i have a 1979 f250 sitting on 40's with a 351 modified and thinking about upgrading in the near future. does putting a 400 crank and rods in make it a 400? i guess im asking is the bore the same in the 351 and the 400 but the stroke just longer in the 400? will the 400 be enough for the tires? and ne1 got ne ideas about gears? what should i put in it? as far as i know they are still stock. or should i scratch the 400 idea and go with more ci's?

 

the only differance between the 351m and 400 is the stroke. so changing the crank and pistons to the 400 ones make it a 400

 

Yes, the bore is the same on the 351m and the 400. You would have to change the crankshaft, rods and pistons. The 351 pistons are longer than the 400 pistons, so if you used the same ones, you'd stick 'em up into your manifold. You can do a pretty good build with a 400, the higher performance parts just aren't as prolific as they are for the 460. Obviously, you could build more power into a 460 than a 400, but you already have a block for a 400, so there's that. With the 400, you wouldn't have to change anything else, it would just bolt right back in where you took out the 351, whereas with the 460 you would have to do a bit more work. So it's all a trade off. Personally, I plan on keeping a 400 in mine. Everybody here will have their opinion. Lots of 'em will be to put in a 460. I say, as long as you do it right, do whichever one fits your wallet and your NFS/horsepower jones.

 

thanks for the feedback ne1 know about how much the swap to a 400 would cost if i done the labor?

 

i would just keep it a 351 and work on a good cam, intake, exhaust, my 351 will spin 38's pretty easy

 

The connecting rods are exactly the same, but the pin in a 351M piston is further from the piston top to make it work. Thaty's why using a 351M piston with a 400 crank will immediately lock the motor when the first piston top hits the head due to longer stroke of crank.

You can take a 351M and get a 400 crank kit from a rebuilder or NAPA and a set of 400 pistons and make a 400 out of that 351M and get same gas mileage and more power / torque.

351M is limited on pistons, a 400 can use a 351 Cleveland piston if you get bushings put in the rod small ends as the 351C uses a smaller pin.

All this occurs because first there was the 351 Cleveland, then the 400 Cleveland as it was called, then after stopping production of 360 and 390s, they decided to make a new 351 based on the taller block 400.... the 351M. 351Ms and 400s have virtually a 351C 2V head on them with ports that flow nearly as well as a BB Chevy.

They lack compression in stock config though and suffered from a retarded camshaft early on, both are "fixable".

What cam are you running?

 

i got a comp cams 268h, it works pretty good, i was thinking about going a little bigger but its worked better then i thought it would

 

All the balancers share the same imbalance weight right down to the 351Cleveland, any will work on any 335 series.

 

Check out Tim Meyer Inc.'s website. He'll have everything you need. But for the whole rotating assembly, I'd say you're looking at $7-800.

Ehhh...I'll agree that the balancers are not exactly the same...but they are balanced the same, a 351M balancer will work on a 400, but the timing marks won't line up. Another thing to keep in mind is, the flywheels are balanced the same, but I've read that there was a bolt pattern discrepancy between the 400 and early 351M's...I dunno how true that is seeing as I've never encountered it...but it's something to keep in mind.



Any head work done, or stock?

 

nope just the stock open chamber 2bbl heads, might be getting a set of aussie 2bbls soon though

 

I knew they were different, and always heard they were balanced differently which makes sense as the extra stroke length.

Wonder why would the timing marks be different? Keyway can't be moved as timing sets interchange. Same front covers?

Now you have me curious, gonna go out and compare them. My results below ... later.

I knew some early 400 blocks had the Windsor transmission bolt pattern, don't recall hearing the crank flange being drilled differently but maybe so. I'll be back later .... going out before it's dark.

 

The dampeners are the same in the 335 series down to the timing indications.Would suspect that the outer ring has slipped on the inner ring if there is a difference,the firing angles are the same in this series.

 

My 400 balancer priopped up under truck near front of 351M and it's balancer. I looked close at rings and got these numbers which I can cross reference on Damper Doctor's web page.

D1AE-AA (FOR3513) as came on my 400 with build date of January 04, 1979.

D5AE-BA (FOR3023A) on my '77 351M as it sits, it's original.

Damper Doctor Online: Casting Number Interchange

Was coming back after correcting my post above to say .... "Yep, y'all are right" ... mostly.

For some reason there's like twice the steel in the outer ring of my 400's damper as is in the ring of the one that came on my 351M.

I also see that my truck's 351M balancer has balance holes drilled in front of ring, the 400 one has no drillings in the balancer at all.

Like I thought they should be, timing marks are located exactly the same, and read from 30 BTC - 10 ATC ... and inner hub of balancer looks to be nearly the same which is the part with the big counterweight except that the 400 balancer has a wider flange to accept the wider rubber and wider outer ring as can be seen below, note how shallow the one on the truck is.



The one for my 400 however, is deeper because the center is made wider for the wider ring.




Anyway, DamperDoctor show both for a 351M or 400 and will rebuild them and sell back to you with a core .... a bit over $100.

I learned something .... Thanks!



.

 

good info everyone

 

I was looking around on the forum about motor swaps and found this. I have a 351m and wanted to swap out for a 400 since there wont be any motor mount changes ect...

My question is how much difference will this swap make? No hopped up parts other than maybe a RV cam and an intake. I'm running BFG 35's and the 351m just dont seem to have the guts. I'd go for a 460 but with all the mount changes and bracket swapping I think I'll just stick to my original block and save myself the headache.