hecilopter

hecilopter

Well Known Member
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".
 
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. :eek:
 
How 6 in 2?

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
 
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Pipes

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.
 
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...
 
We got data

tacchi88 said:
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.
Click to expand...
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 PART IV.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
 
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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 Maverick the pattern is closed

rv6ejguy said:
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.
Click to expand...
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

 
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gmcjetpilot said:
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
Click to expand...
Obviously didn't follow the link to the Mooney powerflow system (M20J exits the back of the cowl, just like an RV system would.)
mooney200hpsm.jpg

And it looks like it might fit:

m20jfrontnocowlmed.jpg

However, price is another story altogether.
 
Data

Mr. G
You have dates, but no dyno. Paper is great for theory, but the dyno is king. Cafe or anyone else making horsepower claims in aviation have yet to display good old "dyno trashing". On the 40 year thingy, got my first drag strip record in '64. I guess I must qualitfy for the 40 year hot rodder. Yes, we were aware of it back then, and like the rest on my compatriots, none of our circle had a dyno. It was caluclation and conjecture, and hopefully good ET on Suinday. Then came weather, but that's another story.
What we have in aviation is a lot of figures, conjecture and no dyno comparisons.
As another member stated pipe lenght calcuilated to 77 inches in length. and that makes most sense since we are dealing with slow reving engines. No matter how we slice it, a pipe will do nothing more that place power at some point of the engies operating range.
I read nothing about the more important component that indeed do create horsepower, such as piston designs and clearances that rival locomotives, fuel air induction, camshaft designs, cylinder head flow (for which AV engines are abismal). These components/areas are the power brokers, not the pipe. It's no wonder that Lycoming has little or no data in this area, and I doubt that anyone in aviation does, Power Flow not withstanding.
On the Power Flow system, I was active in one of the Cherokee groups. By their own statement, they compared a Cessna 172 with a high time Lyc 320 to a Cherokee 140 with a freshly OHed 320. The Cherokee won. I am not exaggerating, this was their claim. They "calclated" that the difference of climb and SL performance, that the Cherokee has at least 23% more power.
Further in one edition of Cherokee Pilots Magazine., their own comparisons of their Cherokee with and without hardly varied more that 2 to 5 mph. Climb 50 to 60 FPM, and top speed same as cruise 2 to 3 mph. None of the figures were within to Piper specs, and a stock Cherokee 140 from a member did indeed perform as specified by Piper without their system.
In effect the claimed increase was no where to be found. As time went on, several owners admited that there really was little if any gain.
Tuned exhaust systems will work in unison with other components, including compression, pistons designed, tolerances, flow, combustion chamber design, camshafts, and associatred valve train, etc., but merely bolting on a pipe ain't gonna do it.
One more small item. Power Flows claim of power claim this "vast" increase in power for a 140 Cherokee. When comparing a Cherokee 140 and 180, we find identical airframes with slightly, very slightly higher gross weight for the 180. The 180 has 40 more cubic inches of displacement, and 30 more real horsepower than the 140. Due to the larger and higher pitch of the 180, it is a grandiose 7 mph faster, climb is 125 fpm more. Now were talking about a larger and more m powerfull engine. After all is dasi and done, a 140 equiped with this pipe cannot match a 180, 23% increas equated to 184hp.
Am I a doubting Thomas, you betcha. Untill I see a dyno in the midst, I will continue to be one. After 40+ years of hot rodding, this "argument" isn't anything new, but a lot of fun, to be sure.
T88
 
gmcjetpilot said:
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

Click to expand...

I'm talking primary tube length here, not collector length.
 
I talked with Power Flow about a year ago and they said there was no use to even consider their style exhaust on and RV as it would do little good. They said the Vetterman didn't drain that much hp, so there was little to reclaim. They said they considered developing one, but due to cowl size and probably little hp increase, they dropped the idea.

We have a Cherokee 140 based on our field that put on the Power Flow early this year and his power increase is very obvious. He is very happy.

Now, I saw a muffled exhaust system at Oshkosh that looked like a Vetterman crossover with two small mufflers. I believe they would fit in the cowl. They claimed (as I remember) about a 3 hp loss and something like 3-5db noise reduction in the cockpit. Anyone know anything about this one?

