Merc. 4 bolt Intake

H

HCO41

Senior Member
I just picked up a Mercury intake manifold w/backdraft carbureter. I'd like to find out about them, what year(s) they were used, etc.:
Manifold: Numbers on top - 8CM-6520
" " bottom - K080 or K0800

Carbureter: Automatic choke
Cast aluminum base
1G50 on top of Accel. pump tower
Venturi = 1.434"
"3" stamped in top 2-1/4" back from air horn

I thought about using the manifold on a stock 8ba with a Rochester 2GC carbureter. Is the bolt pattern the same? Will there be any benefit in either performance or gas mileage? Would combining this setup with a Chev. distributor make sense?
Carbureter looks good, is there any use for it?

Thanks,
Howard
 
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If the carb. has the choke on it ,The manifold is most likely '49- early '50, generally everything ('50- '53 ) had the choke on the manifold.
Seriously doubt the 1.434" venturi, would be closer to 1.062.
 
51 Merc.: Choke is on carbureter. Verturi=wrong word. I took the measurement at the base.
Thanks,
Howard
 
I have used a Merc 4 bolt intake with a Rochester 2g and a Bubba Chev. distributor on three of my old Fords. No vacuum hook up. They run great. Look for a Merc intake from Canada they are aluminum.
Pete
 

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I have done a bunch of research on this to be able to come up with a better solution for my '51 Ford, and here's what I've found. The Mercury 4 bolt manifold has 1 3/8" throttle bores, while the 94 carburetor has 1 5/16" throttle bores. A small base 2GC will bolt right on to a Mercury manifold, but the throttle bores are 1 7/16". I have an aluminum Canadian 4 bolt Mercury manifold. I was able to bore the throttle bores to 1 7/16" almost to the bottom of the manifold bores. I smoothed them out with a couple of carbide bits, and I was good to go. I think this is the way to go for a mildly modified engine in these cars. Carbs are bigger, better, and there are no linkage problems to worry about.
 
Pete and tubman: At least for now I'd like to use the cast iron manifold I have. Aside from weight and good looks, will I get similar results? Does the 2g have auto or manual choke? I'll have to block off a two heat sources used for choke and carb. heat if manual choke is used. I have large assortment of carbide burrs that I can use to match 2g to manifold.
Howard

P.S. What vehicles used "small base" 2g?
 
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There is a carb adapter that was designed to enable circle trackers to run the Holley 2 barrel 300 CFM on a Chevy Rochester 2 barrel manifold. It will let you run any of the various aluminum Autolite carbs used on Fords or Holley 2 barrels (300 cfm or less) with the Merc flathead intake. Not with the Loadamatic distributor of course. ..B.
 
Small-base 2G's were used up til the mid-60's. I have one from a '64 Chevelle with 283. Right out of the box the jetting is about right, and it's totally tight, no leaks.

Since you mount them flipped 180 from the GM position to get the throttle connection on the passenger side, a manual choke is a little bit of a problem. You either have to live with a choke cable that is out when no choke is desired, or run a really long cable all the way around the front of the carb to make it "normal".
 
Howard,

Here's what you need to know. The small base 2GC came early on GM V-8's and some V-6's ('50's - 60's). As I said before, the small base carbs bolt right on to the Merc manifolds (there are some open passages in the bottom of some 2GC"s that may require an adapter/block-off plate). If you mount the carb backwards from it's usual orientation, the throttle linkage and fuel lines drop almost exactly into place. Unfortunately, this puts the manual choke linkage on the wrong side of the carb with a backwards pull. I have an aluminum later model Canadian Merc manifold with provisions for an automatic choke. On this set up, the choke tube is on the proper side of the manifold, and the choke tube mated to the 2GC with a minor bending.

As to the cast iron manifold; it should work as well as a Canadian aluminum on if prepped properly. I used an aluminum manifold because I figured it would be easier to bore. I purchased an arbor and a 1 7/16" cutter from an outfit called "Rotobroach" (or perhaps Rotabroach - hyphens optional). The bad news is that the cutter and arbor cost almost $100. The good news is that it worked so well on the aluminum, that I think it would work well on cast iron. I did mine with the manifold clamped on my benchtop drill press and had no problems at all.

