bore vs. stroke

[Barry_R]

Lots of variables enter into this decision. Airflow is crucial - and a larger bore will permit larger valves - hence better breathing. Since my FE entries are inline valve engines, they are inherently airflow limited - so I use the biggest bore feasable. Guys with better airflow combinations such as canted valve Clevelands will go for less bore and more stroke. The added stroke seems to help with low end and midrange torque - I thinks its a function of more distance traveled under combustion pressure per cycle - an advantage that dwindles at higher RPM - and an advantage that I unfortunately give up while trying to get the top end power I need to compete.

Contrary to some postings, these motors are in no way simple "dyno queens". Although the tuning may be on the ragged edge as we try to get the most points possible, the basic combinations are generally top shelf, and the engines would be pretty darn nice to run on the street. All I'd need to do is back the timing off by 2-3 degrees and "maybe" use a less aggressive cam (depends on your tolerance for spring replacement).

As an example, my 10.5:1 434 inch FE made 678HP at 6500RPM, and 587 TQ. All on 91 octane. It has a steel crank, Carrillo rods, Genesis block, CNC ported Blue Thunder heads, and a T&D rocker system. Nothing is gonna break at 6500RPM unless I screwed up somewhere. The attrition you see in the contest is usually tuning driven - rings, bearings, pistons and plugs getting hurt as the guys lean them out in search of the last possible score number. In your Cobra you would most likely drive that thing forever without pushing it that hard - dynos are usually tougher on parts than any racetrack.