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Why are we having yet another discussion on this?
Joseph, Dave, the total change in stroke that can be achieved with perfect machining can be as much as .25" without a doubt. If you use the current surface of a 3500 rod pin, you can move the rod center .125". This gives you .125" more on the up and down stroke of the rod centerline (in relation to the crank centerline) making 1/4" possible - ever so slightly possible.
gectek, but unless you have access to equipment that can grind to the neighborhood of 50 millionths, this won't happen. Don't waste your time with a nodular iron crank when the 3500 crank is steel and is over 40 rockwell (making it forged according to the machinery handbook). Just press the timing ring off the crank and press a ring on mimicking the 3400 crank, like Joseph did for his 3900 swap.
I see that we might get slightly over .2" maximum.
*BUT* this might not be a bad thing since this can now use 3400 rods with 3500 pistons and the deck height will remain the same. 3500 pistons protrude .010" out of the deck.
I agree with Joseph that it does cost more to machine 6 throws vs. four. The crank has to be offset indexed to turn a rod pin. This means a fixture is made with a locating hole at each throw to make it concentric and able to be turned (you have to find center of each pin). This is actually a long tedious process, especially to make it true with both ends of the crank being variable, with both ends of the crank needing to change centerline -- and -- to be within .0002" (standard machining tolerance). The V8 crank has four centers (four setups), and the 60* crank has 6. Taking into consideration my shop charges $100-150 per setup, the 60* crank WILL cost more to turn - about 50% more.
Joseph, Dave, the total change in stroke that can be achieved with perfect machining can be as much as .25" without a doubt. If you use the current surface of a 3500 rod pin, you can move the rod center .125". This gives you .125" more on the up and down stroke of the rod centerline (in relation to the crank centerline) making 1/4" possible - ever so slightly possible.
gectek, but unless you have access to equipment that can grind to the neighborhood of 50 millionths, this won't happen. Don't waste your time with a nodular iron crank when the 3500 crank is steel and is over 40 rockwell (making it forged according to the machinery handbook). Just press the timing ring off the crank and press a ring on mimicking the 3400 crank, like Joseph did for his 3900 swap.
I see that we might get slightly over .2" maximum.
*BUT* this might not be a bad thing since this can now use 3400 rods with 3500 pistons and the deck height will remain the same. 3500 pistons protrude .010" out of the deck.
I agree with Joseph that it does cost more to machine 6 throws vs. four. The crank has to be offset indexed to turn a rod pin. This means a fixture is made with a locating hole at each throw to make it concentric and able to be turned (you have to find center of each pin). This is actually a long tedious process, especially to make it true with both ends of the crank being variable, with both ends of the crank needing to change centerline -- and -- to be within .0002" (standard machining tolerance). The V8 crank has four centers (four setups), and the 60* crank has 6. Taking into consideration my shop charges $100-150 per setup, the 60* crank WILL cost more to turn - about 50% more.
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