jstringer50

okay,
before my question let me just say last time i posted someone jumped all over me for asking a question that had been asked "a million times before" on this site. sorry, but I want to order these parts in the next day or so and dont have time to look through 100 pages of carb questions. with that out of the way, let me start with the fact that I am extremely new to carbs as well as most other things rebuild related. I have a near stock 350 that I am almost done building on an extremely fixed budget, so dont worry about performance here. I bought a 600cfm holley 4bbl used, and want to mount it (FOR THE TIME BEING) to the stock cast q-jet manifold-yes, I will replace it when i have money, but its what i got 4 now.my question is what kind of adapter will I need to do this, as Im not even really sure what the diff between a square bore or spread bore is, and what category the q-jet manifold even falls into. any info on this is appreciated-thanks

Apeiron

The Holley is (probably) a squarebore carb, the stock intake is spreadbore.

jstringer50

okay,
now if im correct, a square bore carb has 4 equal size ports where the spread bore has 2 smaller and 2 larger, am I right? if so then I have a square bore carb, so I would need an adapter for a square bore carb to a q-jet intake base, right? I found a couple through jegs that are advertised just like that.

Apeiron

A squarebore carb has the centers of the throttle bores in a square pattern, the throttle bores themselves aren't necessarily the same. A spreadbore carb has the centers of the primaries spaced farther apart than the secondaries. Usually the secondaries are much larger than the primaries on a spreadbore carb, but not always.

But yes, that's the kind of adapter you need.

jstringer50

okay cool, thanks for your help-
and just for some clarification, your saying that on a squarebore, if you were to draw a line down the center of the bores all the way around, it would be square, and on a spreadbore this would not be possible due to the primaries being spaced further apart than the secondaries? sorry if that sounds confusing

Apeiron

That's exactly it.