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Floorboard Vibration 4 into 1 Exhaust
- Thread starter Kelly
- Start date
gmcjetpilot
Well Known Member
What plane/ exhaust brand
I think floor board pounding is common for any exhaust, but 4 into 1 my be a little more pronounced. What RV do you have and what exhaust system do you have? How far aft of firewall is exhaust, diameter, distance from belly and angle to belly? I ask because I have a 4 into 1 exhaust. Thanks G
I think floor board pounding is common for any exhaust, but 4 into 1 my be a little more pronounced. What RV do you have and what exhaust system do you have? How far aft of firewall is exhaust, diameter, distance from belly and angle to belly? I ask because I have a 4 into 1 exhaust. Thanks G
Plane & Brand
RV-6 with 0360 coverted to IO-360 with Electronic Mag and Slick Mag and high compression pistons.
Aircraft Exhaust Tech. Brand.
Had slight vibration with Vettermans but not like with this Exhaust. It is a nice foot vibrator.
I will get exact measurments and reply later this afternoon
RV-6 with 0360 coverted to IO-360 with Electronic Mag and Slick Mag and high compression pistons.
Aircraft Exhaust Tech. Brand.
Had slight vibration with Vettermans but not like with this Exhaust. It is a nice foot vibrator.
I will get exact measurments and reply later this afternoon
It sounds as though the exhaust pipe may actually be vibrating against the bottom of the firewall. With only 1/2 in of clearance....mine was like that and has been modified to minimize the vibe. I have a clamp on each exhaust stack, with a piece of tubing mating them together. The tubing has a rubber hose over it, which contacts the fuselage, keeping the stacks clear. Works well.
Sounds like you have the stacks under control. Is you lower engine mounts, where they meet the firewall tight? May be a dumb question, but vibrations can travel through aluminum and end up showing in places that are the least reinforced....just a thought from armchair troubleshooting.
gmcjetpilot
Well Known Member
Hummmm
I have aircraft exhaust Tech also, and mine was one of the first to be made custom from a PVC mock-up I made. I was told mine was one of the nicer mock-ups of the custom RV exhaust they had done, so they used some of my ideas for the off the shelf version. However before you flame for a screwed up design, I looked at their production version and it is not really anything like mine.
I think the vibration is from the pressure pulse coming of the tail-pipe in a concentrated area near the center of the floor. This center of the belly/floor is "soft" (less stiff) from a vibration standpoint. The center of the floor is going to vibrate more than the edges of the belly pan. With the standard 4-into-2 Vetterman type exhaust, the exhaust is divided into two, straddling the belly center-line. With 1/2 the pulses spread out more to the edge you might expect the floor to vibrate less. So I am going to say this is normal. Now how to fix it?
My AET 4-into-1 exhaust (before they had production version) goes back approx 19? from FW, but I think mine will be closer floorboard. I say I think because I have the finished exhaust installed on the engine on a stand but not installed in on the airframe yet. Of course I have not flown with it either.
I was worried about this my self. My back-up plan is if it's too loud or shakes the floor too much is: One) dampen the floor with dense sound proofing at penalty of weight, 2) Extend the pipe back with a 4" dia. (about 17" long) round stainless inline racing muffler at penalty of drag and weight. This would produce the pulse further back on the floor (away from my feet) and lower the noise. Somewhat like what the European?s do or like a "Swiss muffler". (google: Swiss muffler)
If fact item number 2) is my plan regardless of noise or vibrations. I want to experiment with the removable racing muffler exhaust for local flying and cross-country. The idea is it will be removable very easily, quickly for "open header" flying, racing and so on. I think all RV's suffer from floor thumping to one degree or another. My RV-4 did it.
One thing to keep in mind is sonic fatigue. Not to worry you but the rivets may tend to fret (black smoking rivets). Probably the worst thing is a few loose rivets that need to be drilled and re-installed. May be a thin stainless guard on the belly right in the area near the exhaust outlet might help. This added mass will change the floors vibration characteristics and protect the fasteners (rivets) from a direct pounding. The stiff stainless sheet will spread the vibration out. With beveled edges and a pro-seal fillet around the edge the plate will not cause little if any drag. The plate can be bonded on with an adhesive.
G (RV-7)
PS: TELL ME ABOUT YOUR PERFORMANCE! What do you think about performance changes going to 4-into-1 exhaust?
I have aircraft exhaust Tech also, and mine was one of the first to be made custom from a PVC mock-up I made. I was told mine was one of the nicer mock-ups of the custom RV exhaust they had done, so they used some of my ideas for the off the shelf version. However before you flame for a screwed up design, I looked at their production version and it is not really anything like mine.
I think the vibration is from the pressure pulse coming of the tail-pipe in a concentrated area near the center of the floor. This center of the belly/floor is "soft" (less stiff) from a vibration standpoint. The center of the floor is going to vibrate more than the edges of the belly pan. With the standard 4-into-2 Vetterman type exhaust, the exhaust is divided into two, straddling the belly center-line. With 1/2 the pulses spread out more to the edge you might expect the floor to vibrate less. So I am going to say this is normal. Now how to fix it?
My AET 4-into-1 exhaust (before they had production version) goes back approx 19? from FW, but I think mine will be closer floorboard. I say I think because I have the finished exhaust installed on the engine on a stand but not installed in on the airframe yet. Of course I have not flown with it either.
