rustyrivet

My Feedback: (6)

I was told that the rear exaust of a DLE 55 with the factory muffler is just horendous compared to a DLE 55 with side exaust...... and some fields may not even allow an engine with a rear exhaust because of the noise!
Well, this ain't electric flight, and I figured most gas engines are not exactly very quiet anyway. I didn't think the noise on identical sized 55 engines would be that much worse on the aspect alone of rear muffler vs side muffler.

Should rear exhaust vs side exhaust be a real consideraton for noise concerns when I buy a DLE55? .....or is this an exaggeration the guy made to me?

closetguy

My Feedback: (13)

this doesn't answer your question.but I just never thought it was a good design feature to have the carb just above the muffler,just to much heat.

Truckracer

My Feedback: (19)

As far as noise goes, with a chamber or can type exhaust, noise level is pretty much determined by the size of the muffler can. The irritation factor of the exhaust is pretty much determined by the size and number of the exhaust stacks with larger diameter stacks having a deeper, more pleasing sound where smaller pipes have more of a crack sound. A pleasant sound isn't necessarily a loud one or a noisy one and vice versa.

I don't have any experience with the rear exhaust 55 but we have several DLE 30 and 35 / side and rear exhaust engines at our field and with similar sized exhausts, they sound pretty much the same. Certainly, the rear exhaust isn't any louder, at least to the ear though we don't measure them. My guess is the rear exhaust 55 isn't any louder than the side exhaust one when stock mufflers are used with full length exhaust stacks.

Closetguy, I agree with you though and I don't care for the carb being close to the exhaust. You certainly have to introduce cool air to the carb area or a vapor lock can result. There have been several threads in the various forums about this and some people have had to fabricate and install a heat shield between the muffler and carb.

av8tor1977

My Feedback: (6)

I don't have examples to compare, but the shape of the exhaust port and the exhaust port timing can affect noise output. A squared off exhaust port generally makes a bit more power, but also creates more noise, and a sharper "crack" to the noise. An oval shaped exhaust port has the dual benefits of being nicer to the piston ring, while also having a somewhat mellower exhaust sound due to the slower opening of the exhaust port.

While having said all that, it is truly amazing how much of the total noise that comes from a two stroke is the roar from the carburetor. This is of course mellowed on the rear carb engines due to the carbs location, but intake noise is a factor nonetheless.

Then of course there is the prop noise, which can be all over the place according to prop tip speed, prop design, etc.

I also don't care for the carb being so close to the exhaust. As a matter of fact, on one of the twin cylinder engines I made, I arranged it with the carb on top of the crankcase; opposite the exhausts. Of course this would not work in a tightly cowled application.

AV8TOR

Truckracer

My Feedback: (19)

I always though it interesting that many of the Zenoah engines not only use an oval exhaust port, they also use a "V" shaped notch at the top of the port. It was explained to me this helps to mellow the exhaust note by releasing some of the high pressure exhaust gasses before the port fully opens. It does give these engines an interesting nasal quality to the exhaust note .... one that is unique to the big Zenoah's!

Av8tor, you're so right about the noise coming from the carb intake. Some people completely ignore this sound and even Poo Poo you when it is mentioned .... like it doesn't exist. Same with prop noise. I've seen tests where almost half of the total sound coming from some engines is intake and prop noise .... especially so if you have a quiet exhaust.

Lifer

My Feedback: (1)

The horsepower ratings for both engines is nearly identical, but the RA develops its max power at about a 1,000 rpm higher. This, plus the compact muffler makes for a louder engine. The RA is very convenient when it is time to install particularly in a small cowl. If noise is the main consideration, the side exhaust is the first choice.

av8tor1977

My Feedback: (6)

Yep, most people would be amazed at the amount of intake noise there really is on a two stroke.

A couple of years ago I saw a video of a giant scale Ultimate with four electric motors geared to turn a large propellor. When it flew, the prop howl made it sound like it had an engine in it!!

AV8TOR

rustyrivet

My Feedback: (6)

It seems to me that the guy who made the claim that the rear muffler DLE 55ra would be so terrible compared to the side exaust DLE 55 was himself blowing a lot of noisy exhaust out of his r---! I don't doubt that there may be a difference, as much as I doubt that it's so noticeable that I should listen to his advice and not buy the DLE55ra because of it.

Having never done a gasser, I found the info you provided about "vapor-lock" and exhaust heat on the DLE 55ra carb enlightening, and that to be something that I should be more concerned about then the supposed horendous noise. Thanks gents for the input.

