palric

iTrader: (1)

I am trying to understand the diff in terms of results when using standard rod size vs. long rod size for a 350 sbc.

I've seen enough results of standard rods everyone uses them right? What about the 6 inch rod why do engine builders choose to use the long rod over the stock size ?

If you use a long rod do you change the CI of the motor or do you just alter the height at which the rod connects to the piston (what do they call that a wrist pin ?) so if you use a non-standard rod size would you have to use a non-standard piston as well ?

Does this setup make more power ? Less power ???

thx in advance guys,
RP.

Kevin Vandevenne

iTrader: (3)

I am by no means an expert on this, but this is just my basic understanding of using a 6.0 vs a 5.7 rod in a 350. Someone please correct me if i'm wrong.

There are many advantages to a longer rod, but basically what it comes down to is that a 6.0 rod has a leverage advantage over a 5.7 rod. It also will reduce friction in the motor as there is less side loading on the cylinder wall with a 6.0 rod than a 5.7 rod. With a 5.7 rod, when the piston travels up the cylinder, the 5.7 rod starts at a steeper angle, which puts force on the one side of the cylinder wall. A 6.0 rod can start moving the piston up at a lower angle, reducing the load placed on the cylinder wall.

Another advantage is that with a 6.0 rod, the piston will stay near TDC longer than a 5.7 rod. From what I understand, this will generate more downforce (power) as there is a longer time period in which pressure can build on top of the piston, while at TDC. I believe you can run less timing on a 6.0 rod motor as well, which is preferable.

Running a longer rod will not effect CI in anyway.

Weather or not a 6.0 rod is better than a 5.7 rod in a street motor is debatable. You will see gains from the 6.0 rod, but when considering the cost vs return, stock 5.7 rods are probably a better choice, for a mild street motor. I belive with a 6.0 rod, you need a different piston, which i assume costs more than a stock one. Long rod pistons have a shorter piston hieght as the wrist pin is moved up closer to the rings.

Anyways, I hope this answers your questions.

Daz

iTrader: (1)

To add:

Longer rod also goes is slower to rev(thats some high RPM motors use the 5.565 rods..which is another topic..lol)..

6"Rod
Pros
1)Everything that KevinV said

Cons
1)Cost..You need offset pin pistons and theres an issue about the 2nd oil ring..I forgot if its eliminated or moved(custom pistons)..but since these are standard pieces it cost a lot..
2)Heavier..revs slower(but once it gets going..)

dAZ

6speedIROC

iTrader: (3)

You nailed it! Good explanation.

Yah, they almost always move the wrist pin upward on the piston, sometimes even into the bottom of the oil ring.

Cruz'N Bruz'R

I've been told that the motors with the 6" rods don't last as long. Why, i don't know. Ask AcceldZ