I think that trying to bore the manifold out with carbide cutters on a hand-held grinder would be a daunting task.

Good Luck.
 
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Thanks for all the input. This forum saves a lot of time and in some cases, money. I just googled Rochester 2g and found an interesting blog that gives the basic differences between suffixes. I didn't see any reference to bolt pattern so I assume they're all the same and will bolt to Merc. intake. Looks like the 2gc with the auto choke on the carb would work best for me since manifold has heat source I can tap for heat tube.
Thanks for all the help and info., here's the link:
http://oldcarblog.com/?p=41

Howard
 
I've run these 2GC carbs on several engines and boring the intake to the same size as the carb is a definate improvement over just bell mouthing the intake to match. I have a Bpt mill so this isn't a problem.
 
If you bore the Ford manifolds (not Merc) to the 2G diameter, is there a risk of getting into the manifold heat passages?
 
I do think that's a posability. Back in the day when we ran a sports man engine in the stock car the rue;s called for stock looking engine and we took a 34/5 "Hump back" intke and hollowed it out to improve flow and installed a 2GC carb and yes that ran into the hat exchanger. This required a sleeve. We also blocked the heat riser. I still have one of these intakes I'll post some pics.
 
Ross F-1 said:
If you bore the Ford manifolds (not Merc) to the 2G diameter, is there a risk of getting into the manifold heat passages?
Click to expand...

I've often wondered about this. Since you are going 1/8" (.125) larger, you'd be taking 1/16" (.0625) off of each sidewall. I think it would be OK on most manifolds but not on others. I have several extra 8BA manifolds in my stash, and have always intended to do one to see what happens. Perhaps next summer. Since I took only 1/32" (.03125) off the bores of the Merc, I don't think there's much to worry about.

Oh, as a side note, when I did this, I used the cast iron base of an old 2GC bolted to the manifold as a guide for the Rotobroach. It kept the process truer and straighter than I expected, even with my cheap bench top drill press.
 
The thing is, the bores on the 2G aren't on the same centers as the Holley 94, so the material removed is mostly towards the outside of the manifold.
 
I have used the Mercury intake with both the Rochester and the stock Mercury carb.The Mercury is a Holley #850, if you get a 51-53 you can use an electric choke off a new stile carb if you have 12 volts to power it. Both work real well and the don't leak gas!
 
Chuck, Which carbureter, Holly 850 or Roch. 2g can be converted to electric? The Rochester 2GE has the electric choke (12v) that could possibly be used on the 2gc and 2gv but, might not work on the 2g since that carb. was a manual choke unit.
For those who are staying with 6v, an electric choke from the old Holly "bug spray" might work. The carburetors were used on 2 barrel intakes used on modified VWs. If this interchange worked it would save some plumbing and/or linkage problems for the choke hookup.
Any thoughts??
Howard
 
HCO41 said:
Thanks for all the input. This forum saves a lot of time and in some cases, money. I just googled Rochester 2g and found an interesting blog that gives the basic differences between suffixes. I didn't see any reference to bolt pattern so I assume they're all the same and will bolt to Merc. intake. Looks like the 2gc with the auto choke on the carb would work best for me since manifold has heat source I can tap for heat tube.
Thanks for all the help and info., here's the link:
http://oldcarblog.com/?p=41

Howard
Click to expand...


I like your plan Howard! I know the 8CM manifold simply has a heat tube coming from it but I can't recall (could be wrong) anyone actually using it for the choke module on the 2GC. I'd like to see what you come up with to make it work!

Also keep in mind there ARE two bolt patterns. You want the small one. I can't recall all configs but the big pattern feeds fuel from the front.

Lonnie
 
Hi Lonnie,
The 8cm manifold I have has a heat tube running through exhaust crossover with fittings in both ends. One goes to the stock (850) carbureter auto choke housing. The other end has a fitting that runs up into the bottom of the carbureter. I don't know what its function is. The fittings on both ends are press fit. If I end up using the 2gc (auto choke on carbureter) I plan to use one of these heat sources using the press-in fitting and adapting the other end with a fitting to fit the 2gc. If I decide to try the electric option I'll try and find a 6v "bug spray" unit as mentioned above. On the Barn we try anything then share our mistakes!
Howard
 
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