I see that Callies has a 4.250 inch stroke crankshaft on the shelf for the 340 block. Can anyone tell me what problems I might run into if I tried to install one of those into a 340 replacement block?

The crank comes with 2.10 SBC rod journals so I'd probably go with a 6.250 long SBC connecting rod. That leaves 1.205 for the compression height which is tight but I think it would work. The piston would need about 25 cc dish to keep the compression reasonable for pump gas.

I'm wondering about clearance in the bottom end and if the oil pump will fit and stuff like that. I know lots of guys use the 4.00 crank without any issues but I haven't seen much talk about the 4.250 crank.

Any input? Pictures would be great.

Shouldn't be a problem

https://board.moparts.org/ubbthreads/show...e=0#Post5439966

Andy the first thing you have to check is if the block core had provisions for the stroke like all the R3's do. What I mean is you have to see if they filled in the lower part of the water jacket where you have to grind for the rod bolt at the bottom of the cylinder. If you look with a flashlight through the holes in the deck you can clearly see a bump in the bottom of the water jacket.


4.375 stroke with 2.100 pin

The oil pump pickup will probably clear with most steel rods. This rod was 2.100 chevy pin at 4.375 stroke. But this rod had a very beefy big end. Also, I had to change the oil pump at one point and then it had way more clearance and would have not needed that notch.

another

one more

I also had to notch the other side of the cylinder but I also doubt you would have to do that. Oil pan should clear without a problem as well as the cam is not an issue.

anoter

most of the time it,s the rod disign the problem, just make sure you dont use a big rod..

direct conection virgin x block,4.250 magnum with GRP 1200...

I'd be using a 4.250 Dragonslayer with 6.250 long Compstar H beam rods and a Mopar Performance 340 replacement block. So it sounds like those parts have a chance of fitting together. The catalog says that the Mopar block is filled in around the oil pan rails so hopefully that means it can be ground for rod clearance.

I'm not sure how big the Compstar H beam rods are. They are fairly lightweight so I'm guessing they are profiled.

With a 4.060 bore and 4.250 stroke the motor works out to be 440 inches on the button. I'll have to run the CSA numbers to see where the torque peak is but I bet it is low. 3500 rpm or so?

CompStar 6.250" .927" x 2.100"

The combo I ran in FAST was a Callies 4.25 Magnum with 2.0" rod journals and Compstar 6" chevy rods. This was in a stock block. The grinding was very not bad @ the bottom of the cylinders and no prob with clearance to the pickup.

I am not sure if the outside dimension of a 2.0" rod is any smaller thant 2.1". I'd imagine they just change the bore size. The clearancing I had to do was similar to what Dragrcr posted.

That sounds really close to what I'm thinking about. Do you remembe any of the specifics around the bobweight or what the crankshaft weighed?

I talked to Callies today and they figured that a 4.250 crank would weigh about 48 lbs. K1 said their cranks weigh 63 lbs which is a big difference.

Callies said that to get the 4.250 to balance they would need 2 or 3 pieces of heavy metal on each end. They said that the 4.0 cranks usually balance without the heavy metal but the 4.250 usually needs some weight.

I figure the bobweight of this motor will be somewhere in the 1700 gram range depending on how light the piston ends up.

Andy, when they say that the block is filled in they are talking about the oil pan rail. Not the water jacket. All I am saying is with your combo of stroke and rods, if you have to grind a lot, it would be advised to look inside the water jacket. With an R3 they fill that area in and you can go hog wild with the grinding

4.25" Magnum WITH Rifle drilled mains & fully profiled CW's is 46.5 lbs

It's basically just a round skirt piston at 1.31" CH, small dome, .043 ring pack, Vertical gas ports and a .990 pin, setup for GRP 1200 underneath, (piston with ligting progrm @ 450grm

Better keep this one thanks!

1.31 CH means you must have gone with the 6.125 long rods? I was thinking of using 6.200 or 6.250 just to keep the piston away from the crank a little more.

I haven't decided on the ring pack yet. Lots of options at 4.060 bore size including 1.2, 1.5, 0.043, etc.