Hi all, I had a pretty decent look for this info but couldn't find any. I'm sure it must be here somewhere and if someone would like to post a link to it, that's all I really ask.

I'll just say I'm not going to do this, curious is all.
I've read the 425 rods are about 1/2"ish longer center to center than 455 rods.
Is it possible to install these on a 455 crank and into a 455 block with available aftermarket pistons? I guess pistons would need to have the pins closer to the top so as not to crash spectacularly into the heads?
Seems like a way to stroke the 455 with available parts if possible.

Again, I have no idea if this is possible, or if the 425 rods have the same big end journal size as the 455 crank or if it isn't a whole lot of work to get them to fit etc.

There would also be other considerations I'm sure, and if it was that easy lots of people would have already done it.

I'm sure someone has thought about this before though, just can't find where.

 

People have use 455 crankshaft, 425 rods with Pontiac pistons.

 

Thanks kennybill, that setup in a 455 block?

sounds easy but i'm sure there would be a few mods to do for rod clearance etc.

any idea how many more cubes that gives, i guess 40 odd ci.

 

The best reason they put 425 parts in a 455 block is a better cam selection at 39 deg. Some say the 455 parts will not fit in a 425 block. I have never tried it. The 455 block has clearance on the bottom of cylinders for rods. The 425 does not have clearance.

 

Longer rods move the torque peak up about 500 rpm. Longer rods reduce cylinder wall loading. Longer rods increase dwell time at TDC and theoretically decrease ping and improve breathing. To do this you must sit down and calculate compression height and deck height of the piston. Consult your machinist.

 

No, the stroke is determined by the crankshaft ( The distance the rod journal is from the crank centerline) .
Longer rods will change rod angularity , which has some performance advantages . If you can get the right pistons .

 

Correct advice above. 455 rods are 6.7", 425 rods are 7" center to center. No change in displacement, but other effects are as noted in above posts.

 

 

Henry "Smokey" Yunick always said to put in the longest rod possible. He felt the piston would dwell at TDC longer and produce a tad more hp. He was always looking for an advantage no matter how small. He was quite successful. Kind of like "watching your pennies and the dollars will take care of themselves."

 

But with apples to apples component weights, etc, a shorter stroke engine will rev faster due to the shorter axis of rotation. A good example is how a figure skater spins faster when the arms and legs are pulled in towards the body (conservation of angular momentum).

 

There are lots of things that enhance throttle response, rotating weight, compression, intake flow, and so on. Rod length/stroke has little to nothing to do with that.
I've had lots of 455's on the dyno that had excellent throttle response, and a couple of 425's. And I can tell you that different cams, pistons, intakes, carbs and a whole bunch of other stuff effects that. Again rod length is pretty much inconsequential.
P.S. my dyno guy does a lot of mountain motors, 858c.i. BBC. With 15.0:1 compression they rev with the best of them and make 1800hp with no power adders. And they have strokes of over 5.00". Go figure.

 

thanks guys and as always Good points above.
I guess I thought this would increase capacity but of course a stroker crank would be needed to get the piston to travel further down at the bottom of the stroke to increase capacity.

Yes I didnt quite have the brain in the right mode thinking about this.

 

Yes it does, the cylinders in a 425 block are actually about 3/8" shorter than a 455 block, hence why they don't have notches, don't need them.

 

Rod length has nothing to do with displacement, and a longer stroke requires a SHORTER rod, not a longer one. That's why the 455 has a rod that's 0.3" shorter than the one in the 425.

 

 

What have you done ?