I was worried about this my self. My back-up plan is if it's too loud or shakes the floor too much is: One) dampen the floor with dense sound proofing at penalty of weight, 2) Extend the pipe back with a 4" dia. (about 17" long) round stainless inline racing muffler at penalty of drag and weight. This would produce the pulse further back on the floor (away from my feet) and lower the noise. Somewhat like what the European?s do or like a "Swiss muffler". (google: Swiss muffler)
If fact item number 2) is my plan regardless of noise or vibrations. I want to experiment with the removable racing muffler exhaust for local flying and cross-country. The idea is it will be removable very easily, quickly for "open header" flying, racing and so on. I think all RV's suffer from floor thumping to one degree or another. My RV-4 did it.
One thing to keep in mind is sonic fatigue. Not to worry you but the rivets may tend to fret (black smoking rivets). Probably the worst thing is a few loose rivets that need to be drilled and re-installed. May be a thin stainless guard on the belly right in the area near the exhaust outlet might help. This added mass will change the floors vibration characteristics and protect the fasteners (rivets) from a direct pounding. The stiff stainless sheet will spread the vibration out. With beveled edges and a pro-seal fillet around the edge the plate will not cause little if any drag. The plate can be bonded on with an adhesive.
G (RV-7)
PS: TELL ME ABOUT YOUR PERFORMANCE! What do you think about performance changes going to 4-into-1 exhaust?
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With 4-1 exhaust, is the outlet always centered and aiming straight back? I heard it mentioned that when centered it could cause an oil streak on the side of the fuse due to the swirl of the prop wash.
Could the outlet be 'aimed' slightly off axis to counter act the need for rudder trim tabs? The outlet might be too close to the cg for this to be effective.
Chuck
Could the outlet be 'aimed' slightly off axis to counter act the need for rudder trim tabs? The outlet might be too close to the cg for this to be effective.
Chuck
G (RV-7). Thanks for the info. As an added note, during origional construction of floorboard I added 1/2" sound deadning material and installed al angles to stringers and pop rivited an al floor over the material adding strength to the area. Just for kicks and grins, I think we are going to hang a large turn down to see what happens. Not that we would leave it on because of drag etc but just see what happens. Also, have a friend says he might be able to releave the problem with vortex generators. Paint belly with oil and fly to see air flow and stratigically place generators. Might be worth a try.
Performance. The engine has never run smoother. Prop has been balanced to .01. Definately can tell the difference in sound and performance. EGT's are closer. If you apply power rapidly on take off engine wil surge to 2750 before govenor reduces to 2650. Didn't do that before.
Performance. The engine has never run smoother. Prop has been balanced to .01. Definately can tell the difference in sound and performance. EGT's are closer. If you apply power rapidly on take off engine wil surge to 2750 before govenor reduces to 2650. Didn't do that before.
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Design
Do any of the 4-to-1 systems available have headers of varying lengths so the exhaust pulses are evenly spaced at the collector? That's tuning.
Then, do any have long tail pipes, the length such that one pulse is exiting when the next is at the collector? Such would be on the order of 3 feet long. That's for extraction.
I put a tuned extractor exhaust manufactured by Power Flow Systems on my 172 and it added 13-15 horsepower on a 320 (measured by improved time-to-climb). So I know such things work (so do kids driving Honda Civics), but the 4-to-1s I've seen don't look like they embody these two power enhancing requirements.
I, too, am really interested in any A:B results.
John Siebold
Do any of the 4-to-1 systems available have headers of varying lengths so the exhaust pulses are evenly spaced at the collector? That's tuning.
Then, do any have long tail pipes, the length such that one pulse is exiting when the next is at the collector? Such would be on the order of 3 feet long. That's for extraction.
I put a tuned extractor exhaust manufactured by Power Flow Systems on my 172 and it added 13-15 horsepower on a 320 (measured by improved time-to-climb). So I know such things work (so do kids driving Honda Civics), but the 4-to-1s I've seen don't look like they embody these two power enhancing requirements.
I, too, am really interested in any A:B results.
John Siebold
gmcjetpilot
Well Known Member
Well kind of Sort of
Also when you talk about modifications to an engine in a certified aircraft and certified engine you cannot boost sea level power more than a small fixed amount (about %2.5) without going thru a re-certification of that engine, which is a big big deal I know PFS did not do).
Nothing wrong with the Power System 4-into-1, in fact it is great, just wish I would have thought of doing it first. They get almost $4K for some tubes! I payed $600 for my 4-into-1, but it is on a RV and not a Piper. PSF use to publish their tube dia and lengths, but took it off their web site. I checked their numbers. I thought they where close but a little off. However they may be trying to optimize a specific RPM. Also a 4-into-1 for a 160HP/fixed pitch, 120MPH airplane will not be the exact same as a 180HP/C/S prop 220MPH airplane with semi-ram air airbox. With that said their numbers are in the ball park to the 4-into-1 exhaust on my RV.
A 4-into-1 exhaust in a RV will improve engine breathing, improve power balance between cylinders and of course makes a little more HP. However the typical stock no muffler RV cross-over, although far from ideal, is way better than a stock Cessna or Piper exhaust system with a muffler, so you will not see the increase in performance going to a 4-into-1 on a stock RV like you would on a factory Piper.
We experimental guys can boost power all we want, but a 160 HP engine is a 160HP engine in a Cessna or Piper and trying to get a STC to boost SEA level power by a large margin will not be easy to get approval. Yes you can go from 150HP to 160HP with higher compression on a Piper or Cessna, but that STC was eased by the fact it was like an existing certified Lycoming engine in those airframes. Added on turbo STC?s in the past where OK because it is ?normalizing?, meaning it does not make more HP than the stock engine. Although there where many problems with these STC turbo?s. Intercooler STC's add HP at altitude below the max engine rating. LASAR electronic ignition claims to increases HP 5% at 80% power to 85% power, but they claim no HP increase at 100% power. (There is that magic 5% number, Hummmm.)
