Exhaust back pressure and mixture strength

concours · Mar 10, 2023

acotrel said:
A 2-stroke expansion chamber is designed to resonate and stuff mixture back through the exhaust port.

Sorry, this statement is false.
The expansion chamber tuning of pressure waves is designed to have a negative pressure wave available at just the right time when the exhaust port is open, to help improve the flow of intake charge being pushed up from the crankcase, through the transfer ports, clearing the exhaust from the combustion chamber and more effectively filling the cylinder with a less diluted intake charge.
Stuffing exhaust gases back into the exhaust port is not a design target.

Fast Eddie · Mar 10, 2023

concours said:
Sorry, this statement is false.
The expansion chamber tuning of pressure waves is designed to have a negative pressure wave available at just the right time when the exhaust port is open, to help improve the flow of intake charge being pushed up from the crankcase, through the transfer ports, clearing the exhaust from the combustion chamber and more effectively filling the cylinder with a less diluted intake charge.
Stuffing exhaust gases back into the exhaust port is not a design target.

Well bugger me… that’s one of the few things Al has written in yonks that I thought was correct

Exhaust back pressure and mixture strength

concours

Fast Eddie

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