Bob Kelly, 90854, painting
 
Everyone that I know that has put the powerflow on has been extremely happy. The necessity to repitch the C177 flyer's props for 100 less RPM is evidence of these extra power available. A couple guys I know took up a completely tricked out PA28-140 with RAM 160 HP, powerflow, gap seals, and wheel fairings compared to a PA-28-180 with everything hanging out in the wing (both fairly fresh overhauls). The 140 ran away in both climb and cruise. Now granted it doesn't prove anything because of the speed mods, but I fully believe in the power of exhaust systems, and think if there was no real benefit, powerflow wouldn't be nearly as wildly popular as it is.
 
Speed mods

As to the Piper speed mods. having owned 3 of them, the "so called speed mods" did absolutely nothing to gain so much as 1 mph of speed. They did, however, aid in handling, as to speed, nada. This goes as well for the "extra" 10 hp gain when converting a 150 to 160, gain, nada.
In every case where the 10 hp conversion was made was after an overhaul. Of course, there is the everpresent axiom that just because an engine runs, and make an effort to lift an aircraft off the ground, that it is healthy. Nothing is further from the truth, particularly given the technology of aircraft engines.
Still, just as the exhaust pipe arguments, there is no emperical data to back up all these speed mod "claims". However, there are significant numbers of "experiences" that they state do little, if anything to enhance "speed" accept for the improvement in handling.
What is most surprising the the 1.5 or 2 mph gains in speed at 200 mph. A meteortlogical change alone can affect this. A clean spark plug can do the same, change in point gap, and a host of other "little" gremlins not related can make such an infinetesimally small change. Come on guys, 5 to 10 kts is a difference, not 1 or 1.5 mph.
Sorry if it offends any one, it's in no way meant to do so.
T88
 
If there was no difference, how could the above scenario play out? (140 beats 180)? It's all relative. A bunch of small changes = big change. There will always be "factory freaks" as far as aircraft speeds are concerned, but the speed mods work on some level, if put together they can make up for 8 MPH difference in the stock airframe.

Another interesting thing, is that the PA-28 series is a terrible airplane to compare speed mods on, since even with the gear folded (arrow) it's a slug. Too much drag in the airfoil shape, and fairing designs to make it worth the trouble.
 
Speed mods

Mr. Stephen.
I dont't recall that I stated that a 140 beats a 180. I simply stated that the maker of the funny exhaust pipe claimed to add enough power to surpass the power out put od the 180. Calculated (more paper work, and conjecture), the pipe would have surpasses the power output of the 180. Still, and the lighter (slightly) weight of the 140 vs. the 180, it only performed as a standard 140 with the claim additional power of the pipe, which equated to 184hp.
As to the PA28 series being slugs is a matter of opinion. You are obviously thinking that a Piper Cherokee is the same plane as an RV. It's more like trying to compare the performance of a streched limo to that of a finely tuned sports car. regardless of what your choice, the speed mod scenarios occurs in sports car as well as limos.
What ever the application is, the makers (of the spped mods) will tell you that an increase in speed will occur. It don't happen. In the case of Pipers, one manufacturee claims a combined increas of speed of 43 mph, and the funny pipe, and you may have an aditional 20%. Of these claims, not one single MPH is realized.
These claims are as absurd as getting 1 or 1.5 mph out of a 200mph RV. 1 or 1.5 MPH can be be had after good bowl movement (lighter weight, of course).
My original dissertation was that all the horsepower increases/speed mods are nothing more than conjecture, unless in the case of horesepower is represented by dyno figures, as well as "speed" mods with emprical data. The 2 or 3 miles increase claims are "amuzing", and makes for fun reading.
The PA 28 series are not anymore terrible that any other AC, RVs not withstanding, Both have their seperate niches, and both have features that are compromises in nature.
The only reason I'm building an RV is to get the hell away from the beauracracy, in addition to being one hell of a nice airplane. I assure you I was perfectly happy with my Arrow, a 4 seater with only 180hp, and cruise true 140 to 145kts, 8.5 to 9GPH, and no speed mods. Did have LASAR and wing tips(handling only, no speed). I wanted a 4 seat homebuilt, Vans has always been one of my favorites, and when the 10 made the scene, I was slow in ordering, #31.
T88
RV10 N986TP
A&P/IA
 