When Lycoming test stands an engine, say a 160 HP engine, it must make 164HP to 156 HP to be certified as a 160 HP engine. So I suspect to get their exhaust system certified they needed to show they did not boost HP more than 5% of the rated Lycoming HP to get the STC.
4-into-1
John, I am not sure what 4-into-1 exhausts you have seen, but I can speak to Aircraft Exhaust Technologies AET system. I had mine custom made. It has tuned primaries (length and dia) going into a collector and secondary of the proper dia. The secondary (the single tube past the collector) to get max scavenging effect needs to be about 19" long x 2.25" dia. 19.5" is about ideal for a 360 cu-in Lycoming at 100% power. However, some make it shorter for installation purposes. It all is dependant on dia, RPM, HP and displacement you are trying to optimize. If Power systems makes a 36" long collector secondary that is pretty close to a multiple of 19" (19" x 2 = 38"). Cafe Foundation research tested many collector lengths (40", 19.5, 10") and found 20-30" is best length (with little difference). The 10" was too short and 40" worked about the same as 20"-30" @ 2,500 RPM and at high RPM there was a small edge for the 40". The problem with 3 foot collectors sticking out the front of the cowl is DRAG.
PFS makes a "SHORT STACK" version of their product, so the know there is a trade off in external drag and ideal exahust performance. With the RV we can extend the exhaust out the cowl back and down the fuselage. As I said I may extend my 19" collector with another 18" extension / muffler. A quieter cockpit may justify the increase in drag. It should be less drag than the Power System design that has the collector coming out near vertical from the forward part of the cowl. Because the new length of 37" is close to the tuned length little or no HP should be lost.
The effect or loss in scavenging is small with small changes in tube lengths. Also a megaphone or reverse cone end on the secondary is better, but that makes it LOUD! So yes there are small variations. The fact is 4-into-1 will boost power a small amount. More important is it will not loose HP and give you more even power pulses from all jugs. Now combine a 4-into-1 with a new cam profile you can improve engine breathing greatly. The stock Lycoming cam is not designed to take full advantage of a tuned exhaust. Is it worth it? I don?t know; they do cost more. They don?t fit on ?A? models (although AET I think now makes one for the ?A? model, which is wild to go around the gear support. I think I would not go thru that on an "A" model).
As far as jet thrust from exhaust from the previous post, there is a small amount but nothing to write home about. However per the cafe foundation they found 10-20 lbs of thrust available depending on tube dia. Smaller tube more thrust but less engine HP. If you could vary the exhaust nozzle you could play with "exhaust thrust". There was good work about exhaust thrust in the book written by Kent Paser, Speed with Economy. The idea of an augmentor tunnel has been tried on several factory planes. My old Piper Apache had it and many Cessna twins had augmenter tubes on the exhaust. As far as jet thrust the best you can do is point the pipes in the parallel to free airflow. The idea to get jet thrust calls for you to accelerate the exhaust by making a restrictor nozzle. The restrictor increases the velocity but restricts the exhaust. Double edge sword and no free lunch.
There are about 3 makers of off the shelf 4-into-1 exhaust for RV?s: AET, Sky Dynamics and Aircraft Exhaust Systems Specialist.
The engineering science of exhaust is well understood and the Cafe Foundation wrote an excellent article on aircraft exhaust. Their findings, ideal tube lengths and diameters are in their report. When I made my custom exhaust I used this data (which AET already knew) and consultant a racecar exhaust house on the west coast (they make stuff for NASCAR, NHR, marine and off-road racers). They have a computer program for exhaust designing. I gave them the engine data (displacement, bore x stroke, # of cylinders, valve sizes, intake/exhaust port shape size, cam lift duration overlap, induction type, RPM range, primary RPM). To my pleasant surprise they came up with numbers close to right on to that ones Cafe Foundation came up with. Actually I was not really that surprised. I expected them to be close. There was some variation in secondary length, but all in all the dia and primary tubes where basically the same.
The bad news is the ?cross-over? 4-into-2, is not the ideal system that it is assumed to be. It has installation advantages over 4-into-1 and easier to install heat muffs. It does however make uneven power between cylinders. Measure the pipe lengths of a cross over; they vary greatly between cylinder banks. Also the pipes are way off the "tuned length" for good scavenging (34.5" to 37"). The result is uneven power. Cafe Foundation found the 4-into-1 was best followed by 4-seperate-pipes (even power), followed by the ?cross-over? (w/ the caveat it makes uneven power between cylinders). The Y-pipe (Cylinders 1 & 3 together and Cylinders 2 & 4 together) was the worst. G
Well actually your Power Flow System did not ADD 13-15 HP it only got you back to the rated HP, from what you lost with the stock exhaust system. The difference is from the fact the factory exhaust system is so really poor. Your 160 HP engine is rated at 160 HP on a test stand, that is it. In the airframe it may only put out 150HP. An exhaust system alone will never make a 160 HP engine a 170-173 HP engine. No doubt the PFS makes 10-13 more HP but you are getting your 160HP engine that was making 150 HP back to 160-163HP.RV7ator said:
Also when you talk about modifications to an engine in a certified aircraft and certified engine you cannot boost sea level power more than a small fixed amount (about %2.5) without going thru a re-certification of that engine, which is a big big deal I know PFS did not do).
Nothing wrong with the Power System 4-into-1, in fact it is great, just wish I would have thought of doing it first. They get almost $4K for some tubes! I payed $600 for my 4-into-1, but it is on a RV and not a Piper. PSF use to publish their tube dia and lengths, but took it off their web site. I checked their numbers. I thought they where close but a little off. However they may be trying to optimize a specific RPM. Also a 4-into-1 for a 160HP/fixed pitch, 120MPH airplane will not be the exact same as a 180HP/C/S prop 220MPH airplane with semi-ram air airbox. With that said their numbers are in the ball park to the 4-into-1 exhaust on my RV.
