8BA loadamatic dist. with 2GC carb question

gearheadbill

gearheadbill

Senior Member
I have a newly purchased 34 pickup with an merc 8BA engine. I have not started to work on the truck yet; rather I am asking questions ahead of time to get a game plan for future.

This engine is an EAC with a stock 4 bolt flange intake manifold which has a 2GC Rochester carb. My question is about the potential for too much venturi vacuum from the carb, thereby "overpowering" the stock distributor; effectively providing "all in" full advance at idle/off idle with no advance curve up the RPM range. Engine is a fresh (under 500 miles) from a local reputable engine builder; hard starting and gutless under load. Certain to be more than one issue here but just wondering.

I remember having a similar but reversed problem. Engine had a chevrolet distributor and a stock Ford carb. Seemed like the carb didn't provide enough vacuum to advance the timing. My memory could be wrong about this due to old age...whatever.

Anyway, thanks for the comments.
 
There was a discussion on here a week or so ago about a related subject. IIRC, someone asked about running a 4 bbl carb with a Load-a-matic, and a couple of the guys who should know said if you used the ported vacuum from a 390 Holley, it would work. I don't know if a 2G has ported vacuum or not. While I am a great booster of 2G's on these cars, I have always used Mallory distributors so I have never had the chance to try this. I do know some of the 2G's I have used have a number of vacuum ports, one of which may be ported vacuum, so you may be able to make it work. I don't know, as I just cap 'em all off. Perhaps one of the carburetor experts on here knows and can point you in the right direction and tell you which version of the 2G and which port you should use. You're not dead in the water yet!
 
WOW! It's hard to believe how pervasive bad Loadomatic information is! The Load O Matic DOES NOT use only ported vacuum! It uses a blend of venturi vacuum and ported vacuum, controlled by the "spark valve", which adds in venturi vacuum as speed and load increase because ported vacuum drops to near zero as throttle opening increases. So with only ported (or even manifold) vacuum, at full throttle you will have zero spark advance. Instead, what you will have is low power and an overheating engine!
The original Ford and Mercury carbs have special internal passages to provide the proper vacuum signal. Other carbs do not, plain and simple! So either get an original carb or convert to a mechanical advance distributor such as the Chevy.
 
What can I say? Some people who should know say that it may work; don't shoot the messenger. This was just a suggestion that it may pay off if the O/P looks into it a little more. I'm not a real big fan of absolute pronouncements.
 
I have a later version Holley 94 with vacuum port that I may go with rather than use the 2GC that's on the engine now. Looking for all the opinions/input I can get at this time.
 
tubman said:
What can I say? Some people who should know say that it may work; don't shoot the messenger. This was just a suggestion that it may pay off if the O/P looks into it a little more. I'm not a real big fan of absolute pronouncements.
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Sorry tubman, it was not my intent to short the messenger! Rather, I was aiming at the source of such messages. I imagine it's possible to cobble up something to give some sort of spark advance when using a non-stock carb with a Load O Matic, but you won't get the right advance curve for all RPM and load conditions!
 
gearheadbill said:
I have a later version Holley 94 with vacuum port that I may go with rather than use the 2GC that's on the engine now. Looking for all the opinions/input I can get at this time.
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8 BA engine, Max 1 cam, single carb.
I'm running a Stromberg 97, together with a Chev distributor.
The Chev distributor is fitted with an adjustable vaccum advance together with a mechanical adjustable stop at the distributor. This adjustable stop is from Charlie NY. These 2 combinations at the distributor give the best application and power curve can be set up very easily.
Personally I was not happy with the performance of the Chev distributor when only running mechanical advance.
Phil NZ
 
I know squat about the 8BA/94 carb but I do know the 885 for the Mercs pretty well. They started out in 49 with a dual port vacuum both above and below the throttle plate. In 1950, they updated the set up with a small nylon check valve ball to "valve" between the two ports. One port was below (correction just above not below*) throttle plate vacuum and the other was venturi vacuum. This is the only valve in this particular system.
(* It is above the plate until the throttle is opened slightly which puts it just below the plate while the throttle is open enough.)

It may be possible to "adjust" the vacuum signal from a particular port on a non stock carburetor to get close but it is doubtful that the signal would be exactly like the 8BA/94 signal is through out the whole range of operation. It would be easier to modify a Chevy or Mopar distributor to work like one should than worrying about an old Load-O-Matic type. At least a person can use any carb or combo of carbs you want as long as it's tuned to work with the choice.
 
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Question: How much vacuum will there be at the ported vacuum port on a 2G carb at wide open throttle? Consider this: Imagine the 2G carb and Chevy distributor are still on the original Chevy, cruising at 60 MPH. At part throttle, ported vacuum is high so vacuum advance is at or near max. For sake of illustration, let's say mechanical advance is at 20 deg., and vacuum advance adds another 15 deg., plus 10 deg. initial. Now we go full throttle to pass someone. 45 deg. advance will cause severe detonation but at full throttle, ported vacuum drops to zero (or very nearly so) as does manifold vacuum, so vacuum advance goes away and timing advance drops to 30 deg.
Now, if we only have vacuum advance (LoadOMatic) and we just lost our vacuum signal (ported) what happens to the timing? It will retard! At a high enough RPM, air flow through the carb may increase enough to regain some ported vacuum but I doubt it would be the same as the venturi vacuum the Loadomatic was designed for.
Remember, venturi vacuum is what opens the secondaries on a typical Holley four barrel so it is a fairly strong signal.
 
