Square bore vs. Spread Bore 4 bbl. on a flatty

[19Fordy]

When using a 4 barrel carb. on a flathead engine can you use a square bore carb with a spread bore intake? Can you use a spread bore carb. on a square bore intake manifold? Not being a carb. expert I was wondering how you determine which type of 4 barrel carb and intake to use on a flatty. Thanks

[flatjack9]

Need to use the carburetor that is meant for the manifold. All the manifolds I've seen for a flathead are square bore. A spread bore carb would not work.

[JSeery]

You could probably get a spread bore on there with an adapter, but it would not be a good idea.

[tubman]

"Spreadbore" is used to refer to Quadrajet type carbs with relatively small primaries and large secondaries. I don't know of anyone who makes a "Spreadbore" manifold for a flathead and I think, because of their size, they would not be a good choice for a flathead. I think you are referring to the "modern" squarebore pattern (Holley, Edelbrock) vs.the older square pattern used on Carter WCFB's and early Rochester 4Jets's. Most flathead manifolds available these days are for the older pattern and require an adapter for the newer carbs.

That being said, it's a matter of personal choice; do you want to buy a new carb on the Internet and just bolt it on? Buy a 390 Holley or a 450 Edelbrock with the proper adapter and have at it. Would you prefer a more traditional look, chase down a WCFB, 4Jet, or maybe even an early Stromberg, rebuild it and bolt it to your manifold, tune it and go. It's really not all that simple, with jetting, linkage, chokes, and all, but a lot of folks say a 4BBL is the best setup (looks aside) for a street-driven flathead. I had a 390 Holley on my old '36 with a 276" Merc, and it worked just fine. This time though, I've rebuilt a 4Jet and a WCFB and have old Fenton and Edmunds manifolds. I'm going to try some different combinations and see what works best. (I have heard that the old Fenton's are the best 4 BBL manifolds out there, and I think Edmunds manifolds in general are butt-ugly, but I'll try 'em both.)

[Charlie ny]

I really like my Fenton 4 brl intake. I can forward you my jetting etc for the '52 Olds
Rochester 4 barrel I'm running for the last 4 years.
You'd have to really tighten up the vac release on a modern Q-jet to make things happy
on a Flathead.........is my guess.
Charlie ny

[tubman]

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Charlie, it's good to hear that about the Fenton; I'd hate to find out that ugly Edmunds runs better. I'd appreciate the jetting information, as my Rochester is from a '53 Olds, so they should be real close.

I haven't forgotten about the crab cap Mallory I am going to send you; I hurt my hand about 3 weeks ago and don't function well left-handed.

When I referred to a Spreadbore as being unsuitable, I was thinking about physical size more than anything. If you could get one to fit and got the secondaries juuust right, it would probably work fine because of the little primaries. Properly set up, they are probably the best 4 BBL there is.

[19Fordy]

Thank you gentleman for the excellent info.