A 4-into-1 exhaust in a RV will improve engine breathing, improve power balance between cylinders and of course makes a little more HP. However the typical stock no muffler RV cross-over, although far from ideal, is way better than a stock Cessna or Piper exhaust system with a muffler, so you will not see the increase in performance going to a 4-into-1 on a stock RV like you would on a factory Piper.
We experimental guys can boost power all we want, but a 160 HP engine is a 160HP engine in a Cessna or Piper and trying to get a STC to boost SEA level power by a large margin will not be easy to get approval. Yes you can go from 150HP to 160HP with higher compression on a Piper or Cessna, but that STC was eased by the fact it was like an existing certified Lycoming engine in those airframes. Added on turbo STC?s in the past where OK because it is ?normalizing?, meaning it does not make more HP than the stock engine. Although there where many problems with these STC turbo?s. Intercooler STC's add HP at altitude below the max engine rating. LASAR electronic ignition claims to increases HP 5% at 80% power to 85% power, but they claim no HP increase at 100% power. (There is that magic 5% number, Hummmm.)
When Lycoming test stands an engine, say a 160 HP engine, it must make 164HP to 156 HP to be certified as a 160 HP engine. So I suspect to get their exhaust system certified they needed to show they did not boost HP more than 5% of the rated Lycoming HP to get the STC.
4-into-1
John, I am not sure what 4-into-1 exhausts you have seen, but I can speak to Aircraft Exhaust Technologies AET system. I had mine custom made. It has tuned primaries (length and dia) going into a collector and secondary of the proper dia. The secondary (the single tube past the collector) to get max scavenging effect needs to be about 19" long x 2.25" dia. 19.5" is about ideal for a 360 cu-in Lycoming at 100% power. However, some make it shorter for installation purposes. It all is dependant on dia, RPM, HP and displacement you are trying to optimize. If Power systems makes a 36" long collector secondary that is pretty close to a multiple of 19" (19" x 2 = 38"). Cafe Foundation research tested many collector lengths (40", 19.5, 10") and found 20-30" is best length (with little difference). The 10" was too short and 40" worked about the same as 20"-30" @ 2,500 RPM and at high RPM there was a small edge for the 40". The problem with 3 foot collectors sticking out the front of the cowl is DRAG.
PFS makes a "SHORT STACK" version of their product, so the know there is a trade off in external drag and ideal exahust performance. With the RV we can extend the exhaust out the cowl back and down the fuselage. As I said I may extend my 19" collector with another 18" extension / muffler. A quieter cockpit may justify the increase in drag. It should be less drag than the Power System design that has the collector coming out near vertical from the forward part of the cowl. Because the new length of 37" is close to the tuned length little or no HP should be lost.The effect or loss in scavenging is small with small changes in tube lengths. Also a megaphone or reverse cone end on the secondary is better, but that makes it LOUD! So yes there are small variations. The fact is 4-into-1 will boost power a small amount. More important is it will not loose HP and give you more even power pulses from all jugs. Now combine a 4-into-1 with a new cam profile you can improve engine breathing greatly. The stock Lycoming cam is not designed to take full advantage of a tuned exhaust. Is it worth it? I don?t know; they do cost more. They don?t fit on ?A? models (although AET I think now makes one for the ?A? model, which is wild to go around the gear support. I think I would not go thru that on an "A" model).
As far as jet thrust from exhaust from the previous post, there is a small amount but nothing to write home about. However per the cafe foundation they found 10-20 lbs of thrust available depending on tube dia. Smaller tube more thrust but less engine HP. If you could vary the exhaust nozzle you could play with "exhaust thrust". There was good work about exhaust thrust in the book written by Kent Paser, Speed with Economy. The idea of an augmentor tunnel has been tried on several factory planes. My old Piper Apache had it and many Cessna twins had augmenter tubes on the exhaust. As far as jet thrust the best you can do is point the pipes in the parallel to free airflow. The idea to get jet thrust calls for you to accelerate the exhaust by making a restrictor nozzle. The restrictor increases the velocity but restricts the exhaust. Double edge sword and no free lunch.
There are about 3 makers of off the shelf 4-into-1 exhaust for RV?s: AET, Sky Dynamics and Aircraft Exhaust Systems Specialist.
The engineering science of exhaust is well understood and the Cafe Foundation wrote an excellent article on aircraft exhaust. Their findings, ideal tube lengths and diameters are in their report. When I made my custom exhaust I used this data (which AET already knew) and consultant a racecar exhaust house on the west coast (they make stuff for NASCAR, NHR, marine and off-road racers). They have a computer program for exhaust designing. I gave them the engine data (displacement, bore x stroke, # of cylinders, valve sizes, intake/exhaust port shape size, cam lift duration overlap, induction type, RPM range, primary RPM). To my pleasant surprise they came up with numbers close to right on to that ones Cafe Foundation came up with. Actually I was not really that surprised. I expected them to be close. There was some variation in secondary length, but all in all the dia and primary tubes where basically the same.
