Cross Flow, Direct Charge and Loopers...What is the difference and which do I Ha

[SeaKaye12]

Hi,

Every so often I see mention here of at least three different engine designs.Cross Flow, Looper and DirectCharge. At one point someone even posted an image that showed the difference between at least two of them.

I'm still confused.

Which one came first? Are all three still used? One is better for Power and Performance? Another is better for idling and trolling? Another is better for fuel economy?

Lastly...which one is mine? I have a 1977 Merc 850 (4 Cyl) SERIAL # 4721196

Thanks for reading, Chuck

 

[Chris1956]

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

SeaKaye12, Since no one has answered the question, here is my two cents.

Direct charge is Mercury's version of a Cross flow motor. Your '77 is a cross flow, but I am not sure if Mercury continued to call the 850s "Direct Charge" as late as '77. My '73 850 was labeled a "Direct Charge". The cross flow motors have the pistons with the raised "eyebrow"-shaped top. This helps sweep exhaust out of the cylinders and pull in fresh mixture.

Loop Charged motors have a different transfer port configuration, and the fresh mixture under pressure from the transfer ports sweeps out the exhaust. These motors have flat-top pistons.

The most sophisticated Loop-charged motors came on motorcycles. They were called "Seven Port Loop Charged motors". These had carbs mounted halfway up the cylinder, four transfer ports, an intake port, an exhaust port and the seventh port was an elongation of the intake port, and allowed the carb to directly feed the cylinder (bypassing the crankcase), because of the vacuum caused by the four transfer ports. I do not believe that outboards ever had this type of technology, due to the complication of casting this many passages in a multicylinder, water-cooled motor.

 

[Texasmark]

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

There was a comprehensive response within the last month that was reasonably techincal and explained the actual fuel charge movement......may get it in archives search.

Here's my 2c.

Cross flow has the domed piston to help guide the charge thru the combustion chamber.

In '68 OMC introduced a revolutionary engine that was said to be loop charged; i.e. the charge came into the cylinder, hit the head, looped around and blew out the exhaust. To assist this the exhaust had to be tuned so that one of the other piston's discharge gas helped to fire the cylinder that was firing....like holding the fuel charge in the cylinder firing till it fired. That was one reason for the first design being 3 cylinder.....was said that 3 cyl was the only geometry that allowed that to happen.....later on they learned how to do it on 2's and 4's.

As a result, the top of the piston was flat; didn't need the crown (dome). Also the piston had a hole(s) in the side which allowed for the charge to enter and swirl around.

These engines were said to produce more hp per cu in than crosses and most definitely were more economical.

Merc had to do something, OMC had the patent so Merc came out with what was called Direct Charge. Kinda the same critter, but retained the domed piston; had the hole in the piston and the tuned exhaust. I had an '89 115 I6 that was a DC engine. It actually had 2 exhaust systems; 2 sets of 3 for the reason mentioned. It was only 99 cu in, for a 115 prop rated hp engine, and had tremendous fuel economy and torque as compared to my previous 125 OMC that was cross flow.

When the OMC patent crapped out, Merc started looping theirs too. I think '90 was the model year they changed the mid ranges. I think all of their V engines were loopers which date back to mid '80's as I recall. (Lotta ifs, and's, and buts d ) My '02 3 cyl 90 hp is looped.

For some reason Merc kept the old original 4 cyl cross flow and moved it around in the 30 to 50 hp range over the years and finally dumped it, but that was after 50 years of production.

Do to the above reasons, you are hard pressed to find a non-looped 2 cycle engine today.

About all I know about it without some research.

Mark

 

[SeaKaye12]

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Thanks Chris and Mark. I'll keep searching for that older post. I think I may have seen it; not sure. I've tried with the new search tool on this forum and haven't had any luck so far. If anyone else comes across it...please post the link here.

Thanks! Chuck

 

[Clams Canino]

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Direct charge is Mercury's version of a Cross flow motor. Your '77 is a cross flow, but I am not sure if Mercury continued to call the 850s "Direct Charge" as late as '77.

Almost but not so. "Direct Charge" is a MODIFIED cross-flow that MUST be distinguished from the earlier plain vanilla crossflows. If you don't get it right - you'll set the spark advance too far ahead and KILL it.

The 77 is "direct charge" whether it says so or not. In general the direct charge engines went from 1970 to 1988 excluding the 44ci fours that stayed traditional cross flow. (All the motors after 1970 with a 2.875" piston are direct charge.)

Direct Charge outta be called "directed charge". That big "eyebrow" on the top of the piston makes for a better direction of the incoming charge and much better burn efficiancy. So much better, that the max advance needs to go from 34.5 degrees for a 1969 125 down to 21 degrees for a 1970 135 - and you STILL get 10 extra horsepower outta the same 99 cubic inches.

-W

 

[Texasmark]

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Clams, my 89 115 was direct charged.

Mark

 

[Clams Canino]

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Then it was in fact, a 1988 leftover and a 6 cylinder.

In 1989 they made 4 cylinder loopers.

-W

 

[Texasmark]

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Well That's what was on the title. I don't know about the engine marking. Yes it was a 6 and would hang in to 6 grand all day long....never missed a lick. In the 7 years I had it I replaced the water jacket cover (over the cylinder heads), an impeller, and that was it.

Mark

 

[croSSed]

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

One of the things that I've noticed about the difference between loop charged and direct charge motors - if they were carbureted, that is - is that direct charge motors idle better. Two-stroke loopers idle like a full on drag car. Direct-charge motors idle more like a "cammed" street engine. Maybe it's just me, but that's what I've noticed.

TG

 

[Texasmark]

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Re: Cross Flow, Direct Charge and Loopers...What is the difference and which do

Well, I think they made direct charge from 3 cyl 60 hp thru their I6's when they were doing it. My I6 idled like a sewing machine and that was one reason I wanted the 6 cyls back when I bought it.

I never heard a 3 cyl idle, but I now have a 3 cyl looped 90 hp Merc and it is obvious that it is not an I6. Course 90 hp from 3 cyls makes for a pretty big bore so when a cylinder hits, it grinding out 30 hp potential. My I6 was only putting out potentially 19 hp.

Butttttttt remembering my '75 omc 70 hp 3 cyl looper, it idled pretty smoothly as I recall.

Mark