While boring out my Mercury intake to fit my Rochester 2G a hole appeared in the intake below where the carb will sit as shown in the photo attached. Is this going to create a vacuum leak? And, if so, how to plug it?
I would mix up some jb weld matching the substance of the intake(steel/aluminum) gently filling the hole in question and trying to form a uniform round thin skin to conform to the “general” roundness of the bore area in question and then “gently” sand out the extra leaving a fairly smooth wall of sealer. Should be fine, doesn’t have to be perfect, just seal the hole in question and make the repair relatively round like to original hole.
Not familiar with Flathead intakes, but if the hole goes into the plenum or a runner without it actually venting outside the intake manifold you really shouldn't have to do anything.
Plug it. Even if it goes into the heat riser or some other p***age that is completely blocked off, eventually said p***age will fill with fuel and that could result in an unwanted thermal event.
> While boring out my Mercury intake to fit my Rochester 2G a hole appeared > Prolly woulda got more turbulent atomization and go faster with stock bore. So sleeve it back to the way it was with aluminum tube from HomeDepot. Go faster again. Prolly as fast as a 94 or 97.
Those 4 bolt intakes aren't crazy expensive, I think I might just look for another one. I'd be too worried about any repair that could be made that far down deep. I feel like an adapter/riser would be better suited to this job than trying to bore it out to match with a die grinder.
As Jack mentioned earlier, could you bore it out even bigger and then press/Loc***e a similar material sleeve into it. Providing that there will be solid metal left around the hole to help seal it up.
The late "Ol' Ron" on "The Ford Barn" said that's what they had to do back in the day to run a 2G on a stock Ford manifold. I've bored several Merc manifolds to 1 7/16" with no problems. Due to the ongoing scarcity of small base 2G's, I'm playing around with some Carter BBD clones with the same base bolt problem but 1 1/2" throttle bores. It should be interesting. As to the hole in the manifold, I don't remember ever seeing one. I do have a couple of unmolested Merc manifolds and will check when I go to my shop tomorrow. I don't believe it should be there, as it is low enough to break into the exhaust heat chamber around the base of the carb. Connecting the exhaust system to the intake system in that manner doesn't seem like a good idea.
I think a little basic math is in order here, as you seem to have forgotten the role of exponentiation in these matters. The one common figure I have is the throttle bore sizes of the various carburetors concerned. I believe this to be quite indicative of the amount of air fuel mixture they will p*** in a certain period of time. Therefore the relative areas of the throttle bores should give us a pretty good idea of the amount of air/fuel mixture a given carburetor can supply to an engine. Let's look at 4 different carburetors, the 94/97 (used on Fords), the Holley 885 (used on the early fifties Mercury's), the small base Rochester 2G (used on Chevy 265's and 283's), and let's throw in the Carter BBD (used on late model Chrysler Corp 318's. Here you can easily see that the 2G has almost twice the throttle bore area as the 94/97, while the BBD is twice as big. Even the 885 has 66% more throttle bore area that the Ford carburetors. No wonder they used them on Mercury's. The interesting fact is that the 2G is almost 10% bigger than the 885 it replaces on these manifolds. despite having only a 1/16" increase in bore size. This is why boring these manifolds out is so important. One last error. The introduction of turbulence in the air/fuel mixture should occur in the combustion chamber of the engine (thus all of this discussion of quench). The role of the induction channels is to deliver as much fuel as smoothly as possible. Introducing obstructions to this flow will only slow it down and perhaps even cause the fuel to condense out of the fuel/air mixture.
@tubman Can you put the table up on your monitor/screen, then take a screenshot of that. Then saved as a jpg, you should be able to post it here on the forum.
I finally got around to checking my spare Merc manifolds. None of the three I have (2 cast iron and one aluminum) has a hole in that area, so it must be a casting flaw. Since it is probably through to the exhaust heat chamber, any repair should be carefully done. I would enlarge it until I got to solid metal and then use high heat epoxy designed for such a task. It might be better to try to apply it internally by going through the exhaust port on the bottom of the manifold. I'm sure there are others that have more knowledge and experience with things like this who can chime in.
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