[concobra]

Hello David

Thank you for responding to my inquiry regarding the motivation for using the longer rod.

Allow me to respectfully submit the followng observations and paraphrased comments.

1. There are no rules in engine building that hold true for every engine that is built. In other words as it pertains to this verbal exchange a longer rod does not always equate to more torque. The old thinking that a long rod helps an engine produce more torque has been challanged by some of the best engine builders and designers over the last twenty years. To support this statement, Reyer and Morrison tested serveral different rod lengths in a big block chevy and found no to very insignificant variations in torque produced. Their ending comment was, and I paraphrase, don't worry about rod length. just pick your piston pin height and crank through then define the length of rod you need.

Please keep in mind that Reyer and Morrison had no dog in the fight. They were testing purely for the sake of determining rod length advantages or disadvantages. I would submit that most magazine articles are written with a high degree of bias towards embellishing the results. So I don't trust them. Also, how accurate is the test in the magazine? If any other variables were added to the increased rod perspective such as a cam change, head change, manifold or whatever then the results are misleading at best.


If you give in to the concept that additional rod length is a benefit then the question arrises, how much benefit. I would challenge that the piston dwell time and initial decending speed of the piston as the crank rotates pulling the piston down between the original rod length of 5.9545 and the 400m rod length of 6.58 would be insignificant. So why spend the extra money and even more important, the extra time and engineering resources to end up with very little if any gain?

I would submit that power, either defined as torque for HP is created in general in three areas. (Given engine size as a constant.) Air flow, compression, and cam timing. Focus on these three. Understand the intended uasge for the engine and create the correct combination of parts that address this intended usage.

a. Flow your heads. Even if they are stock any engine build and cam selection requires this information to pick the other two catagories.
b. Define the RPM range the engine will need to make power in and pick a cam that meets these needs. Keep in mind the cam must work with your head flow, exhaust type, vacuum requirements and intended usage.
c. Pick your compression ratio based on dynamic compression and not static compression. (Pump fuel octane is a given here.)

I wish you the best on your build.

Humble Submitted
Concobra

PS. Stay away from fast ramp cams such as Comp Cams' Extreme Energy grinds. These were developed for low ration rocker arms and have a tendency to produce excess valve train noise and wear when used with 1.6 ratio and above rocker arms. (This comment is based on my personal experiences and no quantifiable evidence.)