Mercury Through The Years...

**FUJIMO** · 08-31-2018, 11:43 AM

...Massey @ Parker Arizona...

**FUJIMO** · 08-31-2018, 11:44 AM

**FUJIMO** · 08-31-2018, 11:48 AM

**2us70** · 08-31-2018, 11:56 AM

A lot of the alky boats had a second lever on their throttles to control a sliding adjustable expansion chamber exhaust system. Don't know if the post stacker motors like the twister series exhaust systems were some sort of expansion chambers.

Originally Posted by Gordon02

Fujimo, I want you to know that I come on here everyday to see what photos you've found and posted. Pure, genuine appreciation!

Now, I do have to ask all here - were these outboards really a lot faster with these megaphone exhaust installed or were they just louder? Nothing about them resemble anything I've ever used or seen on a motorcycle. I'm from the motorcycle world and I have designed and built my own 2-stroke expansion chamber exhaust. A well designed expansion chamber can actually "supercharge" the 2-stroke cylinder by pushing the escaping fuel/air charge back into the exhaust port just before the piston closes it with the pressure of a sine wave reflecting back from the reversion cone. The result can be as much as 7 psi of "boost" pressure from the exhaust alone. Combine the expansion chamber's design to the effect of increased intake velocity where the flow continues to fill the cylinder even after the piston reaches TDC and the overall affect can be 14 psi combined "boost" into the combustion chamber - referred to as "on pipe".

Are others wrong when they report the megaphone does not do any of this? I've always understood that 2-strokes needed the expansion cone, the belly cone, and finally the reversion cone and a bleed tube end to "supercharge" the combustion chamber while the 4-strokes needed the megaphone to maximize exhaust gas velocity. Thanks again for the photos! Gordon