Are the tips baffled? Pics would help.

Above 3000rpm, the exhaust pressure is working against the system trying to divert it through the prop = killing the solenoids/ cause components to fail prematurely.

You have to look at it as a performance,through-hull design that can go quiet for idle/ no wake zones - not the opposite

What they said for above 3000rpms.

I would swap out the straight tips for muffler tips or add muffler inserts to the tips.

Thanks for all the comments and suggestions! How much sound reduction comes from muffler tips or inserts?

most advertise 4-10% reduction.... most are oriented to keep below legal max limits at idle as the base standards (80-90db)

GGB muffler inserts

For optimum performance you don't want the exhaust to go thru the prop, but the motor still does fine going thru the prop, just going to loose a few hp at top end

4-10db reduction. A 10db reduction reduces the noise level you can hear by more than half.

I have to disagree completely. I ran for 16 years plus with Rex Marine sound selectors closed 90% of the time and never had a reversion issue. Reversion is more likely with poor exhaust design, massive cam overlap, and at or near idle rpm. Above 1000-1200 rpm there is no time in the reversion pulse to go up stream. I know the Rex Marine unit was bullet proof and could care less if it was closed, open or partially open at any rpm.

I've got the old 4 wire CC and the solenoids are in the relaxed/off position when it's exiting the prop.

I've always heard that running >3k RPM (for extended periods) with exhaust going thru prop can overheat the drives; more so if engs have been significantly modified. Anyone know of this is true? Sounds plausible to me.