what is a looper?

[a70eliminator]

I know it's an evinrude motor but what class of and vintage and why is called a looper something about the way it fires?

 

[F_R]

Re: what is a looper?

I know it's an evinrude motor but what class of and vintage and why is called a looper something about the way it fires?

If you are familiar with two-strokes in general, you know that in a crossflow engine the fuel/air mixture is blown into the cylinder through the intake ports, hits a deflector on top of the piston, which directs the charge to the top of the cylinder and "washes" the remaining exhaust out the exhaust ports.

A looper has aimed intake ports and flat-top pistons. Flat topped pistons are much lighter, meaning less recriprocating weight. Also, any time the charge has to go around corners like when it hits the piston deflector, there is a big loss in efficiency.

Chainsaws are all loopers, explaining why they can scream like they do without flying apart.

 

[rockyrude]

Re: what is a looper?

It has to do with the the way the fuel mix gets into/out of the motor. There are two ways the the mix goes in/out. The older motors were cross flows, when the piston goes down it opened both intake and exhaust ports directly opposite each other in the cylinder, causing a "cross flow" across the top of the piston. The newer motors have a "dome" on the piston causing the mix to "loop" over the top, the looping does a better job of getting the exhaust out and fresh mix in with resulting better fuel economy.