is the same casting used for the 4.25 bore block as the 4.5 bore block?

if you bored the 4.25 block to 4.5 , is the wall thickness as thick the same as the 4.5 bore block in it's standard form?

Yes

ursus,

why would merlin, if they are the same, charge 200 bucks less for the 4.25? seems to me i can bore it at a very low cost and end up with the same thing.

28Saber,

It will be cheaper for you to buy the World Products Merlin II block that is already bored to just under 4.50" That way all that needs to be done is honing them to size. The block that comes 4.25" bore size is may be $200 less, BUT when/if you take it over to Performance Engineering or some place similar it will cost you about $375 per block for them just to bore the block out to 4.50" Therefore, it is much cheaper to buy the block from World Products with it bored out close to where you want it. Again, the only thing needing to be done from there is to hone it to size. Hope you understand what I have said.

BTW, I went through all of this the hard way. Preformance Engineering did all the work on my blocks/rotating assemblies. They did an excellent job.

Saber28, ask World products not me, just because you think something does or doesn't make sense does not determine whether it is a fact,,, fact they are the same block and you can bore the 4.25 to 4.56 per world products

ursus,

hey , i'm not doubting you just seems strange

A merlin II can be bored to 4.625" Max.

HIMMM

what are the max strokes (crankshaft) can be used with these blocks?
do you have any idea?

An 11.625" Superblock will accommodate a 5.600" crankshaft.

4.75" is max for the Merlin II. It takes a lot of clearancing and the rods come exceptionally close to the cam.