904 Trans For A Mild 318?

Tech Question


Andy Mack, 1971 plymouth Duster 318

Hi Rick. I have a question. I have a 1971 Plymouth Duster318 car that i and my father are planning on restocloning. My first questionis, will the stock A904 transmission hold up to a mild 318? I have heardthese trannys are aluminum and dont last long. My 2nd question has a lot todo with the last one, how much horse power and torque can I expect from the318, here is what I’m planning on doing:

1: 308 heads from a 360.
2: .450 inch lift cam…. I cant remembr the duration.
3: Hooker headers.
4: single plane intake with a 625 cfm carb.
5: and of course all the goodies like spark plugs, wires, viscous fanetc…

I just mainly want a good fun street car that may see one or two trips tothe track every 6 months. (By the way it will have 3:55 gearing) Thanksrick. Andy


Andy, so aluminum is weak, huh? Tell that to all those 8-seond super stockguys who run basically A-904 internals, lightened with even more aluminumstuff, in stock aluiminum 727 cases!

While a 904 will never last as long as a 727 in high-horsepower / hightorque street applications, building a 904 to last 100,000 miles behind yourrelatively mild 318 is pie, even dead stock it should be OK for a while,just crank up the line pressure. Remember, even some 360 cars came with904s.

Your buildup sounds pretty good. Longtime MA readers know that I generallylike single plane intakes for virtually any performance application, but a318 might — repeat, MIGHT — be the exception. With your gears, and,hoefull, a decent converter, it will probably be fine, but if it seemsespecially doggy at lower RPMs, you might want to do a re-think on themanifold. If you haven’t bought the manifold yet, maybe initially try adual-plane, even the stock 360-4 piece, though heavy, flows pretty damnwell, add maybe a 1″ spacer and you’ll be home.


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