Whoops, you're right. No springs in a loadamatic. And John, he likes original, even if it didn't work!
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By 46yblock - 18 Years Ago
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My distributor is from a '59. Maybe next year I can save enough to buy a new one. Bill thought that the amount of advance provided by the vacuum was too much and that a limiter should be put on the plate.
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By Hoosier Hurricane - 18 Years Ago
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The '59 would not be a loadamatic unless it is a 6 cylinder. If the inlet to the vacuum control is hex shaped, about 11/16" hex, the tip of the control will unscrew, and there will be a spring, some spacers, and maybe some washers inside. The long spacer inside the spring limits the amount of advance, the spring and washers controls the rate. Lengthening the inner spacer will limit the amount of vacuum advance. John
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By DANIEL TINDER - 18 Years Ago
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Mike,
I'll look for that article anyway (even if your distributor is NOT Loadomatic), as I will likely need it myself someday. I'm always trying to track down local rumors of someone with a mint-cond. SUN machine to sell cheap! Race-tuning a Loadomatic distributor seems like a great plan for killing bleak winter days.
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By 46yblock - 18 Years Ago
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I know my dizzy isnt a Loado. Probably should not have confused the thread with reference to it. I was just agreeing with one of Daniel's thoughts about the Loadomatics likely being tuned by hot rodders in the 50s with screws limiting advance. Basically that was what was suggested to me to control the amount of vacuum supplied advance in my 59 model. It could be run with the vacuum line disconnected, but as I understand it that would have a bad effect on mileage. Sorry about the confusion.
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By Hoosier Hurricane - 18 Years Ago
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Try running without the vacuum advance. It may not make much difference in mileage. In the early '60s I had a '56 Fairlane with a 312, mild cam, centrifugal only distributor, 2-4s, 4.27 gear, OD. I got 22 mpg on a trip on a toll road, didn't believe it, checked on the way back, got 21+. John
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By DANIEL TINDER - 18 Years Ago
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Update:
Couldn't find article with photos on mechanical stop for Loadomatic (did I imagine it?). Did find recommended performance Y-block ignition curve though. Since PROPER set-up on a specific motor would likely require a lot of trial & error dyno work (who would bother?), and even with a Sun machine, the inscrutable Holley Loadomatic venturi/manifold vaccum signal would be near impossible to calculate/dial in, it would require a lot of REALLY educated guesswork to achieve the same curve.
Looks to me like you could just drill the dist. housing and install a stop bolt that contacted the eccentric spring-post, after determining the desired max. advance/degree point-plate position (from curve specs.) on a strobe machine. You could then loosen the advance springs and crank up the initial timing by ear safely, until trial & error produced the best acceleration result? (1956 all over again)
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By DANIEL TINDER - 18 Years Ago
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After THOROUGHLY studying the '55 Loadomatic operation manuals, I have come to the conclusion that the reduction in manifold vaccum produced by a long-duration camshaft would NOT have any discernable effect on the low-load advance, as the spark control valve in the carb which regulates that signal is designed to operate (and pass vaccum) at such a low level.
In fact, if John is correct about running successfully without a vaccum diaphragm (cetrifugal only), then the only obvious way to hop-up a Loadomatic system (aside from an advance-limit stop/increased initial timing) would be to merely plug the carb manifold vaccum signal passage to the throttle bore, and set a more performance-oriented spring curve on the SUN machine using venturi vaccum/engine speed data only, calculated from the factory specs. It should then imitate a cetrifugal advance system.
"Loadomatic" was apparently a very successful system engineered by Ford to extract the best performance/enonomy (for the general public) out of the poor grades of gasoline generally available at the time. It WORKED well within it's design limitations!
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