Johnson Outboard Question.

[WaterWitch2]

Just curious. What's the difference between a Johnson crossflow and a looper?

 

[bassboy1]

Re: Johnson Outboard Question.

Loopers have flat pistons, plugs more like that of a car and *may* get better mileage.
Cross flow motors have domed pistons, and flat plugs, and are better suited for low speed and trolling applications.
Most outboards today are looped, but there are some outboards, made for trolling in the 15 hp range, that are still cross scavenged.
There are differences in head appearance that will tell you which is which.
I hope I got this right, as of ten minutes ago, I knew nothing, but figured, what the heck, may as well research it, and learn something new.

 

[AguaSki]

Re: Johnson Outboard Question.

WaterWitch,

I think I have a similar boat and motor as you. Mine is a 1978 SSV-188 with the 140 hp Johnson. We both have the crossflow motor.

Just out of curiosity, what type of performance are you seeing? RPM's at WOT, and top speed?

 

[WaterWitch2]

Re: Johnson Outboard Question.

WaterWitch,

I think I have a similar boat and motor as you. Mine is a 1978 SSV-188 with the 140 hp Johnson. We both have the crossflow motor.

Just out of curiosity, what type of performance are you seeing? RPM's at WOT, and top speed?

I bought it a couple of months ago but haven't had it out yet. Maiden voyage should be this weekend or the next weekend. I'll let you know how it goes.

 

[Frank Acampora]

Re: Johnson Outboard Question.

To further clarify: A cross-flow engine has a deflector cast into the piston head to deflect intake gases up into the cylinder. The gases flow "Across from bypass ports to exhaust ports.

A loop charged engine has the ports specially spaced and the bypass ports are angled upwards to force the gases to describe a loop up into the cylinder and combustion chamber. Typically, a loop charged engine has a flat topped piston with hemispherical heads. The heads have an outer "squish" band to squeeze the gases into the central hemisphere at top dead center. Because this squeezing makes the mixture more turbulent, it burns faster. Thus: a looper needs way less timing advance at WOT--typically around 18 degrees. They also tend to be slightly more efficient because less of the incoming charge bleeds out the exhaust ports. They can also produce more HP per cubic inch because of the efficiency.

By the way: The loop charged engine was perfected in the early 60s by a Polish model airplane racer named Ted Wisniewski and K&B engines. --.40 cubic inch displacement and well over 2 HP--alcohol and nitro--25 % oil--20-30 thousand RPM. He picked up on the work of a Polish physicist named Felix Coanda and also perfected the tuned pipe. You could hear it and actually see the model accelerate when the pipe came on. He was unbeatable and set world speed records. The Japanese noticed and their model airplane engines incorporated his advances, then The Jap bike makers got into the act and developed lightweight bikes that were unbeatable.

Now I'll shut up. I write too much.

 

[WaterWitch2]

Re: Johnson Outboard Question.

Thanks for the info guys. Appears to be a big difference between the two.

 

[Chris1956]

Re: Johnson Outboard Question.

Just to add to what Frank and the others said, the loop-charged motors have multiple transfer ports, while the cross-flow motors have a single large transfer port. The pinnicle of the loop-charged motors was the 7 port loop-charged system used on many motorcycles (never made it to outboard motors). This setup had four transfer ports aimed to sweep almost all of the exhaust out of the combustion chamber, a single exhaust port, a standard intake port, and the seventh port was an elongation of the intake port such that when the piston closed the intake port, and the transfer ports "blew" the exhaust out, a slight vacuum was created and the seventh port let a bit of fuel/air from the carb directly into the cumbustion chamber, boosting power. Of course the carb needed to be mounted on the neck of the cylinder for this to work.