1981 Carb Switch
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1981 Carb Switch
Hey guys, i know you guys have talked before about taking off the stock carb on a 300 Inline 6 and dropping on a 4 barrel carb and we are redoing a 1981 F250 and was thinking about doing this. Could anybody link me to the parts we would need and would work best? Intake, carb and anything else we may need. Thanks 
Elder User
Joined: Sep 2005
Posts: 647
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From: Brumley, MO
Well you need to get a 4bbl intake. As far as I know Clifford, and Offenhauser are the only two who make intakes for the 300. Offenhauser makes 2 intakes that are lower priced than the Clifford intakes. Offy makes a single plane high reving intake, and a dual plane daily driver type intake. I think you will want to go with the Offy Dual Plane 360 manifold. Most people use Holley 390, or Edelbrock 500. You don't want to put 600-650cfm carbs on a 300. If I were going to buy a brand new 4bbl I woild go with the Holley Truck Avenger 470, but I've got a Q-Jet.
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Joined: Dec 2007
Posts: 7,986
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From: Boise, Idaho
If you're interested, here's a writeup I did over on FullSizeBronco.com for my 300 build.
FullSizeBronco.com - 78 - 96 Ford Bronco offroad club, forums, tech, installs
Since you don't have the later year feedback carb/distributor setup, you can easily reuse your current ignition, and pretty much just need to swap in a new 4bbl intake and carburetor. As stated above, the Offenhauser DP is a good choice, as is a Holley 390.
Another I'm thinking of giving a try sometime in the future is a Holley 4175 (80555c). It's a spreadbore replacement for the Quadrajet, and even though it's 650 cfm, the primaries are smaller than the 390, so should offer better gas mileage. I know I'd never use all 650 cfm of it, but oh well.
I'd also highly recommend upgrading your exhaust if you put a 4bbl on there. Stock exhaust is extremely restrictive, and you can only take as much air in the 4bbl as you can push out. Kinda like you sprinting on the track and breathing in with your mouth open but only breathing out through a drinking straw.
Offenhauser 6019-DP Offenhauser Dual Port 6-Cylinder Manifold
Holley 0-8007 Holley 390cfm Vacuum Secondary 4-bbl Carburetor
Also check ebay. You can often get used at a pretty reasonable price.
FullSizeBronco.com - 78 - 96 Ford Bronco offroad club, forums, tech, installs
Since you don't have the later year feedback carb/distributor setup, you can easily reuse your current ignition, and pretty much just need to swap in a new 4bbl intake and carburetor. As stated above, the Offenhauser DP is a good choice, as is a Holley 390.
Another I'm thinking of giving a try sometime in the future is a Holley 4175 (80555c). It's a spreadbore replacement for the Quadrajet, and even though it's 650 cfm, the primaries are smaller than the 390, so should offer better gas mileage. I know I'd never use all 650 cfm of it, but oh well.
I'd also highly recommend upgrading your exhaust if you put a 4bbl on there. Stock exhaust is extremely restrictive, and you can only take as much air in the 4bbl as you can push out. Kinda like you sprinting on the track and breathing in with your mouth open but only breathing out through a drinking straw.
Offenhauser 6019-DP Offenhauser Dual Port 6-Cylinder Manifold
Holley 0-8007 Holley 390cfm Vacuum Secondary 4-bbl Carburetor
Also check ebay. You can often get used at a pretty reasonable price.
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