Chris Nicastro

My Feedback: (3)

Ive run the RA in a Corsair for about 50 flights with zero issues except one. The muffler itself fell apart at the welds or solder joints. I had it welded and it worked fine thereafter.
Ive run the 35RA in a P-38, Zero, Stinson with little to no problems and least of all was noise or heat effecting the carb.
On the P-38 with fully enclosed cowls I baffled the heads and made a tin sheet splitter to block radiant heat from the muffler to the carb. I also ventilated the carb diaphragms for extra insurance.

There is one simple trick to help the carb breathe you can do it with a pressure fitting and a soldering iron. If you have a tight cowl installation and heat is an issue you can drill a hole and solder a pressure fitting in the carb diaphragm plate. Use tygon tubing and run a short length of tube thru the firewall to cooler air or outside. This isn't necessary if the cowl has adequate ventilation.

The noise the stock 55RA makes is under the 98db noise rule based on my measurements. It has a nice throaty character and in flight its only loud when flown overhead and the exhaust is pointing at you.
It seems to like a Xoar 22x10 carbon prop and wooden prop best from my testing of all the popular props in this range. They keep the engine loaded with positive flow thru the carb removing the burble sound made at lower power settings and nose down attitudes. Your hearing the reeds basically because the flow is not consistent.

I did run the stock spark plug to see how long it lasts because I read and was told it was garbage, yes it is. Change out the DLE plug for an NGK CM6 right away.

Anyway, its a great engine, very compact, reliable, powerful and pretty affordable. The laid back plug is how all model gas engines should be made, rear carb too.

Chris Nicastro

My Feedback: (3)

Also, to the OP's original question, the biggest difference between the two exhausts would be a wrap around Pitts or large volume side can vs the small volume direct muffler.
The Pitts with 3 internal angles before the gasses leave the can will make less noise naturally. The RA muffler is small and pretty direct so the exaust noise will be louder.
Because the RA has less restriction and better flow from the carb to the exhaust this engine has slightly better performance than the side exhaust version.
I have a new side exhaust DLE 55 in a TF GS P-51 now that was included in the plane when I bought it. Not my first choice or best installation but I'll give it a try. It has a custom made exhaust so nothing sticks out of the cowl. Thats why for me at least the RA is so much better. No aftermarket exhaust required, its compact and good to go.

If noise is the biggest concern then try it first stock and then buy the Snuffler inserts that quiet the exhaust further.

WRK

My Feedback: (2)

The little triangle openings at the top of the exhaust port are there as an attempt at idle relief, at low speeds these pointed openings
act as sooner opening exhaust ports which cause a bit of low speed power loss enabling a smoother idle.

MTK

The noise factor, as has been stated already, is due to muffler design, intake, engine rpm and prop design, in no particular order of significance. The one thing nobody mentioned is the mounting of either 55. Hard mounting which is typical of almost all, produces the worst, most resonant noise out-put from all sources mentioned.

The DLE55 (either version) noise can be tamed. First off, a soft rubber iso mount will reduce the noise by at least 3db. That's what I use. A 3 blader with at least 10" pitch will reduce it another 1-2 db. A Mejzlik 20x12 carbon 3 blader works well on this engine. That's what I use. On exhaust, I prefer and use a full tuned pipe (ESComposites 55G) which is also soft rubber mounted on the plane. The combination of all the set-up things I described produce a very quiet outcome that gets drowned out by most everything else flying at the field, except some electrics. Noise level will generally be around 90 db at 20 feet. Try them! They are not difficult to do and everything is off the shelf. The soft iso mount is my design and I described how to in one of the threads here in RCU; but Hyde makes them ($$).

In my setups, the rear intake actually resides inside the iso mount therefore intake noise is tamed simply without any intake muffling required...

Truckracer

My Feedback: (19)

Quite a few years ago, I read an article about those "V" shaped notches in the Zenoah exhaust ports. They had a name but I no longer remember what they were called. Also, IIRC, this article was published by Zenoah or one of their distributors. They mentioned the affect these notches had on idle and as you say, this was an attempt to smooth a mag equipped engine out a bit at low speeds ... to reduce the combustion pulses that rattle control surfaces. They also mentioned there was an affect on the overall noise level from the engine's exhaust. That is where I first learned about those notches and frankly, I probably would never have noticed them if someone had not brought them to my attention. I do know for a fact ..... every G-62 I have ever been around or flown had a definite nasal quality to the exhaust note and I, right or wrong, blamed those notches for that unique sound.

av8tor1977

My Feedback: (6)

Anything that bleeds the exhaust pressure out of the cylinder more slowly will affect noise output favorably, and this includes various shaped exhaust port designs. The classic square, or rectangle exhaust port will be the loudest, though the sudden opening offered can aid power, especially if using a tuned pipe. This is not always strictly true, as sometimes an engineer makes the choice of a more oval shaped port to get away with using a larger overall port, with the oval port being nicer at pushing the ring back into the piston instead of breaking it on very wide exhaust ports.

AV8TOR