Turbo guys...question

[Buster1]

Guys with Turbos.  I have narrowed the search to just 3 or 4 231s!  Some have intercoolers, some do not.  All have JPI 700/800s for accurate engine monitoring.

My question is, should I get the one with an intercooler, or is ot okay to not have an intercooler.  Is there any appreciable difference for the engine and longevity that would make the intercooler a priority to have?

[IFlyMooney]

Buster,

One of the main issues with the 231 is heat control.  I believe that an intercooler helps tremendously with this issue.  It reduces the manifold pressure required to produce full horsepower, which in turn reduces the amout of heat generated.  I have been flying my 231 for 15 years and am on my second engine.  I believe that the intercooler has been responsible for making it to TBO with my first engine, and no problems to date on the second.  The other option that I have found to be really valuable is the Merlyn automatic waste gate.  When I added that to my plane, I gain 5-7 knots cruse at altitude.

Good luck on your decision

Kevin

[MooneyMitch]

Welcome Kevin!  I look forward to hearing Mooney things from you. 

[jlunseth]

I have the Merlyn and a Turboplus intercooler.  The intercooler does not produce the cooling that is advertised.  The plane is in for an annual, and one of the things I want them to do is to clean and flush the intercooler, see if that makes a difference.  Willmar tells me that from their point of view, the intercooler helps the engine a little to stay cooler, but they recommend flying the plane to the original MP settings without adjustment.  They also no longer recommend adding an intercooler to a 231.  I make some adjustment.  I take off at 36-37" instead of 40, 40 is just not needed.  I cruise at 31 or 32.  That is pretty much the unadjusted setting for a 231, the adjusted setting for a 252 being 28. 

I am glad I have the intercooler though.  I have heard that the stock engine was difficult to keep cool at higher altitudes (thinner air=less heat conduction), and that is where the 231 is at its best.  I don't have a problem with high altitude cooling, and if the intercooler helps with that great.

[Bob]

 

My 231 has the factory wastegate and is without an intercooler. I believe the only main negative to the factory wastegate would be in the event of a go-around. If you abort a landing, you can NOT add full throttle. If you do, you will overboost. You must advance the throttle up to 39LB. This obviously adds another item to your workload while you are reconfiguring the plane. Good training will keep you from overboosting!

On the 231 the redline is 40LB and I believe the factory wastegate opens at 42LB. What I keep wondering is, why did the factory install wastegates that dump extra pressure at 42? Something tells me that if the factory wastegate opened at 40, it would become impossible to overboost. Maybe this was done to get higher HP numbers?

As far as the intercooler goes, I have not had enough experience yet to share facts. But I will tell you what my gut says. They are not needed and the whole need is placed out there by the people selling them.

I am new to Mooneys but have a 25 year history with Porsche automobiles. It is very interesting to compare the Mooney to a Porsche. First of all the Mooney owners and Porsche owners are both true enthusiasts! Both groups just love what they own! Learning and understand the mechanicals is a high priority. And they both can talk about their interest, every chance they get, up until the next event or gathering. I know this is a little off thread, but it ties to the next paragraph.

What I find interesting is, back in the early 90's, the Porsche 911 Turbo guys were always talking intercoolers. The factory sold the 77 vintage cars without intercoolers and they came factory installed them on the 88 cars. Does this sound like the 231 and 252? All the 77 guys talked, talked and then purchased the intercoolers to upgrade. Then those guys stopped talking, because the change was not very noticeable. At the same time the 88 guys were buying larger intercoolers. But they kept talking because they had a BIG polished intercooler. They did not talk about how much faster or cooler the car ran, just BIGGER. The Porsche wastegate was set below redline not above like the Mooney. You could not overboost a factory 911. The guys that got a adjustable wastegate for the 911, would use it to increase boost for more power, not to keep from overboosting. Of course the Mooney has additional factors due to altitude, but I still think a whole intercooler craze is just silly.

