It appears some people have not heard the term 'throttle response'. Mopar guys worry about throttle response because they are smart [ post # 22].
There was a reason Mopar used a smaller carb on a 383 than it did on a 440, even though the same cyl heads & cams were used.
The size of the carb, & the type, should be determined by the engine/car specs. A mild engine, heavy car, will perform better with a smaller carb.
A 3310 Holley has large throttle blades, 1 11/16" pri & sec. A 625 AVS/AFB has 1 7/16" pri blades & 1 11/16" sec blades. It will be more responsive off idle & at cruising speed on a mild engine where the engine will not be able to use more 600+ cfm at peak rpm.
A souped up 383 will be able to use more airflow, & an 800 TQ with small primaries will give best overall performance.
Most of the above is misleading and wrong starting with the last thing he says and that’s the smaller primary TQ on a 382 is better than the large primary TQ.
110% wrong wrong wrong.
Been there, done that, never ever put the small primary TQ on any 383/400 in favor over the big TQ.
Throttle response is improved with a larger primary carb. 110% fact, been there and done that. MANY TIMES!
What I read into the OPs post is that he just wants the engine to run 'right'. It has stock heads & stock manifolds & sounds like a modest, if not stock rebuild. That means he does NOT need a carb that provides enough flow for the engine to pull to 6000 rpm.
This is true but also wrong. Been there and done that many many times. The larger carb, even though it’s potential of 750 or greater cfm worth of flow will never be taxed much less seen, will provide better throttle response and over all power in all driving rpm’s.
Even there done that.
The very large r/s ratio of the 383 is going to make it even more sensitive to carb sizing at low rpms. You have to go through the low rpm range to get to the higher rpm range...
That is why choosing a carb with smaller primaries will pay off. While the 625 AFB/AVS are not called spread bores, in operation they act the same. Small pri for great throttle response, big secs for power.
This is convoluted. The 625 is not a spread bore nor does it act like one. It is a square bore carb and always has been always will be. It has always been seen as one. There’s a huge difference between the slight offset in the sizes of the throttle blades and a Thermoquad, Rochester carburetor.
Post #29, 440 4 speed.
Bigger engines need bigger carbs. There are no 750 carbs on lawn mowers, lol....
Ridiculous- next
The carb flow/size also has to be sized to the engine tune & the amount of air the engine needs to make peak hp.
Incorrect. That’s why there are small 600 AFB carbs on 440’s. A 1966 Imperial comes to mind with its AFB without the secondary velocity valve over the secondary side.
A 383 that has aftermarket ported heads, big cam, headers, single plane intake is going to make peak power at a much higher rpm than a 440 motorhome engine. It will likely need a carb that flows more air.
750 AFB does work well on a 440, but the 440 has 15% more cubic inches to feed than a 383.
A smaller 625 AFB would better on a stock-ish 383, which is why Chrys used the 625s.
Partially correct. Emissions and fuel mileage were also part of the plan. Carter sold the 750 at a higher cost. Hence why it wasn’t on every vehicle that could benefit from one.
As someone above mentioned, (
@Some Car Guy) I am starting to agree and wonder, do you actually work on your cars? Do you even own one for real or not? The crap I’m reading here is neck deep in BS.
Problem is,
@beanhead is probably 100% correct.
