Tuned exhaust

[JOhnH]

I couldn't find anything on this. I received some advertising about a tuned exhaust system which claims increased climb rate, faster cruise, service ceiling increase or fuel savings.

The theory sounds plausible but the claims seem a little too optimistic.

But I was wondering if they may have another benefit. My Cessna 172n with the O360 upgrade has always seemed to run with high CHT values, except for #2, which seems ok. But #s 1, 3 and 4 may reach 450 during climb and high 390s/low 400s during cruise. I have to throttle back (less than 2350rpm) or run full rich to keep temps down. I have had three reputable A&Ps look at this and the best they can come up with is to pull out the EDM700 because it is giving me too much information.

Would/could a tuned exhaust possibly help the CHT problem, or are all the effects of the exhaust too far removed from the cylinder head. My hopeful logic is that if the tuned exhaust would allow me to keep the same speed at lower RPM, I would achieve the lower CHT and save fuel. Does anyone have any ideal how much such a system would cost?

 

[Lawreston]

I don't know about the CHT factor but the Powerflow Tuned Exhaust is a winner. I have it on my 1971 Skyhawk(0320-E2d). She's off the ground sooner than original, climbs like crazy(1200 fpm not unusual). I don't know how much one can believe the "Up to 23 additional horsepower" advertised claim, but she definitely has more performance. When I bought it in 2005 it was around $3500; suspect it's changed since then. Mine is the latest version(at that time).

HR

 

[gismo]

I couldn't find anything on this. I received some advertising about a tuned exhaust system which claims increased climb rate, faster cruise, service ceiling increase or fuel savings.

The theory sounds plausible but the claims seem a little too optimistic.

But I was wondering if they may have another benefit. My Cessna 172n with the O360 upgrade has always seemed to run with high CHT values, except for #2, which seems ok. But #s 1, 3 and 4 may reach 450 during climb and high 390s/low 400s during cruise. I have to throttle back (less than 2350rpm) or run full rich to keep temps down. I have had three reputable A&Ps look at this and the best they can come up with is to pull out the EDM700 because it is giving me too much information.

Would/could a tuned exhaust possibly help the CHT problem, or are all the effects of the exhaust too far removed from the cylinder head. My hopeful logic is that if the tuned exhaust would allow me to keep the same speed at lower RPM, I would achieve the lower CHT and save fuel. Does anyone have any ideal how much such a system would cost?

A "tuned" exhaust can increase the volumetric efficiency of an engine which is another way of saying it will allow the engine to develop more power but it cannot increase fuel efficiency unless the valve timing is so bad the engine is dumping raw fuel out the exhaust (tuned exhaust can improve fuel efficiency in valveless two-stroke engines because they do just that). You're not going to see any CHT benefit, chances are CHTs would go in the opposite direction, either from the higher power produced at the same RPM or from lowering the RPM and making the same power.

 

[Henning]

I couldn't find anything on this. I received some advertising about a tuned exhaust system which claims increased climb rate, faster cruise, service ceiling increase or fuel savings.

The theory sounds plausible but the claims seem a little too optimistic.

But I was wondering if they may have another benefit. My Cessna 172n with the O360 upgrade has always seemed to run with high CHT values, except for #2, which seems ok. But #s 1, 3 and 4 may reach 450 during climb and high 390s/low 400s during cruise. I have to throttle back (less than 2350rpm) or run full rich to keep temps down. I have had three reputable A&Ps look at this and the best they can come up with is to pull out the EDM700 because it is giving me too much information.

Would/could a tuned exhaust possibly help the CHT problem, or are all the effects of the exhaust too far removed from the cylinder head. My hopeful logic is that if the tuned exhaust would allow me to keep the same speed at lower RPM, I would achieve the lower CHT and save fuel. Does anyone have any ideal how much such a system would cost?

Tuned exhaust isn't likely to cure your issue unless you have a collapsed muffler which is a possibility. Leaning properly is more likely. I would also check the ignition timing and baffles.

