Thread: 5.7" VS 6" Rod

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I am retired from a career in "theory" and I am certainly a learning novice in SBC technology. Further the talking is over for me since I have gone ahead with brand new 5.7 rods in my 350 rebuild, but I would like to learn more with respect for the experience of engine builders, especially of the SBC design. First a partial answer to the thread question may be found in the article on a long rod in a 400 block to make a 350 as found in:

http://www.airflowresearch.com/artic...le03/A3-P1.htm

There the advantage seemed to go to the longer rod and there is dyno data. Of more interest to me as a real puzzle is how the dwell time can be different for TDC and BDC as shown in the Isky site above. How can this be? The only way I can see this is through a small amount of slop in the piston pin, but in an ideal circle conversion of linear motion to circular motion I can't visualize why there should be a difference in dwell time between TDC and BDC. In another site this is said to be equal:

http://www.chevymania.com/tech/rod.htm

The point overlooked in the discussion above is that of fuel octane and detonation. The long rod in the first site above ran on 87 octane at 11:1 C.R. and I briefly considered purchase of a 383 based on 5.7 rods with only 9.5:1 C.R. but that engine required 93 octane fuel. So can someone explain to me how the dwell time can be different for TDC and BDC? In addition is it not better to opt for a more powerful engine on more common (poor) low octane fuel. This is just a theoretical discussion for me but I hope to learn more about "my" engine, the SBC 350.

Don Shillady
Retired Scientist/teen rodder