Modified engine question

So i had a 351m crate that i broke down to dress up. After some advice i ended up getting the cylinders bored out 90 over and having the heads shaved down to increase the compression ratio. at the time the machinist said Id be looking at about 9.5 to 1 ratio on compression and would need to run high end octane fuel. I don't know if those numbers were right or if it was a good move. Would I be better off starting over, or will it be ok?

 

A 400 is not the same as a 351M.  A 351M shares many parts with a 400, but the 351M displaces 351 cid and has a 3.5" stroke.  The 400 displaces 402 cid and has a 4" stroke.  Further the 351M only used the poorer 1975+ heads with the restrictive exhaust port, while early 400's (1971-74) used 351C 2V heads.  People often think that the 351M/400 is one engine, but that is two separate engines (351M and 400).  Ford used this label on engines to describe the engine family (for 1975+), not the name.

 

Any  335 series engine block (351C, 400, 351M) is usuaully only good for a ,040" overbore from what I have heard.  I doubt it was .090" over.  Not only would the block not go that far, but there wouldn't be any pistons for that size.

 

It's a good idea to boost the compression, but there is really no good aftermarket pistons for a 351M.  Your best bet is to stroke it to 400, and get some decent pistons from Tmeyer Inc.  He's got the only decent pistons for the 400 Ford.  He's also pretty much "the expert" on Ford 400's.

 

 

 

I don't think I'd keep that block if it was actually .090 over.  Like I said, .040 is usually the max for these blocks.  Plus, I don't know how accurate that 9.5:1 number would be considering how low compression the 351M was in stock form.  They'd have to shave a TON off the heads and I think it'd throw other things out because of the amount of material removed.  You might be best off to tear down the engine and do some measurements to see what you actually have. 

 

I still think though if you are going to stick with a 351M you should stroke it to 400.  There are no good aftermarket 351M pistons.  TMeyer sells decent pistons that will give you around 9.5:1 compression with stock heads and they also zero deck to help prevent detonation problems. 

72FordGTS wrote: A 400 is not the same as a 351M.

I only said it's the same size as it will fill the same space as the 351M.

 

 

missing distributor rib?

 

 

core plugs in the valley?

 

 

anybody ever seen a factory 400-4V intake (Rare is an understatement)

 

casting code, XE as in Experimental

 

 

EGR plate