Ian,
There isn't any performance advantage and I have only see it done once in 8 years.
I think the old K spec engines did have a tendancy to drop the inlet valve when the collet failed and the valve stem had a nasty habit if sticking itself out of a different part of the cylinder head than the valve guide - not nice and expensive. Using the exhaust collet reduced the incidence of failure, however.
With the newer engines (probably E spec on) Honda installed a simply cap through which the valve moves mad of a rubber like material. Now if a valve collet fails the valve does not tend to fall all the way into the cylinder and the repair bill is a new collet and an oil change.
Graeme
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