Tech1 posted a reference to several discussions by Ron Iskederian, one of which essentially says that the longer rod length only makes a small improvement in power. Clearly R. Iskederian is an independent thinker with a lot of experience, but almost all of his discussions negate current trends. I am particularly interested in the discussion of longer duration exhaust timing compared to the data in "Ryans Dyno tests".

http://www.ryanscarpage.50megs.com/combos1.html

In particular Ryan's Example 56 shows that the case of a cam with a longer duration exahust pattern still benefits from the use of 1.6 rockers only on the exhaust valves. This seems to say that both higher lift and longer duration help scavenge better. Maybe R. Iskederian's point is well taken for long duration cams but Ryan's Example 56 seems to say that for mild cams only a bit longer in duration than stock do need more exhaust duration and lift. I have wondered for quite a while why most of the Isky cams have equal duration for exhaust and intake patterns. I guess the point is well taken that the only way to actually figure this out is with actual dyno runs but boy these different views are confusing!

Don Shillady
Retired Scientist/teen rodder