exhaust headers - cyl. overscavenging ?

[Artsi]

Hello

I've been wondering a procedure how to verify whether my engine has a presence of cylinder overscavenging.

Engine in question is a 1504cc four cylinder, naturally aspirated, twin carburated (a pair of 40mm Dell'orto down draft), 304º cam seat to seat (= 260º at 0,050" valve lift), 103,5º lobe separation, cam currently timed at 4º advanced.

Running an exhaust gas temperature gauge (EGT) would of course show indication of raw mixture being drawn to exhaust header, where mixture burning would elevate temperatures. Problem is where to draw a line between okay temps, and what temp rating would indicate presence of overscavenging.
Are there any guidelines what temps virtually zero cam overlap engine would produce? Any significant deviation from such table would most propably be a result of overscavenging. (I assume this to hold ground if ignition timing is mapped properly.)

Thoughts and suggestions are most welcome.

-A.

 

[evelrod]

Go get an EGT if your concerned about this issue. The single probe versions are relatively inexpensive. A digital pyrometer could possibly be used instead. At any rate, based on my experience with several of my engines that were built very near your specs, I would say that "overscavenging" would be the least of your worries.

Rod