231, no intercooler or wastegate?

[Sable1]

As my deal on a 231 fell through this summer, I continue to search for a bird with the right combination of bells, whistles, (and more importantly) good care, and price - in other words, a good value.

So my question is: how important is an intercooler and (or) an automatic wastegate? I know they can both be added, but i believe it probably makes more sense to buy a plane that already has them, if that's what I want. I have talked to a few people, and have conflicting opinions, but not any good reasons why.

I've seen a few planes without either, and they tend to cost less. I'm wondering if it's really worth the extra money.

As for my type of flying... Based in the upper Midwest (MSP area), not many flights in the mountains, no low IFR, a fair number of $200 hamburger runs.

Any thoughts or comments are greatly appreciated.

Tedd

[carusoam]

Inter coolers are the key to maintaining the air temp entering the engine. High temps lead to pre ignition challenges.

Automatic boost controllers are the key to not over boosting the engine. High ICPs are not good.

If you don't have an engineer to operate your engine while you fly, these are both beneficial.

Overall, these items are for the health of your engine and have a payoff further down the line.

Some upgrades have a higher critical altitude and that is a measure of performance...

I prefer the extra set of cylinders to the turbo. so I might have missed some critical detail.

Best regards,

-a-

How did I do?

[DonMuncy]

From a technically correct standpoint, intercoolers and automatic wastegates are the way to go. For someone wanting the very peak in performance, they are a necessity. I have had my non-IC and non-AW 231 for 13 years and, frankly don't really find that I need them. It is a bit of a nuisance having to deal with the throttle etc. without the automatic wastegate, but once you get used to it, it isn't very much trouble. If I were buying today, I would prefer getting one with them. But if I could save $10,000 by not having them, I would have to seriously consider it.

[Sable1]

Carusoam - you did great, thanks. 

I like to think I'm not a ham fisted flyer and with the proper training would be able to manage both the temps and compressions as Don does.  But of course everyone thinks they're an above average pilot....  (A little more background on me - 400+ total time, first aircraft purchase, only a few hours of turbo time - enough to give me the bug!)

Part of my delimna is not just the price difference, but what's actually available.  If it were just a matter of spending $x more for an identical plane, it would be much easier.  Try to put a price tag on it, and decide if it's worth it.  But there are so many other factors that get tossed in.

My preference is definitely to have both.  But I came across a mid 80's 231, low total time, mid time engine, P&I in good shape (as much as you can tell from the pics), decent avionics (G-430, Century 2000 AP) and from what I gather it's been very well taken care of.  Under $90k.  This has been a hard one to pass up.

Don - Thanks for your insight as well.

[ArtVandelay]

Ok, so if you are careful with the throttle, you don't need the wastegate and if you don't fly higher altitudes you don't need intercooler, the problem is, when you buy any plane, you don't know how the owner flew it? I guess this is where the prebuy comes in.

[Z W]

The auto wastegate and intercooler help make the engine more "fool proof."  I've never flown without them, so this is all information I got off these forums, but if you're careful and make sure you don't overboost or over temp, you don't "need" them.  The intercooler does boost your critical altitude, but frankly, very few of us ever go over FL200 for safety reasons.  I would put no value on that feature, myself.

 

After several hundred hours in a K model, I wouldn't really think twice about flying one without those features, as long as it had a full 6-cylinder engine monitor.  I would think very carefully about buying one.  Even if the seller convinced me he didn't overboost or over temp his engine, I would worry about the guy that owned it before him, his buddy that he let borrow it for a weekend trip, the CFI he let ferry it for maintenance, etc.  I would not count on a mid-time engine purchase lasting very long, in other words.

 

I also would be very nervous to let another pilot fly my plane without me in the cockpit to watch the MP and temp gauges.

 

If I were new to the K model Mooney, I'm not sure I would have the same attitude about flying one.  I've learned a whole lot since I started flying my auto wastegate and intercooled 262.  It's all familiar now.  Adding in the stress of overboosting the engine by moving the throttle 1/2" too far in would not make for pleasant transition training.  But that's just me.

