Mooney 231 vs. 252

[AA5Bman]

Hey guys and gals,

I don't post often - or maybe ever - but I thought I would toss a question to you readers. As you might notice from my screen name, I own a Grumman Tiger, which I like but do not love, and am thinking about trading up to a Mooney M20K.

I've done a lot of research and I'm wondering if someone can help out. Basically, everything I've read says that the 252 is a significantly better airplane: intercooler, automatic wastegates, infinitely variable cowl flaps, speed cleanups 'n all. The question is, are they $50,000 dollars better?

If one were to get a 231 with the merlyn wastegates and intercooler mod, would that fix the problem with the 231's -LB's engine? Would it be as fast as a 252? What are real owner's pireps regarding actual cruise flight speeds for 252s and 231s? By the way, is the 252's fuse longer than the 231?

If money were no object, I'd run out and get a 252 immediately and not ask so many questions, but alas...

Thanks for all the help,

Mike

 

[HPNPilot1200]

We normally true out around 160 - 170 in the 231 depending on cruise altitude, burning 10.5 gph. I haven't had any real issues cooling the TSIO-360 in the 231 low or at altitude (17k+). The 252 may give you a slight increase in speed, but it depends if you're willing to pay for it. If you can pick up a 231 for the right price, I would say go for it. Use the extra money to upgrade the avionics.

Best,
Jason

 

[Dr. O]

The more power you make, the shorter the engine life and the higher the maintenance costs... How fast can you afford to go?

denny-o

 

[SCCutler]

In my research before I bought my plane, Mooneys figured prominently; I saw many 231s with Merlyn wastegate controller and intercooler added, both of which are said to be a Big Deal. I also looked into buying into a 231 club, and the members thereof said that they had had excellent reliability, founded principally upon (1) good training of the members in proper engine operation and (2) consistent maintenance. From all of that, I had concluded that, if I found a well cared-for 231 for the right price, I would certainly have considered it.


But, of course, I discovered that what I really wanted was a Bonanza, so that's what I got... and I am serenely happy with it.

 

[bbchien]

The MB-1B IS what you want. I've owned many setups, and you really really want the set and forget wastegate.....

 

[AA5Bman]

TI've owned many setups, and you really really want the set and forget wastegate.....

Exactly. I'm not interested in buying a un-modded 231, with the crazy MP settings and all - sounds like a nightmare. My question then becomes is it okay just to go with a 231 which has the "set and forget" mods, or do I really need to consider paying $50k more to get a plane with the -MB engine.

 

[Anthony]

Are you looking for high altitude operations or just increased speed? Would an M20J make sense?

 

[Fast n' Furious]

I have owned my M20K (252TSE) for four years. It's a wonderful airplane and I looked at a bunch of 252s and 231s before buying this one. If you want to talk serious Mooney stuff, send me a PM with your phone number and I'll be happy to share the good, the bad and the really, really, really cool stuff about this airplane.

 

[AA5Bman]

A couple of reasons for the turbo: I live on the west coast and do a lot of traveling in the high desert and in the mountains. I find that in my Tiger, there are times I would really like to get up to 15,000 feet or more if it were possible. Also, I assume that the turbo would help when departing an airport with a DA of, say, 8,500+ feet which happens regularly enough to be of concern, although I recently had an A&P tell me it wouldn't help much in that situation which caught me by surprise (comments?).

Yes, I've thought about the M20J, but there's not much difference in price between an M20J and a 231, so why not get a turbo if it makes sense? There's a big difference in price between an M20J and a 252, of course, which is kind of why I'm asking the question.

And, yes, speed. I won't deny it.

 

[Anthony]

I hear ya. I had my Tiger in Colorado for three years and while it was OK a higher service ceiling would have been nice. IIRC the M20J has a 18K feet service ceiling. A turbo would certainly help in high DA situations. Don't know what your A&P was talking about.

 

[AA5Bman]

Yeah, the M20J is definitely an acceptable fall-back position. I understand they do very well at high altitude. All things being equal though (price), I'll take the turbo every time, which is the reason for the question about the 231. Not really sure I want to pay the money for a 252, but if I can make a good buy on a modded 231 and get most of what I need and an engine that won't self-destruct, then that's perfect.

 

[Anthony]

A modded 231 sounds like the ticket.

 

[Clark1961]

Also, I assume that the turbo would help when departing an airport with a DA of, say, 8,500+ feet which happens regularly enough to be of concern, although I recently had an A&P tell me it wouldn't help much in that situation which caught me by surprise (comments?).

I think it'd be best not to consult that A&P on things turbo.

