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I have an 85 dodge diplomat that I plan on turning into a street sleeper. Right now i have the original 318 an a 383 block sitting around. I think it might be safer going with the 318 first an move on up to the 383 soo. . . question is i would like a A833 four speed to go in the car but without sacrificing the bench seat up front an i would like to put a 8 3/4 "489" casting in the rear. An does anyone know how to get a M-body to handle in the corners?



The Diplomat M body cars were available with a police package that was very effective for handling. I think it was called a S-21 package. The same option was often used in the taxi cab package.

The front swaybar is 1.25 inch, the rear was .75 inch. The rear cop springs had front eye segment bushings that had the 'comfort' holes filled with 3/8" rod and had red paint on the bushing. They had the police 15x7" steel slotted cop rims with dogdish caps. The rims weighed 2 lbs more the other factory steel 15" wheels. The extra steel helped to keep the wheels from flexing on hard corners.

The steering box is more performance oriented than stock.

The 8 1/4 rear axle is plenty strong. An 8 3/4 from b body 1966-67, or 1968-70 can be modified at the perches and used.

I have had a BB in an F body. I had it well sorted. There are many issues to consider. A 360 and a 383 are equal in performance when modified.

360 = 383? NEGATIVE!

360
cast crank
1.88 intake valves
small doglegged port heads(probly cracked)
long thin cyl walls
4 head bolts per cyl
wet intake manifold
expensive to get cu inches

383
forged crank
2.08 intake valves
bigger ports
5 bolts per cyl head
dry airgap intake stock
cheap to make into a 426

My advice is a hot rodded 318 or 360. It will be a better balanced car that should satisfy your needs.

I also did the 4 speed swap, but with bucket seats. An automatic with a shiftkit and 2400-2800 stall would be plenty of fun, (just tight enough for regular driving). I also found the 3.21, 8 1/4, rear axle to be the best compromise.