[RJBrown]

Early 231 engines were considered to have 1000-1200  hour lifespans because of the No intercooler, No automatic wastegate configuration. People quickly found that they could NOT operate them as advertised and make TBO. To get the performance promised they HAD to be "abused" Those that treat a 231 with "kid gloves" and get it to last might as well fly a 201. A 231 without BOTH is incomplete and price should deduct for missing parts. These are parts that should have been there from the start. Once Mooney learned what they were doing with turbos they built the 252. All turbo Mooneys built since have had both. ANY 231 flown without should be considered run out at 1200 hours.

 I bought a 12 year old 231 with about 1100 hours expecting 1800 TBO. It became a Rocket at 1200 hours. The Rocket is set up properly and will easily go beyond TBO. I sold the Rocket in 2003. I planned on buying a turbo when I bought the MSE 4 years ago. In my research I looked at every 231 listed for over a year and tried to determine how long the engines had lasted. Pretty easy on first runs. Planes listed with 600 hour motors and 1800 TT were easy to see 1200 hour original engines. I looked at and compared over 30 aircraft and determined that as of 2009 231 were STILL averaging about 1200 hours per engine and the ones that went further ALWAYS had been topped.

 I live in Denver. The reason to buy a turbo is just west of where I sit. 16,600' MEAs lie 10 miles from here. To operate between 15,000' and 20,000' you need both the wastegate and the intercooler. A pilot can rationalize anything he wants to, hell I rationalized a J.

 If you operate a 231 the way Mooney recommended it has to have both to survive. Even with both it is still the most "fragile" turbo configuration Mooney ever had.

 You will find that anyone who defends the 231 without both is based at or near sea level.

 The longevity issues of the 231 went into my poor decision to buy a MSE (J). My next plane will be a Rocket. Rocket engines cost no more at OH than do 231/252 engines. They perform better and, contrary to their 1600 hr TBO, last longer than the TSIO-360s. With the higher fuel consumption cost as the only downside to a Rocket vs. a stock K it is just too hard for me to trust a 360 after flying a 520.

 Besides POWER CORRUPTS! and in this area I have surely been corrupted. It was sad to own the MSE where every flight was a disappointment knowing what a Mooney airframe can do when powered by 305Turbo HP.

[Sable1]

Zane, I think you hit the nail on the head. There is always going to be some history lurking, and trying to hedge my bet as much as possible seems like a good idea. And you're also right about the transition training. Not that it can't be done, but it will call for more hours with an instructor (additonal $$) as well as the added stress.

RJ - WOW.  You make some really good points.  I've not really looked much at the Rockets - maybe I should be.  Based about about 700' MSL, I can see where some of the local opinions I've received have come from.  I'm not really excited at the thought of a $50k overhaul at 1200 hours.  Like most things - it's a pay me now, or pay me (more) later...

The search continues...

[Dave Marten]

The auto wastegate and intercooler really made the 231 a winning combination. Yes they can be effectively flown without but the real performance potential and engine longevity is easily attainable with the two 'must-have' mods for any 231. If you want 'em buy one moded.

 

Bullshit flag on the play! A well flown and maintained 231 will make TBO! Don't take my word call a Mooney Service Center and ask. Just like any other airplane take a look at who/how it was flown and maintained is key.  

 

Here is a good example of a well flown and maintained 231 on this site:

 

http://mooneyspace.com/topic/10596-holiday-sale-1980-m20k-n231rx-reduced-91-k/

[RJBrown]

The critical altitude is limited on a stock 231 by the fixed wastegate. On a 231 the wastegate is "partially open" at low altitudes giving too much boost. This make throttle position critical to prevent overboost. At higher altitudes the waste gate being "partially open" looses too much boost and reduces critical altitude.