osxuser said:
Everyone that I know that has put the powerflow on has been extremely happy. The necessity to repitch the C177 flyer's props for 100 less RPM is evidence of these extra power available. A couple guys I know took up a completely tricked out PA28-140 with RAM 160 HP, powerflow, gap seals, and wheel fairings compared to a PA-28-180 with everything hanging out in the wing (both fairly fresh overhauls). The 140 ran away in both climb and cruise. Now granted it doesn't prove anything because of the speed mods, but I fully believe in the power of exhaust systems, and think if there was no real benefit, powerflow wouldn't be nearly as wildly popular as it is.
Click to expand...
I was talking about this scenero. Before the speed mods and pipe, the 180 ate the 140 for lunch, after it was the opposite. You can't say there was no gain. Speed mods don't add up to more MPH, they give a certain percentage of less drag over the base airspeed. In other words, the first speed mod done should give advertised gains, but every one after that will give less due to that extra 1-2 mph of extra speed already there. For instance, our C177 cruises at 125kt's with no speed mods. There is a cowl mod that should yield 8-10 mph, after that if we did the late model wheel pants (which normally give 3-5mph) we wouldn't see the full gain, because we are already going faster, and therefore there is more parasite drag. If we started speed mods on the C177, I'm guessing out of the 30+ advertised mph increases we could see about 15 of those with all the mods combined. Which still isn't bad (140ish kts). The one thing that is advertised that is a little bit more marginal as far as working is VG's.
 
tacchi88 said:
Mr. Stephen.
These claims are as absurd as getting 1 or 1.5 mph out of a 200mph RV. 1 or 1.5 MPH can be be had after good bowl movement (lighter weight, of course).
Click to expand...

It would take a serious gastrointestinal disorder!

According to Van's published data, to gain 1 mph on an RV-7 just by weight reduction requires that the weight decrease by 400 lbs.

That's the difference between their gross weight (1800 lbs) and solo weight (1400 lbs) performance figures. The top speed at 1800 lbs is 217 mph, and at solo weight it is 216 mph.

I'm just trying to dispel the belief that weight makes a significant difference in top speed. Weight has a significant effect on fuel economy, rate of climb, stall speed, takeoff and landing distance, but not on top speed. That belief comes up every time we discuss speed, and it just confuses the issue.

Cheers,
Martin
 
Power Flow for RV's

videobobk said:
I talked with Power Flow about a year ago and they said there was no use to even consider their style exhaust on and RV as it would do little good. They said the Vetterman didn't drain that much hp, so there was little to reclaim. They said they considered developing one, but due to cowl size and probably little hp increase, they dropped the idea.

We have a Cherokee 140 based on our field that put on the Power Flow early this year and his power increase is very obvious. He is very happy.

Now, I saw a muffled exhaust system at Oshkosh that looked like a Vetterman crossover with two small mufflers. I believe they would fit in the cowl. They claimed (as I remember) about a 3 hp loss and something like 3-5db noise reduction in the cockpit. Anyone know anything about this one?

Bob Kelly, 90854, painting
Click to expand...
Bob, I agree with Power Flow because all there gain is not as much they are making MORE HP, they are just allowing the engine to make rated HP plus a little more verse minus rated power.

The Cross-over is a fine configuration because it is easy to fit and has room for two heat muffs. However as I posted before 4-into-1 is a step above. It may not be like the increase "Piper" people see going from the stock Piper exhaust to a Power Flow, but it is an increase over cross-over. RV'ers who fly with the X-over and switch observe all the changes in need for prop repitching and in the case of constant speed, ability for it to keep up. In a free words more climb, speed and performance.

As far as climb in the other post. True weight is a player in climb to a great degree, cruise very little.

Not sure about all the Piper vs. power Flow stuff, but in theory they will increase HP over a stock Piper. Stock exhaust are not efficient at all, not horrible but not good. G
 
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Seems like the big issue is getting a collector tube long enough. One of the early posters (maybe even the first) touched on Supertrapp mufflers. I use one my bike with EXCELLENT results. Higher hp and tourque than any other system I tried, despite how well engineered it was. Taking a muffler like a Supertrapp (other muffler may work, but Supertrapps are known for decreasing reversion) and bolting it to the end of a shorter primary can be adjusted to make it act like a longer primary.

Any thoughts?
 
come on george

george, you know its "negative ghost rider the patern is full" :p :D
anywho, on a car, which is probally much more efficient than a 4 cyl lyc. a back pressure of 1 psi or more causes some fairly obvious power issues. check this all the time by removing the O2 sensor and installing a gague. if the needle moves you have issues. (usually smoked cat con) just not much scavenging there. seems to me the vetterman set up is about as good as we need. but then look at what all bob has done to his for the sake of some speed. guess i'll always be the last one there. :(
 
Supertrapp Mufflers,,,,, NO NO NO

Please look at the new post about Supertrapp Muffler installed on EXP airplanes.

Titled: (MUFFLERS on RV EXHAUST SYTEMS Good and Bad) by: rv969wf. Alan
 
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