anyone know about or have 6.25 rods in their 400? is there extra machining neccesary for these rods? What crank and pistons are neccesary and what compression, and displacement did u end up with?

Same question for 6 inch rods.

I think a 427 small block would be cool if its workable.

thanks!

PS - where was the power band at, what was the avg and pk TORQUE (what i care about), and avg/peak hp?
what heads and cam?

Thanks and sorry for all the questions

 

Before you ask a question like that, do the numbers.

The 400 stroke is 3.75"; half of that would be 1.875". The height of a stock SBC block, from crank centerline to deck surface, is 9.025" more or less. So: 1.875", + 6.25", = 8.125"; that leaves about 7/8" between the center of the wrist pin and the top of the piston. The wrist pin is .927" diameter; half of that would be .4635"; add that to the number above, you'll find that the top of the wrist pin is less than 7/16" from the top of the bore. The top compression ring is usually about .25" below the top of the piston; in a racing pistoon it would probably be 1/16"; so the top of the pin bore would be all the way up almost to the top ring, certainly past the second ring.

I certainly wouldn't build an engine that way. However an aftermarket tall-deck block would allow it to work.

A 427 small block in a stock block is workable. However, if you use a used block and you bore it out .030" over like usually is done, you come out with a 434. I've built that.

Rod length doesn't alter displacement. The 434 in question used 6" rods. With 6.25" rods and a 4" stroke, the wrist pin would almost come out of the block, and there would be no room at all above it for rings or the top of the piston. So, a 427 with 6.25" rods is impossible in a stock 400 block.

 

ok....it doesnt have to be a 427....i just thought it would be cool if possible.

but what about my question...does a used block have to be altered?

i was just thinking that the longer the rod the more torque and when i saw 6.25, it caught my eye. at about 1100 bucks for just the 6.25 rods...i think i might just go with the 5.7 or 6.0s at about 5-600.
thanks
Rick

 

Ummm..... yeah.

To use 6.25" rods in a 400, somehow you'd have to add about ½" to the distance between the crank centerline and the deck surface.

I don't know right offhand how to do that in a machine shop though. Somebody else might have a plan.

But you don't need to increase the rod length to something that won't fit inside the block, in order to make a 427 SBC out of a used block. 6" rods, which do fit in a stock block, work fine. Changing the rod length doesn't affect the displacement, so you could build a 265 or a 434 SBC with 6" rods or 5.56" rods, if you could find them in the right journal diameters, and you could find pistons or have them made which you probably could.

I don't know how to explain this any more clearly, I've even given you the dimensions of all the parts, maybe I don't understand what you're asking.

 

i understand you. thanks for your help.

i did not know before that rod did not affect displacement.
i thought however, that if you got a crank with a shorter throw and then put a longer rod it would be real torquey. forget about the 427 crap, i was being childish.

thanks again.

 

jeez i sound stupid...if i shorten the throw on the crank, the stroke will shorten right? seems like i want to put a longer stroke crank with the same 5.5 rods? or perhaps the 5.7 rods.

 

There's no particular reason to "forget the 427".

What is it that you would actually like to do?

 

an engine based on the 400 or 402, blueprinted and balanced ( i want this thing to run like a dream), stroked (in hopes that it will create more torque with ease), bored out of course.

In doing this however i would like a displacement number that is both high and *pleasant sounding to the ear* (i.e. 427, 420, 454?).

i am hoping to use the AFR 210s or perhaps some edelbrock victors...i hear they are pretty good.

thanks RB,
Rick