This is a new one on me.

318 strokers I always asummed everyone used 340 or 360.

How much can you overbore the 3.91 bore?

Would an Ohio Crankshaft 4.1 crank fit or even the 4.25 incher?

The 318 needs to be sonic tested before big over bores but the trends I saw when testing them was the 67-about 71 blocks had very thick walls and most would be fine at .090 and some even more. The mid 70s to early 90s were a crap shoot, one I tested was an 87 roller block and had places as thin as .078 with the standard bore. The magnums all seemed more consistant and could usually take a .030 safely but not much more. Whatever you get needs to be sonic tested because of core shift and now years of abuse such as people useing water instead of antifreeze and rusting htem out.

There are guys running 4.25 or more cranks in them a lot of it depends on the rod and rod journal size you run as well as the core shift in the block you use.

I built a 318 stroker (390cid) because I had a 1968 block and found a new set of Ross pistons for $300.

K1 4" crank, Eagle Rods (purchased from Todd Marsh "Sasquatch" owner of Marsh Performance) Ross flat top pistons, Edelbrock heads (OOTB), Air-gap dual plane, BG 750 silver claw, Comp solid cam (.540/.555 252/262 @.050 106 lobe sep) TTI headers, 727, Dynamic 9.5” converter, 3.91 gears in a 8 ¾ sure grip, carter mechanical fuel pump, full exhaust with Dynomax turbos, full interior, 3,400lbs race weight ran 11.35 at 118mph shifting at 5,700rpm

This winter I’m putting a roll bar in, pulling out the stock tank and going to a 5 gal fuel cell, Mallory 140 fuel pump, moving the battery to the trunk, moving to a spool and 4.30 gears, M1 intake, Holley 950 Alcohol car, and hopefully doing a valve job and some minor porting on the heads and hope to be running 10.90s next year.

I saw a 3.875 inch crank for a 340 mentioned in Hot Rod Mag.

Who makes this?

A 318 with +.030 overbore this crank would make for a 378 CID small block.

Would this be a good combo for a carb + turbo setup?

Anyone else have a combo as good or better as these guys?

I Love 318 block, esp the big X on both ends.

Most know the roots of the X block were based on the older truck blocks, so some of the old 318s are pretty good blocks.

I sonic checked an '88 rollerblock, and found it to be very consistent in wall thickness, with 6 cylinders at appx .205" thrust side before boring. A slight core shift on cylinder 1 and 2, I took care of by offset boring, and I ended up with all cylinders at appx .160 on the thrust sides, most had the same on the other side, and one cylinder was slightly thinner. When sonic testing, I found that the cylinder is more even than older ones, that are thick on the sides and thin against the neighbours.
This block was bored 4" and installs cast MP magnum 4" stroke pistons, ported 302 heads with 1.88/1.60 valves, and a little hotter hydraulic roller cam. It will be assembled this spring....
And, I X my fingers!!!

Always under rated! 318's can be made into fantastic engines and better get used to it as 340-360's dry up--I guess it makes way more sense to go with magnum roller stuff these days but a guy on a slim budget can make a great unit with careful parts selection --usually the stuff others discard.