Hello!

I own these two engines and use them for two airplanes, a Piper cub and a Piper Cherokee.

For some reasons I decided to switch between the engines and put each one on a different airplane but a problem came up, the ASP's muffler is too long and doesn't fit in the new airplane.A muffler extension won't do the work so I switched between the mufflers, the ASP goes now with the OS muffler and vise versa. The only problem I can see now is a difficulty for the ASP to hold low RPM.

I assume switching the mufflers might not have been the brightest idea so I wanted to ask if anyone has an opinion about it. Could I harm the engines this way?

Thanks.<br type="_moz" />

I would not say you could HARM your engines, but definitely the performance, in many aspects, is affected.

Basicaly, different RPM ranges sets up different muffler "lenght", thus, generally the muffler "lenght" is designed to work well on a RPM range.

You might also be having problem with too low or too high backpressure generated in the muffle, which drastically changes the idle set up due to the fuel feed variation in this situation, where the venturi effect on the carb is quite weak.

PS.: I assume you have already spent some time working on your idle needle valve after the muffler swap...

You know...I have an ASP 52 2s that doesnt run well on the low end/idle.  And now that you bring this post up I may now know why.  My other ASP engine runes and tunes just fine.

The stock ASP muffler has a baffle inside which creates about an inch or more of the overall length of the muffler.  The plane I installed it in would not allow me to keep the baffle in without much modification of the firewall (as the muffler would actually be inside the fuse and exit from its side).  So, I just removed the baffle and it fit better by being at least an inch shorter.

However, I have not been able to get a good tune on this engine either on the low end.  So, now your post has me intriqued to say the least.  I'll have to take the engine off and bench test it with and without the baffle to see the results.  Doubt I'll do it any time soon as I have put this plane on the back burner for now...but just thought I would add this to the topic.

Removing the baffle substantially changes the backpressure (make it lower), and this is more noticeable in the idle tuning, because all the blablabla (fuel feeding in idle by pressurized fuel tank due to low venturi effect in this condition).

The baffle may also have some fine tune effect related to the pressure waves trough the muffler, but I believe that, if ASP had tuned their mufflers, it was tuned for high revs. Thus, removing the baffle would not make difference in the idle due to the pressure waves bad tuning.

I have a Magnum GP .15 engine that runs the stock muffler without the baffle, and I added a 5" silicon tube to "guide" the castor oil out of my plane AND try to keep the backpressure similar to the original...

Thanks for your insight. Maybe it does or doesnt have anything to do with the low end tuning.And I really dont have a comparison as I bought this engine new for the sole purpose of putting it in this plane. So when building, I knew that the baffle had to go...and never ran it with the baffle installed.

Ive had no problems with OS engines and thier conical/funnel shapped baffle insert (which at most reduces the length of the muffler by less than 2mm). I only noticed that the OS baffle made the engine a bit quieter. I may/may not have noticed a power difference.

I think Im gonna pull this engine, put the baffle back on it and shelf it until I can come across a 40 size ultra stick. On a stick I can muss around with tuning easier than the current plane which has an enclosed cowling (my issues are notwith the cowling as I was trying to tune/maiden the plane with it off, just FTR).

Hi!
It has definitely nothing to do with how the engines are tuned!
Both these silencers are the same inside ,only the exhaust diameter differs.
The ASP has a little less diameter and the OS some more.

Have you tuned (set the low end needle) your engine after the change of silencers?

Thanks Marcio,

All make sense, I will have to come up with different solution.

Hi Jaka,

Of course I tuned it, not much of a difference.

These muffler differs not only by their diameter but by their length also.

Anyhow, even though I am not experienced enough to feel the difference in performance, I have came to a conculsion that each engine will probably work better with it's own muffler.


Another thing, if anyone have an input on it, would OS 46 FX provide sufficient power to fly a 3.7kg Piper Cub?


Thanks.<br type="_moz" />

I think you might be thinking of an older model ASP muffler. As they are definitely different, at least the canister portion of it is.

Here is a pic of an OS muffler



And the ASP like I am talking about (assuming the OPhas the same muffler)



The shiney part in the middle is the baffle, which can be removed.

The baffle in an OS muffler looks like a funnel shaped deal and nothing like the baffle inside the ASP. At least on my engines it is this way.

I removed the baffle in my 52 which made the muffler can at least an inch shorter. Thus thinking this is causing my tuning issue for a reliable idle. IDK???

Anyway, not trying to be argumentative here. Just trying to get the facts out there about the differences in the two mufflers and my experience with my own 52 when removing the baffle.

Hi!
Yeah! You are correct!
But switching silencers would still work. albeit a little less power when using the smaller one.

You are confusing the baffle and the muffler extension.

Virtually all mufflers have a disk or cone shaped baffle to help reduce the noise and to increase the back pressure. Removing this baffle can give you some increase in rpm, but may result in a slightly harder to tune engine. If you have considerable experience with engines, you shouldn't have any trouble.

The shiny extension is a different thing. Larger displacement engines need a muffler with a larger volume. Rather than make a new casting die, most manufacturers have taken to adding volume by adding an extension in the middle and using a longer center bolt. Your .52 muffler is more than likely exactly the same casting as a .46 muffler with the extension adding the needed volume for best power. You'll see some .75s and .91s using a .61 muffler casting with the extension.

If you use the OS muffler, or take the extension out of the ASP muffler, you may notice a small drop in rpm on the same prop.

No disrespect, but you are wrong. The shiney thing on the ASPmuffler ISthe baffle(it also extends the length of the muffler...but is the baffle as well nonetheless). Ihave had it apart and in the center of it is a disc that has slotted holes all the way around...almost like a fan. This disc cannot be removed from the center of the extension(ie "shiney piece").

There is NO funnel shaped baffle inside the ASP muffler.

Ihave tried finding a picture on the web of this baffle with no luck. I can take a picture of mine and post it if anyone is that interested in seeing it. I am attaching a crude drawing I just did of what it looks like (no, no artist and was done with MSPaint lol). The disc is flat...no funnel shape to it. its made into the extension. I cant remember if it is centered or closer to one end or the other. The grey lines are the slotted holes I speak of. The center is open to allow the bolt to pass through to hold both pieces together.

Also, I appologize to the OP for kind of hijacking this thread. I just wanted to say my tuning experience was similar to his and the only thing I had done to my engine was remove the baffle/extension.