ORIGINAL: earlwb

There is something of a whole lot of art and science involved with valve overlaps and how much is enough.
Generally you adjust the overlap timing to coincide with the exhaust system and its scavenging effect at a specific RPM range, which can be quite narrow in some cases. To take full advantage of it, one needs to have a exhaust system designed for it. But normally as the overlap increases the power developed moves higher up the RPM band. But with a small 4 stroke engine that is revving over 10,000 RPMs already, the valve overlap can be quite extreme anyway.

Now with model engine the timings or degrees of overlap can vary from larger engines as there is a scale effect that occurs as the engine gets smaller and smaller. The air and fuel don't change size as the engine gets smaller, so that remains constant.

There are some valve overlap calculators for determining the camshaft to use or to make.
http://www.wallaceracing.com/camcalc.php
http://www.rbracing-rsr.com/camshaft.html

These valve overlap numbers can give you an idea as to hot an engine is setup too.
ref http://speedtalk.com/forum/viewtopic.php?f=1&t=23156
APPROXIMATE adv overlap ''operational'' reference chart:

10* - 40*….towing
30* - 60*….ordinary street
50* - 75*….street performance
70* - 90*….street/strip
85* - 100*...race
95* - 115*...Pro race

The thing is, his operational reference chart right above, only seems to fit Big Blocks properly. If you take percentages and scale things down for small blocks, it ends up looking like this:

9* - 35*….towing
26* - 53*….ordinary street
44* - 66*….street performance
61* - 79*….street/strip
74* - 87*….race
83* - 100*...Pro race