I know by reading the tech articles that the cast crank block is a different part number, but what exactly is different about it? I've looked over the one that I have carefully and nothing has jumped out at me yet. I assume a forged crank would drop right into it but maybe there are small differences in clearances or something?

I haven't gotten around to sonic testing it or checking the hardness yet so I need to do that stuff next.

Someone correct me if I'm wrong...

I believe the answer is that journals size is different, bearing journal is wider and walls are thinner in the later block with the cast crank.

_________________
My truck is a Frankenstein creation
Built from the dead carcasses of others
And brought BACK TO LIFE!

Cast SL6 cranks have narrower journals to give the connecting cross-sections more material mass, the diameter of the journals is the same.

I did talk to a person who told me he took a forged crank and installed it into a cast crank block by welding-up the crank's main journal edges to fit the narrow cast crank bearings. He also swapped-in the earler con rods to avoid reworking rod journals.

This all makes sense but personally, I have never done it so I can't guarantee it to work.

It is a good idea, a way to use the later cast blocks and the stronger forged cranks and get the lower surface area / friction of a narrower main bearing. Too bad there is all that welding to do.
DD

Thanks for the info. Guess I need to get myself a forged crank block so I can do a better job of comparing them.

I did go ahead and sonic check that cast crank block that I have. Block ID stamp is 8 225R E.

This block is pretty thick compared to the V8 stuff. Not too sure how it stacks up against other /6 blocks since this is the first I've ever checked. Major thrust walls were all up around 0.250 which is pretty thick. Thinnest walls are between cylinders of course and run in the 0.180 range. For comparison, it is hard to find a 440 block that has 0.250 on the thrusts and the tween walls on a 440 are often in the 0.125 to 0.140 range.

Well, I thought I new what I was talking about. I've been doing a lot of reading (especially Doc's stuff). I've been lurking around the message board for three months...

I bought a truck with a slant recently; and, although the engine is fresh (3k miles) it still needs a lot of work and doesn't run right. So, I'm getting ready to do a little work on it

You see, my father is <i>convinced</i> that a six cylinder isn't capable of performance (he keeps pointing out a neighbors "10 second car"; or, refering to his Camaro -- both have small blocks in them). I am going to prove him wrong

_________________
My truck is a Frankenstein creation
Built from the dead carcasses of others
And brought BACK TO LIFE!