Slabside500
New Member
Okay, so long story short, I have a 1968 Dodge Monaco that's bone stock save for the fact that about 20 years ago, the original 383 2 barrel (stock dual exhaust and 906 heads) was rebuilt with what I assumed was a date correct 4 barrel carter carb and intake manifold. Fast forward to now, the carb has to be rebuilt due to leaking seals. To my surprise, I found that the carb is a Carter 4299s atop a 2205968 intake, which would make them from a 1967 383.
From the research I've done, here's my issue as it stands....
The part numbers for the intake and carb are different from 67' to 68'. Due to the 906 heads, the 68' intake was revised to a medium riser with a 3.44" manifold height and with larger throttle bore sizes that the previous year. The 67' intake was a low riser with a 2.80" manifold height. The 68' intake has a 50% increase in runner CFM volume than the 67' in order to properly compliment the amount of air the 906 heads can move. I'm worried that this intake is starving the engine since it's more restrictive than what the factory originally used. From what I understand even the car's factory 2 barrel intake had these improvements over the 67' intake.
As for the difference between the carbs, the 67 is an AFB while in 68 they used an AVS.
(I honestly don't really know the difference between these two other than the AVS is supposed to be better designed and more efficient- if someone could explain between the two I'd be grateful).
I'm also unsure how large the difference in CFM is between the two. I've found conflicting information that the 4299s flows either 535 or 575 CFM, while in 68' a stock carter 4 barrel would have flowed 600-625 CFM (Having said that, I'm pretty sure that the 4429s is still flowing more air than the factory 2 barrel).
So what I'd like to know is what would you guys do? As far as I see it, an engine is just a big air pump, and the more efficient you can move the air in and out of the engine, the better. The heads and exhaust are fine, but the intake is the weakest link in the chain so to speak. Carb-wise, does anybody know for sure what a carter 4299s 4 barrel flows? If it's 575 CFM then I'll rebuild and keep it, since it's probably still flowing more air than the factory 2 barrel, as well as it's a hell of a lot easier to tune a small carb up than it is a big carb down. Otherwise, I guess my best bet would be to try to find an AVS carb that actually belongs under the hood.
From the research I've done, here's my issue as it stands....
The part numbers for the intake and carb are different from 67' to 68'. Due to the 906 heads, the 68' intake was revised to a medium riser with a 3.44" manifold height and with larger throttle bore sizes that the previous year. The 67' intake was a low riser with a 2.80" manifold height. The 68' intake has a 50% increase in runner CFM volume than the 67' in order to properly compliment the amount of air the 906 heads can move. I'm worried that this intake is starving the engine since it's more restrictive than what the factory originally used. From what I understand even the car's factory 2 barrel intake had these improvements over the 67' intake.
As for the difference between the carbs, the 67 is an AFB while in 68 they used an AVS.
(I honestly don't really know the difference between these two other than the AVS is supposed to be better designed and more efficient- if someone could explain between the two I'd be grateful).
I'm also unsure how large the difference in CFM is between the two. I've found conflicting information that the 4299s flows either 535 or 575 CFM, while in 68' a stock carter 4 barrel would have flowed 600-625 CFM (Having said that, I'm pretty sure that the 4429s is still flowing more air than the factory 2 barrel).
So what I'd like to know is what would you guys do? As far as I see it, an engine is just a big air pump, and the more efficient you can move the air in and out of the engine, the better. The heads and exhaust are fine, but the intake is the weakest link in the chain so to speak. Carb-wise, does anybody know for sure what a carter 4299s 4 barrel flows? If it's 575 CFM then I'll rebuild and keep it, since it's probably still flowing more air than the factory 2 barrel, as well as it's a hell of a lot easier to tune a small carb up than it is a big carb down. Otherwise, I guess my best bet would be to try to find an AVS carb that actually belongs under the hood.