The Stovebolt Site Forums The Shop Area Engine Shop intake manifold stud spacing

about two years ago i picked up a 56 gmc 270 for the ashton that i didnt use but its now going into my 40. the carb that was on it was a rochester which didnt come with it originally but it worked. since i had a zenith to put on the 270 i had the carb rebuilt and had it as a spare. when i got my 51 6100 dump with the original 235 engine the carb(rochester) was messed up so i went to put the rebuilt one on the dump and it didnt match the stud spacing on the intake and it confused me and i put it back on the shelf.

fast forward to today, i picked up a 59 235 a couple of weeks that so far looks promising to replace the 51 235. the 59 carb looks like it needs work so when i go to test run it i thought id use the rebuilt rochester. i removed the 59 carb and went to put on the rebuilt one and it doesnt match the stud spacing. looking at the bottom of the throttle body the rebuilt one's bore is much smaller than the one from the 59. everything else on the exterior of the carbs is identical. when did the stud spacings change and what application was this narrower stud spacing carb for?

Mike,

It looks like the post-to-post distances were 2 11/16 and 2 15/16.

Look towards the end of 3.726 - Insulator had dimensions.

Look for the dates and applications for:
3692797
3602799

605392 was used in place of the insulator, on carburetors with governors.

Tim

are these engine related casting #'s or carb #'s ?
the tag on the carb is 7004475 E9
i could'nt find a listing on my carb application chart for that number

Mike,

Check the link above, again. The link was the wrong one.

The part number is for the carburetor to manifold insulator. The MPB entry shows the years for the two carb's bolt-spacings.

Sorry,
Tim

tim, thanks. now i can see why it wont fit. maybe i can just swap out the throttle body temporarily. or maybe it can be permenant depending what i find. i find it funny that it fit on the 56 270 intake.

Swapping the throttle body would probably be a mistake, unless everything aligns properly above it- - - - -venturi size, idle and vacuum passages, etc. I believe the small-diameter carbs were designed to run on the 216 engines, not the 235's. If you do manage to get the small carb to bolt on, it will run pretty rich due to higher venturi velocity for any particular RPM you're running. It might also restrict full-throttle RPM, but it's not likely you'll be doing much wide-open running unless you're pulling a heavy load in a lower gear.
Jerry

Edit: The small-venturi carb might have been intended to be a quasi-governor on the 270 to prevent over-revving in the lower gears. The 401 V-6 in my fire truck has a tiny Stromberg 2-barrel, probably for the same reason.
Jerry