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5.7 or 6.0 inch rods????

2K views 4 replies 4 participants last post by  4 Jaw Chuck 
#1 ·
Im planning on building a small block 400. Im going with a roller cam, roller rockers, and forged crank and pistons. I want this motor to rev to 7000rpm safely. Ive been told the longer the rod you go with the less beating the crank will take and it will give you more torque. Will a 5.7 inch rod be sufficiant or would a 6 inch rod be better to use, and will a 6 inch rod work in the 400 without major machining? Any advice would be very helpful, Thanx alot.
 
#2 ·
it is true longer rods take less beating. if you get forged rods it is not as much of a concern. I JUST built a 400 w/ 5.7" It was briefly metioned that i might want to use 6" but i declined, as i wanted to go the safe route. Besides, i wasn't sure how high that would push my pistons, so i can't answer the machining queston on 6" rods. g/l with the engine. can't wait to get mine in my truck. hopefully tomorrow!!
 
#3 ·
they make pistons at a reasonable price for the 5.7 rods and they make Them for 6" for a little more,now this is what happens when you put longer rods in, the ring pack gets tighter and higher on the piston because the piston pin has to be located higher on the pistons, if the pack gets too tight the piston may rock in the bore causing failure at high rpms,such would be the case when using 6" with a 400 crank,therefor I would go with 5.7 if useing a 3.75" stroke,but if I were useing a 350 crank the 6" would be the way to go
 
#4 ·
The difference is mostly academic and theoretical and does not matter one wit on the street. If you are racing on the ragged edge then go ahead and spend the cash to get the last 5 HP out of it by running the 6 inch rods but in reality on the street you would never know and will just be spending money on a part you will never see and never feel the difference. Besides when you shove all those rings together to fit the longer rod in you are running into a reliability issue, rings are spaced a certain distance apart for a reason-durability.

Forget the magazine articles and run what God gave that engine, you won't be sorry.
 
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