More on so-called Tuned Exhaust

[Bruce Fenstermacher]

OK George you don't believe an exhaust can suck and I do.

If and exhaust could suck as I believe then you wouldn't need individually tuned intakes just the ability to increase the fuel adjustment.

A fellow who raced 1/2A model airplanes gave good seminar and demonstration way back when I wasn't really interested i the subject. I though he was full of it till I listen to his program ans saw the demonstration
1/2A uses the Cox .049/.051 engine. We normally ran them with no exhaust or open ports. He and many others where able to tune the header/muffler to gain more rpm over stock open ports. Of course the fuel adjustment needed to be richened but there was no other modification to the engine. Bolt the header/muffler over the open ports. Adjust the length and richen the fuel and presto more rpm all with the same prop.

Of course as you mention my experience is with 2 stroke engines but I see no reason why it wouldn't work on a 4 stroke. Again you would have to have the application that fits the power band created.

I'm thinking one reason we don't see much of a tuned exhaust not just headers or reduced back pressure systems in auto racing is there are to many other easier ways to gain much more horsepower.

[N1478D]

OK George you don't believe an exhaust can suck and I do.

If and exhaust could suck as I believe then you wouldn't need individually tuned intakes just the ability to increase the fuel adjustment.

I'm thinking one reason we don't see much of a tuned exhaust not just headers or reduced back pressure systems in auto racing is there are to many other easier ways to gain much more horsepower.

NO NO NO! Can you imagine if when we started up, we could hear down deep in the engine compartment . . . " a little higher, no, just a little bit higher . . AHHHHHHH THAT'S IT!" That's why we don't run tuned exhausts - still poking fun Bruce.

[Walker]

If it's power you're looking for, there's no replacement for displacement. I still think that the concept of these low compression ratio, low RPM engines has not changed since the thirties and there isn't much you can do to improve them without affecting other things, one mainly being engine life. No doubt, you can gain some performance by doing something like playing with the exhaust, but what are you going to save? How much gas do you save?(How much gas can you buy with the cost of the conversion?) How much more power? What if you lunch a new engine for other reasons? What will the shop try to blame when you drag it back to them? Truly, no offense is intended, but if the setup you have isn't doing it for you, change it. Get a bigger engine or bigger plane, or smaller one. But, if your motive is just to have fun and experiment with it, I think that is the best.

[zero.one.victor]

"There's no substitute for cubic inches" was the axiom we used to use.
Of course, more tuned cubic inches is better than more un-tuned cubic inches....... "there's more than one way to skin a cat" also comes to mind. Say you want "more power" (ala Tim Allen on Home Improvement)--there's more than one way to get it. One guy increases displacement via bigger bore, another increases displacement by longer stroke, still another leaves displacement alone & increases performance by improving efficiency-- intake, exhaust, carbeuration,timing/ognition, cam/valves. Given the regulated nature of aircraft mod's, a bigger (stock) engine is probably the easiest way to go.

Eric

[GAHorn]

"If and (sic) exhaust could suck as I believe then you wouldn't need individually tuned intakes just the ability to increase the fuel adjustment."
I rest my case. (And how many magic exhaust makers recommend such?)

[Bruce Fenstermacher]

George you are assuming the engine wasn't running rich to begin with. If it was and you made the change you'd see an improvement.

Look I've never said it works with our FARs which limits the engine rpm to 2700 and our static rpm limits how much pitch you can through at any more power youmay create.

I thought the discussion here was given no regulations does a tuned exhaust, meaning the impulses of the exhaust are timed to add in the extraction of the exhaust, works on 4 cycle engines of the type we use in our aircraft.

[GAHorn]

Just to make sure there's no misunderstanding, or possibility of hurt feelings,...I'd like to say that my only reason for participation in this msg thread is in the interests of discussion...and theorizing amongst friends....
There's no intent on my part to require agreement with my own opinion on this matter...only an interest in pursuing an interesting discussion. Having said that....
Bruce...if the engine was runnning rich to begin with....then it seems to me the best way to make it run better is to correct the fuel-mixture condition problem...not monkey with the exhaust.
With regard to our airplanes,...yes the TCDS and FARs certainly place limits on what we can legally do. But even without regard to those considerations, I maintain it takes a lot of active imagination and wishful thinking to believe that an exhaust system....any system...even a magic system...will "suck" creating a vacuum for subsequent combustion cycles to realize any performance gain. If we were to create a huge chamber and evacuate it of all atmosphere so that it had an over-abundance of negative pressure within the chamber, and then piped the exhausts from a 4-cycle engine to that chamber....it would still require an incredible amount of imagination to believe that somehow that vacuum could "suck" additional horsepower out of a piston travelling on it's exhaust stroke. The imagined relief of exhaust pressures from that piston are just that....imaginary.
It takes a goofy kid like me, who built his first go-cart out of a Briggs & Stratton lawnmower engine and got the silly idea of using ordinary galvanized plumbing fixtures and a water-valve to close off the ordinary outlet of the exhaust gasses and re-direct them thru a hose to his bicycle tire as a lazy way to inflate bicycle tires to figure that out. An idling 1.5 hp Briggs lawnmower engine will completely explode a bicycle tire, folding the rim inward in the process. I can assure you that engine had little cognizance of "back-pressure" from the exhaust. (I also found out that Schwinn tire rims are not commonly available and only Schwinn dealers have them. They are different from all the others and cost an entire summer's lawn-mowing profits.)
I have closed the exhaust valve completely and observed the engine "lug" down and stop, also. It takes more than you might imagine, and involved quite a bit of hissing and fussing before it happened. (This truly defines the concept of "anecdotal" evidence.)
Race-car enthusiasts (and boaters, modellers, etc. etc.) as a genre are a unique group. They will spend incredible amounts of money on infinitesmally small (imaginary) gains. That's part of their hobby...pursuit of that which they hope is unobtainable to their competition. Tuned exhaust systems are really way out there on the fringe of sanity in a crowd whose sanity is already in question.
But to think about that idea,....an exhaust system that "sucks".... is a real leap, IMHO. Imagine that, if you will,...atmospheric pressure already being 14 psi at sea level...and a manifold pressure gauge in that exhaust system already reading 30 in. HG with the engine at rest....actually reading LESS with the engine running! I'll wager a whole case of Becks against someone demonstrating that!

[zero.one.victor]

Seems like this tuned exhaust horse is plenty dead already--quit beating on it!

[blueldr]

George,
When you're happily flying home from having a "Donkey Dick"
installed on your lifes delight and you see the the five grand
deduction in your check book, you just KNOW In YOUR HEART that
you have twenty five percent more power.

[blueldr]

P.S.(To the above)
And you know damn well that you're gonna burn a lot less fuel!

[Bruce Fenstermacher]

OK George you and I are on the same page as to why we're discussing this topic . We disagree about the potential of the exhaust. I'll be on the lookout for info to support my position and be sure to PM you if/when I find some so Eric won't have to learn about it.

BTW you aren't the only one using galvanized pipe on a B&S. First as a 'Tuned Exhaust" then as an air compressor. Never got far enough to blow up a Schwinn tire/rim but I did find out early on about the "odd" size of the Schwinn rims.

I'm assuming like me you had no sophisticated equipment to test your B&S engines after you exhaust other wise you might have a different view of this subject.
(Could pass that last one up. I swear I went faster with that straight pipe)

Hot air almost exhausted. (the last one I promise)

[170C]

This discussion brought to mind something totally unrelated to the subject, but retrieved something from the past for me-------------Do any of you remember the device where you could remove a spark plug from an engine and screw in the little unit which would then air up tires, etc? Most of my growing up years my Dad had one and I have used it countless times, but after leaving home I don't ever remember seeing another one. (Also remember the "old" guys talking about when they were young and had Model A Ford's that they could raise the hood when the engine was idling, grab all 4 ignition wires/plugs and ground out the engine to the point of killing it!----Boy, not me )

[doug8082a]

[lowNslow]

George, your "HO" is duly noted.

[zero.one.victor]

(for those who can't tell, the one without the bat is the exhaust pipe)

Doug, I love it!

I might as well get another lick or two in. A friend of mine has considerable time in a flying club 172 both before & after a Powerflow exhaust was installed. FWIW, he sez there was a noticable increase in performance -- not his airplane nor his money spent modifying it, so that's probably about as impartial an opinion as is possibleto get from someone who's actually flown one before & after.
But I still can't get past the looks!

Eric