I have a question I am building a 406 and I purchased a set of 5.7 rods for it. I did it mainly because I heard that it was alot better to put 5.7 rods in those motors. I was wondering what does it do? Does it make that much of a difference? Does it increase horsepower or Torque? Does it increase the displacemnet at all?

 

rod length affects rod angle doesn't change displacement. best to research it a little more before you commit your self, and rod lengty depends on the pistons you have, if you have pistons yet.

 

I bought pistons for a 5.7 rod 400 crank along with them. My question is what are the benifits to a long rod 406? would it be torque or horsepower?

 

TTT

 

Torque or HP. Probably neither. You just get a better rod angle, which can reduce high rpm stress. This is good in a circle track car that sustains high rpms. In a street car the advantage is probably none to very little.

 

If your talking 5.7 versus 6inch.. there will not be much difference on a 400. You really not going to move the power band up much if any. Intake minimum cross section area plays the largest role in powerband location. Much more than cam timing really.

If your talking 5.565" verus 5.7", you get a much higher quality rod and piston with 5.7 selections. Even more so than 6" selections.

Small block 400s tend to sign off at 6500 or less anyway.. don't worry about it bc any good quality aftermarket rod can live at 7000.

 

I don't plan on bringing it past 6000 RPM's. I was talking about going from a 5.565 to a 5.7 rod. I was just wondernig why I heard that this was the way to go.

 

it is not quite as strong as a 5.7 bolt from what I understand. That and the piston selections for 5.565 suck severly.

 

There are 2 reasons this is the way to go. The first is because 5.7 rods are more readily available in high quality configuration. The second is the rod ratio. The higher rod ratio puts less side loading on the piston, increasing durability and reducing friction, and increase piston dwell time at TDC promoting a better burn and lowering the chance of detonation. Both of these increase torque and hp, though not by a seat of the pants feelable amount.
There is a reason that if your looking at crank, rod, and piston kits for 383's and 400's one of the first kit upgrades is going from 400 sized rods to 5.7's, if they even offer a kit with the 400 rods, a lot don't. Hope this answers your questions.
John
Oh yeah, bear in mind that you may have to clearance a little bit for the 5.7 inch rods, sometimes you do, sometimes you don't. Depends on the rod and rod bolts

 

Actually clearance is the main reason that I don't have the motor back yet. Teh rods are hitting the cam on the rod bolt so the machine shop is going to clearance them for me for $60.

 

HEy rhuarc30 you got to pu at least a 406 in that projuect IROC of yours. Then they would all be over 400 cubes!