Square bore carb on spread bore intake?

-
swingingdart

swingingdart

Well-Known Member
Joined
May 4, 2010
Messages
996
Reaction score
149
Location
Cassville, Missouri
I put a square bore carb(carter AFB) on a mid 80s dual plain spread bore.
I had someone tell me putting a square bore carb on a spread bore intake would hurt performance, and just generally would not work as well. Is it okay to put a square bore on a spread bore intake?
 
I have seen the Edlebrock Preformer intakes leak at the base of the carburetor, they make a steel plate to help seal the base when using a square bore carburetor on the spread bore intake
 
swingingdart said:
So no real issues except for leaking around the carb base?
Click to expand...
Not really, go with it.
The issue is when you try to run a spread bore carb on a square bore manifold, especially with a divided plenum. Even with an adapter its tough to get full secondary flow (if they even open all the way).
 
Edelbrock makes that thin steel plate. No need for a thick aluminum adapter. That plate is like 14 bucks from O'Reilly.
 
The plate makes the weird spreadbore shape a square shape with an even flange for sealing. These are mandatory when running the 4010/4011 carbs as well as the "summit" branded Holley 4010 copy as their flanges are not solid but are like webbed. Try getting these sealed to anything without that plate short of an old 4 hole 273 stock intake, and it would probably still not clear the blades in the primaries.
img_20180926_210229-jpg.jpg
3-MzyE4S577dzke62YQWtlFkx5eva-iB3gWCPI8Vmt4UMScjiEQj1bkkwknQ-NRWxm54pDE8mr0ZPoBvQld95QUQHT8iL3SF.jpg
 
Will it work? Sure. Will you get optimum flow without added turbulence or swirl? Anybody's guess. FWIW, it's better to have the plenum and carb base matched for optimum flow and performance. But to answer your question directly...if the butterflies open and you have no air leaks, it'll run.
 
Years and YEARS.........decades........ago, I ground out the primaries to match a square bore on my 71 340 intake. Always been a bit sorry, why? No EGR on a 71
 
swingingdart said:
Wanting to get away from the 80s iron intake... my 318 needs more umph! :)
Click to expand...
Two of the best flowing intakes were the factory 340 spread bore TQ intake, and it's predecessor, the slightly off-square factory 340 intake for the Carter AVS. Heavy? Yes. But I weighed mine against the Air Gap RPM I have and came up with only 25 lbs difference between the two. In other words, the weight of a case of bottled water on your passenger floor board. With a 318 you'd have to match the head ports to the manifold. It would be hard to match the performance on a 318 between that and an expensive aftermarket manifold.
 
My suggestion would be keep the spread bore manifold, port match the heads, and slap on a TQ. You will burn the house down with that combo and with the air valve secondary on the TQ, you'll never over-carb.
 
Captainkirk said:
Two of the best flowing intakes were the factory 340 spread bore TQ intake, and it's predecessor, the slightly off-square factory 340 intake for the Carter AVS. Heavy? Yes. But I weighed mine against the Air Gap RPM I have and came up with only 25 lbs difference between the two. In other words, the weight of a case of bottled water on your passenger floor board. With a 318 you'd have to match the head ports to the manifold. It would be hard to match the performance on a 318 between that and an expensive aftermarket manifold.
Click to expand...
What is the running cost of a stock 340 intake?
 
That was Pishta's pic. The manifold he posted was the early slightly off-square bore for the Carter AVS. The spread bore 340 manifold for the TQ has HUGE secondaries. Like this:
30323821085_4e119f41b2_c.jpg


30162508631_a008acf07f_c.jpg


Look in our for sale section. They come up frequently.
 
Last edited:
Captainkirk said:
That was Pishta's pic. The manifold he posted was the early slightly off-square bore for the Carter AVS. The spread bore 340 manifold for the TQ has HUGE secondaries. Like this:
View attachment 1715673731

View attachment 1715673738

Look in our for sale section. They come up frequently.
Click to expand...
Boy, those look very similar to he mid 80s intake I have on it now. Except the 340 doesnt have the egr crap I had to cover up.
Do you know if the 340 out performs the 80s dodge four barrel intake?
 
Someone would have to run both style of intakes back to back with that carb, and tune it for both, on a dyno or the drag strip to validate those assertions of hurting (and it may be so) or not working as well. Of course there are likely some who will say they noticed a difference :bs_flag:but was that slapping the carb on both with the same settings or after possibly tweaking the idle adjustment screws, pump shot etc? I doubt most of us would never notice any difference either way, aside from time slips at the strip. Slap it on and roll:thumbsup:
 
swingingdart said:
Boy, those look very similar to he mid 80s intake I have on it now. Except the 340 doesnt have the egr crap I had to cover up.
Do you know if the 340 out performs the 80s dodge four barrel intake?
Click to expand...
Both 340 manifolds I have do have the EGR wells. Both the TQ and AVS used them for the chokes.
 
You must log in or register to reply here.
-

Back
Top