Now I have to tell where my mooneyspace username came from.  It was my License plate number for my 911 turbo years ago.

I guess all our opinions come from our experiences, so I must stand firm on saying NO to intercoolers and wastegates!  My engine is only about 400 since factory overhaul at this time.  I will post an update to my views in about 10 years, I hope, at about 1800hrs.

[RJBrown]

 When I flew 231NH as a stock 231 heat was the limiting factor for operations at any altitude. The oil temperature was the first sign. The oil temp gauge was an important part of my scan, it was where the first indications of over temp showed up. Any thing to reduce temp on a 231 is a plus. The Merlyn allows full power to a greater altitude. The fixed wastegate limited the turbo at higher altitudes. With the higher power at altitude I would want an intercooler.

After the engine went on my 231 it was converted to a Rocket. The Rocket has two intercoolers. Heat was never a problem again.

Though I have never operated a 231 with just a Merlyn I would want both it and an intercooler if I were to buy one. The higher you fly the less effective the cooling is. Though the air is cooler at altitude it also has less mass and conducts heat away from the engine less effectively. 

 I consider both the Merlyn and the intercooler required components on a 231 and would deduct the cost of adding them from the sales price of one.

I had stopped to post at this point but then read the next post. Here is my reply to it.

I preface my next remarks. Please dont be offended ILXLR8. You opinions ARE from your Porsche experiance. That experiance does not apply directly to the 231.

I believe the Porsche\ Mooney argument is Apples/Oranges. It totally misses the point. OVERHEATING is the issue NOT go fast. There never was a overheating issue with the Porsche. The Enemy of any aircraft engine is heat. That goes triple for a turbo at high altitude.  Anything that pulls heat out of an engine at altitude helps. My MSE makes less than 100HP at altitude. My Rocket made 305HP at 24,000'. The cooling needs are night and day

"My 231 has the factory wastegate and is without an intercooler. I believe the only main negative to the factory wastegate would be in the event of a go-around. If you abort a landing, you can NOT add full throttle. If you do, you will overboost. You must advance the throttle up to 39LB. This obviously adds another item to your workload while you are reconfiguring the plane. Good training will keep you from overboosting!"

The advantage of the Merlyn is both no overboost at sealevel and more power at altitude. The original wastegate is fixed not variable. It HAS to be set to overboost at sealevel otherwise it would begin to lose power from sealevel just like a non turbo. The fixed wastegate then limits boost and causes the 231 to start losing MP at a lower altitude. The Rocket is able to maintain 100% power up to 24,000' BECAUSE it has a variable wastegate. Adding a Merlyn to a 231 increases it's critical altitude.

"On the 231 the redline is 40LB and I believe the factory wastegate opens at 42LB. What I keep wondering is, why did the factory install wastegates that dump extra pressure at 42? Something tells me that if the factory wastegate opened at 40, it would become impossible to overboost. Maybe this was done to get higher HP numbers?"

 The wastegate is NOT the type that opens to limit boost, it is preset, Fixed in one place. The popoff valve opens at 42" and dumps pressure. The wastegate does not open and limit boost. Because the wastgate is "fixed" it then creates a lower critical altitude. Mooney did it to save money. It was a BIG mistake.

[IFlyMooney]

The  Merlyn automatic waste gate does not prevent overboosting.  You still have to be careful to not put in too much MP.  The wastgate "automatically" adjusts for altitude and therefore creates full horsepower up to 19K ft.  The factory "fixed" wastgage only creates full horsepower up to 14K ft.  This is why I saw an increase in crusing speed at altitude.  The popoff valve is to hopefully prevent damage to the engine from an inadvertant overboost.  My understanding is the if this were to occur, the turbo would have to be pulled so that the popoff valve could be replaced. ( I could be wrong on this)  That is why the popoff valve is set to 42" with the max at 40".

[Buster1]

So far we have 2 FOR, 1 AGAINST (ILXLR8's gut ;-)), 1 ON THE FENCE, and 1 with no advice to the question at hand.

