LOP with A36TC

[Tim Walter]

There is a lot of discussion on this site and others about LOP operation with TAT converted 520 and 550 engines, but not so much information about LOP operations with factory turbo 520UBs.

The aftermarket conversions are all turbonormalizing, rather than tubrocharging and this leads me to have a few questions that have so far been unanswered.

First of all, deakin and others say (basically), run the throttle wide open and use mixture to set the power.

Well, that doesn't work in the TSIO520UB where the MP boosts to 36", so does that mean pull MP to 29"? actually, it seems like 31" is a more "standard MP" for the TSIO520UB since that is the max cruise value ? maybe?

Either way I'd like to see if any of you are running LOP with this engine, and what your experiences are.

Here are my numbers.

First of all, yes I installed GAMIs and worked with GAMI tuning the injectors to get it just right, those guys are great BTW, can't recommend them highly enough.

secondly, I had new spark plugs, and had the mags overhauled and got everything just right, this took a few months tweaking here and there.

I also have a JPI700.

All these things are required before you can get anywhere LOP with this engine.

Running ROP basically uses huge amounts with this engine, to keep the cylinders cool (380F max)

I see fuel flows of 22gph at max cruise: 31" 2400rpm 11500' 10C OAT

Getting LOP to run smooth only works well for a few power settings, the best I have got so far is 29" 2350rpm 11500' 10C OAT 15.1gph

the 15.1gph using the (13.9 * ff) / 280 formula gives 75% HP

this runs pretty smooth most of the time and gives me about 165kts at 11500'

CHTs are all around 360 to 380, TIT about 1600F (50 < than the 1650 redlne)

that's about 10 to 15kts slower than I could get ROP at max power, but is 7gph less !

How do these numbers compare to others?

Anyone else out there running this engine LOP ?

[Barry Foust]

Tim,
I ran my B36TC TSIO 520 UB LOP at 23/23 at 12.9 gph  and if I remember it was getting 140KIAS at 12000 MSL. CHT's 320-350.   It is slower then the speed you are running. But i don't mind a little more time in the air in a great plane.  The one problem I had was I could never get below 15 F degrees  LOP without the engine running a little rough.  Enriching the mixture brought it back to peak and everything smoothed out.  My thinking was the 23/23 was probably somewhere around 55% power at most and so running at 5 or 10 degrees LOP wasn't going to harm the engine as long as the cylinders stayed below 380.  I had the GAMI's and had them tuned through several iterations.  Although it is possible they could have been balanced further.  John-Paul told me the 1/2 gallon per hour spread between 1st cylinder to reach peak EGT and last last cylinder to reach peak EGT was about as close as you could get.  The 1/2 gallon delta is where I stopped.  I attended a BPPP training weekend and at the maintenance class a year ago.  One of the BPPP mechanics said there was something about the cam, timing or lift in the TSIO 520 UB that prevented it from running smooth LOP.  He said it wasn't just the turbos but all 520's.  I don't know?  He did say that RAM profiles their cams for the 520's more like the 550's and that is the only way to get a 520 to run smooth LOP.  I don't know. 

Fast forward a year,  I just installed a TCM factory rebuilt engine with TCM tuned nozzles. The TCM's are not nearly as balanced as the GAMI's were and not nearly as smooth LOP.  I chose not to go with the RAM as I have read articles and heard anecdotal stories that the RAM cams were spalling, I don't know first hand, maybe it was a lifter problem and all engines had it.  Either way I went with a factory rebuilt and plan to swap the TCM nozzles for GAMI's as soon as I can.  Then work on balancing them to <then 1/4gph delta between first and last EGT to peak. 

The BPPP guy was pretty knowledgeable and so I am anticipating the roughness being there as well, I hope not but it sounds like that's what were stuck with on the 520's. 

The other thing I notice is running LOP turns out to be quite a bit different at different altitudes for some reason.  I have no idea why?  For example at 12,000 I might get Cylinder # 4 EGT to peak first and at 8000 I might get # 5 to peak first.  I thought that was strange? My guess is it has something to do with the air coming out of the compressor hotter at higher altitude and maybe being closer to one Cylinder rather then another. I have no idea.  All in all It has been a great plane.  One thing I will say is I like to keep my Cylinders below 380 in all conditions whenever possible. 

I can check on a 31" 2400 number on my plane and see if it yields the same 22gph as yours to keep it below 380. I suspect they are the same in that regard. 

Barry Foust