ok so i got my hands on a 400M. its punched out .30 has about 60k miles on it, and i got it for free basically. i went a head and threw in an upgraded cam, springs and new valve seals, also got new lifters, pushrods and gear drive. im going to upgrade the oil pump as well. im looking into getting an intake and carb setup for it. i had the stock one on it and id like to go with a 4bbl.

My question is what do you guys think would be the best size carb...ive been told 650 by some....750 by others....im not quite sure, everyone has their own opinion...im just looking for some good reasons as to why i would go with a certain size.

Thanks in advanced

 

It depends on what you would be using it for ...

Get the edelbrock performer intake with a 650 cfm carb.

2v carbs develop more torque than 4v carbs do at low rpm.

BTW <> there isn't an M after 400.

The M goes after the engine 351 as in 351M
The engine class is 351M/400 or 335 series

 

i was told a 650cfm carb...but then someone told me to go with at least a 700cfm to get power out of it. for the 4v carb, what do you think would be better mechanical secondarys?

 

I have vacuum secondaries.

I get better fuel mileage with the 4v over the 2v because I don't punch it to the floor everytime I'm in it.
I believe the mechanical secondaries are less gratuitous than the vacuum type.

Have a peak at this.

http://www.thirdgen.org/newdesign/tech/pickacarb.shtml

 

It all depends on what you intend to do with it and what you are putting it in. Do you want low end torque or high rpm hp? What cam are you running? Whats the weight of the truck/gear ratio/tire size? All these things should be factored in. I ran a built up 400 in my 78 supercab for a number of years with a Weiand action plus manifold and a 600CFM Holley (that I tweaked on) and it did just fine up to about 4500rpm and then started running out of breath. But that was just fine for my needs cause the torque off idle was great.

 

well i have a 79 supercab and im running 31x10.5x15 on it. the truck is pretty heavy, but its stock for the most part. i put a simple towing cam in it, i want basically raw power off the line with ability to pull a heavy load if need be. the gear ratio im not sure of, its stock but i never checked it out. i read that article mil1ion...thanks it helped a little, i think im goin to run a 750cfm holley with vacume secondaries...just not sure what intake manifold to run

 

You don't want anything that ends with *RPM*

This means a part for running HIGH rpms.

That's why I suggested the performer by edelbrock

 

Mil1ion is absolutely correct. The performer with a 650 carb will give you what you want, especially with a cam designed for lower end torque. A bigger carb will just use more fuel and probably create a stumble off the line. Vaccum secondaries work better too, unless you are blasting down the 1/4 mile at high rpms.

 

Whether you decide on an Edlebrock or a Weiand manifold, just make sure that its a dual plane-not a single plenum. On mine I also added a 1 inch thick four hole spacer-not an open spacer. The goal is to get just the right size plenum (intake volume) to promote a good vacuum signal right off of idle. That will give you the best off-idle torque.

 

Here's a little calculation to remember for choosing a carb:
Engine displacement X intended usage RPM / 3456 = carb cfm

like this:
400 (displacement) X 5500 (rpm) divided by 3456 (constant) = 636 cfm (round up to 650)
This will set you in the right direction. Any bigger and you will likely have a bogging problem in different situations. (maybe not at idle or WOT, but on the way there, or stumbling, dead spots)
Now, make of carb is totally up to you! (Holley, Edelbrock, etc)
I have only been into Edelbrocks; I find them very easy to tune, and forgiving. Holleys can get you more power, but frustration usually comes on the way there.

Oh, and yeah, I agree that using an 'M' after 400 is not politically correct.
Reason being, the 400 was around long before the 351M was ever heard of. It is an 'M' designation because it was a modified version of the 400. Wait til you hear what different things 'M' might mean! lol
They had to distinguish this engine from the 351C, because they are quite different blocks. It is also the difference of one year in time. (up to 1974 it is 351C. After 1974, it is 351M) The 400, no matter what year, is still a 400. That's it! You have a great engine there.

Mark

 

My dad worked at Holley for 42 years. One of the engineers at holley took my truck my truck in and tried several carbs. The "1850" 600cfm with vac seconds and electric choke was the best all around. It starts good and idles well with 268 comp cam. The "3310" 750cfm ran good also.

 

He added the electric choke, all 1850's come with a manual choke (just so nobody tries to buy a new one like that). The 1850 is a universal 600 but it doesn't come with a Ford kickdown lever. A kit is available to change the front throttle shaft to add the kickdown lever, though.They are good carbs and run well on most engines.

 

I have a dual plane edelbrock performer intake and a 650 Thunder series off road. I noticed a big difference in low end and throtle response compaired to the edelbrock 750 and factory intake. This setup is on a 78 F250 supercab 4x4 with a 460.

 

where can i find one of these kits?

 

Thats a LOT of RPM's for a 400...... But I do agree with your suggestion.

I would suggest a 600 CFM carb, 650 if the engine has mods