An automatic wastegate opens fully at sea level to eliminate boost. As a airplane climbs the automatic wastegate closes and provides more and more boost as the airplane climbs. Once the waste is fully closed and the turbo is getting all it can you are at critical altitude. A fixed, or partially open, wastegate never allows the turbo to receive the full amount of exhaust pressure. This is what limits critical altitude. Zane from Missouri and Don from Texas are examples of a flatlanders that finds a 231 and it's limitations OK. It is not just the height that a plane can reach that is important but the climb rate at altitude that also makes a difference. The intercooler plays a very small role in the critical altitude equation. Because it cools the intake charge it does allow for a fractionally more power at the same vacuum setting.

There are many pilots that do not understand how their turbo system works and why. A lot of them have posted here.

[Z W]

Critical altitude of the stock 231 is 14k. I fly in the high teens regularly (once or twice per year in the mountains, too), and almost never am I trying to get 100% power above 14k. I use a cruise climb setting.

You can take off from any airport in the Rockies at 100% power in a stock 231 on a hot day. If you really need 100% power above 14k, it would probably be for an icing situation that should have been avoided.

That is why I would put little or no value on the critical altutude / service ceiling increase. Nice to have, but... Meh.

[Lood]

A friend of mine bought his 1980 model 231 in 1982 with only 200hr since new. He handled it perfectly and flew it all the way to TBO without problems - took him about 26 years!

It certainly is not the same as the 252, but when treated correctly, it will last. I do agree with all the above sentiments on the risk when buying a used one. Some pilots are just not made to fly behind a turbo and you'll never know how it was treated. If I had the money, I'd buy either a timex airplane and fit a factory reman or I'd buy from someone that I know really well.

[chrisk]

Moving back to the original question.  If you want a plane with an intercooler, buy the plane with it already installed.  I believe there were two companies that had STCs for the 231 with an intercooler.   When I checked last, kits were not available from either, but I have seen some traffic that indicates one may have had a recent production run.

 

On the technical side, it's important to understand what the stock 231 has and what an intercooler and waste gate will do for  you.  First, the waste gate in the stock 231 is fixed.  This means some exhaust goes to the turbo, in all cases.   So, even if you are at 8000 feet and 50% power, exhaust is being diverted to run the turbo.  This generates heat and inefficiencies.  And because 8000 feet is below critical altitude, even at 75% power, you still are still making the turbo work harder than it needs to (which generates heat).   An automatic waste gate should reduce this issue, as the turbo only runs as much as it needs to.   Keep in mind however that there are multiple types of automatic waste gates.   Everyone wants an absolute pressure controller, where you set the MP and the controller keeps it there, independent of altitude.   What you can get for the 231 is a differential pressure automatic waste gate controller (Merlyn).  This should work by trying to maintain a differential pressure between the turbo output and the manifold pressure (i.e. the pressure difference on both sides of the throttle).  This will allow the turbo to only work as hard as necessary, but you can still over boost the engine.  --but overboost protection is not something to worry about.  Realistically, the only place you will overboost is on take off / go around, and even the absolute pressure controllers can have issues here due to lag in the system. 

 

An intercooler should allow higher power settings (or lower RPM), particularly at high altitudes.   When the turbo compresses air, it gets hot.  The intercooler is basically a radiator the cools the air before it is consumed by the engine.  Excessively hot air, being consumed by the engine, can cause detonation.  --So without an intercooler, if the CDT gets to high, you will have to reduce MP.   With an intercooler, you should be able to use the temperature after the intercooler, which is probably 50+ degrees cooler.   --But, a dirty intercooler can have drastically lower performance.

[fantom]

There are many pilots that do not understand how their turbo system works and why. A lot of them have posted here.

LOL

I'm still trying to understand how any of these contraptions ever get off the ground. Let's not even start on all the ADS-B combinations and permutations.

[RJBrown]

A Merlyn equipped 231has a critical altitude of 19,500, not a small difference. A Rocket's critical altitude is 24,000. I have had a 231 to 22,000 and a Rocket to 26,000. A stock 231 flown to TBO was never ask to perform up to book levels. A 231 with waste gate and inter cooler flown carefully can both perform and last.

