leave 240 stock to turbo it,or add 300 crank

need some help here an hope you guys can help me out. i have a stock 1969 240 block i want to turbo charge. but i was thinking on adding a 300 crank to give me some higher revs.my question is..... well it give me more power with the turbo.an what type of piston go with the 300 crank?......... or should i stay with the stock 240 and dont add the 300 crank.........let me know what you guys think,
thanks

The 300 crank will reduce your revs, not increase them.
The 240 crank is much stronger since the main and rod journals overlap slightly.

...but you cannot make up for the lesser displacement by further increasing the boost; The head mounting is the same and that is going to be the limiting factor in boost level. The head gasket is not a well supported as you would like in a boosted engine.

So there's no black and white answer.

i thought i use the 240 rods on the 300 crank, to give it more rev.

That won't do a thing for RPM potential.
240 rods will lessen the side loading on the pistons which is always a good thing, even more important when you boost the combustion pressures with a turbo

okay so I guess I will put my 240 back to stock. of course with forged pistons. i would guess in 69 that the compression was 9:1

How much power are you wanting to make?

... and how much boost are you planning to run to get there?

well.i would love to get 300hp or more at the rear wheels. boost i would guess at 7psi max. i am puting it in my 65 falcon wagon. love to have it run 12's...... that my goal,

djfalcon10":2t2ppgdg said:

well.i would love to get 300hp or more at the rear wheels. boost i would guess at 7psi max. i am puting it in my 65 falcon wagon. love to have it run 12's...... that my goal,

Click to expand...

Lets say around 400 hp at the crank.
The 240 would need head porting with larger valves along with a matching cam to get 400 hp using low boost.
Head work is still a good way to go even if you were doing a 300.
You can meet your power goal using less boost.

Consider using a 300 non-efi head in either case.
The combustion chamber is larger allowing you to use a flat top piston in the case of a 240
or a shallow inverted dome piston in the case of the 300.
Also the larger chamber has less valve shrouding and doesn't require as much work when installing larger valves.

The 240 connecting rod (without the oiling hole in the big end) makes a good performance rod after the beam has had the forging parting line removed, then polished and shot peened. Install ARP rod bolts and then have the rods resized.

With the 300 head and 240 crank, you can use forged 302 sbf flat top pistons with a 1.6" compression distance to get around an 8.5 compression ratio with a zero deck height.

When using the 240 rods and 300 crank, it would be best to use a custom piston with a 1.2 compression distance and around a 25cc reverse dome dish.
Custom pistons using 2618 alloy are around $90 a piece.
The short pistons used in this combination weigh a lot less than stock and the piston skirt does not protrude as far out beyond the bottom of the cylinder bore at BDC as the stock pistons do.