Looks like the Cadillac 368 is so reviled that nobody is making pistons for it anymore. I've found a couple of pairs, and a set of four, but can't nail down 6 the same, except for a $700 auction listing on the unmentionable website. The offset grind in the Cadillac article results in a 3/16" stroke increase, only half of which (3/32" = 0.09375") needs to be accommodated at the top. The "Cadillac" piston has a .029" short compression height, and the 292 rod is .053" shorter, leaving the pistons about 0.045" in the hole on an unmolested block, very similar to the stock configuration. This gives roughly 9:1 with an 848 (79cc) head. Note that the Cadillac piston pins are larger than both the 261 and 292, requiring that the rod ends be opened up to accept the larger pin. I'm wondering why I couldn't just offset grind the crank and use the 292 rod, but mate it with a 261 piston, which would end up about 0.016" in the hole. Compression would be about 9.5:1, without decking the block or milling the head. And, since both the 261 and the 292 use a 0.927" piston pin, shouldn't they mate without modification? Or is there another difference I'm not aware of? Any other reasons this wouldn't work? (Rod to piston skirt clearance?) Thanks for any insight. 261 Caddy 261 stroked 261 Bore 3.75 3.80 3.78 (+30 Pistons) Stroke 3.938 4.125 4.125 CID 261 281 278 Head Volume cc 95 79 79 (848 head) Swept cc / cyl 712.7 766.6 758.6 Compression 7.13 9.08 9.49 Piston comp height 2.036 2.007 2.036 rod length 6.813 6.76 6.76 1/2 stroke 1.969 2.0625 2.0625 total 10.818 10.8295 10.8585 block height 10.875 10.875 10.875 piston below deck 0.057 0.0455 0.0165
We used to buy piston blanks from Jahns but I believe they have been bought out. They had a cheap cast and a moderately priced forged piston line. Google "piston blanks" and see what comes up. You can then bore the pin hole for any pin size and compression height and choose your ring size. We have a piston cam grinder but never use it as round pistons aren't that noisy (depending on clearance) and setup is easier. On cast pistons I prefer the ones with the cast in pin reinforcing plate. If you can find an old McQuay-Norris catalog it lists pistons, rings, pins, by size rather than application. Also has all the engineering data like compression height and ring groove size and location.
261 Tom foolery The whole thing is a waste of time because you cannot rev. a 261 overly much with out it dying rapidly and catastrophically . The 261 alone or even a really well built 235 will have amazing power and it's not like you're going to spin the tires with any old tech long stroke engine unless you're rich and like re placing broken blocks a whole bunch . It looks cool on paper but in real life this is another loosing proposition .
Other than being a waste of time, any reason this wouldn't work? Not planning to wind it to 6,000rpm, just want something a little different and I'm a big fan of torque.
Power Building Then build it bone stock taking the time to properly balance everything and CC & match the combustion chambers , new stock 261 cam and solid lifters , you'll be amazed at the torque ~ this is after all , a TRUCK engine so it's got sufficient torque to twist the U-Joints to scrap if you so choose . Anything over 3,600 RPM's is over speeding this long stroke 1940's Tech engine and will destroy it rapidly .