[jlunseth]

The Merlyn is not a fully automatic wastegate.  In a 231 with a Merlyn the pilot still needs to manage the MP and it is possible to overboost the engine if you are hamhanded.  The difference between the factory configuration and the Merlyn is that the factory engine, as mentioned, was a fixed wastegate, basically just a hole that allowed some exhaust gases to escape so that the turbo would not overspin.  I believe it was adjustable on the ground, but definitely not in the air.  That meant that as the aircraft gained altitude, some exhaust gas (power for the turbo) was always being wasted and that, in turn, limited the critical altitude (the altitude at which the aircraft could produce 210 HP (100%)).  An additional problem with the factory configuration was bootstrapping.  If the engine produces more power it puts out more exhaust which makes the turbo run faster, which puts more compressed air into the induction system, which causes the engine to produce more power, etc.  It could have some difficulty finding a stable setting. 

 

The Merlyn is a differential controller, not an automatic controller.  It manages the difference between ambient air pressure and induction air pressure.  So if you take off where the ambient pressure is 30" and you set the MP for 36" at takeoff, the Merlyn will manage the induction air so that it is 6" more than the ambient air pressure.  That is an overgeneralization, but that is what the Merlyn tries to do.  So if you ascend in the air column to an altitude where the ambient pressure is 28", the Merlyn will produce 28+6=34" .  The pilot needs to adjust the MP as the plane climbs if the pilot wants to continue to produce 100% HP.  The good news with the Merlyn comes in two forms.  One, the Merlyn virtually eliminates bootstrapping.  I really don't see it in my aircraft.  Second, the Merlyn manages the differential pressure by opening and closing the wastegate, which does two things.  One, it allows the turbo to run slower in general and still produce the needed MP, and that means better turbo life.  And two and probably more importantly to those of us who use the flight levels, it increases the critical altitude.  Merlyn says it goes to 19,500, give or take, my actual experience is that it is more like 22,000.  This makes a major difference in the ability of the aircraft to climb efficiently to cruise in the flight levels, and it also helps keep the engine temps lower on the way up and once established.  The climb rate becomes truly anemic once the aircraft can no longer make 100% - in the range of 100 to 300 fpm, and the ability of the air to cool at those altitudes is fairly poor.  What I have seen in my Merlyn equipped aircraft is that Compression Discharge Temp. (CDT) will exceed redline somewhere between 18 and 20,000, and you would no longer be able to climb.  Here the intercooler becomes a big plus, because the CDT redline no longer is relevant.  The purpose of the redline is to protect the engine from detonation due to high induction air temp(IAT), and IAT in the intercooled engine will be much cooler than CDT, in the flight levels I will commonly see around a 100 degree temp difference.  So the engine is protected from detonation, and runs cooler.

 

Based on what I have seen in my aircraft, I question how they could have done the testing that produced the rated ceiling of 24,000 for the 231.  You simply can't get that high without CDT exceeding redline.  Probably did the testing on cold winter days, and it probably took a very long time and a lot of patience to climb the last 10,000 feet, since the factory critical altitude was around 15k, give or take.

 

Another minor consequence of the differential controller is that if you descend, as I generally do, by simply tipping the nose over and establishing a descent rate (I use 500 fpm), you will need to pull off about an inch of MP to compensate for the increase in pressure due to ram air.  You will also need to periodically adjust the MP on the way down because as the ambient pressure increases, the MP will also increase. 

 

The Merlyn takes some management by the pilot, it is not "set and forget," but it is pretty easy to fly with.

[Sable1]

Thanks to everyone for their thoughts and insight.  As is usually the case - I learn something every time I log in here.

Hopefully some day soon I'll be able to contribute with some actual experience of my own.  In the meantime, I'll have to continue standing on the shoulders of the giants here...

Thanks again!

