Hello guys,

Maybe someone can point me in a right direction. I recently installed KS rear exhaust tuned cannisters in two different planes. Both with DA 150's. I was told by DA to have the headers lengths at 11 1/2" measuered along the centerline of the pipe from the mounting flange to the end. This was done with the header laid and measured on it's side. Attached the cannisters with about 1/8" gap to the header.

My question. Why would the engine seem to be very, how to put it, touchy, peaky, or very responsive at a certain point along the throttle transition which makes the engine seem like it was just kicked in on nitro. There also seems to be a small dead spot for throttle responce just prior to this drastic change in rpm's. Is there something I am missing ? I tried to change the curve on the transition to no avail. This is my first setups with this type exhaust systems.

Any advive would be helpful.

Thanks

Two problems:
first --there is no perfect length for tuned header pipes
secondly - you did not address which props you use and what rpm range to are using.
The correct length is made up from the rpm band desired and how easy it is for the engine to get there .
It is not uncommon to get incomplete advice -or understand what is going on.
Your problem - most likely is you are using too much prop load to allow th engine to match the setup.
There is a lot of plain old Bull sh it afloat about how certain setup can produce power increases and how the engin can be induced to pul bigger props .
In a nutshell -most setups which are tuned - raise the torque - or move the best torque further up the rpm curve.
Torque is increased if the engine will pull the same prop faster --than it did with NO tuned system.
Here comes the rub-----
When an engine produces more power -especially from a tuned system --it needs more fuel to do this
So
In order to do that -the carb must be set richer ----which makes the upper rpm band speed --harder to reach
Once the engine reachs resonant speed - the torque INCREASES and that takes more fuel.
So, how to fix that problem is the question
1-- you simply reduce prop load, allowing the engine to more easily reach into the "resonant" rpm.
2-- or you increase the header length and if the total pipe/header combo is right - the engine now moves up with little stumbling.
There is no free lunch
to pull more prop load - the pipe length may need to be quite long
the rpm gainwill not be as great but the rpm and resonant length will work
A lighter model will unload the prop more easily than a heavy draggy one - so a setup which worked on one plane may be no good on another
On your engine, the DA150 -- maximum power on th e cans/pipes will be in the 6000 rpm band -well into it - NOT under 6000
a 30x10 Mejzlic will likely give you the best power -easiest transition
Cramming on more prop load will just make it all worse

Hello Dick,

First off, thanks for the reply. Very informative. I ran tuned exhaust on pattern ships in the early 80's, but these gas engines have me baffled when it comes to this subject.

Yes, I was incomplete in the info provided, my fault there. It is hard to get a solid answer with out the proper info.

As for prop choice, I was using both an AirModels 28x12 and a Mejzlic 28x12. Both are 3 blade props. I see that plently of guys are using 28.5x12 Mejzlic 3 blade props. I really would like to run a 2 blade to help in the 3D envelope but would consider the well suited 3 blade. I like how quite these types of setup are and so do the neighbors. I did not have a way of checking the rpm's but the engine prop combo pulls the 40%Carden 330 weighing in at 41 lbs with no effort. I had gone with the suggestions of Brian Huffmier at DA on header lengths and several others thought it was about right for me. I knew that adjusting them may be necessary, but just don't want to botch a set of headers until I can understand more.

The engines throttle responce all starts out well on the lower end, it is that when I get up to say mid range, I am moving the stick quite a bit with no noticable rpm change and them BAM, it is on the top end. Like I said, I have played some with the curve, but no help. IThis weekend, I switched back to stock mufflers and the throttle responce is exactly and perfectly like I like it. Every throttle click advance, I can notice a rpm change and quick throttle advances are taken with no hesitations. This is why I am having a time understanding these can setups. I do run my engines just a bit on the rich sideon the low end, meaning that after a start the engine and taxi out to take off position, it takes just a bit to clean the engine out and I don't have any problems after the first 10 - 20 feet of take off roll. The high end is set close to where it needs to be cause I am not hurting on vertical power. It will pull vertical for as long as I want with no loss of power noticed on cans or stock mufflers. Upon landings, I find my engine temps to be between 160-170 degrees. I have never had any issues with my engine setups on stock mufflers with this way of thinking on engine tuning for me.

I will have to look into your advive on this problem. I did not expect this to be easy as the pattern planes weren't, but I am just trying to make sure that my understanding is there before I botch anything up.

Thanks for the advice and info.

Just a couple of more things--
Some guys futz with the throttle curve to patch this setup a bit . again- smaller props are a good fix-
My own fix is easier - I run two large, open, non tuned cans on my 42% Radiocraft
The engine/ can/ prop combo ZDZ160J/JMB cans/14x30 ZM prop, is extremely quiet and having given the model to other fliers to try, all agree this setup is absolutely seamless in throttle response.-
The big difference in my setup and your in cowl muffler setup -is noise reduction. (mufflers and higher pitched two blades)
If you decide to try in fuselage cans --avoid any which require specific header lengths - these also tend to have a step in them if the prop load is not matched .

