Power/Speed increase from Muffled exhaust

[hecilopter]

Did anyone read the article in the last RVator where they compared speeds of the RV-10? If I read it correctly, there were 3 exhaust systems.

System 1 was 2 straight pipes, no muffler.
System 2 was 2 pipes into 1 common muffler, added about 3 miles per hour due to increased power by more efficient fuel burn.
System 3 was 2 pipes, each muffled independently. Added another 5 mph over System 2 and about 20(?) HP!

If this is the case, would we see similar results in an O-360 by putting 2 straight pipes, muffled indepently? Why has no one done this? I have heard of power-flo exhaust systems but I thought this was 4 into 1. If anyone has experience in this please respond, sounds like an easy way to get a little extra "uumph".

[mark manda]

I've been looking at motorcycle mags wondering what's out there that will possibly work.

Used to run Supertrapps on straight pipes and adjust the number of plates for noise and back pressure. I called Lycon but they said they didn't have any dyno numbers with mufflers.

Times are changing, I think it's the way to go. It just has to be safe and work.

I heard one story where a guy built a Harmon Rocket, never had access to the web or anyone else's input and he heard you need mufflers. So he ran and a dual exhaust along the bottom of the fuse halfway down. Something out of a Midas Muffler shop.

The first time he went to a fly-in-- and saw how he was the only one-- how ugly they were; he removed them and tossed them on the spot.

Don't want that.

[gmcjetpilot]

I assume you are talking about a 6 cylinder engine? Here is the firing order of a 6 banger:

front of engine,
looking down
cyl-2.....cyl-1
cyl-4.....cyl-3
cyl-6.....cyl-5

Firing order: 1-4-5-2-3-6

front of engine,
looking down
4th.....1st
2nd.....5th
6th.....3th

Typical of 6 bangers is tie all three cylinders on one side together and than into one collector, than overboard. The left and right sides are independent. Since you have alternating firing on the left and right band this works.

However on the 4 banger it does not.

front of engine,
looking down
cyl-2.....cyl-1
cyl-4.....cyl-3

Firing order: 1-3-2-4

front of engine,
looking down
3rd.....1st
4th.....2nd

You can see you get two firings on the right and than two subsequent firing's on the left; on the same side. If you try to make a "Y" pipe into one collector is not efficient. Stuffing two exhaust pulses 180 degrees apart into short pipes, collecting into one is not great. It is better to just have 4 separate pipes. So what works for the 6-banger does not work for a 4 banger.

Now what you are talking about is the "Collector" pipes; Collector pipes are where the primaries (single pipes from each cylinders) collect and join together into one. This collector is usually the final pipe until exit. A 4-into-1 or 6-into-1 is best and all primaries joint into one big collector. One the other hand sometimes the collectors may join again into another collector. That is what cars do; they may have two separate collectors tied into a "Y" pipe and than out the back, but many have "dual exhaust". Two separate pipes to the rear bumper. Since the pipes are so long back-pressure is an issue so separate (and bigger) is better. Some times the "DUAL exhaust" there has a "H" pipe to tie the left and right "dual exhaust" together to balance the pipes. The "H" is too far down the road to allow may be some scavaging or back-pressure reduction.

The most efficient (power) for most engines is a "Header " system where all the primaries of the "TUNED" length collect and than you have one long collector (or proper critical) length from there. This promotes something call scavaging. The diameter and length of the primaries and secondaries are critical for scavaging to occur. If you can't get good scavaging due to firing order, pipe length or other factor, than sometimes separate pipes are better than a bad primary / collector system. Sometimes separate primaries for each cylinder is better, no collector at all. Look at a P-51, short pipes, 12 of them sticking out the side of the cowl. There are 4-into-4 or 6-into-1 pipes for RV's.

With the typical O-540 the left & right side (bank of cylinders) is separate, just for practical space and installation reasons. 4-into-1 is hard to fit. 6-into-1 gets to be more of an issue. The issue is "Balanced" or "Tuned" pipe length, meaning the same length primaries, is just hard to accomplish, so a little compromise from ideal is made for ease of installation.

Now what about the collector-collector for the 6-banger, kind of a modified 6-into-1, but 3-into-1 first and than the 2 collectors going 2-into-1. Well chance is connecting the left and right bank may help, using a final collector pipe if all is properly sized (and the primaries and their individual collector's are size to match the final collector). Chance is Van found it was just better to keep the left and right collectors separate. The performance change may have been from changing the individual collector lengths when he added or subtracted mufflers.

The bottom line what works for a 4-banger does not work for a 6-banger, in part due to the firing order. Chance is if you can't collect all primaries into on collector with matched length pipes and a collector of proper diameter and length, separate may be best. George

[tacchi88]

It's not surprising that Lycoming has no dyno figures on mufflers. This is proven by the GA aircrafts of the same makes and varied systems, performance being so close, that they can be called identical. It's on no surprise since to extract any benifits from an engine spinning at a maximum of 2700 rpms would require pipes to be as long as the aircraft.
In the case of 4 cylinder, simple crossover seem to be effective, though whether or not they make or waste power is conjecture without emperical data, I.E. a dynomometer.
The 4 bangers do prefer the 4/1, but with collector being as far as possible, and equall runners. sitll no emperical data.
With six cylinder the same holds true,
Claims, but no data.
From on hand experience with an experimental Pietenpol, using a Corvair, the following was performed.
The conversion was using the stock Corvair, which is nothing more that a pipe flat against the exhaust port. After "straightening" out other problems, the final "mod" was to alter the exhaust pipes. The formula used was the JAR formula method, tried and proven for many, many years of engine modifications.
It consisted of using curves exiting the exhaust port and chaneling onto a larger diameter pipe. The second and third cyclinder to flow similarly but onto the larger diameter, and equidistant. The result was 200 rpms static, and push the Pietenplo past 100 in SL flight. The Pete is more comfortable at 85.
The JAR formula uses the basic flow patterns coming out of an exhaust port. The original Corvair port would "choke" the engine due to exhuast gases "bouncing" back due to the sharp, adrupt shape of the exhaust pipe. It also cause slightly higher CHTs. The bends offered smooth flow, no bounce back, and as the gasses passed through the larger portion of the pipe, and due to cooling, would completely extract spent gases.
The JAR method formula is Just About Right. The performance gained was not mesurable without a dyno, but it simply indicated that the system was "chocking" the engine. The new pipes simply made use of the engine's real potential. It's very doubtfull that it added horsepower.