The bad news is the ?cross-over? 4-into-2, is not the ideal system that it is assumed to be. It has installation advantages over 4-into-1 and easier to install heat muffs. It does however make uneven power between cylinders. Measure the pipe lengths of a cross over; they vary greatly between cylinder banks. Also the pipes are way off the "tuned length" for good scavenging (34.5" to 37"). The result is uneven power. Cafe Foundation found the 4-into-1 was best followed by 4-seperate-pipes (even power), followed by the ?cross-over? (w/ the caveat it makes uneven power between cylinders). The Y-pipe (Cylinders 1 & 3 together and Cylinders 2 & 4 together) was the worst. G
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Show Me The Money
G,
I'd like to know which, if any, of the three 4-into-1 manufacturers you mention have demonstrated successful application of theory and models by empirical, real-world, repeatable performance test results against a commonly accepted baseline. How do their results stack up against competitors vying for the experimental dollar? I'm sure if one had proven performance benefits over, say, a Vetterman cross-over, it would be all over the web, which it isn't, and the marketplace would sort chaff from grain. As it is, I suspect there's precious little difference, what might be is lost in the noise of other variables, so the big market share wound up with the first offering high quality, good fit, and off-the-shelf delivery at competitive attractive prices.
Theory's fine, but executive summary results, please.
John Siebold
G,
I'd like to know which, if any, of the three 4-into-1 manufacturers you mention have demonstrated successful application of theory and models by empirical, real-world, repeatable performance test results against a commonly accepted baseline. How do their results stack up against competitors vying for the experimental dollar? I'm sure if one had proven performance benefits over, say, a Vetterman cross-over, it would be all over the web, which it isn't, and the marketplace would sort chaff from grain. As it is, I suspect there's precious little difference, what might be is lost in the noise of other variables, so the big market share wound up with the first offering high quality, good fit, and off-the-shelf delivery at competitive attractive prices.
Theory's fine, but executive summary results, please.
John Siebold
gmcjetpilot
Well Known Member
Yes I can
If you are interested there is a 3 or 4 part report on exhaust on http://www.cafefoundation.org/ THIS IS A FLIGHT TEST REPORT (NOT THEORY), using a Mooney with a Lycoming IO-360 A1B6. You need to take a look, this is where theory meets the sky. This is not just numbers but a well instrumented engine using a EPG method of recording pressure pulses (Exhaust Pressure Graph). In addition they had intake pressures and every other conceivable parameter monitored and recorded in real time. ALSO, they tried several exhaust systems on the same aircraft for direct comparison. WHAT MORE DO YOU WANT?
I agree with you that some of the 4-into-1 exhaust that the collector looks short, but it does not mean it will not work. Even PFS has a short collector version of their product.
Sorry I can't give you recommendations; you are on your own. It is not my job to do summaries or compare products and my opinions are my own. In fact my advice is worth every penny of what you are paying for it. (THIS IS WHERE THE CAFE FOUNDATION COMES IN, WHICH THE EAA DECIDED NOT TO FUND OR PUBLISH THEIR REPORTS IN SPORT PILOT ANYMORE. PLEASE WRITE EAA, OR CAFE FOUNDATON WITH YOUR OPINION: http://www.cafefoundation.org/survey.html)
I like the people at AET (http://www.aircraftexhaust.net/), the workmanship is outstanding, innovation in heat muffs and price is why I picked them. Armed with the right info, you know that the 4 pipes should be about equal length (about 34.5x1.75) and the collector should be about (19x2.25). It really is not too hard to figure out.
I can tell you I have followed all the fastest RV's to see what makes them fast and almost every one has 4-into-1 exhaust, except one, which has a 4-into-4 (Tracy Saylor, Dave Anders, Richard Jankowski). Obviously they have more than exhaust pipes going for them, but it is part of the picture. Look under at the cowl exit of the next race winning RV; you will see one big fat pipe sticking out. The idea of "Headers", exhaust scavenging to promote induction is real old. Hot Rod?ers have been doing it for 60+ years. Also I forgot most of the professional airshow performers and comp aerobatic pilots have 4-into-1 exhaust. Don't know what else to tell you.
As I said the down side of a 4-into-1 is it is harder to fit (heat muff) and from the start of this thread, may give you more floor "thumping". The standard cross-over found on a RV is fine, just not ideal. The DELTA HP between a RV cross-over and a 4-into-1 may be small, but the 4-1 should be smoother as shown by flight test (not theory). (Ref. Cafe research and flight-test above).
As I said you have to see the big picture: exhaust, intake, and cam, compression all have to work together. Changing just one thing is not going to be magic. Life is too hard for it to be that easy.
Personally I am not trying to make a lot more HP just smoother more efficient HP. I am conservative with stock cam and compression. If you are interested there is a 3-4 part report on exhaust on cafefoundation.org, it is worth a read.
As far as the market goes and Vetterman, great product, fits well on all models of RV's including "A" models. It also provides a good place to put carb heat and cabin heat mufflers. 4-into-1 cost double and does not fit "A" models. 4-into-1 is not for every one, but in theory and practice a 4-into-1 from pure performance is better. Is it worth the trade off of the ease of installation and cost, the market will tell, but I don't worry about what that means to one brand or another. I look at the data for my own use and spend lots of time studying the topic. I share my knowledge and opinion freely to help others make an informed decision. I think one of the most important factors is safety. As long as the darn things don't crack, fall off, catch something on fire you are good to go.
Aircraft Exhaust Technologies also makes crossover systems for the RV. I would buy there product if shopping for a crossover system because of the better cabin heat combined with a muffler (sound). They are a large shop and I think are related to Aerospace Welding Minneapolis, Inc, which does high end stuff for the aerospace industry. So they are not a fly by night outfit. As far as Vetterman they have a great rep and never had one of their exhaust so I don't know.
