What does the term Looper mean?

[79Rude115]

Rookie question - what exactly does "Looper" mean?

What year did it start on the john rudes?

 

[F_R]

Re: What does the term Looper mean?

In a conventional cross-flow two stroke engine, fuel goes from the crankcase into the cylinder via "bypass ports". The fuel charge then bounces off a deflector which is part of the piston, which directs it to the top of the cylinder and pushes the remaining burnt exhaust gasses out the exhaust ports on the other side of the cylinder. Every time the fuel charge is redirected or hits something (like the piston deflector), it decreases efficiency. The piston deflector is also heavy, meaning wasted energy through recriprocating mass.

On a loop charged motor, the intake ports are aimed so the incoming fuel charge is directed to the top of the cylinder, swirls (loops) and pushes the exhaust out the other side. In addition, at the last instant exhaust tuning shoves any new fuel back into the cylinder. The pistons are flat topped and much lighter for less recriprocating mass or wasted energy. They are generally capable of withstanding higher RPM. All modern chainsaws are loopers.

The 1968 Johnson/Evinrude 55hp were the first modern loop charged OMC motors.

 

[79Rude115]

Re: What does the term Looper mean?

Thanks for the info

So basically all Johnson/Evinrude motors post 1968 are loopers?

 

[Texasmark]

Re: What does the term Looper mean?

Nice Job FR. 8)

Mark

 

[Texasmark]

Re: What does the term Looper mean?

Woops! I goofed.

The 55 hp OMC came out in '68 looped. Evinrude called it the Triumph; don't remember what Johnny called it.

As I recall, it was years before their 4 cy engines were looped and when they started looping them, you could buy a 4 cyl looper or non looper in the same hp range; but the loopers had a much larger powerhead and cover. Had to do with the exhaust port timing you mentioned.

Seems that 3 cyl was the right number to get the sonic pulse reflections making it most efficient or something and at first that was all that was looped. Merc had what they called direct charge that was similar but had to wait for the patent to run out before they could loop....I assume. Since their big engines were 6 cyl, it was easy to use 2 ea 3 cyl exhaust tubes to get the reflections. Don't know what trick OMC used to finally get the 2's and 4's looped.

I know one thing; having had a '72 125 John cross flow and a '89 Merc 115 direct charged, the difference was easily 2:1 in fuel economy.

My 2c, probably half correct, if that much :%

Mark

 

[CFronzek]

Re: What does the term Looper mean?

Looper is a a contraction of "Schnurl Loop" Invented by a guy (probably a German) named Schnurl. And, with appologies to FR, it's just a different and more efficient way of charging the cylinder on a two -stroke engine.

 

[79Rude115]

Re: What does the term Looper mean?

Again thanks!

Sorry if I am being redundant but I would really like to know which models are considered loopers and which are not.

As far as the V4 John Rudes are concerned when did the loopers start?

 

[CFronzek]

Re: What does the term Looper mean?

Looper is a contraction of "Schnurle Loop" Invented by a guy (probably a German) named Schnurle. And, with appologies to FR, it's just a different and more efficient way of charging the cylinder on a two -stroke engine.
One of the advantages/drawvbacks of a two-stroke is it breathes so effectivly that it's capable of producing big HP numbers. But the good breathing allows some raw fuel to pass out the exhaust port before firing.

 

[wilde1j]

Re: What does the term Looper mean?

Again thanks!

Sorry if I am being redundant but I would really like to know which models are considered loopers and which are not.

As far as the V4 John Rudes are concerned when did the loopers start?

First year for V4's was 1985 with the 120/140's.

 

[Walker]

Re: What does the term Looper mean?

The 60degree motors are all loopers. As someone already mentioned the older 120', 130's, and 140 loopers were noticably larger both in displacement and visual size than the crossflows.

 

[alden135]

Re: What does the term Looper mean?

L acks
O nly
O perating
P ower
E asily
R uins your summer

:devil: