Well kind of Sort of
RV7ator said:
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
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.
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