I have a 400 already and a chance to buy a 351 Cleveland for $200.

 

I did it years back. Mine were 4 barrel heads and I had to use car manifolds. It ran well, but not any huge difference over the stock heads. Also, because of the car manifolds, I had to notch the frame to mount the exhaust pipe on the passenger side. This caused stress cracks in the frame within a year of daily use and abuse. If they are 2 barrel heads, your stock manifolds should work fine.

 

I'd scrap the 400 and use the 351C. :-)

 

i dont get it 2bbl heads and 4bbl heads whats that mean

 

The 4 barrel heads have larger intake and exhaust ports in the heads. The 400 or 351m has 2 barrel heads. The exhaust manifolds will not seal the 4 barrel heads larger ports.

 

this truck will be used for Sunday Drives, one truck pull a year, and bragging rights over my buddies 79 Bronco with a fairly stock 460. I want to keep the 400 because this truck was bought brand new by my Grandpa and has 54,000 miles.

 

The 4 barrel Cleveland heads were considered by some to flow too good for a street engine. I've been told that using the 2 barrel Cleveland heads on a 400M raises the compression ratio from @ 8.2 to 1 up to around 9.5 to 1. I don't think it is an exact bolt on but from what I hear wakes these low-compression smog motors up a bit. I was going to do this on my 78 F250 but ending up selling the truck before I got the chance.

 

They bolt right on. I really did not notice much difference. My motor was bolted to a mustang 4 speed. I hated that motor. It ran very poorly. I wound up pulling it all out and went with a 390 automatic.

 

two barrel cleavland heads are essentially the same as 351/400 heads. not worth the time to put em on imo

there are two basic 4 barrel heads. one is the open chamber and the other is the closed chamber (often refered to as "quench heads") installing the open chamber 4 barrel heads on a low compression 400 would probably not result in much performance gain. howerver if they are the closed chamber variety it will substantially raise the compression ratio of the engine. if this swap was performed with a matching 4 barrel manifold and some headers (also install an aftermarket timing chain and gear set, the factory one retards cam timing) you will have a beast on your hands.

disclaimer: i had just woken up when i posted this, and i am not (by a long shot) a 335 series engine expert. if you visit the 335 series sub forum you will find the experts on the subject there.

 

The closed chamber 4v heads on a 400 will be pingers, because the 400 piston is SO far down in the hole at tdc. You would need to get the piston up in the block and milling the block won't do it. You would need to get a set of TMI's pistons because they have been designed to be higher in the block. You will also need the intake spacer plates because no one makes a big port 400 intake manifold, you have to run the cleveland intake. The open chamber 4v heads just bolted on to a stock bottom end won't even run as good as the stock 2v heads. There is no real difference between the stock 400 heads and the 351c 2v heads and they are real close in cc's so they don't raise the comp ratio.