by Bob Doty

360 Stroker Motors

The 360 is an excellent engine as it stands. It shares the common rod length with the 340, the basic block, heads, manifolds, etc. The crankshaft has a larger main journal diameter, but the same rod journal size as all small blocks. My personal performance preference is the 360 over the 340. The primary reason is the longer stroke. 3.31 vs. 3.58. This allows more bottom end torque, the ability to use more camshaft and still be streetable, and less gear in the rearend. I have built identical engines on the 340 block and the 360 block, and the 360 will be about 2 to 5 tenths quicker in the quarter mile. It simply does not have to work as hard. This sometimes does not sit well with the legendary 340 diehards. The 340 is an excellent engine, but I leave them for the restoration crowd. The 360 is cheap to acquire, plentiful, and tough. The cast crank is basically bulletproof and will work forever to 6500 RPM.

The 360 may be stroked in a couple of ways. I have built two stroker 360 engines and they were awesome performers. Each was built in a different manner. The standard configuration is a .040 over 360 with an aftermarket crankshaft with about a 3.79 stroke. They are available from 2 or 3 different sources including Mopar Performance. They must have the 360 main journal size. (there are also the same cranks for the 340, with the smaller main journal size.) Once you acquire the crank, you must have custom pistons....because of the longer stroke....otherwise the pistons will strike the head at TDC. Remember that only half the stroke increase is at TDC and the other half is at BDC. You could consider milling the piston approximately .105, but would have to consider the thickness of the top of the piston.

Another method is the welded up crank, then offset ground to get the stroke increase you desire. This method is currently popular for the 440 to get to the 498 displacement size. It is also somewhat costly.

The third method that I have used to build my first 360 stroker back in 79 or 80 was to cut the rod journal down and offset grind it. We cut it down to 2.00 small block Chevrolet rod journal size and offset ground it to get the stroke increase. I used 6.00 length Chevrolet rods (Carillo) and Ross Pistons. We bored the early (71) 360 block .080 and ended up at a calculated 392 cubic inches. It was a screamer for about 10 races (oval track) and then the crank flange broke off. I built the twin to it with the same results. (harmonics).

The 3.79 stroke with a .040 overbore is 383 cubic inches. The early 360 blocks (71 to 73) will accept an oversize of .080. This is due to the fact that the 340 and 360 shared the production tooling until the demise of the 340 in 1973. The standard bore size of the 340 was 4.040 inches and the 360 was 4.000. You can overbore the 360 to the 4.040 size and still have the material to go to a .040 over 340, or 4.080 inches. There have been successful bore jobs to 4.100 on the early blocks. That would be a .060 over 340.

The bottom line is can be done. Is it cost effective with the crank work and the custom pistons? Probably not. A .060 over 360 is 372 cubic inches. Eleven cubic inches is not worth $2000 to me.

There are custom cranks for the 340 and 360 on the market that result in 406 cubic inches. They all cost about the same, so if you are going to go......go first class!!

Thanks for the time.

Bob Doty

Page updated November 22, 1997

Return to the HMCC Tech Page

Return to HMCC Home Page