[osxuser]

As powerflow has maintained, their exhaust system simply "gives back" 20+ hp to the engine, not increases the rated power. I'd like to see someone try to mount a powerflow from a M20J onto a RV. That would kick butt.

http://www.powerflowsystems.com/

Click on products and then M20F/J. The price might be lower if they were told it was for an RV, I think the experimental market is something they are looking at tapping into...

[gmcjetpilot]

Originally Posted by tacchi88

In the case of 4 cylinder, simple crossover seem to be effective, though whether or not they make or waste power is conjecture without empirical data, I.E. a dynamometer.

tacchi88 check out the Cafe Foundation research and flight test.

http://www.cafefoundation.org/

CLICK ON RESEARCH and Exhaust studies

Direct links:
http://www.cafefoundation.org/aprs/EPG%20PART%20IV.pdf
http://www.cafefoundation.org/aprs/epg.pdf


This is not new stuff. If you give a race exhaust designer the RPM, stroke, piston diameter, valve size, induction length/dia/geometry, ignition timing they will design "header" to optimize anything you want. I did this with one company and it came out very very close to what the Cafe Foundation came up with (above). They have computer programs and dynos and make stuff for Pro NASCAR and NHRA teams, among other types of racing teams. The physics of exhaust design is very much well described by physics and math. By controlling primary length/dia and collector and length and diameter you can gain power thru "scavenging". For the record the cross over is OK, but it lacks balanced tube lengths, which causes uneven power from different cylinders (different tube lengths). The cross over does produce some scavenging but it is almost not enough in my opinion from the data I have seen to justify it at as the best option for all builders. 4 separate pipes has same advantages, one being even power and low back pressure. Of course 4-into-1 is by far the best, but all you hot rodders knew that (40 years ago).


I had a custom exhaust made for me per the info I got from the Cafe Foundation and other sources. The company that made it knew all the tricks and made a great 4-into-1 header, Aircraft Exhaust Technologies, Inc:
http://www.aircraftexhaust.net/

Many of the 4-into-1's do not have the proper collector length. Even Aircraft Exhaust Technologies, Inc makes an if the self unit with a short collector. Why? Well you loose a little performance but the short collector looks better and people want that.

As far as POWER FLOW, it would look ugly and draggy having the collector poking out the front of the cowl. I mean it has to be done on factory planes due to room and is the only way to get the proper collector. However EVEN Power FLOW sells a "SHORT" collector compromise. Don't get me wrong if I had a Mooney I would have a POWER FLOW.

My custom exhaust has the full length collector 19-20". A megaphone would help but the noise factor is a little bit much.

Bottom line is there's nothing new and the cross-over is WAY over rated. However it's SO True that factory exhaust systems are so restrictive that when something like a Power Flow is installed, you are really just getting back to the rated HP and may be 5% more, which makes a big difference. However a Power Flow on a RV, replacing a "cross over" will not produce the difference you see when replacing a factory exhaust.

G

[penguin]

Originally Posted by osxuser

I'd like to see someone try to mount a powerflow from a M20J onto a RV. That would kick butt.

Just call Sky Dynamics, they have the same type of system for just about every tail dragger RV

http://www.skydynamics.com/homepage.html and click "Exhaust Systems"

Pete

[rv6ejguy]

The optimal primary tube length for a Lyc running at 2700 rpm would be about 77 inches. You wanna hang that on your RV? Ugly, heavy, prone to lots of thermal expansion and vibration/ cracking problems.

[gmcjetpilot]

Originally Posted by rv6ejguy

The optimal primary tube length for a Lyc running at 2700 rpm would be about 77 inches. You wanna hang that on your RV? Ugly, heavy, prone to lots of thermal expansion and vibration/ cracking problems.

Negative top gun it is 2.25" x 19.5"-30" collector, where 19.5" is good enough. Check out the cafe foundation research. Most of the off the shelf 4-into-1's make a concession to ugly prevention and use a 11" collector. Even then 4-into-1 is better. My stinger is almost parallel with the belly and looks cool. This will not crack with slip balls, slip joints at the collector. One like this has a 1000 hours with cracks. Also all the welds a done with inert gas filling the inside, stress relieved and made of the good stuff, SS 321. These are made very well, welds are aerospace quality and the pripes are "tuned". G

[osxuser]

Originally Posted by gmcjetpilot

As far as POWER FLOW, it would look ugly and draggy having the collector poking out the front of the cowl. I mean it has to be done on factory planes due to room and is the only way to get the proper collector. However EVEN Power FLOW sells a "SHORT" collector compromise. Don't get me wrong if I had a Mooney I would have a POWER FLOW.


G

Obviously didn't follow the link to the Mooney powerflow system (M20J exits the back of the cowl, just like an RV system would.)

And it looks like it might fit:


However, price is another story altogether.