So no matter what, a tuned pipe will increase your efficiency over a log dump as his current exhaust is. He can opt to turn that increase in efficiency into performance or fuel economy, his choice to make at the moment he needs either.
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So no matter what, a tuned pipe will increase your efficiency over a log dump as his current exhaust is. He can opt to turn that increase in efficiency into performance or fuel economy, his choice to make at the moment he needs either.
It's not the welds, it's the paper thin metal next to the welds that is the problem.
dell30rb
Final Approach
Well its a bit of both - its hard to weld on paper thin material with your run of the mill MIG without weakening it. Fine line between burn through and not enough heat to make a strong weld. And an exhaust is exposed to all kinds of vibration - heat - yada yada
All those welds are TIG, not that it makes much of a difference....
Skylane81E
Final Approach
The flange weld is the only factory one, and the welds aren't the issue, the issue is the parent material is eroded so thin that it'll break next to the new weld, and that's only if the guy is good enough with a TIG torch to not blow it out trying to get a bead.
Stickers are free and they buy you all the cred you paid for...It was funny seeing all the stickers on cars "Man, all those guys sponsoring you?" "No" "Then why are you advertising for them? BTW, that has to be the fastest tool box in the pit..."
BTW, If I was gonna put unsponsored stickers on my stuff, it would be for the worst crap on the market.
The flange weld and the vertical weld on the left side of the pipe. The crack is in a repair weld and the vertical weld on the right of the pipe is probably a repair also.
Neal Howard
Cleared for Takeoff
A massive exhaust leak that close to the port/flange can end up warping the exhaust valve.
MAKG1
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Hmm, I'd expect an engine analyzer would be much more effective.
Tuning exhaust is generally only good for a few percent in power, and then only at the tuned RPM. It doesn't change fuel characteristics significantly (BSFC is unchanged, so fuel consumption goes up in proportion to power increase -- i.e., not much). It behaves rather precisely like around 1 inch of extra available manifold pressure, at best, and proportional to air density. The tuned RPM will move around with EGT, as it's a function of the local sound speed in the tube. It matters if you're drag racing, but not much in any other application. However, if you're going to do it, now is the time. It won't do much damage (it may change drag characteristics, depending on where the pipe goes).
The fault looks like it might be corrosion damage. Welds can encourage that, and a tuned exhaust would make it worse, by concentrating heat at specific points on the pipe. Exhaust pipes under maximum performance can get red hot, which encourages rapid oxidation. Temperature gradients also encourage cracking due to expansion stresses.
How could this cause an engine failure? It could cause the exhaust valve to warp or burn by introducing oxygen into the valve during overlap. But that would be roughness, not a complete failure. Expensive to repair, to be sure. I suppose the heat could melt something critical. But on its own, it's hard to see an imminent failure coming up. I do agree that it's worth it to get on the ground and check it out as soon as reasonable.
Tuning exhaust is generally only good for a few percent in power, and then only at the tuned RPM. It doesn't change fuel characteristics significantly (BSFC is unchanged, so fuel consumption goes up in proportion to power increase -- i.e., not much). It behaves rather precisely like around 1 inch of extra available manifold pressure, at best, and proportional to air density. The tuned RPM will move around with EGT, as it's a function of the local sound speed in the tube. It matters if you're drag racing, but not much in any other application. However, if you're going to do it, now is the time. It won't do much damage (it may change drag characteristics, depending on where the pipe goes).
The fault looks like it might be corrosion damage. Welds can encourage that, and a tuned exhaust would make it worse, by concentrating heat at specific points on the pipe. Exhaust pipes under maximum performance can get red hot, which encourages rapid oxidation. Temperature gradients also encourage cracking due to expansion stresses.
How could this cause an engine failure? It could cause the exhaust valve to warp or burn by introducing oxygen into the valve during overlap. But that would be roughness, not a complete failure. Expensive to repair, to be sure. I suppose the heat could melt something critical. But on its own, it's hard to see an imminent failure coming up. I do agree that it's worth it to get on the ground and check it out as soon as reasonable.
In all the years I've heard that and growing up working on cars and engines, I have found zero evidence of that. It's pure OWT poppycock IMO.
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Pretty much all of the backpressure required to keep the valves from burning up has been developed before the header junctures. Running with no pipe may sound like crap but it won't hurt your engine.
John221us
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Welding it back together will not be an option. I will replace whatever needs to be replaced. Whether or not I install a tuned exhaust is another issue. If it is $1,000 vs $5,000, I am not sure that I should spend that on this plane to increase the performance (and I hear it does make a difference on this plane). If it were a safety issue, I would. I would not sell a plane to someone, if I knew about an issue that compromised the plane's safety. If the pipes are aged out and paper thin (which it sounds like they are), then I will replace them.
What's 10% in fuel savings worth to you? That's typically the gain one gets out of tuned exhaust. Note: This will only work if you fly the same speed profile as increase in speed requires an exponential increase in fuel.
Neal Howard
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Everybody's entitled to their opinions. I've seen firsthand a warped exhaust valve from a Lycoming that had a broken exhaust stack, so I know it can and does happen.
John221us
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The 10% fuel savings doesn't mean much to me. The plane is pretty economical, already. The increase in climb means a lot, but only if I keep the plane. I will have to wait and see what the price difference is, but I will probably be better off putting the money towards a different plane. My panel is VFR only and this plane will never be able to handle high altitude airports, even with the tuned exhaust. I wouldn't mind a little more speed, either, but that would be secondary to climb performance and a better panel.
