Exhaust building

Olibuilt · Feb 26, 2013

I'm building a experimental Cub 180hp. I want every hp possible from the stock engine.

I have a nice dented AtleeDodge front and rear stacks, and a AtleeDodge muffler with bashed heat muff.... But I don't want the muffler between the engine and firewall.

The front and rear stacks cut at the ''Y joints'' could be use to built a crossover, with 2 exhaust pipe relatively easy I think..

Just like this:

Is it good to run the engine without any muffler, any restriction????
Will I gain any performance or just a loud engine??
What about the unequal pipe lenght like shown in the pic??

Thanks

Lowrider · Feb 26, 2013

I can't testify regarding an 0-360 but a lot of engines were designed to have some level of back pressure. An old hot rod engine builder used to say that the exhaust must equal the intake in a smooth way. The air cooled hot rodders are the ones to ask.

Are you going with electronic ignition?

Toothcarpenter · Feb 26, 2013

I am running a Vetterman dual exhaust, no muffler system, sourced from Van's, on my Bushmaster, with 0-360/constant speed Hartzell. I was worried about the noise, but had heard an almost identical set-up, at idle, taxing, and on takeoff. It seems like it should be louder than it is. The prop, seems to make as much or more noise than the engine. I've had a number of different people pay attention to the noise, when I fly by, and they say it is not loud, just sounds like an airplane. Surprises me, that it is not obnoxiously loud. There must be a bunch of RV's running around with these systems, as that is an item they sell as a Lycoming accessory,for their kits.. Two into one, crossover system. I have no idea, if it makes a backpressure differential to have the unequal pipe lengths. That thought of needing some backpressure to run well, must be a bit of a myth, as dragster engines run pretty short stacks. The noise, for me, just hasn't been a problem, either inside when operating, or to observers. I live on a little lake, that is kind of down in a low spot, where sound echos. I have had neighbors take a listen, and no body has commented of it being any different than any other airplane that goes by.

jaypratt · Feb 26, 2013

I have Vettermans exhaust on my exp 0 360 Cub it has cabin heat and carb heat. Works great! I really like it.

Tractor flyer · Feb 26, 2013

I have Vetterman exhaust on a RV8 which also has cabin heat but not carb heat and came with single heat muff but put one on other side and works very well. Anyways the exhaust works very well and no complaints on noise what so ever. Really do not think you need a muffler performance wise.

In Ag flying world they put on straight exhaust to make more power.

NimpoCub · Feb 26, 2013

Mine is a Vetterman X-over with no muffler. Neighbors told me it barks a bit more on TO but in cruise, no diff. Nice to have Xtra room in front of the firewall & no heat there. I had to order another heat muff, 1 for carb, 1 for cabin.

knucles · Feb 26, 2013

Used straight exhaust for years on different models , including home made systems , no problens that i encountered. Years ago i towed my RV 4 into a muffler shop . We used their steel pipe to bend up and weld the two left cylinders two into one and same on right side. Flew it for years .

Roger Peterson · Feb 27, 2013

My Vetterman exhaust looks just about like that.

cubunltd · Feb 27, 2013

toothcarpenter. Dragster engines are high horsepower engines that are supercharged and therefore don't rely on backpressure. However you don't need a muffler to create backpressure. the way the pipes are designed, diameter of pipes etc. all contribute to some backpressure

Olibuilt · Feb 27, 2013

My existing crossover mesure 1.75''. What size should I use for the 2 downpipes? What about a good source for heatmuffs for carbheat and cabin heat??

Cub Builder · Feb 27, 2013

There are some really good web sites to help you design your exhaust if you really want it to work for you. One of my favorites is http://www.mez.co.uk/mezporting/exhaust_length.html. I used this to design a new exhaust system for my other plane a few years ago. The performance results were much better than expected. However, the original exhaust, which I had also built, essentially broke just about every rule in exhaust design, so the previous exhaust had been an exceptionally bad. You probably aren't going to design much more than either primary headers, or primary headers with a 2-1 collector and tail pipe. These web sites can be a big help with getting the pipe size and length right. Exhaust technology is more about creating the desired flow velocity with pipe sizing and the desired length based on resonate frequencies (rpm). That will help you get the best you can out of your engine.

A Google search for something like "exhaust design" or "Exhaust Design Calculator" will produce a lot of hits, some of which can be very helpful in designing a performance exhaust for your plane.

-CubBuilder

brown bear · Feb 27, 2013

What about a good source for heatmuffs
[url]www.robbinswings.com[/URL]
DW

Toothcarpenter · Feb 27, 2013

Re Dragster engines; I am so old, I can remember normally aspirated engines with short open stacks, like 10 inches apiece. . Ran fine, at high RPM. Not sure it would work over the whole range. Also we ran normally aspirated boat engines with short dry stacks(again; back in the day.heheheh) Re; what is important. You can access those heat muffs from Vans, but I cringed at the cost. They work wonderfull. It is such a simple idea, there must be several sources of heat muffs. I really liked the Vetterman stainless ones. Kinda like pay to play someone said about the CC gap seals. Anyway, I have also dealt directly with Vetterman. He was really a nice, helpful, and trusting guy. I cannot remember why he didn't want my credit card. He wanted me to send a check when I recieved the item, if it was what I wanted. I would do business there again in a heartbeat.

