maddart
Well-Known Member
Can a 750cfm vacuum secondary carb be used on my 383-4 speed? The car has a mopar performance purple camshaft and 323 gears. It will be street driven.Or will i need to look into mechanical secondary?
Vacuum Secondary on a 383-4 speed
- Thread starter maddart
- Start date
Dans 68
Well-Known Member
The original equipment carb on my '68 383 4-bbl 4-speed Charger has a vacuum secondary, so the answer is yes. 750 cfm may be a bit large for an almost stock 383 but it probably would adjust out just fine.
Dan
Dan
69 Runner
ADMIN wif a corner office (Deceased - RIP)
ALL Mopar Performance cams are"purple shafts", so that part of your question doesn't mean much. WHICH cam is it?
But as Dans 68 said, (actually) all the factory 4 barrels on 383s were vacuum secondaries
But as Dans 68 said, (actually) all the factory 4 barrels on 383s were vacuum secondaries
supernova1969a
Member
Seem to be having same problem ,I had a 750 mechanical secondary Carb on my 383,with big cam, as soon as secondarys opened motor would choke and stall, so I tried 750 vacuum, better but still way to much carburetor. Thinking about a 650,or600 jetted up.any suggestions?
Meep-Meep
дворянин
I'm sure there are more problems going on then just the carb and I'll second the "what purple shaft cam" question. What's the timing doing? What's your compression pressure - as in do a compression check. Too much cam and not enough compression will turn that 383 (or any engine) into an anemic Briggs and Stratton.
To answer your question a 750 vac secondary will work if you have the right combo. I ran one on my warmed over 383, but with an auto. You may have to put a heavier spring in the secondary diaphragm, but that's part of tuning. If you have a mild engine you'd be better off with a 600-650 though.
To comment further on carbs: "jetting up" a carb does nothing but make your engine run richer as basic jet size is determined on how much air passes through the venturi. You should always start with the factory jet settings and select a power valve or power piston springs based on manifold vacuum. Don't fall for the old "600 that's been jetted up to a 650" trick. This can't happen in our universe.
To answer your question a 750 vac secondary will work if you have the right combo. I ran one on my warmed over 383, but with an auto. You may have to put a heavier spring in the secondary diaphragm, but that's part of tuning. If you have a mild engine you'd be better off with a 600-650 though.
To comment further on carbs: "jetting up" a carb does nothing but make your engine run richer as basic jet size is determined on how much air passes through the venturi. You should always start with the factory jet settings and select a power valve or power piston springs based on manifold vacuum. Don't fall for the old "600 that's been jetted up to a 650" trick. This can't happen in our universe.
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