40 Deluxe said:
Question: How much vacuum will there be at the ported vacuum port on a 2G carb at wide open throttle? Consider this: Imagine the 2G carb and Chevy distributor are still on the original Chevy, cruising at 60 MPH. At part throttle, ported vacuum is high so vacuum advance is at or near max. For sake of illustration, let's say mechanical advance is at 20 deg., and vacuum advance adds another 15 deg., plus 10 deg. initial. Now we go full throttle to pass someone. 45 deg. advance will cause severe detonation but at full throttle, ported vacuum drops to zero (or very nearly so) as does manifold vacuum, so vacuum advance goes away and timing advance drops to 30 deg.
Now, if we only have vacuum advance (LoadOMatic) and we just lost our vacuum signal (ported) what happens to the timing? It will retard! At a high enough RPM, air flow through the carb may increase enough to regain some ported vacuum but I doubt it would be the same as the venturi vacuum the Loadomatic was designed for.
Remember, venturi vacuum is what opens the secondaries on a typical Holley four barrel so it is a fairly strong signal.
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Thank you. This speaks directly to the question/problem I was unsuccessfully trying to ask. Under load the ported vacuum signal is lost and most "modern" carbs will not supply the venturi vacuum required by the Loadamatic distributor to keep the timing advanced.

Re-reading my OP...very muddled but I believe I see the issue more clearly. Thanks to all who chimed in. I need all (and more) of the help I can get.
 
gearheadbill said:
Thank you. This speaks directly to the question/problem I was unsuccessfully trying to ask. Under load the ported vacuum signal is lost and most "modern" carbs will not supply the venturi vacuum required by the Loadamatic distributor to keep the timing advanced.

Re-reading my OP...very muddled but I believe I see the issue more clearly. Thanks to all who chimed in. I need all (and more) of the help I can get.
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And how about if the ported vacuum port ( above the throttle plates) turns into manifold vacuum when throttle is opened . Direct manifold vac then the load a matic would keep the advance.

Some good speculation on this post the only way to tell is hook it up and drive it!!!:eek:
 
i believe the vacuum port on the 2GC on my 64 chev 283 is what Holly calls a "timed spark vacuum source" on their 390 CFM carb and that is designed work with a GM canister type vacuum advance, but i do not believe would work so well with a Ford "loadmatic" distributor. just my thoughts. i do know that the vacuum signal on the 2GC is non existent at idle buy do not know what the signal is at higher RPMs.
 
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BUBBAS IGNITION said:
And how about if the ported vacuum port ( above the throttle plates) turns into manifold vacuum when throttle is opened . Direct manifold vac then the load a matic would keep the advance.

Some good speculation on this post the only way to tell is hook it up and drive it!!!:eek:
Click to expand...

Seems to me that even though ported vacuum becomes manifold vacuum as the throttle is opened, at full throttle manifold vacuum drops to zero so the load o matic will drop the advance.
 
I may be off some here, but i "think" Charlie NY said"ij you want to use the load a matic & run a single 2 bl; run a 1 or 1 1/16 inch y block carb". I had one on my 8ba...worked good?!. Just say'n. m
 
I've been running a 2G for 3 yrs now, with a MSD distributor (HEI clone) running off manifold vacuum It's a great combination, a much better carb than the 94/2110's. If I were in the OP's position, I'd change the distributor to a GM style and never look back. Just think, no PV problems, no leaks, and depending which 2G he has, about a 30% increase in max CFM.
 
BUBBAS IGNITION said:
And how about if the ported vacuum port ( above the throttle plates) turns into manifold vacuum when throttle is opened . Direct manifold vac then the load a matic would keep the advance.

Some good speculation on this post the only way to tell is hook it up and drive it!!!:eek:
Click to expand...

Ross F-1 said:
I've been running a 2G for 3 yrs now, with a MSD distributor (HEI clone) running off manifold vacuum It's a great combination, a much better carb than the 94/2110's. If I were in the OP's position, I'd change the distributor to a GM style and never look back. Just think, no PV problems, no leaks, and depending which 2G he has, about a 30% increase in max CFM.
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Bubba: I have...NO power at all. It's a fresh 255cid. Should make the pickup have more "pickup" than it does, I would think.
Ross: I am convinced that this the way for ME (just me) to go. I'm placing an order with Bubba soon.
 
I've been running a 2GC on a bored out Merc intake on the 280 for the past 3 years with a Gm dist set up By Richard and the results are excellent. Been posting the numbers for years, it works.
 
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