Cross Flow vs. Loop Charged

bertherr

Petty Officer 3rd Class
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Jun 10, 2001
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What is the difference between a loop charged and crossflow induction system on two stroke engines? I understand the operating pricipals of a single cyclinder two stroke engine. Is the difference related to whether or not cylinders are isolated in mulicylinder two strokes? :D
 

JB

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Mar 25, 2001
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45,907
Re: Cross Flow vs. Loop Charged

Howdy, Bert.<br /><br />In cross scavenging the scavenging charge enters the cylinder opposite the exhaust ports and is deflected up to the combustion chamber by a deflector cast into the piston top. It then descends the exhaust port side and exits the exhaust port.<br /><br />In loop scavenging the scavenging charge enters the cylinder from both sides and is directed to the side opposite the exhaust ports. It then loops up through the combustion chamber and down to the exhaust ports.<br /><br />Loop scavenging is far more efficient, is less expensive to build, allows higher compression ratios without complex combustion chamber shapes (flat top piston), allows lighter pistons and works well with over-square engines (bore larger than stroke length).<br /><br />Schematic probably has elegant color graphics that can illustrate the differences far better than my words.<br /><br />Red sky at night. . .<br />JB :)
 

bertherr

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Jun 10, 2001
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Re: Cross Flow vs. Loop Charged

Well put. Thank you, Bert.
 

G DANE

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Re: Cross Flow vs. Loop Charged

If you compare i exa. a 30 Hp looper to a 30 HP crossflow, the power at wot should of cource be equal. Will the looper give more HP at lower rpm and more hole shot ?
 

Terry H

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Sep 25, 2001
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Re: Cross Flow vs. Loop Charged

G Dane...I replaced a 140 crossflow with a 120 looper and got better hole shot and more rpms. Crossflow wot is 45-5500 rpms and the looper is 5-6000 rpms. I use a jep pump and it is direct drive if that makes a dif. Also displacement is about 20% more on that particular size looper. I also really like the sound of the looper...deep throated kind of macho sound from the exhaust. I havn't had much in the way of problems from either one and I run them very hard...Snake River whitewater. just a Thought
 

bertherr

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Jun 10, 2001
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84
Re: Cross Flow vs. Loop Charged

The looped charged system sounds good. Are there any advantages to the less efficient, harder to manufacture cross flow design? Less emissions maybe? Thanks, Bert :D
 
D

DJ

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Re: Cross Flow vs. Loop Charged

Bert,<br /><br />The Crossflow OMC's were simply the technology they had at the time. They stuck with it for a long time simply because they had the manufacturing tooling to build them and they were relatively inexpensive to build.<br /><br />The looper technology came out in the late/mid 60's with the 3 cylinder-now a 70 hp. It was a natural progression to the loop technology for other engines.<br /><br />The crossflow was a very reliable design as is the loop technology. Each had their own minor operation differences, noises, etc.<br /><br />The loop is more efficient.<br /><br />I am restoring a Rude cross 90. I've owned many of the cross v-4's and some loopers. Horsepower/horsepower, they all generate their rated hp. The loop just adds some low end grunt.
 

bertherr

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Jun 10, 2001
Messages
84
Re: Cross Flow vs. Loop Charged

Thanks. I noticed in the latest edition of Trailer Boats maggazine, in the marine power guide, that very few current outboards have the cross flow induction. Only a few small HP Johnsons, mercs, and Yamahas. Bert. :D
 
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