[RJBrown]

The reason for the 24,000' service ceiling was to benefit the marketing dept. They wanted 200+knots/231 MPH and could only get it by abusing the heck out of it at 24k. 201 is 1 mph over 200 mph while 231 is 1 mph over 200 knots both were marketing goals not results of solid engineering. The 252 with a proper induction system got a 28,000' service ceiling the increased altitude is where the additional knots were gained. In reality the 252 is not really 21 MPH faster than a 231. It was just properly configured to run up high. Mooney RD got lazy on the early 231 using essentially what Piper had used to power the turbo arrow. In the arrow that engine package was given a certified ceiling of only 20,000' Even limited to 20,000 in the Piper it still resulted in poor reliability. To achieve the speed and altitude the factory sold us both the wastegate and the intercooler need to be added. Or it needs to be flown like a 201. Flatland pilots who are impressed with 15,000' cruising altitudes and poor climb rates up high and treat the plane carefully can reach TBO. It is one or the other. Performance or longevity a stock 231 will not deliver both. With both additions AND a thoughtful pilot the 231 can be flown as meant to be and have a reasonable shot at TBO. ANY used 231 engine with unknown history should be considered a 1200 hour motor.

[ArtVandelay]

The reason for the 24,000' service ceiling was to benefit the marketing dept. They wanted 200+knots/231 MPH and could only get it by abusing the heck out of it at 24k. 201 is 1 mph over 200 mph while 231 is 1 mph over 200 knots both were marketing goals not results of solid engineering. The 252 with a proper induction system got a 28,000' service ceiling the increased altitude is where the additional knots were gained. In reality the 252 is not really 21 MPH faster than a 231. It was just properly configured to run up high.

And the 262? Who did the marketing testing for that?

[RJBrown]

262 was not a Mooney product. Mod Works, thank God they are gone, was the developer of that STC. They put a TSIO360MB in a 231. Not a full transformation but close. The choice of names was I am sure one ups man ship with absolutly no speed to back it up. Just a name someone thought sounded good.

[gjkirsch]

The reason for the 24,000' service ceiling was to benefit the marketing dept. They wanted 200+knots/231 MPH and could only get it by abusing the heck out of it at 24k. 201 is 1 mph over 200 mph while 231 is 1 mph over 200 knots both were marketing goals not results of solid engineering. The 252 with a proper induction system got a 28,000' service ceiling the increased altitude is where the additional knots were gained. In reality the 252 is not really 21 MPH faster than a 231. It was just properly configured to run up high. Mooney RD got lazy on the early 231 using essentially what Piper had used to power the turbo arrow. In the arrow that engine package was given a certified ceiling of only 20,000' Even limited to 20,000 in the Piper it still resulted in poor reliability. To achieve the speed and altitude the factory sold us both the wastegate and the intercooler need to be added. Or it needs to be flown like a 201. Flatland pilots who are impressed with 15,000' cruising altitudes and poor climb rates up high and treat the plane carefully can reach TBO. It is one or the other. Performance or longevity a stock 231 will not deliver both. With both additions AND a thoughtful pilot the 231 can be flown as meant to be and have a reasonable shot at TBO. ANY used 231 engine with unknown history should be considered a 1200 hour motor.

Having owned a couple of 231's and flew a number of 252's before buying a Bravo, I found the 252 about 10 knots faster than the 231 up to the mid teens and then going up from there as altitude increased.  There was a lot less fiddling with the throttle on climb and descent in the 252 as well.  One 231 I owned had the meryln waste gate and intercooler and the other had neither.  The one with nothing was actually faster but it was an 85 model with smooth belly and covered wheel wells.

[RJBrown]

Having owned a couple of 231's and flew a number of 252's before buying a Bravo, I found the 252 about 10 knots faster than the 231 up to the mid teens and then going up from there as altitude increased.  There was a lot less fiddling with the throttle on climb and descent in the 252 as well.  One 231 I owned had the meryln waste gate and intercooler and the other had neither.  The one with nothing was actually faster but it was an 85 model with smooth belly and covered wheel wells.

Great info. A 252 is about 11 MPH faster not the 21 Mooney inferred. Sounds about right. My 231 experience is a bone stock 1980 for about 100 hours then about 750 in the same plane as a Rocket.