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The number of years and usage required for payback might also enter into the equation.
Yep, which is why I posited it as a question and gave him some data to make the determination. If he wants a different plane anyway, it's not worth much.
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10% fuel savings? Sounds way optimistic to me.
MAKG1
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Really? Doesn't that mean a POH addendum and an STC to tune an exhaust?
I've seen a number of claims of that in automotive circles, usually from small manufacturers trying to sell something they don't have the facilities to substantiate. I've run the numbers, and I simply don't see it. I see gauge pressures in the intake of no more than one inch, full throttle, and no change in BSFC. So, fuel savings for identical power production is zero. The only way I can make savings appear is by adding fudge factors to the volumetric efficiency. IMO, that makes it BS.
The issue is not resistance in the tubes. That's negligible. It's managing the pressure waves in the exhaust.
And in general, you need to tune the intake as well to see any effect at all.
And please do not make up dependencies. You do not need exponential increase in fuel for a given increase in airspeed. It's a cubic dependency on TAS, and linear dependency on density at these far-subsonic airspeeds. That's far short of exponential.
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John221us
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PowerFlow claims a 30-50% increase in climb for a Cherokee with an O 320 and I have received feedback from a previous post from someone who installed and said that they experienced this and had to actually repitch thier prop to keep the engine from redlining in cruise.
http://www.powerflowsystems.com/products.php?cat_id=6&pid=22
I do believe that it makes a difference. It is more a matter of how much do I want to spend on this plane.
MAKG1
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Sorry, I call BS, unless your previous "feedback" had a constant-throttle aircraft.
The solution to overspeeding in cruise -- if this ever really happened -- would be to reduce the throttle. No need to change the propeller.
Even a normal unmodified 30+ year old Cherokee with over 2000 hours on the tach will redline in cruise at low altitude if you keep it at full throttle.
As for claiming 50% improvement? See my previous comment about automotive claims. It sure sounds like the same thing.
There is a very pronounced placebo effect (well, technically, it's a "confirmation bias") with performance. Especially if a lot of money or effort has been spent to get it.
wabower
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And always wise to remember the FAA requirements for documentation of performance claims by STC applicants.
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John, it is an improvement yes but I also have to question how much. I think ten percent is optimistic. If I was going to keep the plane ten more years and put 200 hours a year on it I'd say yes but otherwise, do some math.
I would kindly advise that people selling mods tend to overstate the benefits thereof.
It would be useful to keep in mind that an STC for an exhaust system or any other mod like VGs, gap seals, special wingtips, special hubcaps, etc. means that no one found an adverse effect to the aircraft as a result of the mod. Not that the aircraft was faster or better. Just that it wasn't less safe that the original.
Whether your wallet would end up lighter after a modification is another matter, and we all know how that would turn out.
Skylane81E
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Yep, however given how lousy aircraft exhaust systems usually are I buy that there could be a rather large benefit, but 10% seems a little on the high side of likely...
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That reminds me of the intercooler STC (Airflow Systems) on my Turbo Arrow. At least they were honest.
"When installed, fuel consumption will be equal to or less than that of an unmodified engine."
In other words, if it didn't do a damn thing, it still met the MFG's claims.
"When installed, fuel consumption will be equal to or less than that of an unmodified engine."
In other words, if it didn't do a damn thing, it still met the MFG's claims.
Skylane81E
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Agreed, but an intercooler shouldn't have been overlooked by Piper in the first place either!
John221us
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The quote from Knisley Welding came in at $1,250 for the replacement pipes. I am going that route.
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So that is a preformed pipe and flange that will bolt and clamp into place, or will there be fitting and welding required? Or is this a send off your exhaust and they send back an overhauled unit? That's usually the greatest value, especially if they have a good jig.
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John221us
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Thanks for all the input. The tuned exhaust sounded interesting, but I am anxious to get the plane flying again and I don't want to over invest in it, as I am still interested in moving up sooner than later.
If you're moving up the $1250 rebuilds sounds good, but if that is just to repipe it, don't be surprised if it costs $2000 when they get it and find the muffler ends are in too poor of condition to weld to so you need a muffler too. Just the way it is, you're due; exhaust gas is corrosive stuff.
John221us
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My shop checked the muffler and said it was in good shape and a lot newer than the pipes. They are probably the originals. The $1,250 doesn't include labor or gaskets, so I do expect it to cost more and won't be surprised.
If your muffler is good expect the full bill to be about $1700 all in.
Don't mess around with exhaust systems.. They live a hellish life and can kill quickly.... The heat is unbelievable to a non motorhead.. Henning can vouch for the operating temps. This motor is running 1450 or so EGT's.. My motor is run at 1650 +...
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Skylane81E
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Nothing quite like flying a turbo twin at night...
wabower
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Hell, my louvered doors are glowing! That's why I want to build a water jacket around my augmentors to provide cabin heat water so I can get rid of my gasoline heater, I hate those things. As a mechanic I think using these things is two links in an accident chain.
You know you suck having your own dyno...
You could use a big generator though and make the grid buy the electricity. Billy used to tune the big boys in the supper time hours where spot prices were highest.
wabower
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They're nothing more than a partially-contolled gasoline fire in a trash can. Why would that make anybody nervous?