You guys ain't makin' this easy on me!

[Bob]

Buster,

My gut is killing me right now!

[jlunseth]

Yes.  Here is my understanding of the wastegate issue.  In the aircraft, the turbocharger is a compressor that is driven by exhaust gas in order to increase intake air pressure to make up for the loss of pressure as the aircraft ascends.  The turbo operates at very high speed.  To keep it from operating beyond its speed limit, some of the exhaust gas is discharged through the wastegate.  In the stock 231 that wastegate is fixed, in other words the amount of gas that is allowed out the wastegate cannot be varied to suit the needs of the engine.  The fixed wastegate is in effect a hole of a fixed size.  The only variability to the turbo speed would be caused by lower or higher exhaust pressures at lower or higher throttle settings.  The fixed wastegate in this setup is a compromise. 

One effect of this is that when the stock 231 hits critical altitude at 15000 (from my manual), the wastegate is still allowing exhaust gas to escape.  The "escape hole" is still the same size as at sea level.  The variable wastegate (such as a Merlyn) is able to adjust the rate at which exhaust gas that would be used to drive the turbo can escape.  So at lower altitudes and lower power settings where not alot of turbocharging is needed, the wastegate allows more exhaust to escape.  At higher altitudes and power settings, the variable wastegate is able to fully close, taking advantage of exhaust that the fixed wastegate would be wasting.  That allows the variable wastegate to increase the critical altitude, and it also means that the turbocharger is not being spun at an unnecessarily high rate of speed at lower settings and altitude.  The wastegate has very little to do with overboost management, it is certainly possible to overboost an engine equipped with a variable wastegate by using full throttle at sea level.  Firewall throttle in a turbocharged engine is there to be used higher altitudes. 

The settings that are above 40 MP I believe are the popoff valve settings, not the wastegate. 

The car and the airplane are different animals.  The car never expects to operate at .5 ATM.  The car engine and turbo are designed to produce full power at full throttle at sea level, and the engine is designed to accept the consequent pressures.  The aircraft needs to be able to produce full power at high altitude, and the throttle setting for that is way more than the engine could accept at sea level.  The better turbo design for the aircraft is one that can vary the amount of turbocharging (by varying the wasted exhaust gas) as altitude is varied. 

[Buster1]

Got it.  All the ones I am considering have the Merlyn Automatic Wastegate.  I think that is a must these days.  Great explanation, thank you.

So even though you don't think your Turbo Plus is doing much, you recommend it?

[jlunseth]

Well, I am glad I have one and I am glad a prior owner paid to put it in.  I have heard bad things about the temps that people who have the stock 231 experience at high altitude.  I don't have that problem, at least not at 17,500, which is as high as I can legally go right now.  Maybe in the 20's (when I complete my instrument ticket) I will see it, don't know.  I respect the opinion of the people at Willmar, and they don't recommend it, but say it "helps the engine a little," i.e. it keeps things cool at altitude. 

There was a recommendation made (article on the MAPA site) to fly the 231 with Merlyn and intercooler to the throttle settings for a 252 (which has a variable wastegate and intercooling).  The primary reason for that would be the theoretically denser air provided by the intercooler.  Pretty much everyone I have talked to who has the Merlyn/intercooler 231 says the 252 settings do not work, and some say to fly the Merlyn/intercooler equipped 231 to the settings for a stock 231.  My personal experience is that is not exactly right either.  Use three or four inches less on takeoff, and at least an inch or two less at cruise, but not much less. 

I started cruising at 28", the plane was too slow.  I went to 30 and still a little slow.  31 seems to work good.  Will experiment more when the plane comes home.

I should also disclose that I talked directly to Turboplus, and they were adamant that I should be getting a greater differential temp. (difference between CDT and IAT) than I am seeing, so maybe cleaning the intercooler will help.  If it does I will report back.  They also said I should see a higher differential temp. in the 20K+ altitudes, and I can't go there yet so can't say if they are right or not.  It would be nice.

