SonexBuilders.net

This is the post I sent to Sonex Tech Support today. I'm posting it here in case any of you have a suggestion. I am really out of ideas at this point and very frustrated and almost sorry I stayed with AeroVee and didn't go elsewhere for an engine. When it ran right I was happy with the performance but after a year with no solution I've about had enough.

"I have been having problems still with the turbo charger I added to my aerovee last spring. In take off I go to full throttle but still only get 35 inches of map. When flying last fall I would occasionally get the full boost of over 40 inches and would have to retard throttle to keep boost at 40 or below. For the last 2 months of flying I have not seen full boost. I don’t believe it is due to a faulty map gauge as I can tell the difference in sound and feel. At altitude I set up for 30.5 to 31 inches and have normal speeds of 142 tas above 3500 msl this is the same as always. In looking for cause I have ensured the intake is tight throughout the system. I removed the exhaust pipe and cleaned all trace of carbon from the waste gate port and flapper. The actuator has a lot of resistance to being pulled open by hand and is set to hold the waste gate closed tightly. Cylinder pressures are all over 70 over 80 with a leak down test on a cold engine. The carburetor is in tune as far as egt temps from rich to lean. The engine is set up at 7 to 1 and I use auto fuel but find no difference with 100LL. I have a cruise prop installed. I don’t know what else to look at or try to solve this issue. Any suggestions would be appreciated."

Bill,
Sorry to hear you are struggling with MAP. Here are my thoughts as to MAP issues. Most are long shots, but I wanted to think of all possible solutions.

- Use Tracerline dye in your fuel to see if you are loosing any pressure at WOT. It will clearly show any and all leaks.
- Check all the spark plugs for proper sealing between ceramic/threads and at the head
- Check to make sure the turbine is spinning smooth
- Check the oil supply going to the turbo
- Remove the air filter to see if that is causing any restrictions to intake
- Secondary timing check. Have you run with just the primary or secondary to see if the secondary is off. I cannot get full MAP at 10 degrees BTDC. I am still making small adjustments but found my performance goes up on just the primary. The mag check at 2000 didn't show me that.

Here are a couple of tests that may help isolate the issue:
Engine idling on the ground. The engine is "trying to breathe" but the throttle is retarded to idle. The result is a significant vacuum in the induction manifold, as the engine consumes the air in the induction manifold but the closed throttle blocks the inflow of air to take its place. In the cockpit, this shows up as a very low MP reading (typically, something on the order of 12" to 15" if I recall. I can check this weekend) far below outside ambient (around 30" at sea level).
But suppose there's a leak in the induction plumbing somewhere between the throttle and the cylinders. Since the ambient air rushes in through the leak, this shows up as a higher-than-normal MP indication at idle…perhaps 17" instead of 14". The engine will also be idling leaner than usual-since the leak lets in more air but not more fuel-so the engine may have slightly higher CHT or even momentarily hesitate upon throttle up.

The other test is to use altitude to check for leaks. Since ambient air looses 1" per 1,000 ft, have you tried WOT at various altitudes to see what happens to your MAP? I would be curious to see your 30" and WOT MAP at 10k ft when the outside ambient is ~19". Does the MAP jump around or bleed off at level cruise? If so, that is an indication of a leak. The turbo is spooling hard but unable to keep up with the leak at high altitude/power settings. Since you are loosing at lower alt, the leak would have to be larger, and the high altitude will grossly magnify it.

Any internal engine issues can cause MAP issues too. Are all of your EGT/CHT still consistent or is one higher/lower than normal? A cold/hot EGT/CHT can be an indication of a cyl not taking a full breath properly.

I'm sure you have already checked:
- Check the valves to ensure a valve tolerances have not gotten too tight and staying open to long

When I was having issues maintaining MAP, it was an intake leak between the T off the turbo and the intake ports. I only found it because after several hours of flying the blue hue of the 100LL was barely visible on the head of cyl #3. If I had tracerline, it would have been easy to spot.

I hope something in here can help you! I'd be happy to get together and play around, even put my new turbo on yours to see how it performs. Just let me know what I can do!

Josh

That stinks Bill, sorry to hear about your troubles. I wish I had good suggestions to offer you, but all I have are basic guesses. But I do want to ask you...does your engine run well (i.e., smooth) all the time? No troubles with operation?

A few guesses from me...

- Is it possibly your throttle and/or throttle cable simply not allowing full travel of the slide on the AeroInjector? If there's a kink in the line or a jam on the slide you may have a physical limitation on the carb.

- You said you have already checked the intake system for leaks, so that rules out a big reason why turbo'd engines don't get full power. How about an exhaust leak? Any cracks in the exhaust pipe? (highly unlikely but you never know...) Any leaks around the turbo housing or where the turbo mounts to the exhaust system?

- If none of those, it almost has to be the turbo control valve. Have you looked over the pressure control tube that runs from the turbo to the controller?

- Is there a casting issue or similar with the waste gate controller and the turbo housing? Meaning, does the flapper sit and cover the waste gate and make a good seal?

I'll keep thinking but hang in there! Don't give up hope!