I took my turbo Dakota up to Leadville in early July. On departure I climbed out at 1,000 fpm. The guy in the right seat who has more than 12,000 hours in small aircraft said that is the fastest he'd ever climbed out of Leadville. Normally aspirated engines lose about 2% power for each 1,000 feet of density altitude. That arithmetic is simple in that a normally aspirated engine would lose ~17% of it's power at 8,500 feet while the turbocharged engine wouldn't lose that power.

Sure, at the higher density altitudes the true airspeed will be a bit higher for a given indicated airspeed which means a bit more runway will be needed, but it's really nice to have full engine power.

 

[AA5Bman]

Yeah, that's basically the way I figured it. I think we were having a misunderstanding or something - the turbo at high DA is, as far as I can tell, a no-brainer. I'll continue in my search for a good 231 with the right mods.

 

[PilotAlan]

Normally aspirated engines lose about 2% power for each 1,000 feet of density altitude. That arithmetic is simple in that a normally aspirated engine would lose ~17% of it's power at 8,500 feet while the turbocharged engine wouldn't lose that power.

It's actually more like 2.5-3% per 1000 feet of density altitude (depending on altimeter setting, etc). At 8500ft DA you are actually right around 75% power (or 25% down).

 

[Walt]

AA5Bman,
I think it you have most of the advice can be given on the subject. I would add that finding an exceptional airplane is hard to do. In this case I would not be as concerned with the model as the condition. I have been operating turboed aircraft for 30 some years and obviously like the performance advantage. At high DAs the turbos are worth the cost. The problem is many turboed aircraft get abused. It takes a good prebuy and some good instruction from a knowledgeable Mooney instructor to keep you from spending a load on it after you buy it. Take your time and hire some good help. What ever you have to spend will be worth it. Good Luck!

 

[sba55]

The more power you make, the shorter the engine life and the higher the maintenance costs... How fast can you afford to go?

denny-o

That's not really true. Maybe in practice it often turns out this way, but that's because it's easier to abuse larger engines and people unknowingly tend to abuse engines. Then again....I peaked at the digital CHT gauge we had in one of the 172s during instrument training and saw 449 degrees during some maneuvers. Then it fell rapidly to 340 during the descent. Ironically, this was with a CFI who was worried about shock cooling, but he didn't seem to mind this

Out of curiosity, do 231s have intercoolers from the factory? If not, I'd look into getting one....

-Felix

 

[AA5Bman]

Out of curiosity, do 231s have intercoolers from the factory? If not, I'd look into getting one....

No, they don't, unfortunately. I wouldn't consider a 231 without the addition of both an intercooler and an automatic wastegate.

Okay, next question: which Mooney will fit my 9'6" longboard and land at a gravel strip 1,000nm deep in mexico? Just kidding!

Thanks for the help, guys.

 

[Trapper John]

That's not really true.
-Felix

Sure it is. At a given RPM, more power means more cylinder pressure which means greater ring pressure on the cylinder walls, and more load on connecting rod and main bearings, all of which means more wear. Plus there's more heat to dissipate, which is harder to do at altitude where air density decreases which makes the less dense air a less effective heat transfer medium.


Trapper John

 

[sba55]

Sure it is. At a given RPM, more power means more cylinder pressure which means greater ring pressure on the cylinder walls, and more load on connecting rod and main bearings, all of which means more wear. Plus there's more heat to dissipate, which is harder to do at altitude where air density decreases which makes the less dense air a less effective heat transfer medium.


Trapper John

You're mistaken. More power from an engine doesn't by any means mean more pressure per cylinder. That's why we have more than 4 cylinders. That aside, in what engine do you think cylinder pressures will be higher - a TSIO3xx or a IO5xx?

And we're not taking into account different materials that they use t compensate for different power outputs. That and the fact that 95% of people run their IO3xx ignorant of good practices (which is usually the opposite of what the POH and Lyc/TCM say).

-Felix

 

[Ted]

Remember, he may not actually have any experience running engines on dynos, doing detonation testing, doing endurance testing, or any of the other things that would give one knowledge of what actually is good or bad for an engine, but he did stay at a Holiday Inn Express.

 

[Trapper John]

You're mistaken. More power from an engine doesn't by any means mean more pressure per cylinder. That's why we have more than 4 cylinders.

When I said "at a given RPM", I figured you would also know the number of cylinders would be constant.

It's all about mass flow through the engine. More power takes more mass flow, more mass flow at a fixed RPM means more cylinder pressure. You can think of an engine as the inverse of a pump if it helps.

That aside, in what engine do you think cylinder pressures will be higher - a TSIO3xx or a IO5xx?

Depends on the static compression ratio, the amount of boost on the turbocharged engine, camshaft profile and ignition timing, among other things.

And we're not taking into account different materials that they use t compensate for different power outputs.

Such as?


Trapper John