xlr82v2

My Feedback: (1)

Anyone ever try a Mousse Can Pipe on an OS 25FP?

What size can? How many more RPM did you get out of it with what prop?

Thanks for any help... just wondering if it's worth the trouble of getting the stuff to do it.

PaulSwany

My Feedback: (45)

I ran on on a 25 fsr... It was getting 17,000 rpm on a 9x4 prop!! was awesome!!! I got mine from Kentucky Hobbies... But I can't find the web address right now....

PaulSwany

My Feedback: (45)

Found it... Flying Z hobbies... http://www.flyingzhobbies.com/main.html Click on the Specials link to see the header and pipe setup.

Goinstraightup

My Feedback: (26)

Dave McDonald says use a 1.5 dia. X 4 inch can on that engine. I was just asking him the same question. He also likes the 9-4 or the APC 10-3 prop on that combo.

Dave McDonald

My Feedback: (19)

Yesterday I checked the RPM of an OS 25FP with the 1.5" by 4" can, and also tached it without any muffler at all. Both open exhaust and with the MCP read 15,200 rpm with a MA 9x4 prop, OS #8 plug, and 15% Mach 7 fuel. I didn't have the stock muffler with me to see how it compared, but usually a stock muffler subtracts several hundred to a thousand rpms over open exhaust.

This 25FP w/MCP is being flown in a PBF where precise and instant throttle response is critical for maximum fun. Awhile back I tried a 1.5" by 5.5" long can, but it screwed up the throttle response.....so I put the 4" can back on. Unfortunately, I didn't bother to tach the 25FP with the 5.5" can.

Someday in the near future I'll tach the 25FP with the stock muffler, and also with the 5.5" long can to see how they compare.

jlguru

Dave correct me if I'm wrong, I'm new to this MCP stuff, still
"shocked and awed" by the performance of this simple design, and trying
to make sense of it all.

But I thought the critical dimension on a MCP is the average distance
gasses travel from the exhaust port to the exit point of the muffler
(it should be a multiple of the length of the pressure pulse generated
by the 2 cycle engine). Thus the length/diameter of the inner tube
relative to the exhaust port is more important than the absolute
length of the can. All other things being equal, it would seem to me
changing just the can would result in minimal performance change.

You report a significant difference between a 4 inch can and a 5.5 inch
can. Are there other geometry differences between the two MCP's?

Also, I'm curious as to the sensitivity of the design to the diameter
of the outlet hole. My two MCP's (one on an old OS46FX, and one on
an OS40SF) are currently at .25 inches. Yet the outlet on the stock
muffler is larger. What would happen if I enlarged the outlet hole?

Live long, and prosper
Jerry L. Gubka

Dave McDonald

My Feedback: (19)

You're not alone. I've been tinkering with MCPs for about 8 years and still haven't figured why they work so well. But they do.....so I keep tinkering with them.


I'm not an expert on tuned pipe theory, but I used to run real tuned pipes on several planes in the past. From what I've read and experienced, your explanation is basically correct for real tuned pipes. But keep in mind that real tuned pipes are almost always tuned at full throttle for maximum power. They work great at full throttle, or at idle, but usually screw up the mid-range throttling characteristics as the engine goes on and off of the pipe. On a fun fly plane where precise throttling is important, these sudden changes in RPMs during throttling can be very annoying, which is why I don't like real tuned pipes on fun fly planes.

My first experience with a MCP was "Shock And Awe". Here was a simple White Rain can producing a similar power boost to an expen$ive Macs tuned pipe (Shock). But what really blew me away was the throttle response. The engine smoothly throttled up and down without any RPM surges (Awe). This MCP seemed to contradict everything I understood (or thought I understood) about tuned pipes.

After 8 years of tinkering with MCPs on engines sizes from .15 to .90, I havent found MCPs to be critical at all. In fact, I've pretty much given up on trying to understand how they work. Instead I usually end up tinkering with several different size cans to see which one works best on a particular engine, in a particular plane, and with a particular prop.


There was a significant difference in the throttling characteristics between the two cans. The 5.5" can created power surges during throttling similar to a real tuned pipe.....which is why I took it back off. Later on I'll rerun the test with the 5.5" can to see if there was also a difference in the maximum power output.


From my experience, the outlet diameter of a MCP doesn't seem to be critical to acheive maximum power. And the length of the stinger tube doesn't seem to matter at all. In fact, I rarely bother to install a stinger tube anymore.

But the outlet diameter does effect the backpressure which gets fed to the fuel tank. More backpressure usually means more consistent needle valve settings since the fuel is being force fed to the carb. And the more backpressure, the more the high speed needle valve needs to be pinched down. And this is where adjusting the outlet diameter of the MCP becomes useful.

If you have an engine that goes rich in the mid-range, reducing the outlet hole of the MCP results in more backpressure, which results in pinching down the high speed needle valve, which results in a leaner mid-range mixture.

For an engine that goes lean in the mid-range, increasing the outlet hole of the MCP results in less backpressure, which results in opening the high speed needle valve, which results in a richer mid-range mixture.

By adjusting the size of the outlet hole, you can tune the mixture setting in the mid-range, which results in even better throttling characteristics. And this is where having a short stinger tube comes in handy so you can pinch it down with a pair of pliers to fine tune the backpressure....as long as the diameter isn't too small to begin with.


Yep, I've noticed this too. I used to bore out the exhaust hole on stock mufflers to reduce backpressure and get more RPMs.....and the MCP seems to go against even that theory.

Take a look at the size of the outlet hole on the MCP on a TT 42GP in my Fazer. You wouldn't think a 42 size engine would hardly run with this small of an exhaust hole, but it turns an 11x4 at 15,600 RPM, which is within 200 RPM of a TT Pro 46 with a stock muffler.

Are you beginning to see why I gave up trying to understand these MCPs?

xlr82v2

My Feedback: (1)

Ok, I can see that I need to acquire a MACS header, and go looking for beauty products

Which hairspray will make my engine have fuller body and bounce? So I'm looking for a can 1.5x4? I'll have to ask the wife to help with this one, she'll get a kick out of that!

Also, which header size do I need (short, med, long)? The 25FP/MCP is going to go on my Taco. I would think the Medium would be the best size, or does it matter? I guess it just determines how low the MCP will be on the fuselage?

Also, where do you put the pressure tap? On the can or on the header?

Goinstraightup

My Feedback: (26)

Yes, the header size is determined by what your plane size is and what it takes to get your can in the right spot on your plane.

All the info I've seen (and what I've always done) is to put the pressure tap on the can. All the instructions I've seen recommend against putting the pressure tap on the header.

jlguru

Dave:

Thanks for the response. Guess I'll just lay back and enjoy it without
fully comprehending what's going on. LOL ... guess I was speaking the
truth when I told my compatriots "... it's black magic!". MCP's look
like yet another consumer of hours of experimentation
(or tinkering/fiddling as my wife calls it).

Live long, and prosper
Jerry L. Gubka