I have a 400 and was wondering what benifits would come from putting 351c heads on it i know it's possible but what would it help and what makes those heads so great?

 

by 351C heads, which ones do you mean; U.S. production 351C 2V, U.S. 4V open chamber, U.S. 4V closed chamber, or the Australian production 302C closed chamber heads?

in 1975 the M/400 heads were changed in the exhaust port area to be more restrictive, these heads will have a casting code of D5 or higher. none of the U.S. 351C 2V open chamber heads have the restrictive X port, nor do the Aussie 302C heads.

at some point the M/400 heads got A.I.R. passages in them too, i'm not sure if any 351C heads ever got the A.I.R. passages?

most of the M/400 heads have valve retainer/rotator set-ups that limit the amount of cam lift you can use before the retainers hit the guides.

the 4V heads are a different story all together

 

Find a set of early 351C-2V open chamber heads and put larger valves into them. They will flow as good as the 4V heads at low lifts and will not need any adapter plates as with 4V heads. The Aussie heads will raise your CR too high with a stock piston, unless you get a long duration cam, they also need larger valves and porting to flow good.
The closed chamber 4V heads will boost your CR, but you will need at least 93 octane fuel. The open chamber 4V heads would be my last chioce for use on a 400. All 4V heads will require adapter plates and a 351C-4V intake manifold.

 

I have the 4V heads on my engine and i love them.They're not much on bottom end but on top end they scream.

 

did you have to change much on your engine?

 

i also run 4 barrel heads on my 408. the question is what are you gonna use it for? i ran aussie heads for about 3 yaers, small dish forged pistons equalling 10.75 points of compression.ran pretty good. would run on 89 octane with 32 degrees total advance with out a hitch. i then found some nice closed chaber 4-barrel heads, all i can say is hang on to your drink! you will need adaptor plates as was mentioned but its worth it. again you will want up the compression and a good sized cam.there is a guy in australia casting 4-barrel intake manifolds for m motors check back and ill get you the name.

 

To run 4V Cleveland heads on a 400 you will have to have the intake adapters and valley pan cover and you also then have to use a Cleveland intake.Before you install the plates you also have to shave a little off of them,because you have to use 2 sets of intake gaskets.I think I shaved 1/2 of the gasket thickness off each one.if you don't do this procedure your intake won't bolt up.

 

it's too much work for me just now because i'm gonna use the truck for getting to school and driving around so i'll probably stick to the stock heads. but now i know for the future thanx

 

m heads are just fine. you will lose all your bottom end with 351c head. unless yourplaing on turning 6500rpm. stay with m heads

 

by 351C head, which do you mean; U.S. production 351C 2V, U.S. 4V open chamber, U.S. 4V closed chamber, or the Australian production 302C closed chamber head?

 

i can tell u from experience that the aussie heads are great if youre only gonna turn 5000 rpms and not look for high horsepower. youre 400 internals should be fine to 5000 rpms all day. after that the heads just cant flow anymore to produce the big power on the top end, trust me ive tried cams intakes carbs headers, and all the like. if this is a daily driver and u need the grunt down low 2v heads are great aussie or us. difference being compression. dont over cam the thing i cant stress that enough. these engines make huge torque perfect for trucks! the m heads are nothing to write home about. theyll get you down the road but thats about it. 400 are great motors if you do just a couple things, if you have specific questions about tricking one out ask away ill share all that i know.

 

"...trust me ive tried cams intakes carbs headers..."

What intakes did you try? Any 351C intakes with spacers?

 

well right now im using a twin carb tunnel ram by weind topped with a couple mechanical secondary hollies equalling 900cfm. prior when i was sand dragging the motor had a stock cast iron 4v cleveland intake with a single 750mech. holly, to keep me in a lower class. at that point the motor didnt see over 6000. now with a solid lifter cam and the tunnel ram shell pull till it spits the crank out, but i limit it to about 6800. i started out with a set of 2v heads and a edelbrock torquer intake, it would have been great for a log splitter!