Carburetor Swap
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Cargo Master
Joined: Dec 2004
Posts: 3,362
Likes: 22
From: Florence, SC
Carburetor Swap
I have the chance to get an almost-new carburetor for my 85 302 and I need some opinions for my application.
It is a Holley 4 barrel carburetor CFM 450. It does not have the high-idle feature that my current worn out 2 barrel has. Is the carburetor too small or too big? Will I really need the high idle down South where it hardly gets cold?
What stock carburetor do I have? I know it is a 2 barrel Autolight, but what is the CFM?
Thanks!
It is a Holley 4 barrel carburetor CFM 450. It does not have the high-idle feature that my current worn out 2 barrel has. Is the carburetor too small or too big? Will I really need the high idle down South where it hardly gets cold?
What stock carburetor do I have? I know it is a 2 barrel Autolight, but what is the CFM?
Thanks!
Elder User
Joined: Oct 2004
Posts: 984
Likes: 0
From: Winnipeg, Manitoba
You've likely got the run of the mill 500cfm 2 barrel carb that Ford has run on my V-8 engines over the years. 450 cfm would seem a bit small.
Keep in mind, you'll need to change the intake manifold as well. Some other things to think about. Is your truck standard or automatic? If it's an auto, the carb will need to be for an auto, so that it provides linkage for automatic kick-down, manually shifting it down will eventually burn up your transmission.
I'd lean towards a 600cfm sized carb, with vacuum operated secondaries.
Keep in mind, you'll need to change the intake manifold as well. Some other things to think about. Is your truck standard or automatic? If it's an auto, the carb will need to be for an auto, so that it provides linkage for automatic kick-down, manually shifting it down will eventually burn up your transmission.
I'd lean towards a 600cfm sized carb, with vacuum operated secondaries.
Post Fiend
Joined: Oct 2003
Posts: 9,176
Likes: 4
From: Western Central NV
You have one other option. You can buy an adaptor that goes from a 4BBL to a 2BBL manifold. as for the auto trans yes it must have a place to hook up your kick down, without it you are shifting against the govenor in time you will hurt the tranny. You could find a junk carb with kick down and change it out but your looking at alot of work.
Elder User
Joined: Oct 2004
Posts: 541
Likes: 0
From: Fleming Ga
When you are talking about not having a high idle, are you talking about a choke? I live down south also and it gets cold enough on some winter mornings where you would need a choke until the engine warms up. If nothing else you would need to install a manual choke cable for those cold mornings. Yes 450 cfm is going to run the engine too lean under load. The 500 cfm from the original carb was about as small as you could go.
Elder User
Joined: Oct 2004
Posts: 984
Likes: 0
From: Winnipeg, Manitoba
The adapter idea is a no-go. There are adapters for putting a 2bbl on a 4bbl intake, mostly used in stock car applications. The other way around, you'd have to block off the secondaries, and render them useless as far as linkage is concerned. It'd be pretty tough to do, considering the general size and shape difference of the mating surfaces.
