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Hey guys,
We're going to do a little "bench machining" today  It's kind of like bench racing, but we're theoretically talking about engines, not how fast a car "should" go 
Most of this stuff is off the top of my head, so the figures aren't exact, but I just wanted to post about what we're trying to figre out over here because Nick at VT and I have received a lot of questions regarding the availability of a stroker 420A block. We know another vendor sells them, and we're looking into how we would be able to do it. This is what we came up with:
There are quite a few problems presented with using another crank. Two cranks that are similar to the 420A cranks are the 2.4 liter Chrysler crank, and the 2.5 Liter Chrysler crank. The 2.4 crank has a 101mm stroke and the 2.5 crank has a 104mm stroke. Using either of these cranks would totally screw up the rod:stroke ratio of the 420A, and you'd end up with something like a 1.20x rod:stroke ratio. So, unless you're only planning on running the motor to like 4500rpm, you're SOL. There's just too much stroke, no matter what you do with the rod length. Not only that, but you'd have to have custom rods, and custom pistons made. Not too far out of the ordinary, but there's more. The 101 and 104mm cranks have a wider main bearing surface. It's wider by around .060", and the mains are larger in diameter that the 420A cranks. How do you fix the diameter? You'd have to machine the mains down something like .300" (I think this value is larger than this, but I can't remember off the top of my head.) So, let's say we machine the diameter of the crank to fit the 420A diameter, and that's successful. Now, we've still got the problem of the wider bearing surface. How can this be fixed? Well, it could be fixed using a thrust bearing with a thicker shoulder on the thrust face, but those aren't avaiable. How else could it be fixed? It could be fixed by spray welding the crank, and having it machined back down. So, you've fixed that problem.
But it still goes all the way back to whether the crank will fit into the block or not (which we haven't measured) and whether or not you'd run a 1.2x:1 rod:stroke ratio. There's a snowball's chance that we'd ever try to make a 101 or 104 mm crank work in a 420A block. It's not going to happen.
What's another option? We can get custom forged cranks made. No thanks. Do you guys want to spend $4500+ for an assembled motor? I didn't think so :p
The other option? Offset grinding the 420A crank. I'm not confortable selling something like that, though. VT <i>can</i> do that, but I don't think they want to, either. Offset grinding that crank would put some pretty small bearings in it, and it becomes a question of how much you can offset grind the crank. Apparently you can offset grind them enough so that they become 2.2 liters, but you're not going to make up much more displacement than that.
So, we still haven't come to a conclusion on what we're going to do, but I just wanted to let you guys know we're working on it.
-Scott Glassbrook
FasterThanYou
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Motofool, if you read this, let me know when your done. Ive called a LOT of places looking for someone who could do the fabrication with no luck. It was like trying to find someone to put my stock sides on (called about 20 places, no luck)