 

[PW_Plack]

Powerflow is STC'd on many certificated aircraft, but those with fixed-pitch props may exceed engine redline due to the power increase if the prop pitch is not increased. If your prop pitch is optimized for cruise and you don't normally see full RPM on takeoff or climb, that might be OK, as long as you remember to pull the throttle back when you level off.

 

[Ted]

Sounds to me like you aren't running rich enough in the climb, or else are flying at too low of an airspeed in climb. While 380F is the temperature I shoot for at all points, 390-410 on a parallel valve O-360 isn't bad. Consider leaning it more in cruise, this should help.

Any A&P who tells you to pull out your engine monitor because it's giving you too much information probably doesn't understand what it's telling you.

 

[gismo]

I couldn't find anything on this. I received some advertising about a tuned exhaust system which claims increased climb rate, faster cruise, service ceiling increase or fuel savings.

The theory sounds plausible but the claims seem a little too optimistic.

But I was wondering if they may have another benefit. My Cessna 172n with the O360 upgrade has always seemed to run with high CHT values, except for #2, which seems ok. But #s 1, 3 and 4 may reach 450 during climb and high 390s/low 400s during cruise. I have to throttle back (less than 2350rpm) or run full rich to keep temps down. I have had three reputable A&Ps look at this and the best they can come up with is to pull out the EDM700 because it is giving me too much information.

Would/could a tuned exhaust possibly help the CHT problem, or are all the effects of the exhaust too far removed from the cylinder head. My hopeful logic is that if the tuned exhaust would allow me to keep the same speed at lower RPM, I would achieve the lower CHT and save fuel. Does anyone have any ideal how much such a system would cost?

450F is way to high and will likely shorten the life of your cylinders. Methinks you have a baffle issue.

 

[Ted]

450F is way to high and will likely shorten the life of your cylinders. Methinks you have a baffle issue.

Possible, or he's leaning more than he should during the climb.

 

[JOhnH]

Sounds to me like you aren't running rich enough in the climb

Possible, or he's leaning more than he should during the climb.

Except that I run full rich during climb. And when I try to lean during cruise, the CHT climbs. Baffles and tuning have been checked by three A&Ps and no problems found. I had hoped that when the engine was replaced the problem would disappear, but it didn't.

I run straight 50wt oil (aeroshell 100+) and I change it every 20-25 hours (hobbs time) and have the oil analyzed. Perhaps I should switch to a multi-grade oil. By the way, the engine has about 200 hours and I use about 1 qt every 7 or 8 hours.

 

[Henning]

Except that I run full rich during climb. And when I try to lean during cruise, the CHT climbs. Baffles and tuning have been checked by three A&Ps and no problems found. I had hoped that when the engine was replaced the problem would disappear, but it didn't.

I run straight 50wt oil (aeroshell 100+) and I change it every 20-25 hours (hobbs time) and have the oil analyzed. Perhaps I should switch to a multi-grade oil. By the way, the engine has about 200 hours and I use about 1 qt every 7 or 8 hours.

What speed are you climbing? Just wondering because a Vy climb is awfully steep with a 180 conversion. You also might consider climbing out lean of peak.

 

[JOhnH]

What speed are you climbing? Just wondering because a Vy climb is awfully steep with a 180 conversion.

Vy is 73kts but I keep the nose low and maintain about 80kts IAS. to try to keep the temp down. We can climb at about 1100 fpm, but I keep it down to about 5-600 fpm.

 

[bbchien]

IAPTBAA, these are painful problems to diagnose. But "full rich" does not necessarily make book fuel flow. The mechs need to be looking at why you're not sucking righ enough at "full rich". Or maybe you are. But it would be helpful to know....

What do you have for a carb?
And are you sure there is not an induction leak?

 

[Henning]

Vy is 73kts but I keep the nose low and maintain about 80kts IAS. to try to keep the temp down. We can climb at about 1100 fpm, but I keep it down to about 5-600 fpm.