[carusoam]

Does anyone measure air temperature before and after the intercooler?

The car guys trying to minimize chance of detonation will often notice a 75 deg F lowering of charge air temperature at or near sea level.  (not alot, but still useful, especially in the summer months).

The plane guys will find rejecting heat to the atmosphere valuable also.  (not alot available from an intercooler at altitude, but still useful)

Under some conditions, managing the turbo ROP probably can balance out whether there is an intercooler or not.

Four ways to reject heat (from the engine to the atmosphere). Air cooling, ROP, lower intake air temp, oil cooling.

At high power settings it is probably helpful to use all of the cooling available. 

For me, all too complex for casual east coast flying.  I applaud the extra efforts the turbo guys put in.

For those on the mission of fly highest, fly fastest - control boost, cool every way possible, and run best power ROP?

 - Anthony -

[N9937c]

My 231 came to me with intercooler. I normally see 60 - 70 degrees c. reduction of temperature across the cooler. If I couldn't find my " dream" 231 with the cooler, This would be my first purchase. I live in the land of Texas and see 100 degree F. days  more than my share. Really tames the temps.

larry

[RJBrown]

These pictures show the main differences between the 231 and the 252.

[N9937c]

I am wondering about some of the statements made above.  

To ILXLR8     If you are operating your engine at the parameters you have listed above your engine is SERIOUSLY in danger.

Perhaps you mean 39 in. and 40 in. instead of your listed parameters.

I am at a loss to  explain why an aircraft engine mfg of large high performance engines does not skip the time and expense of turbo intercooling their new designs to accomodate your theory. MOONEY must have wasted untold $ with the ACCLAIM.

I  cannot think of a mechanical system that will perform longer and better at a somewhat reduced temperature.

My nickel

 

larry

[KLRDMD]

I have about 1,000 hours experience with a number of different turbo systems. Currently I have an F model with the RayJay turbo. Before the F, I had a Seneca III and before that a Mooney Bravo. The Bravo had both intercooler and automatic waste gate. The Seneca and F model did/does not. The Seneca had TSIO-360-KB engines, so they are very close to the stock 231 engine.

The bottom line is, at least in my opinion, it doesn't make a hill of beans difference to have an intercooler and/or automatic waste gate or not. You simple learn to manage the engine you fly behind. Yes, an automatic waste gate reduces your workload a bit, but in the big scheme of things it isn't that big a deal. If you can learn to properly fly a Mooney in the first place, you can learn to manage your engine.

Buy the airplane that has everything else you want and take it as it comes, with or without an intercooler and/or automatic waste gate.

[FlyingAggie]

Buster,

In looking for 231, I asked the same question to several knowledgable brokers and received diameterically opposed answers.  The new management at Willmar claimed the  AUTO WASTE GATE was far more important than the INTERCOOLER and David at All American said the INTERCOOLER was more important than the INTERCOOLER.  I have seen comments by owners like Ken who have the even the original -GB and later -LB engine claim you don't need either and they are just expensive comlications.

In preparation for owning, assuming the prebuy goes well, a 262 in a couple of weeks, I have been reading John Eckalbar's book on Flying High Performance Aircraft.  The chapter on turbo charge operation convinced me of the value of the intercooler, when you go through the thermodynamics.  The TSIO360-MB engine in the 262 has both automatic wastegate and intercooler, but only the intercooler reduces the amount of heat going to the engine at altitude.  (If you are below critical attitude the waste gate will "waste" heat to the atmosphere, keeping the engine somewhat cooler when you are down low.)  Because air gains heat the more you compress it and the higher you go (especially with an autowaste gate maintaing max pressure up higher) the compression ratio goes up making the intake air hotter the higher you go. 

