Square Bore versus Spread Bore

[Nickrt]

I have one of each and a Holley spread bore carb (don't remember the size though I would guess 600 or 650 cfm). The spreadbore is installed on my old rotted Scout's 392 that I hope someday to rebuild. I have a good sounding 345 in the '72 Scout I just bought. Want to put a 4-barrel on the 345 and run her until I get around to freshening up or at least swapping the 392 in - at least 5 years. (392 has some valve train noise and has already been through one cam lobe in its past - from recent posts I am guessing bad cam bearings).

Looking for opinions - the most economical is to pull the spreadbore manifold and carb from the 392. The easiest and fastest is to use the squarebore that I have lying around (I want to keep the 392 running so I would have to swap the 2 barrel setup back onto to that motor). Thinking the spreadbore is also better on fuel with the small primaries.

For clarity, the spreadbore came off of a 1979 (or '80) 345 while the squarebore was the original manifold on the 392.

Any opinions would be great.

[jeepdaddy2000]

I perfer spread bore carbs over square's due to the increased throttle response the smaller primaries provide. However, to my knowledge, all Holley spread bore's are of the mechanical secondary design. I have found these a poor choice(flame on Jonny!)in most offroad applications,as well as being poor MPG performers. My preference is the Q-Jet or Economaster for spreadbore applications, and the AFB for square applications. As for your Question....I would go with the square bore, as this will keep the 392 complete without having to do a lot of swapping.

[Ben Perkins]

The best thing about the square bore is all the many of the new fuel injection products, ie:Holley, use the pattern. Gives you better options in the future.

[KimoChow]

I am intersted in finding a spread bore adapter for a non T.Q. carb for my 79' 345 anybody know?

[bmacguyver]

the only diff in spread bor to square bore adapters is 1 vs 4 hole and alluminum vs composite. i think they run around $30 -$ 40 with gaskets and all the needed hardware at most parts stores.

hth

mac

[SCscoutguy]

I am intersted in finding a spread bore adapter for a non T.Q. carb for my 79' 345 anybody know?

I bought this adaptor when I was planning on running a 1406 on my spreadbore and it is still brand new in the package. I am sure your local Napa or Autozone will have one but if you cant find one PM me. Semper Fi, John

[Nickrt]

Still haven't determined exactly what carb I have on my 392. It is a dual feed with electric choke. I appears to me to be a spread bore and I know that the manifold is a spread bore.

Curiosity has got me - anybody recognize this Holley?

[jeff campbell]

it's definately different from any holly i've seen in a while?jeff notice the diff in the fuel bowl's!?

[Nickrt]

I bought it from Summit Racing ~9 or so years ago. Looking for receipts - unfortunately Summit's online order records don't do back that far.

[timpage]

I've seen Holley Spreadbore/Quadrajet replacements sold on Ebay, but dont recall models. Search on Ebay, perhaps that can give some clues.

Tim