All the best. G
PS: I hope you did not take offense about comments made about (PFS) Power Flow Systems STC'ed tuned exhaust for Pipe, Cessna and Mooney. They are worth it and very cleverly designed, and no doubt they have proven performance outright. The performance gains are great but in part it is from the fact the factory exhaust was so terrible. You would never see this improvement fitting a PSF system on a RV. As far as experimental exhaust being better than a PSF, I hope I did not imply that, because it is a moot point. Experimental 4-into-1 exhausts would not fit into of the factory planes the PFS is made for, mostly because they have nose gears structure. As far as cost they had to pay for the certification and they are making money. Nothing wrong with that; however that is why I am building a 2nd RV and not buying a Piper. PFS system is ideal for adapting a tuned exhaust in an existing design where the heat muff and structure demand a certain configuration. The only thing that I see that an experimental 4-into-1 exhaust has over the PSF, and it was unavoidable, is the PSF design needs several 90 degree plus bends to get the job done. Hats off to them.
I do want to point out that PFS offers "SHORT STACK" option for some of their exhaust kits, to eliminate the 3 foot long exposed collector secondary. So as you pointed out some of the experimental 4-into-1 exhausts may have shorter collectors, so there are compromises in optimum exhaust lengths for the sake of installation. What effect does a shorter collector (stack) have? I don't know but this is what cafe foundation could help determine.
John, I could not agree with you more, but theory is a great place to start. I agree with you that some of the 4-into-1 exhaust that the collector looks short, but it does not mean it will not work. Even PFS has a short collector version of their product.RV7ator said:
If you are interested there is a 3 or 4 part report on exhaust on http://www.cafefoundation.org/ THIS IS A FLIGHT TEST REPORT (NOT THEORY), using a Mooney with a Lycoming IO-360 A1B6. You need to take a look, this is where theory meets the sky. This is not just numbers but a well instrumented engine using a EPG method of recording pressure pulses (Exhaust Pressure Graph). In addition they had intake pressures and every other conceivable parameter monitored and recorded in real time. ALSO, they tried several exhaust systems on the same aircraft for direct comparison. WHAT MORE DO YOU WANT?
I agree with you that some of the 4-into-1 exhaust that the collector looks short, but it does not mean it will not work. Even PFS has a short collector version of their product.
Sorry I can't give you recommendations; you are on your own. It is not my job to do summaries or compare products and my opinions are my own. In fact my advice is worth every penny of what you are paying for it.
(THIS IS WHERE THE CAFE FOUNDATION COMES IN, WHICH THE EAA DECIDED NOT TO FUND OR PUBLISH THEIR REPORTS IN SPORT PILOT ANYMORE. PLEASE WRITE EAA, OR CAFE FOUNDATON WITH YOUR OPINION: http://www.cafefoundation.org/survey.html)I like the people at AET (http://www.aircraftexhaust.net/), the workmanship is outstanding, innovation in heat muffs and price is why I picked them. Armed with the right info, you know that the 4 pipes should be about equal length (about 34.5x1.75) and the collector should be about (19x2.25). It really is not too hard to figure out.
I can tell you I have followed all the fastest RV's to see what makes them fast and almost every one has 4-into-1 exhaust, except one, which has a 4-into-4 (Tracy Saylor, Dave Anders, Richard Jankowski). Obviously they have more than exhaust pipes going for them, but it is part of the picture. Look under at the cowl exit of the next race winning RV; you will see one big fat pipe sticking out. The idea of "Headers", exhaust scavenging to promote induction is real old. Hot Rod?ers have been doing it for 60+ years. Also I forgot most of the professional airshow performers and comp aerobatic pilots have 4-into-1 exhaust. Don't know what else to tell you.
As I said the down side of a 4-into-1 is it is harder to fit (heat muff) and from the start of this thread, may give you more floor "thumping". The standard cross-over found on a RV is fine, just not ideal. The DELTA HP between a RV cross-over and a 4-into-1 may be small, but the 4-1 should be smoother as shown by flight test (not theory). (Ref. Cafe research and flight-test above).
As I said you have to see the big picture: exhaust, intake, and cam, compression all have to work together. Changing just one thing is not going to be magic. Life is too hard for it to be that easy.
Personally I am not trying to make a lot more HP just smoother more efficient HP. I am conservative with stock cam and compression. If you are interested there is a 3-4 part report on exhaust on cafefoundation.org, it is worth a read.
As far as the market goes and Vetterman, great product, fits well on all models of RV's including "A" models. It also provides a good place to put carb heat and cabin heat mufflers. 4-into-1 cost double and does not fit "A" models. 4-into-1 is not for every one, but in theory and practice a 4-into-1 from pure performance is better. Is it worth the trade off of the ease of installation and cost, the market will tell, but I don't worry about what that means to one brand or another. I look at the data for my own use and spend lots of time studying the topic. I share my knowledge and opinion freely to help others make an informed decision. I think one of the most important factors is safety. As long as the darn things don't crack, fall off, catch something on fire you are good to go.
Aircraft Exhaust Technologies also makes crossover systems for the RV. I would buy there product if shopping for a crossover system because of the better cabin heat combined with a muffler (sound). They are a large shop and I think are related to Aerospace Welding Minneapolis, Inc, which does high end stuff for the aerospace industry. So they are not a fly by night outfit. As far as Vetterman they have a great rep and never had one of their exhaust so I don't know.
All the best. G
PS: I hope you did not take offense about comments made about (PFS) Power Flow Systems STC'ed tuned exhaust for Pipe, Cessna and Mooney. They are worth it and very cleverly designed, and no doubt they have proven performance outright. The performance gains are great but in part it is from the fact the factory exhaust was so terrible. You would never see this improvement fitting a PSF system on a RV. As far as experimental exhaust being better than a PSF, I hope I did not imply that, because it is a moot point. Experimental 4-into-1 exhausts would not fit into of the factory planes the PFS is made for, mostly because they have nose gears structure. As far as cost they had to pay for the certification and they are making money. Nothing wrong with that; however that is why I am building a 2nd RV and not buying a Piper. PFS system is ideal for adapting a tuned exhaust in an existing design where the heat muff and structure demand a certain configuration. The only thing that I see that an experimental 4-into-1 exhaust has over the PSF, and it was unavoidable, is the PSF design needs several 90 degree plus bends to get the job done. Hats off to them.