John Eckbalbar summarizes the value of the intercooler like this:  "The bottom line is running the turbo can cause heat problems.  First, the compression pushes the induction air temperature up to the point where the cylinders may as well be inhaling from an oven.  Second,you push more air into the cylinders, so you burn more fuel and get more power.  But burning more fuel releases more  BTU's, which also means more heat in the engine.  All this means cylinder heads, valves, pistons, exhaust stacks and everything else run hotter in turbo charged engine, especially those using high boost.  This weakens the metal and increases wear.  It also hurts fuel economy, because you may end up fighting the heat by flying with extra rich mixtures or with cowl flaps open. But even more important, the higher induction air temperature move the engine close to to its detonation limits. The reason for this is obvious---detonation occurs when end gas is pushed to the auto-ignition during the combustion stroke, and the higher the air temperature, the higher the end gas temperature.  In view of this, it would seem anything that reduces induction air temperature will be a boon to the turbo pilot."

So I guess the next question is how well do the after market intercoolers work on 231"s?  Do they produce the same cooling as the one's that TCM installed  at the factorythat went into the 252?

I had both intercooler and autowaste gate on my "must have" lists when I was looking for a 231.  With the -MB engine, I will have both.

Alan

[KLRDMD]

Quote: FlyingAggie

John Eckbalbar summarizes the value of the intercooler like this:  "The bottom line is running the turbo can cause heat problems.  First, the compression pushes the induction air temperature up to the point where the cylinders may as well be inhaling from an oven.  Second,you push more air into the cylinders, so you burn more fuel and get more power.  But burning more fuel releases more  BTU's, which also means more heat in the engine.  All this means cylinder heads, valves, pistons, exhaust stacks and everything else run hotter in turbo charged engine, especially those using high boost.  This weakens the metal and increases wear.  It also hurts fuel economy, because you may end up fighting the heat by flying with extra rich mixtures or with cowl flaps open. But even more important, the higher induction air temperature move the engine close to to its detonation limits. The reason for this is obvious---detonation occurs when end gas is pushed to the auto-ignition during the combustion stroke, and the higher the air temperature, the higher the end gas temperature.  In view of this, it would seem anything that reduces induction air temperature will be a boon to the turbo pilot."

[jlunseth]

I think Buster is asking how well the intercooler works in the 231.  I don't think there is any question that it contributes in the much different (and higher priced) set up of the 252.  I see a max diff. temp. of 40C, which is not nothing, but does not seem to be a major contributor to the engine either in terms of power, but is a contributor to better temps.   

LOP cools things, yes, but you are also perceptibly dialing down the power output of the engine.  I haven't been able to try it enough yet to be sold on it, or not sold. 

[KLRDMD]

Quote: jlunseth

LOP cools things, yes, but you are also perceptibly dialing down the power output of the engine. 

[jlunseth]

Well, I am not trying to pick an argument here and I will admit limited experience with it because I had a 711 in the plane and it broke before I could do much LOP.  That said, I have GAMI's, tested by Willmar so I know the flows are good, Merlyn, Intercooler, rebuilt fuel system, new baffles, and the couple of times I ran LOP (50 degrees), the power output dialed down considerably, as did the aircraft speed.  Maybe I need more practive, or to learn to do it right. 

[FlyingAggie]

Ken,

I didn't want to quote the entire book , but Eckalbar devotes an entire Chapter on Mixture Control and is a advocate of LOP operations.

Alan

Quote: KLRDMD

It there is something else that reduces engine temperatures, and it seems the author quoted above is not discussing it, or has no knowledge of it. That is lean of peak (LOP) operations.

[danb35]

Quote: jlunseth

Maybe I need more practive, or to learn to do it right.

[KLRDMD]

Quote: jlunseth

I will admit limited experience with it because I had a 711 in the plane and it broke before I could do much LOP.  That said, I have GAMI's, tested by Willmar so I know the flows are good, Merlyn, Intercooler, rebuilt fuel system, new baffles, and the couple of times I ran LOP (50 degrees), the power output dialed down considerably, as did the aircraft speed.  Maybe I need more practive, or to learn to do it right.