Whats difference between cross flow and loop charged?

[mannyq]

What is the difference and advantage between a cross flow and loop charged?<br /><br />What are the 2 square ports on either side of the flushing port (exhaust relief??) on a 2000 Johnson 115? I know water comes out of the P hole but don't see anything out of those ports.<br /><br />Thanks.

 

[walleyehed]

Re: Whats difference between cross flow and loop charged?

Fuel/air induction method, piston design, port design. <br />Most of the modern outboards are now "Loopers", and usually 60deg blocks-more compact in size. <br /> I guess I didn't really answer your question.....the square ports are drain-backs, and some of the holes near there are lower-unit drains for the cavities that exist internally in the lower sections.<br /> Some of these locals allow easy water passage when off plane at idle, and allow a place for excess water to bleed off at high speed, as you will notice the high-speed water pick-ups are streamlined, and force water to the pump-the excess is bled-off.......

 

[walleyehed]

Re: Whats difference between cross flow and loop charged?

I think there was a thread a day or two ago that addressed the differences in power between the two. Try a search for Loop charged, or crossflow.

 

[rickdb1boat]

Re: Whats difference between cross flow and loop charged?

web page<br /><br />And there was this past post from JB <br /><br />The simplest 2 strokes use cross flow, cross charge or cross scavenging (same thing). The fuel/air mix travels from the crankcase and enters one side of the cylinder. It is then deflected toward the head by a deflector on the top of the piston, crosses the top of the cylinder and comes down the other side toward the exhaust ports, which are opposite the scavenging (intake) ports. Because the charge crosses the cylinder from one side to the other, we call it cross flow, or cross scavenging. It's weaknesses are: the deflector on the piston prevents ideal combustion and complete scavenging, limits compression ratio and makes the piston heavier than a flat-topped piston would be.<br /><br />Loop charged or loop scavenged (same thing) engines are preferred. There are two sets of intake, or scavenging ports. They are set roughly opposite each other and angled toward the side of the cylinder opposite the exhaust ports. The two scavenging charges enter the cylinder and merge at the side of the cylinder opposite the exhaust ports, turn up, and LOOP over themselves back down to the exhaust ports. The result is more complete scavenging with a more concentrated charge. The flat-top piston is lighter, allows ideal combustion geometry (domed combustion chamber, centered spark) and maintains a more even temperature.

 

[walleyehed]

Re: Whats difference between cross flow and loop charged?

Interesting web page Rick, thanks for sharing!

 

[jethro 25]

Re: Whats difference between cross flow and loop charged?

thank you rick. Your answer was exactly what I wanted to know.I have a thirsty 140 loop but remember my fathers disgustingly economical loop 70.so economy is not the issue, I guess.