The SituationWe recently learned that Diamond Racing has introduced a new line of forged pistons for 383 stroker engines. these flat-top pistons are designed to produce around a 10.0:1 compression ratio when used with a 3.75-inch stroke crankshaft and 84cc heads (read Edelbrock). Well, that news sounded great to us since we had a clean '67 vintage 383 block sitting under the shop bench, along with a crankshaft that had been rescued from a rusted-out 413. So we whipped out the VISA card, grabbed the phone, and started in on project 432.
The Short-block CombinationOne of the first questions that people will have about this combination is why bother stroking a 383 block when stroked 400 blocks are all the rage? After all, putting the 3.750 stroke crank from an RB motor into the 400 block yields 451 ci rather than 432, and the bigger bore of the 400 allows the motor to breathe a little easier. those are all good points, but we had a nice clean 383 block sitting in our garage all ready to be used in a project. And since Ma Mopar cranked out about 3 million of these little 383 blocks back in the day, the odds are pretty good that plenty of you readers have them sitting in your garages also.
Putting a 3.75-inch stroke crankshaft from an RB motor into a B-block takes a little bit of machine work, but it isn't anything that a fairly well-equipped shop can't handle. The mains need to be turned down to the B-block size of 2.625 inches from the RB size of 2.750 inches, and the counterweights need to be trimmed down or heavily chamfered so they'll clear the main webs. Since we knew we would be using a lightweight rotating assembly, we went ahead and turned down the counterweights on a lathe to an overall diameter of 7.20 inches. This was small enough so it had plenty of clearance in the block, and it reduced the weight enough so the assembly was easy to balance.
The Diamond pistons we used are designed to work with 440-length rods, but since they require a 0.990-inch piston pin, a stock 440 connecting rod won't work unless the pin bores are machined. Reworking a set of stock rods can get expensive by the time all the necessary work is complete, so we decided to check out what the aftermarket had available. We found a company by the name of 440Source that is selling forged I-beam big-block rods with 0.990-inch wrist pins, and big 71/416 ARP rod bolts for only $395 a set. That price seemed too good to be true, but we ordered up a set and took them to our machinist. As far as he could tell, the quality on these rods was excellent for the price. The rod bolts are high-quality ARP units, the bore sizes and concentrics looked good, and the fit and finish was better than expected. We're not trying to convince you these rods from 440Source are better than, say, a set from Carrillo, but for this particular engine combination it was a better deal to buy these rods for $395 than it was to rebuild a set of 30-year-old LYs.