crankshaft interchange question

[Relax360]

I know the 318 and the 340 have the same stroke but do they interchange?
Any machine work needed? Also the cast crank what power level should I look for a forged unit?

 

[rumblefish360]

They'll swap without fitment issue. Balance is another.

A cast crank will hold a good bit of power. If your running a 600 HP engine, it'll last a short time vs a 500 vs a 400 etc...

What is it your doing with the engine/car.
If it's a weekend warrior car, then I would safely yeild at 500 HP for long life.

 

[moper]

The 318 has lighter counterweights because the rods are lighter. It's been commonplace with bracket racers to use 318 and 273 cranks with 318 rods for years. Cast Mopar cranks are still very tough. A cast 318 crank will live at 450hp easilly. Block machining begins to get rather critical when you really want to make power on a cast crank of any type.

 

[perfacar]

hi, 318 steel crank, 58#, 340 steel crank 58#, 340 cast 52#. the front and rear throws are drilled on a 340 crank, 318 /273 are not. mopar did that to compensate for different piston/rod weights for balance.