If that's all the climb you are getting out of a 180hp N, you have a problem. I would inspect the internal baffling of the muffler and/or induction leak problems. If that doesn't show anything I'd look at the cam timing.

 

[Pilawt]

Vy is 73kts but I keep the nose low and maintain about 80kts IAS. to try to keep the temp down. We can climb at about 1100 fpm, but I keep it down to about 5-600 fpm.

Hm. I have a 172N with 180 hp and long-stack Power Flow, and at sea level it gets 500-600 fpm in cruise-climb at full throttle and about 110 KIAS. That speed provides plenty of cooling airflow.

An extra benefit of Power Flow, BTW, is a noticeably quieter cabin.

 

[N801BH]

Possible, or he's leaning more than he should during the climb.

Too bad he doesn't have a fuel flow gauge, like a JPI450, or Shadin or one of the others to confirm the true fuel flow... It is possible the carb has the wrong main jet, or the mixture control is set incorrectly. Maybe they used the 160HP carb on the 180 HP upgrade...

After reading all his posts I would guess the issues are, in decending order of possibilities.

1- Wrong fuel flow
2- Bad baffles
3- Retarded ignition timing
4- Collapsed muffler or tailpipe
5- Late cam timing.

The Tuned exhaust will help the motor breath better which will create more heat as more power will be made, The fact he said he hoped the problem would go away with the new motor might be a clue. I don't know the set up for going from a 160 Hp to a 180 HP. Do they use the same exhaust system ? If so is it too restrictive for the additional 40 cubic inches?

 

[JOhnH]

To answer a few questions: I do have a JPI FS450 fuel analyzer. It is amazingly accurate. If it says I have used 25 gallons, when I fill it up it will take 25 gallons +/- a few tenths.

When I put in the new (reman) O-360, I was replacing an older O-360 that had blown up in flight forcing a landing on a highway. There was no salvageable core. The old O360 had the same CHT problem.

As for leaning too much during climb, I take off at full rich and the temp still climbs to near 450 until leveling off even though I keep the climb rate low and the IAS speed high. When I level off, those warm cylinders will come down to 390ish. If I lean at all, the temps slowly climb from there.

As I said, I have had three separate A&Ps from different shops look at this and noone can find anything to cause it. Is there such a thing as a shop that specializes in airflow and temps.

I am curious about taking off at lean of peak. Wouldn't that make it hotter?

 

[N801BH]

To answer a few questions: I do have a JPI FS450 fuel analyzer. It is amazingly accurate. If it says I have used 25 gallons, when I fill it up it will take 25 gallons +/- a few tenths.

When I put in the new (reman) O-360, I was replacing an older O-360 that had blown up in flight forcing a landing on a highway. There was no salvageable core. The old O360 had the same CHT problem.

As for leaning too much during climb, I take off at full rich and the temp still climbs to near 450 until leveling off even though I keep the climb rate low and the IAS speed high. When I level off, those warm cylinders will come down to 390ish. If I lean at all, the temps slowly climb from there.

As I said, I have had three separate A&Ps from different shops look at this and noone can find anything to cause it. Is there such a thing as a shop that specializes in airflow and temps.

I am curious about taking off at lean of peak. Wouldn't that make it hotter?

My JPI 450 is outstandingly accurate too.... I guess my question is... Give us some flow numbers.. I am sure Ted will chime in with honest and dependable feedback....

Oh yeah,,, Henning is a motorhead too.

 

[Henning]

Ok, the fuel is checked correct, have the CHT probes been proven calibrated accurately?

 

[Ted]

I am curious about taking off at lean of peak. Wouldn't that make it hotter?

Yes. You can't run an O-360 lean enough for that to work. Some of the higher-powered engines that can run LOP well can do LOP climbs successfully. When you lean out from full rich, your CHTs should increase until you get to about 50 ROP EGT, after which point they should start to decrease again.

