Replace bad 351m or go to a 400?

[Garyp]

My 351m has blow by a few pistons and valves and its all ready over 0.60, so looking at a short block and getting heads done.
I'm wondering why not just get a 400 instead.
Thanks for any advice.

 

[paul rondelli]

Check out this guy rocking a 400

 

[Whipsaw]

No replacement for displacement... still, you're looking at replacing all the parts that no longer bolt to the 5.8, what ever they are (PCM for one? or is it a carb?). Unless it's the same block and heads, I've not looked into it.

 

[johnnyreb]

My 351m has blow by a few pistons and valves and its all ready over 0.60, so looking at a short block and getting heads done.
I'm wondering why not just get a 400 instead.
Thanks for any advice.

Have you thoght about re-sleeving it? In case you want to keep it all original and keep the value up.

 

[johnnyreb]

No replacement for displacement... still, you're looking at replacing all the parts that no longer bolt to the 5.8, what ever they are (PCM for one? or is it a carb?). Unless it's the same block and heads, I've not looked into it.

Also some parts are balanced--that can,nt be inter changed with some motors.

 

[blksn8k]

429/460 is also a fairly easy swap. Bolts up to the same tranny. I did a 460 swap in place of the original 351M on my cousin's '78 Bronco back in the early '80s. Should be even easier now with better motor mount and exhaust options.

 

[johnnyreb]

429/460 is also a fairly easy swap. Bolts up to the same tranny. I did a 460 swap in place of the original 351M on my cousin's '78 Bronco back in the early '80s. Should be even easier now with better motor mount and exhaust options.

I put a 390 in one of my 78 bronco and didn,t have much problem. Mostly the exhaust on the drivers side. I put it the the one with the 4 speed transmission. I use the 390 bell housing too.

 

[johnnyreb]

I put a 390 in one of my 78 bronco and didn,t have much problem. Mostly the exhaust on the drivers side. I put it the the one with the 4 speed transmission. I use the 390 bell housing too.

I also had to cut some out of the towers where it sit down in.Not much.I think it has about a 3 inch clearance at the back of the motor.

 

[ledzilla]

No replacement for displacement... still, you're looking at replacing all the parts that no longer bolt to the 5.8, what ever they are (PCM for one? or is it a carb?). Unless it's the same block and heads, I've not looked into it.

The 400 and 351M are pretty much the same motor. Identical blocks. Only real difference is the crank, pistons, and carb calibration. They use the same connecting rods and everything else. My '78 LTD wagon has a 351M and I've been working towards rebuilding a 351M into a 400 and swapping it all out. The hard part is getting a crank. There are very few retailers with a new crank for a 351M/400, typically have to source from a junkyard and have it machined. Haven't seen much in the way of new connecting rods, either, but from what I've read the stock rods are strong and can take a lot of power (maybe 600hp). New pistons are easy to find, though. I do seem to recall there being one vendor out there with a 351M/400 stroker kit that has a full rotating assembly, but it was somewhere around $3K, I think.

 

[johnnyreb]

The 400 and 351M are pretty much the same motor. Identical blocks. Only real difference is the crank, pistons, and carb calibration. They use the same connecting rods and everything else. My '78 LTD wagon has a 351M and I've been working towards rebuilding a 351M into a 400 and swapping it all out. The hard part is getting a crank. There are very few retailers with a new crank for a 351M/400, typically have to source from a junkyard and have it machined. Haven't seen much in the way of new connecting rods, either, but from what I've read the stock rods are strong and can take a lot of power (maybe 600hp). New pistons are easy to find, though. I do seem to recall there being one vendor out there with a 351M/400 stroker kit that has a full rotating assembly, but it was somewhere around $3K, I think.

I think the rods are different too.

 

[ledzilla]

I think the rods are different too.

They are not. The difference in the 351M to the 400 is the stroke length which is managed entirely with the crank and the height of the pistons. The 351M has taller pistons to make up the difference with the shorter stroke, but the connecting rods are the same.