Cub Builder · Feb 27, 2013

I played with the calculator I had linked, and found that it was giving some very strange numbers, so deleted the link to the exhaust calculator and put in a link to a different calculator that makes a bit more sense. I don't have the actual valve timing for the Lycomings, but can make a decent guess at them. An O-360 comes up with a primary tube ID of 1.838" with a primary length of 74" for a full wave pipe at 2700 RPM.

The exhaust I built for the O-200 on my other plane was built to be half wave for 2750 rpm, so the tubes are all around 36" in length. With the smaller displacement, my tube ID is roughly 1 3/8". It has a nice bark to it without being really noisy and the exhaust gave it a pretty decent boost in performance.

-CubBuilder

cubunltd · Feb 27, 2013

Hey toothcarpenter, I'm not so young either and i do remember normally aspirated dragsters. Your right they ran not too bad at wide open throtlle but didn't really idle too well , did they? Anyway i see your from Coeurd Alene. I visited and flew out of there for awhile some years ago. Beautiful country. Love it out there. I'll be back someday.

john

Lowrider · Feb 27, 2013

A lot of the idle issue is the cam. I had side pipe cut outs on my 68 GTO and they were VERY loud as evidenced by the tickets I got back then. I don't like loud exhaust now except a little bit on the Harley. I have Long Shots and they are only loud when I want them to be loud. What are you riding John? I have an '03 Lowrider...hence the name.

cubunltd · Feb 27, 2013

lowrider, i figured you rode with a handle like that. i ride a 2001 softail deuce bored to 1550 cc's. screamin eagle hi compressin heads, forged high compression pistons, screamin eagle mid to hi range cams and long shots. lowered an inch and a half in back. just realized your from sandpoint. Your the second person i talked to today from idaho. i spent some time in coeur d alene a while back and flew out there. been to sandpoint and various other back country airports also. love it out there.

john

Lowrider · Feb 28, 2013

John,

I gave up hot rodding bikes after I sold my '73 Ironhead. I did have a Bandit but #3 son took it to college with him. I'm left with two 400 DRZ's and a TW200. The T dubb is a hoot to ride and it is like a mountain goat on the trails out here. You oughta just pack up and move out here...we just move here from MD.

Back to exhaust building...well sorta...Oli, are you using an electronic ignition on you 0-360?

Olibuilt · Feb 28, 2013

Lowrider said:
Back to exhaust building...well sorta...Oli, are you using an electronic ignition on you 0-360?

For now, I'll be using Slick magneto with carburator.

Thanks for the heatmuff source.

C-YQK · Feb 28, 2013

Olibuilt
If your cub is exp you should definetly make use of the 4-1 technology out there
lots done by EAA proving that 4-1 boost horsepower

I used the shop in Princeton Minnesota. Built up a mook-up sent it to them the fabed it up had it ceremic coated heat and carb heat muffs and the sound is awsum!!!!!
Need more info send me a PM

Gary

WhiskeyMike · Feb 28, 2013

That exhaust in your first post is the trick set up as far as I'm concerned. And you own it already. You can tell how well the engine is running from the sound, but it isn't annoying. Very relaxing. As far as I'm concerned there was a very noticeable difference in power. This photo was taken in Massa Cinquale, Italy, before we packed it up and shipped this Cub to Steve Pierce's.

C-YQK · Feb 28, 2013

C-YQK said:
Olibuilt
If your cub is exp you should definetly make use of the 4-1 technology out there
lots done by EAA proving that 4-1 boost horsepower

I used the shop in Princeton Minnesota. Built up a mook-up sent it to them the fabed it up had it ceremic coated heat and carb heat muffs and the sound is awsum!!!!!
Need more info send me a PM

Gary

Olibuilt
The place where I purchased my system from is Aircraft Exhaust Inc.
Princeton Mn 800-770-7287 763-631-9342
Good luck
Gary

PerryB · Feb 28, 2013

Backpressure does NOT help an engine make more power. I think this old saw comes from people running a stubby 4 into none system and not getting as much power as a stock system due to a lack of acoustic effect, and reversion. That system in the picture looks to be very good from an airflow standpoint. It has its cylinders balanced 360 degrees apart per side and plenty of collective length. This makes for good acoustic tuning (drafting). A crossover/balance tube just downstream of the Y's would probably produce a small net gain but you'd probably have to put it on a dyno to actually see it, because the collective pipes(tail pipes) are relatively short. You'd also have the inconvenience of having both sides tied together, unless you slip-jointed it. As Gary said above, a 4 into 1 (with plenty of collector length) would probably make the most power.

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