REFLECTOR:Engines - TSIO520

[reflector@tvbf.org]

>>My plan is to manually "Turbo Normalize" them by running around 30 inches.<<

Ok, I hope I wont get kicked off the forum for this but I have a '76 Cessna T210 now. (Aluminum AND a Continental! My God what have I become!? :) )

That plane has a TSIO-520-M. It makes 280 HP @ 2700 RPM/32 MFP. Basically turbo normalized. It has a 1400 hour TBO. 

The very next year model, the 77 T210 went to 310 HP with a 5 minute limit by simply turning up the turbo controller to 36 inches max boost. That extra 30 HP for 5 minutes knocked 200 hours off the TBO bringing it down to 1200. Then later they came out with the R model that kept the 310 HP rating but bumped the TBO back up to 1400.

Then there is a 325 HP as used in the Cessna 340 twins and it runs about 40 inches boost. I'm not sure of the TBO on that model. 

On the Cessna forums the vast majority of owners of any of these TSIO-520 series engine are doing well TBO wise - They are Jug munchers one and all! :)

>>I've been told that the reason the TSIO520 eats a set of jugs every 800 or so hours is because of running them at 40 inches of MP. This should allow a more reasonable 1500 to 2000 hours of use out of the jugs.<<

How to sum up hundreds of hours of forum debates over the years? One piece at a time I guess...

Cooling- A mental trap I fell into years ago and it took me a bit to work my way out of... Since everyone knows it's cold at altitude I always (foolishly) assumed that engine cooling at higher altitudes was *easy*. However, it turns out that since air density drops cooling gets much more difficult as you climb. Even though you may still have X number of cubic feet per minute of air moving through the engine fins (or radiator) you will have far fewer molecules of air per cubic foot carrying away heat. At 18,000 feet air density is at 50% of sea level. So in effect I only have half the cooling capacity.

Now in a normally aspirated engine I loose power as I climb so the ability to generate heat and the ability to shed heat both fall off at the same rate and the universe remains in balance Grasshopper. By cheating the will of the universe with a turbo my ability to generate heat begins to exceed my ability to shed that heat. Then the universe punishes the man who defies it with his ungodly turbo with very short cylinder life. 


VD - TCM Valve Disease.

In 1981 TCM changed the manufacturing process of their cylinder head. The short version of the story is that they no longer get the valve precisely centered in the seat. The valve cools by conducting heat to the head via the valve seat. Poor seating leads to warping and burning. Big bore TCM's *from the factory* are not even getting 300 hours anymore let alone making TBO. Internet forums are rife with stories of owner's trying to get satisfaction under warrantee with TCM. One must bear in mind that this is *manufacturing* flaw not a design flaw. Rebuilt engines from quality shops that pay attention to valve train geometry still do well. 

With the popularity of "factory remans" though VD is an epidemic.

Choke: There was a problem with the choke or ring step area wear. TCM did make some changes to the manufacturing process and this one seems to be under control these days.

Ditto for Millennium- they had some choke wear issues about 5 years ago but seem to have them resolved as well with their second generation cylinders. (as an added bonus they cleaned up the breathing and you get 5% to 7% more power with the gen 2 Millenniums.)

ECI is having a huge AD right now on their 520 cylinders. They had a metallurgy problem and they are literally blowing cylinder heads through cowlings right now. 

Then pile in on top of all of that the great LOP/ROP debate. Very short version is that for any given percent of power setting ROP is the hotter way to achieve it. Most people are running ROP therefore hotter

Next is the max fuel flow issue. 

At high power settings these engines utterly depend on fuel flow to stay cool. (the old saying "fuel cools" is true after a fashion but not for the reasons people generally think. It comes back to Peak Pressure Pulse (theta p) timing- the same issue as LOP/ROP) 

Your fuel flow (FF) gauge has a redline. It really throws pilots because that redline works backwards from the redline on every other instrument in your panel. When you shove the throttle all the way in the FF redline is the *minimum* and not the maximum! Your FF should EXCEED that redline! This is critical! 

When I was shopping for T210's I checked out 5 planes before I bought the one have now. Not a single one of those airplanes got up to redline FF at full power. That lack of fuel flow will without a doubt kill cylinders and that lack of FF seems common in my limited experience.

One last factor. TCM and Lycoming CHT redlines are too high. They run between 460 and 500 degree fahrenheit (df) The strength rating of the metal alloys used in engine construction drop as the temps climb (just like composite airframes) The drop in strength is exponential. At 200 df you are still near full strength. At 300 df you have dropped some,  by 400 df the curve is getting sharper and by 420 df substantial strength has been lost and is heading south fast! 460 df is just way too hot. 

Now factor in that FAA only required one CHT probe and the regs call for that to be on the hottest cylinder while in climb. (Certification trials spend a lot of time and effort on climb cooling but oddly do not give a lot of attention to cruise cooling.) In the 210 #5 is the hottest cylinder in climb but once you level off and the airflow rearranges itself through the cowl #1 becomes the hottest. With stock instrumentation you would never even know this! 

Now lets put all that together. 

The stock Turbo Cessna driver is cruising along high altitude. He is set up 50 df ROP (the hottest place you can run the engine) His single point CHT gauge is well "in the green" even though that cylinder is around 450 df at greatly reduced strength. Meanwhile cylinder #1 is well over redline temp but he has no idea. 

He can't understand why he only got 800 hours out of his cylinders when he was so careful managing his engine. 


However, as usual *I* think I have all the answers! ;)

I trashed the TCM jugs at the first sign of trouble which was at about 400 hours. (anybody want to buy 6 jugs cheap?) I now have the gen 2 millenniums. (and in theory with the improved breathing that boosts my 280 horses up into the 294 to 299 HP range) 

I have a JPI GEM complete with TIT. I have it programmed to alert when any cylinder hits 400 degrees F. (df). I have that engine monitor right next to the "sacred six". It is in my scan and NOT on the far side of the cockpit. It starts flashing if I hit the programmed limits. Very nice. *my* redline is 400 df but I fly at 380 df

My take off fuel flow nicely exceeds the redline (red line is 32 GPH and I am flowing 35 GPH)

I climb VERY rich ROP then cruise LOP again never exceeding 400 df. In LOP cruise I can run 75% power all the way up to 23,000 feet (give or take depending on time of year) and keep the CHT's right around 380 df. Every now an then I will switch from LOP to ROP and watch the CHT's shoot up.) Over 23,000 even LOP I can't get much more than 55% power AND stay under 400 df on the CHT's. And frankly, "I can't drive 55" so even though the airplane is certificated up to 29,000 feet I have only taken it to 25,000.

So, since I have my fuel flow very high on take off, I have the best cylinders available and I *always* keep my CHT's under 400 df I think I am going to do very well TBO wise. 

Only time will tell.
  
>>As far as the turbo plumbing, I don't know at this point.  That's why I  asked the group if anybody has been down this road.  Maybe I would end up  running it as a normally aspirated IO520?<<

Ah shoot Scott. I was going to answer this but I am all typed out for one day. Which means I have to be boring everyone to tears! Sorry! :(  I have lots of mental CPU time invested in topic so if you can take any more of my rambling I'll tackle that topic tomorrow?

DM Rob