I do want to point out that PFS offers "SHORT STACK" option for some of their exhaust kits, to eliminate the 3 foot long exposed collector secondary. So as you pointed out some of the experimental 4-into-1 exhausts may have shorter collectors, so there are compromises in optimum exhaust lengths for the sake of installation. What effect does a shorter collector (stack) have? I don't know but this is what cafe foundation could help determine.
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N941WR
Legacy Member
This may not apply but...
One of my other hobbies is auto crossing a '99 Miata and in the Street Prepared class I run, I am allowed to change the intake and exhaust but not modify the engine.
(Edited for George. Bad, bad English on my part.)
In dyno testing different headers I have found that 4-into-1 headers (Remember we are talking about 1.8L, dual overhead cam, water cooled engine, could it be any different?) produced more power at redline but it came on late in the power curve when compared to a tri-Y or 2-into-1 header. The tri-Y design produced slightly less total power than the 4-into-1 header but it produced more torque in the 4,000 to 6,000 RPM range (7,200 RPM rev limiter) which is more usable for my type of racing and track events.
It seems to me that if you are racing and are going to run your engine wide open (100% power), the 4-into-1 exhaust is the way to go. If you are going to fly at 75% power the 2-into-1 setup is most efficient.
Just another thing to think about.
One of my other hobbies is auto crossing a '99 Miata and in the Street Prepared class I run, I am allowed to change the intake and exhaust but not modify the engine.
(Edited for George. Bad, bad English on my part.)
In dyno testing different headers I have found that 4-into-1 headers (Remember we are talking about 1.8L, dual overhead cam, water cooled engine, could it be any different?) produced more power at redline but it came on late in the power curve when compared to a tri-Y or 2-into-1 header. The tri-Y design produced slightly less total power than the 4-into-1 header but it produced more torque in the 4,000 to 6,000 RPM range (7,200 RPM rev limiter) which is more usable for my type of racing and track events.
It seems to me that if you are racing and are going to run your engine wide open (100% power), the 4-into-1 exhaust is the way to go. If you are going to fly at 75% power the 2-into-1 setup is most efficient.
Just another thing to think about.
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gmcjetpilot
Well Known Member
Good point
Quote from Cafe foundation exhaust report:
"Crossover systems are in some ways half way between the independent pipe system and the collector system. They still exhibit higher opening pressures than the 4 into 1 collector system, put they enjoy larger, longer duration negative waves after there P wave than do independent pipes."
My interpretation of above: This is saying at the time of overlap where the exhaust and intake valves are open the crossover has higher pressures in the exhaust pipe. We want lower pressure or negative pressure (vacuum) to help suck fuel into the cylinder thru the partially open intake valve. The greater this negative pressure and duration during overlap the more savaging you get. This means the exhaust helps cause a negative pressure in the cylinder to promote the intake of fuel. What the crossover lacks in negative pressure it makes up in duration. Unfortunitly the cam overlap duration is not optimized to take advantage of this. With that said the crossover would be better down low (RPM). The 4-into-1 has more negative pressure and it starts eairlier. The 4-into-1 could benifit from differnt cam timing as well, where the overlap happened sooner, since the collector "comes on pipe" sooner in the cycle than the crossover.
Firing order: 1-3-2-4
Engine looking down and exhaust x-over pipes
|
|
| 4--------------3>|
|.........................|
|.........................|
Number 2 & 1 are tied together, where 1 goes over to 2, than back
Number 4 & 3 are tied together, where 4 goes over to 3, than back
Number 1 & 4 are long,
Number 2 & 3 are short
Number 1 is the longest
Number 3 is the shortest
So the firing order: (1)longest - (3)shortest - (2)short - (4)long
Basically every cylinder has different total length pipes and some of the lengths are not optimal. Is it a big deal, No. Will it produce slight difference in power pulse between all cylinders, yes. However the difference is fairly well balanced from left to right, front to back, but Lycoming has an off sided/one-sided firing order anyway, where the left bank (1 & 3) fires, followed by the right bank (2 & 3). This does not help regardless of the type of exhaust.
Now what is better? We only have touched the surface of exhaust design and is exceeding my understanding (doppler phenomenon, sonic and deflected wave). We do know what has worked in the past, the "off the shelf" generic crossover is a pretty good compromise. One thing I know from my aerospace experience is everything is a compromise in an aircraft. There is NO optimum exhaust for an aircraft! Reason is we operate in a wide range of power and altitudes from 100% sea level to 55% at 16,000 feet and differnt RPM's.
Quote Cafe Foundatrion: "The 4 into 1 collector exhaust systems appears to offer the best combination of low opening pressure, some pumping gain and good scavenging." (no offense to U-all crossover-ers)
G
I is related and great observation. I think that if you TUNE the pipe well (lengths, diameters) you can optimize specific RPMs/MAPs.N941WR said:
Quote from Cafe foundation exhaust report:
"Crossover systems are in some ways half way between the independent pipe system and the collector system. They still exhibit higher opening pressures than the 4 into 1 collector system, put they enjoy larger, longer duration negative waves after there P wave than do independent pipes."