Sorry, I had understood from your original post that you weren't running full rich in the climb. If you are, I think that Ben has given a good synopsis of potential problems. You may very well not have enough fuel flow on takeoff and climb.

What I also don't know much about is the cooling of the 172. One of the problems that can arise with these engine conversions is higher CHTs. Parallel valve Lycomings also have pretty bad cooling in general.

 

[JOhnH]

Ok, the fuel is checked correct, have the CHT probes been proven calibrated accurately?

My A&P says yes. But I am beginning to think he gets defensive when I ask him because this has been going on so long and he hasn't fixed it yet. I would really like to find a good A&P that will take a thorough look at it from scratch. Preferably someone within about 200 miles of Daytona Beach Florida.

 

[bbchien]

To answer a few questions: I do have a JPI FS450 fuel analyzer. It is amazingly accurate. If it says I have used 25 gallons, when I fill it up it will take 25 gallons +/- a few tenths.

When I put in the new (reman) O-360, I was replacing an older O-360 that had blown up in flight forcing a landing on a highway. There was no salvageable core. The old O360 had the same CHT problem.

As for leaning too much during climb, I take off at full rich and the temp still climbs to near 450 until leveling off even though I keep the climb rate low and the IAS speed high. When I level off, those warm cylinders will come down to 390ish. If I lean at all, the temps slowly climb from there.

As I said, I have had three separate A&Ps from different shops look at this and noone can find anything to cause it. Is there such a thing as a shop that specializes in airflow and temps.

I am curious about taking off at lean of peak. Wouldn't that make it hotter?

Let's have some fuel flow numbers, then.

 

[JOhnH]

Let's have some fuel flow numbers, then.

In general, I get better than 9gph. Depending on the length of the trip, altitude, temperature, I usually get around 8.5gph and sometimes as low as 7.5gph, on a cool day when I lean more.

I will be checking back later this evening but I just got called by a customer for a mini-emergency.

Thanks for all the advice so far.

 

[Henning]

My A&P says yes. But I am beginning to think he gets defensive when I ask him because this has been going on so long and he hasn't fixed it yet. I would really like to find a good A&P that will take a thorough look at it from scratch. Preferably someone within about 200 miles of Daytona Beach Florida.

I think it's time for you to find another set of eyes to put on the situation. If you find your way down here give a shout.

 

[DavidWhite]

I like my powerflow. worth the cash IMO.

 

[SCCutler]

To the OP: your CHTs are too high. Were you stating that you are at 9GPH during the climb?

 

[JOhnH]

To the OP: your CHTs are too high. Were you stating that you are at 9GPH during the climb?

No, that is during cruise. During climb it varies a lot but I recall seeing 14gph pretty often. I don't pay much attention to it during climb or descent. But I will.

Another issue is that during descent/landing, the EDM 700 often flashes cooling > -60 and as much as (-)80. Sometimes even when going to idle after run-up it flashes rapid cooling. I know there is a lot of controversy regarding shock-cooling, but it does worry me so we are real careful to go full rich prior to any descent and we try to make shallow descents when possible. Sometimes, it is not possible without a go-around.

We never practice t&gs because of the rapid cooling followed by rapid heating.

I would really like to find a good shop or A&P that that specializes in cooling and would get into this. I even took it down to Certified Engines (the people that sold me the rebuilt engine) and they worked on it for about 5 hours on a Sunday and the only thing they found was a bad capacitor on the mag. But it was interesting watching him wind those safety wires when he re-installed the prop.

 

[denverpilot]

We never practice t&gs because of the rapid cooling followed by rapid heating.

Which happens, of course, on every other takeoff and landing that's not a T&G and definitely on go-arounds...

What a silly rule.

Airplanes falling out of the sky everywhere from T&G wear on engines, too.

 

[N801BH]

No, that is during cruise. During climb it varies a lot but I recall seeing 14gph pretty often. I don't pay much attention to it during climb or descent. But I will.