Dick, Again, thanks for the advice. Attached are pics of what my setup was that is givig me problems, I have in the mean time put the stock mufflers back in the plane to try to get some flights on the plane. Other then mine being rear exhaust, it looks like I am using a simialr can mufflers that you are.

Thanks,

I'm sorry that I don't really have any additional insight to provide to you that Dick hasn't but I'll back up what Dick is saying. I tested some pipes for RC Showcase (AMTs) on a 160 Champ (on the bench) and found that I could get a clear increase in rpms- but lost the nice smooth throttle response. I could have played with it some to get the best comprimise- but I just didn't have the energy to fool with it.

I have the current Super 160 (like Dick shows in the picture) with the exact same headers and JMB mufflers in a 40% scratch built 260 and find that the power is way more than adequate, the setup was easy to do and the throttle response is great. For me, if power is already in abundance then this is the way to go. If you need more power, I can certainly understand why the tuned pipes would be a consideration. I see guys putting 150/160 class engines in these big planes (like the CA 3.3 Yaks) and going to the tuned pipes- they seem to be happy with them but, if I were to do one, I would just go to a bigger engine and try to forgo the pipes.

Tool Time Tim might not agree with me though.....

I have a set of MTWs mounted in a Carden Extra that I will be trying soon- it will be my first plane with a "header length critical" exhaust system. I haven't heard about issues with these like I have with the long tuned pipes so hopefully I'll like it- we'll see.


Dave

PS- The workmanship in the pics looks really nice. Are you planning on baffling the engine? The temps you quoted above seem very good so perhaps it's not needed- but I read where Tony Dalton took some in-flight temps on a DA100 and was up in the 280s.

Dave, You may have misunderstood something. I am using the can muffles from KS, not the tuned mufflers that look like softball bats, as I call them. Mine are short and fat with a rear exhaust. If I came across as them being a tuned muffler, I may be at fault in my description. That is why I attached some pics.
I do appreciate all the help I can get to understand this setup, cause I do like the less noise thing. Just looking to have enough power for 3D'n also.

Guys, Here are a few pics of my reent retro fit into my Carden Extra and I am having similar problems. Thought these would help with the setup and mufflers that I am using.

Whoa- yea, you are right- I thought you had installed the long tuned jobs.

Now that I understand correctly, I am surprised to hear about your issues. What you describe sounded to me more like what I hear from guys using the very long "baseball bat" types. I hope I don't have the same issues with the MTWs. If I do, I'll have a set for sale!

FWIW, my understanding with the MTWs was that the header length was 12 1/2". Perhaps the KS are different- but as Dick describes, lengthening them would probably help your situation.

It's probably a real PITA but if you were to mount the engine on a stand and experimented with header lengths you might be able to figure it out more easily- rather than mucking up your plane.

Dave

PS- I had the pleasure of meeting you down at Bealton a few years back- I was hanging out with Elton and Rob Sarlan and you and your brother (no Matt) came down for the weekend.

not all cans are the same internally -far from it
basically a short head pipe then a large interval from end of pipe to baffle (say 4-6") will give best NON tuned performance - the larger diameter (higher volume expansion room) is also a big help.
the "tuned cans" are trickier to get right --than proper tuned pipes .
getting more power is easy --getting good even throttle response - not as easy . For my money the big JMB beat any of the cans on the market - they are NON tuned . just make shortest possible header and go fly

Dave,
Boy you hang around a real group of character? Naa just kidding, nice guys them two. I haven't seen Rob in awhile though. I saw Elton down at Joe Nall. I haven't been able to make Bealton the last few years for varios reason, one being a surgery. Not suppose to have one of those during our short flying seasons. Hope I can go back soon though. Had fun there. Matt gave up flying this year and is planning on moving out to Vegas next month. What a waste of talent for now anyway ?
This cannister muffler thing has me ready to go and stay with the stock mufflers....Simple. Just don't have the handle on these mufflers yet, but working at it. Will be talking and looking at a few guys setups this weekend.

Dick, As I mentioned to Dave above, I will be talking with guys and looking at a few planes this weekend, so maybe seeing first hand and maybe measuring will help ? Thanks.

Joe,

Rob just moved to Florida and is building a new house at an airpark. Every house has a hanger- only about 20 houses total so he has no issues flying models too. The original MX2 - the green and blue on- is one of his neighbors and Rob has flown in the plane. He has his pilots license and a Maule (SP?). He is living the dream...

Haven't seen Elton in a while- though he will be at the XFC I see. Don't know if you are going but if you do, tell him I said hello.

If you can't get your muffler situation fixed to your liking- try the JMBs. RC Showcase has them in stock. You will be really happy with the way they keep the engine quiet and don't affect the response. Fairly inexpensive too- like $200 a pair. Tell Mike Dooley I sent you.

Dave