… isn‘t half of the joy of flying talking about how things work and how to improve it?
Indeed 
A great technical discussion.
For Turbo owners, it is highly recommended to learn in detail how the system works, and what to expect from it.
The Service manuals often give guides on how to check the health of the Turbo system by doing critical altitude tests (When MP starts to drop=Wastegate completely closed).
The forums is a great place to discuss issues, performance and symptoms.
Main Turbo in California is a great shop to get help. They will take the time to help you troubleshoot your system, and have reasonable prices for repair/OH/exchange.
Here is a great Troubleshooting guide on Turbo systems (and engines in general)
Ram Aircraft Engine Troubleshooting
Yes Peter it is the K&N filter. In my case I could see the difference from before and after.
Indeed this has become a very interesting discussion and I am impressed by the quality of contributions. Thank you guys.
The RAM manuals are excellent reading.
And as to the discussion about whether turbos are useful or not, I’d say the following:
- Imagine an IO-550, derated AND built (lighter) to deliver only 200 HP in cruise with lighter parts etc. This would be a seriously interesting alternative to a turbocharged IO-360. Simple, robust, economical, cool running, and it would deliver 200 HP from sea level to probably FL120. An ideal solution for a non-pressurized cross country aircraft such as the DA40 or Cirrus SR20.
- In a pressurized aircraft, the turbo is needed to generate the cabin pressurization. A pressurized piston powered aircraft is very complex mechanically and its maintenance costs are correspondingly high. But it has one huge benefit versus its turbine powered siblings: it can fly down low efficiently. This not only saves fuel, it save (me) a second plane for these 1000 Euro VFR burger runs.
I think that a small turbocharged engine still has more advantages over a big bore engine, even below 12k ft. There’s a reason why all car manufacturers are downsizing their engines and adding a turbo for economical reasons, even at MSL.
Except that very few car engines spend their lives delivering anything like 70-85% of their potential power, and their turbos operate on light duty most of the time. Aircraft engines have a much harder life and turbo-charged ones even more so. That is why most do not get close to TBO without top-end work, however much the exceptions are more widely vaunted than the norm.
I think the main difference is the duty cycle, water cooling and less need to achieve a low weight and gearbox-less simplicity.
A 2 litre car capable of say 130mph is doing only about 30% power at 70mph (the UK speed limit).
I am convinced that car engines are as reliable as they are not because of some magic “brilliant engineering factor, made possible by huge volumes and fantastically clever people” but due to a good knowledge of the various failure modes and how exactly these interact with the typical application. And the car manufacturing industry is very clever at playing this just right.
Look at VW… their 2 litre turbocharged diesels with the “cheating” software were as reliable as anything else out there. But once they fixed the cheat, which wasn’t some massive change in the ECU mapping, things have started to come apart all over the place. Justine’s car, 5 years old, failed a few months after the “fix” and this appears to be pretty standard. The car was also a lot slower. And cars in the old days were much less reliable despite also having been designed by equally clever people and made in vast numbers. The electrics were marginal, with crappy connectors, etc. Cars have become so reliable not by some amazing engineering change but by countless small changes over decades, based on knowing what breaks on a population of millions of cars in the field and fixing just that and nothing else because fixing the “else” costs another €1 VW are replacing the EGR valve for free (£1000) but they are not replacing the actuator which will also be extra-shagged. It’s all about doing the absolute minimum and the car business is very good at it. Well, normally they are very good at it; the dieselgate scandal has shown just how close they play it.
And no car runs at say 65% of max power the whole time. I would be amazed if a truck did actually. But the truck has a heavy water cooled diesel, with weight being a non-issue. A turbo aero engine which is aircooled has still got the same thin wall sections (to get an IO540 down to say 200kg) which it had before somebody got the idea to turbocharge it. It worked mostly OK before the turbo, just about, and the turbo pushes it over the edge in most installations – just as Wilco says above. Not only is the engine producing high power for much longer (typically, climbs are at 100% power) but many installations are blown to a higher than surface MP. And the mission profile is pushed further out: longer high altitude flights and most likely more hours a year. No wonder something starts to break.
