Hey I was wondering what would be the best carburator for my 400. I am planning on going with a Edelbrock intake and carb. I hear people say to use the 600-650 cfm, and I hear others say use a 750 cfm on big blocks. I also plan on putting back on the stock heads after they've been reground and sealed, but upgrading to a roller tip rocker setup (not the full roller rockers). I will also be using a bigger cam like a 214/224 duration and a .510/.536 lift. I will put headers on too. This will be going into a 1966 F-100 and used as a weekend street machine. Does anybody know what would be the best way to mount this engine, engine is a 78 and both trucks are 2 wheel drive and way the same front end. I was wondering if i should reuse the 400 mounts and custom fit or if some other mount would work better. The 66 had a 300 in it at one time. Your help would be greatly appreciated.

 

with your cam, rpm range, and your heavy vehicule go with a 650....

 

I just posted this in the 73-79 forum:

Well, I finally decided to spend the cash and go to a carb correctly sized for my engine.

I have a 400 in my 77 F150 4X4 and since building the engine about 10 years ago, it has had a Holley 750 CFM Vacuum secondary carb. It had always idled rich, was picky about jets and would have absolutely no bottom end power below about 2000RPM. Power braking it would just result in the engine not going over the torque converters stall speed since it was out of the power band of the big carb.

So my financial situation allowed me to buy a 600 CFM Holley Vacuum Secondary and just put it on the truck the other day. It now idles much more smoothly, and can either light up the rear tires, or push the front end down the street from all the new low end power it has. I haven't had a chance to take it out on the open road and really see how much more responsive it is at part throttle due to rain and road construction around the house.

I'm sure it needs to have all the carbon blown out since it has run rich for so long. New plugs are already in place and I am sure they are much happier than the old set that came out.

The lesson is bigger isn't better when sizing a carb. Manifold vacuum and venturi flow is key to the carb acting correctly, and I now understand exactly how much.


My cam is the Edelbrock 218/218 @ .050 with a Weiand dual plane manifold, long tube headers into a 2.25" dual exhaust with flowmasters.

 

I have a 1979 f-250 4x4 with the 400. It has had a Carter AFB on an Edelbrock intake since about 4 miles after it was purchased new. It has a 212/212@.050 Comp cam in it.

The carburator is a Carter AFB performance carb, it is part number 9637. It is a 625 cfm carb.

It has excellent low end response while also allowing the truck to get down the road with the rest of the traffic, usually my own common sense kicks in band I watch my speed before the carb quits supplying fuel. Low end response usually means I am leading the pack from the light. Part throttle response is enough to put your passenger's head into the back window by the time they get straightened out you will have passed the car you were wanting around. I have pulled a trailer and hauled everything from other cars and tractors to building materials. I have been very happy with the performance.

 

Thanks everyone!