Does exhaust valve duration have any effect on engine performance? I mean obviously it would if it were not long enough, but what is the problem on the other extreme by making it too long?

Seems intake valve duration is very critical in determining engine performance, what effect does exhaust duration have?

Exhaust valve duration should be fairly close to the specs of the intake valve, not exact, but close.
Reason being, is the volume of air brought into the cylinder on the intake stroke is going to have leave the cylinger on the exhaust stroke. And were the exhaust valve open for a very short duration comparitively to a very long intake valve duration, performance would suffer because not all of the exhaust gases would be expended.
I know that doesn't explain it very well, but I hope it helps.

EVO=exhaust opening EVC=exhaust closing
IVO=intake opening IVC=intake closing


EVO timing maintains combustion pressure late into the power stroke.
a small, (stock cam) has late IVO and early EVC. this has minimum overlap which also help to prevent exhaust gas reversion into the intake.
(so it idles smooth and has good low end power.)

a mild street cam uses the same late IVO and early EVC but has more overlap, this is to maintain combustion pressure but have a better scavenging effect. it will have some exhaust gas reversion into the intake. it has mild overlap (this slightly effects idle and smoothness at low RPM)


in a big street cam the EVO timing doesn't care about maintaining combustion pressure as much and goes for maximum exhaust pumping action. the IVC has to balance this by having medium overlap so it can try and close in time to pull in everything it can while minimumizing exhaust gas reversion. (this makes the nice loppy idle and power later in the RPM cycle.)

the short version is if you have the exhaust open for too long you will have to much overlap with the intake valve and loose combustion pressure early. then you will need to keep your rpm's high and rely on the cams scavening effects and increased exhaust pumping abilities to make power.