Boring out "A" manifold to "B"size ?

G

Greg out west

Senior Member
Hi Guy's,



I'am running a "B" block. I'am also using a "B" carb. Is it worth boring out the A manifold to the "B" size ?. Also somebody was saying you can get a drill bit at Harbor frieght ?. It's 1 1/8th I think ?.



Can I open up the A manifold at home ?
 
Model A throat is about 1-3/16". Model B throat is about 1-5/16".

Make sure you drill or bore in line with the manifold passage, which is NOT perpendicular to the carb mounting flange.

Personally, I use better drills than are available from Harbor Freight, but then I have them for the day job.

Joe
 
Yes it is worth the time to do if you want the full benefit from the "B" carb. I have the procedure to drill one out on my website. Look on the "Services" page and for the link (You can do it yourself) that will open up a series of pictures. I have some tips noted on each picture as to the process. It may take a few moments to load as there are a number of pictures. (1.78MB) I run one on my Pheaton with an "A" carb or "B" carb depending on what I am doing. The "A" carb gives me about 2 MPg better fuel economy. The "B" gives me a lot more power at highway speeds. From 45 MPH on up is where I see the greatest performance difference of the "B" carb. BTW: MPG for the "B" at higher speeds (55 to 65 MPH) is the same as the "A" carb at the same higher speed. Typical "Club function" touring speeds of 35-45 MPH is where the "A" carb gets better MPG. Good Day!
www.durableperformance.net
 
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Yes boring out helps, even with an A carb. But if you have no way to do it. You can tapper the id of the manifold to the size of the B carb. With a air grinder or burring ball tool. Other words get rid of the sharp step. That helps also, but for high speeds boring is the best way to go.
 
Hi, I'm running a B manifold on my A with a b carb & all I did was take the two mounting bolts & grind away the threads at the top approx 3/8" & it allows the carb to be twisted counter clockwise enough to line up correctly.It's worth the effort, only takes a few min. The other option is Dave Renner @ Renners Corner in MI. actually sells the two bolts machined away the correct amount to make it all line up. Good luck! Joe
 
Might be a lot of work for most here but, I made a mandril to align the A manifold on a Bridgeport and got a drill bit the correct size to bore the manifold out. This was for Brent because he does several per year. Even with a machined alignment mandrill the A manifolds vary in intake port size so care must be taken to align it correctly. Just a little adjusting and it works great. You must be careful when boring it to the optimum size because you can cut through the side of the updraft port. 1 19/64 is the correct size to bore it. The bit was 75$ so it was a quality bit and will last forever doing this even as many as Brent does.
 
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