Another issue is that during descent/landing, the EDM 700 often flashes cooling > -60 and as much as (-)80. Sometimes even when going to idle after run-up it flashes rapid cooling. I know there is a lot of controversy regarding shock-cooling, but it does worry me so we are real careful to go full rich prior to any descent and we try to make shallow descents when possible. Sometimes, it is not possible without a go-around.

We never practice t&gs because of the rapid cooling followed by rapid heating.

I would really like to find a good shop or A&P that that specializes in cooling and would get into this. I even took it down to Certified Engines (the people that sold me the rebuilt engine) and they worked on it for about 5 hours on a Sunday and the only thing they found was a bad capacitor on the mag. But it was interesting watching him wind those safety wires when he re-installed the prop.

1- 14 gallons per hour is adaquate fuel flow for a 180 HP at sea level,, which you are at.. Look at the baffles and ignition timing real close..

2- full rich on decent with the throttle pulled back, or even at full throttle, will make it run cooler,,,, not hotter.. IMHO.

 

[dell30rb]

If you won't do touch n go's because of your engine monitor then maybe it is giving you too much info...

 

[JOhnH]

2- full rich on decent with the throttle pulled back, or even at full throttle, will make it run cooler,,,, not hotter.. IMHO.

You are right, but what we do is go full rich a few minutes before descent in order to pre-cool the engine as much as possible. If we begin a descent while still running warm, the cooling rate during descent is greater.

But I am mostly concerned with the consistently high CHT. It never reaches red-line, but it is above recommendation.

 

[N801BH]

You are right, but what we do is go full rich a few minutes before descent in order to pre-cool the engine as much as possible. If we begin a descent while still running warm, the cooling rate during descent is greater.

But I am mostly concerned with the consistently high CHT. It never reaches red-line, but it is above recommendation.

One thing I didn't mention but comes up alot in the experimental circles....

The intake of cooling air is the nostrils in the front of the cowling behind the prop. Most builders try to keep those as small as possible to get minimum drag and maximum airspeed. In alot , if not most cases the real problem is the size of the discharge opening in the rear bottom of the cowl.. Basic rule of thumb is 1.5 X the size of the intake...... maybe your application has some type of restriction in that area preventing the motor from properly cooling ... Too bad I am not closer... it sounds like a fun challange to figure out your dilemma..

Ben.

 

[Henning]

No, that is during cruise. During climb it varies a lot but I recall seeing 14gph pretty often. I don't pay much attention to it during climb or descent. But I will.

Another issue is that during descent/landing, the EDM 700 often flashes cooling > -60 and as much as (-)80. Sometimes even when going to idle after run-up it flashes rapid cooling. I know there is a lot of controversy regarding shock-cooling, but it does worry me so we are real careful to go full rich prior to any descent and we try to make shallow descents when possible. Sometimes, it is not possible without a go-around.

We never practice t&gs because of the rapid cooling followed by rapid heating.

I would really like to find a good shop or A&P that that specializes in cooling and would get into this. I even took it down to Certified Engines (the people that sold me the rebuilt engine) and they worked on it for about 5 hours on a Sunday and the only thing they found was a bad capacitor on the mag. But it was interesting watching him wind those safety wires when he re-installed the prop.

Not a worry; not to be taken as an endorsement of doing t&gs, but the reason you are avoiding them is not valid.

 

[Henning]

One thing I didn't mention but comes up alot in the experimental circles....

The intake of cooling air is the nostrils in the front of the cowling behind the prop. Most builders try to keep those as small as possible to get minimum drag and maximum airspeed. In alot , if not most cases the real problem is the size of the discharge opening in the rear bottom of the cowl.. Basic rule of thumb is 1.5 X the size of the intake...... maybe your application has some type of restriction in that area preventing the motor from properly cooling ... Too bad I am not closer... it sounds like a fun challange to figure out your dilemma..

Ben.

Yep, all sorts of funkiness can go on. I offered to look at it if he flew down here. It does sound like a fun one.

