For a mild/stock 400 a 600 cfm carb would work fine
For a built 400 I wouldn't go over 750 cfm at all.
650 would most likely be what I'd use.

 

Yeah okay thanks. 650 cfm is what I was thinking of also.

 

Nerdinger, My 400 has the Weiand with a Holley 750 and it works very good with the mild cam upgrade and headers into true dual 3". But i agree with the others that if you have to buy a new carb, go with a 650. I actually need more agressive mods to utilize my 750, but, it was on the shelf of my garage waiting to be used.

 

I put a 650 Holley Truck Avenger on mine. I'll let you know how I like it when we go muddin. Still need drivelines.

 

Allright, 650cfm definately sounds like the way to go for me then, thanks everybody.

 

Ok the basic things really wake these engines up.
Put you a 600 CFM carb(edelbrock or holley), new intake(Edelbrock Performer 400 or Weiand Action +Plus), a RV cam and lifters(like the comp cams 255 DEH ), matched valve springs, valve spring retainers, valve locks, valve stems seals, a double roller timing chain(set straight up to zero), headers and duals.
I did all of this MBBFord did above with exactly the same stuff, except for the duals and the headers for I ran out of moolah. I threw in some roller rocker arms, flat top Badger pistons, and shaved the heads down 18 mils.

The thing sure seems to run lean. Runs good, but lean. I put in the next stage up metering rods in the carb, but still seems to run lean. Also, I have no idea what the compression is now. The original stock #s are about 8.4 to 1, but it's higher than that now.

Any suggestions?

 

you won't need anything bigger than a 750 cfm infact lots of pople told me that was too big. but i had to recalibrate it to run richer to get a little better performace. but it will run pritty good right out of the box. i don't know what kinda milage it gets i just fill it when it needs it.

 

A 600cfm carb is plenty for the 400.

 

hey smoulding, if you say you have a 600cfm on yours but it runs lean wouldn't it be better to put a bigger carb on it and have it run richer? i'd rather have it a little rich than lean. plus i had to RICHEN up my 750 cfm on a 351M. better performace if you get the thing tuned right.

 

I already have the 600cfm carb on there. It would be less expensive for me to put in the right jets and/or metering rods in the 600 than to buy a 750. Even on a 400ci engine at 5000rpm, it will not suck up 600cfm worth of air, so the 600 is ok. Just have to tune it right. I'm thinking of putting in a air/fuel meter to see what it's doing.

 

ya you will just have to spend some time to get the jetting right.

 

I thought I might go 12% richer in the cruising mode Ref 17 in this chart for the 1406 carb. http://www.edelbrock.com/automotive/eps_1406.html.

I already replaced the stock metering rods 4% richer, and the thing is still way too lean. Its turning my plugs into crispy critters, not to mention what it must be doing to my badger flat top pistons. I won't run it anymore without a richer combo.

 

What makes you think it is lean?

You shouldn't have to go more than one stage rich.

Sometimes with a big cam people use a weaker step-up spring, because they don't have enough vacuum to pull the rod into cruise mode and the motor runs in power mode even at idle.

Maybe you have too much vacuum and need a stiffer step-up spring to get the carb into Power Mode sooner. Put a vacuum gauge on it, and see when your vacuum drops enough to get you into Power Mode.