My interpretation of above: This is saying at the time of overlap where the exhaust and intake valves are open the crossover has higher pressures in the exhaust pipe. We want lower pressure or negative pressure (vacuum) to help suck fuel into the cylinder thru the partially open intake valve. The greater this negative pressure and duration during overlap the more savaging you get. This means the exhaust helps cause a negative pressure in the cylinder to promote the intake of fuel. What the crossover lacks in negative pressure it makes up in duration. Unfortunitly the cam overlap duration is not optimized to take advantage of this. With that said the crossover would be better down low (RPM). The 4-into-1 has more negative pressure and it starts eairlier. The 4-into-1 could benifit from differnt cam timing as well, where the overlap happened sooner, since the collector "comes on pipe" sooner in the cycle than the crossover.
Firing order: 1-3-2-4
Engine looking down and exhaust x-over pipes
fwd-prop end
|<2----------------1|
|
| 4--------------3>|
|.........................|
|.........................|
accessory end
Number 2 & 1 are tied together, where 1 goes over to 2, than back
Number 4 & 3 are tied together, where 4 goes over to 3, than back
Number 1 & 4 are long,
Number 2 & 3 are short
Number 1 is the longest
Number 3 is the shortest
So the firing order: (1)longest - (3)shortest - (2)short - (4)long
Basically every cylinder has different total length pipes and some of the lengths are not optimal. Is it a big deal, No. Will it produce slight difference in power pulse between all cylinders, yes. However the difference is fairly well balanced from left to right, front to back, but Lycoming has an off sided/one-sided firing order anyway, where the left bank (1 & 3) fires, followed by the right bank (2 & 3). This does not help regardless of the type of exhaust.
Now what is better? We only have touched the surface of exhaust design and is exceeding my understanding (doppler phenomenon, sonic and deflected wave). We do know what has worked in the past, the "off the shelf" generic crossover is a pretty good compromise. One thing I know from my aerospace experience is everything is a compromise in an aircraft. There is NO optimum exhaust for an aircraft! Reason is we operate in a wide range of power and altitudes from 100% sea level to 55% at 16,000 feet and differnt RPM's.
Quote Cafe Foundatrion: "The 4 into 1 collector exhaust systems appears to offer the best combination of low opening pressure, some pumping gain and good scavenging." (no offense to U-all crossover-ers)
G
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gmcjetpilot
Well Known Member
Ain't it pretty
Here are some pipes I had made. They are as close to "tuned" as I could make them (click to enlarge):
G
Note the heat studs (on cyl #1 pipe): This is where the heat muff wraps around (not shown). AET has cool dual chamber heat muffs for their crossover systems. Theses are soooo much more efficient. The studs are welded onto the pipes with special equipment and are used in certified applications.
Here are some pipes I had made. They are as close to "tuned" as I could make them (click to enlarge):
G
Note the heat studs (on cyl #1 pipe): This is where the heat muff wraps around (not shown). AET has cool dual chamber heat muffs for their crossover systems. Theses are soooo much more efficient. The studs are welded onto the pipes with special equipment and are used in certified applications.
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rv969wf
Well Known Member
4into1 exhaust problems with the floor vibration.
I custon built my own 4 into 1 exhaust and ran into the same problems..... I resolved it with a few changes. Go to this web site: http://ph.groups.yahoo.com/group/JamesAircraft/photos copy and paste it then open it up.... Join the James Aircraft group, it is free and look at the photos I have posted. Photos are under Alan Judy or rv969wf. I have over 50 plus pics. The latest pics on the exhaust will not resonate the floor board and it sounds very good when doing a flyby so what I've been told. It has a very deep throaty sound to it, much different then the other RV's and the noise DB is not that bad in the cockpit.... Alan
I custon built my own 4 into 1 exhaust and ran into the same problems..... I resolved it with a few changes. Go to this web site: http://ph.groups.yahoo.com/group/JamesAircraft/photos copy and paste it then open it up.... Join the James Aircraft group, it is free and look at the photos I have posted. Photos are under Alan Judy or rv969wf. I have over 50 plus pics. The latest pics on the exhaust will not resonate the floor board and it sounds very good when doing a flyby so what I've been told. It has a very deep throaty sound to it, much different then the other RV's and the noise DB is not that bad in the cockpit.... Alan
az_gila
Well Known Member
Short vs. long...
George..... I believe the PowerFlow "Short" refers to the amount sticking out of the cowl.. not the actual length of the final exhaust portion....
It's more bent pipe under the cowl... in the Grummans, this might be causing extra heat under the cowl and reducing battery life, which is just behind the vertical muffler portion... the jury is still out on this...
gil in Tucson ... with a "long stack" PowerFlow on my Tiger...
gmcjetpilot said:
George..... I believe the PowerFlow "Short" refers to the amount sticking out of the cowl.. not the actual length of the final exhaust portion....
It's more bent pipe under the cowl... in the Grummans, this might be causing extra heat under the cowl and reducing battery life, which is just behind the vertical muffler portion... the jury is still out on this...
gil in Tucson ... with a "long stack" PowerFlow on my Tiger...
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gmcjetpilot
Well Known Member
Heeeres Johnny
Roger that, as Johnny Carson would say to Ed McMahon, "I did not know that, that is some wild, wacky stuff!" Thanksaz_gila said:George..... I believe the PowerFlow "Short" refers to the amount sticking out of the cowl.. not the actual length of the final exhaust portion....
gmcjetpilot
Well Known Member
Awesome pics
Hey that's fine, set the bar high, it gives an average builder like me something to shoot for. Cheers
Dang that is perddy. I studied engineering and aerodynamics but there is one truth, if it looks right, as your cowl exhaust installation does, it's going to fly right. As far as the original post, the gent that started the thread was quite outspoken about his vibration issue, but most builders with 4-into-1 do not complain. Anyway AJ nice work, I love the pictures, but you are starting to give me a complex about my work.rv969wf said:
Hey that's fine, set the bar high, it gives an average builder like me something to shoot for. Cheers
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