 

[JOhnH]

Yep, all sorts of funkiness can go on. I offered to look at it if he flew down here. It does sound like a fun one.

And I hope to make it to Ft. Lauderdale sometime in the not too distant future. Which airport do you call home?

As far as t&gs go, I have always been told that too hot is bad and too cold (too fast) is bad, but rapidly going from hot to cold to hot to cold to hot to cold is the worst thing.

 

[Henning]

And I hope to make it to Ft. Lauderdale sometime in the not too distant future. Which airport do you call home?

As far as t&gs go, I have always been told that too hot is bad and too cold (too fast) is bad, but rapidly going from hot to cold to hot to cold to hot to cold is the worst thing.

FXE is closest to me and Banyan has an excellent pilot shop if you need anything.

As to "shock cooling" a 172 in air, it's impossible. If you had a convertible flying submarine, you'd want to not let the engine water cool right after a hard flight, but outside of that, as I said, "not a worry"; old wives tale.

 

[bluerooster]

Powerflow is STC'd on many certificated aircraft, but those with fixed-pitch props may exceed engine redline due to the power increase if the prop pitch is not increased. If your prop pitch is optimized for cruise and you don't normally see full RPM on takeoff or climb, that might be OK, as long as you remember to pull the throttle back when you level off.

We hadda re-twist the prop on the Cherokee 140 when we installed the Power flow.
It still climbs like crazy, and we would conservativly plan for 115kt cruise, at 7.5gph.

 

[DutchessFlier]

Your climb rate fuel flow sounds normal, and in level cruise, well, that depends on many environmental factors and leaning technique. I also fly behind the 360 conversion in a 172N, and see temps similar to yours, only for a few moments but not consistently. BTW do you notice which cylinders run warmer than others? In my plane the #1 and #3 are consistently warmer than the #2 and #4, not into the 400's but warmer. Its hard to get consistent temps across all the cylinfders in a carbureted engine, due to variations in fuel flows to each cylinder as well. I also have a oil temp probe installed and it never gets higher than 180-185 degrees.

Many folks I speak with who have the 360 conversions say that they tend to run warm(er). Lycoming gives 500 degrees as an absolute max CHT, but I would not want to go near there. If you are in the 300's CHT in cruise, you should be okay. Do you use the lean find function to lean the plane in cruise flight?

BTW have you tried to dump the engine data from your JPI into a computer and run it on a graph? Might be a good idea for you.

I just put in the JPIEDM700 (and I do understand now how flying behind the monitor it's hard not to constantly be checking it in flight and it can seem to provide an overload of info at first). I have had the FS450 for a while. I'm still breaking in my cylinders after a top overhaul, and getting used to the engine monitor.

I'm running straight mineral oil through the next oil change, then back to multi vis phillips X-C20-50 and camguard.

Keep us informed as to your progress.

 

[Gary]

We hadda re-twist the prop on the Cherokee 140 when we installed the Power flow.
It still climbs like crazy, and we would conservativly plan for 115kt cruise, at 7.5gph.

What pitch did you twist it to?

115kts. is pretty good for a Cherokee 140! What altitude and RPM do you get those cruise speeds? I do like the construction of the PowerFlow, potentially a replacement if and when the stock exhaust wears out.

Gary

 

[bluerooster]

What pitch did you twist it to?

115kts. is pretty good for a Cherokee 140! What altitude and RPM do you get those cruise speeds? I do like the construction of the PowerFlow, potentially a replacement if and when the stock exhaust wears out.

Gary

I don't remember the twist just right bingo, but it was 60-something I think 63" (but don't hold me to that figure). I would cruise at 2350 RPM, which would give me 115 indicated. And for some reason it was consistent between 3000'-8500'.
The guy who now owns it allows that it's the fastest 140 on th' planet.

You can see the powerflow hangin' under the cowling.

 

[Skylane81E]

I might think about swapping that #2 probe to another cylinder to see what happens...