Turbo - Static MAP vs. in-flight MAP?

[Sonex1517]

Noel

When I had my turbo installed, I had “extra” throttle available. Full throttle was well over 40” MP

Just FYI

[Outlaw6]

Got turbo cooling installed and I'm only getting 37" MAP. Tightened all the intake connections, no change, read through this forum again and saw NWade said waste gate actuator screws in, not swivels. Sure enough my jamb nut was loose and it let tension off the waste gate. Didn't have time to test, but I hope that's it.

[WannaFly]

YES WASTE GATE SPRING TOO WEAK. Lutrom said it first
I"m running the prince prop also so sonex said they could not help but when I said I was over 3000 rpm I got the green light. First flight was Jun 3 '19 maxed out at 33" MAP... Been flying for 25 hours when it occurred to me the waste gate is working! I was going to wire it shut but my dad suggested just adding pre-load. So I tightened the screw all the way up--got 1" per turn of screw!! Then had to add a bunch of washers to get the waste gate further off the mount maxed out at 37"...I asked Kerry about sending me a stiffer spring and he said I was on my own to experiment with it---So I ordered the 4.41 psi (.3 bar) spring that was supposed to be in it and it got me 35" wow what a difference! Like I siad i've been flying at 32-33" and just jealous watching Michael farly just add MAP at will... i"m going to do what G.Maralis said--add a booster spring on the outside...

oh....new problem I think my spark is fading out over 34" keep it under 33 and it runs smooth will put in new plugs and see if they can handle the boost.. As Tim the Tool Man Taylor says... 'MORE POWER!!!!"

[wlarson861]

These are all symptoms of the piston bearing failing. The aerovee turbo needs cooling to keep it producing power. I was an early adapter and got lower power within a few hours of flying the turbo, The factory rebuilt my turbo but it was only a couple of hours before the turbo sized again . I have changed to a Jabiru and am very happy with the upgrade. Had I known then what I know now I could have saved 11000 bucks. Once the turbo puts out less than 40 map it is doomed to fail at some point. I would say that if you have the turbo and don't have the cooling packaging you are doomed from the start.

[Spaceman]

Hey Noel did you ever figure out the definitive solution to your issue? I am tuning my aeroinjector and just did the first full throttle run; I was mostly paying attention to RPM vs Mixture vs EGTs, but I noticed pretty much the same performance that you had when you started this thread. At full throttle the most I got was about 3160 RPM, and 33-34" manifold pressure.

I haven't done anything to troubleshoot yet, since I was focusing on mixture stuff so I didn't really think about the RPM and manifold pressure until I got home and looked at the data. I guess I'll start with adding some preload to the wastegate actuator, and if that doesn't do anything maybe replace the spring?

Also, for what it's worth, I have a temporary 54x48 Sterba prop installed for now while I wait for the P-Tip I ordered, so I didn't expect the exact correct parameters, but I was surprised to get nowhere near 40" manifold pressure!

[NWade]

Hey Noel did you ever figure out the definitive solution to your issue?

Yes, the definitive solution to my issue was that the White spring in the wastegate actuator was too weak - see my post earlier in this thread from late Oct 2018. Switching to a blue spring (per this image/chart) gave me an extra ~5 inches of boost at full WOT. Since that is about 2" more boost than spec, my solution is going to be to limit throttle travel at low elevations. With the white spring I could slightly change the max boost by adding pre-load to the actuator; but in the end the blue spring with no preload was the only way I could achieve the 40" MAP called out in the manual.

If you look at the spring chart I linked to above, the white spring is rated for 0.3 bar (and will start actuating at slightly less pressure). This is equivalent to ~8" - 9" of mercury. Add that to sea level pressure on a standard day (29.92) and you get ~38". Which is close to what I was seeing. The blue spring is rated for 0.5 bar (and again, starts actuating slightly below that), which is equivalent to ~11" - 14.7" of mercury. This would put max boost between 41" & 45" at sea level on a standard day - this is beyond what Sonex/Aeroconversions specifies, so I would urge caution to anyone who follows in my footsteps. I think that for many AeroVee Turbos, some preload and/or frictions in the system cause the effective spring rate of the wastegate to be just a touch higher than what is spec'ed for these springs; thus many folks can achieve 40" MAP right out of the box. But variance in setup and the exact spring strength (i.e. unit to unit variance) may leave a few folks 1-3" short.

NOTE: Your situation, being 6" short of the magic 40-inch number, may have a different root cause. First, using a temporary/different prop may not give you the same results. Second, I would urge you not to assume the wastegate actuator is the issue unless you've done testing and eliminated other potential causes (such as induction leaks, exhaust manifold leaks, throttle-travel limits, assembly errors in the wastegate actuator system, and instrumentation errors). If you can record engine data with your EFIS/EMS, warm up the engine for a minute or two and then slowly sweep the throttle up to full over ~5 seconds, and then smoothly pull it back down. Pay attention as you advance the throttle - do the MAP and RPM stop rising before you hit the throttle stop? After engine shutdown, grab the engine data and look at a graph of the MAP. If you see it plateau or have a small drop before the engine RPM starts to decline, that may be an indication the wastegate is opening too soon.

Best of luck,

--Noel
Sonex #1339
(stuck in sanding & painting hell) :-D

[pfhoeycfi]

Do you have a part # and source for the blue spring?

[NWade]

Peter -

I bought my blue spring on Amazon.com in late 2018, but the link is no longer good. A similar listing on Amazon has a bad review stating they didn’t get the pictured part so I’m hesitant to recommend that link/listing.

If you Google the part number shown in the chart that I posted, you can find the exact spring for sale directly from Kinugawa (the manufacturer of the wastegate actuator that came with my
AeroVee Turbo): http://shopping.kinugawaturbo.com/kinugawaadjustableturbowastegateactuatorspring441psi03bar-1.aspx

Note that the Kinugawa units come in different styles, with two different types of spring - the straight spring (which I linked above) has an actuator that can be adjusted via preload on the wastegate arm. They also sell a more-adjustable wastegate actuator that uses conical springs. I have no idea if Sonex has changed the parts they source/use for the wastegate system over time, so double check the actuator & spring style you have before ordering one of these blue springs.

Enjoy,

—Noel

[Spaceman]

Thanks for the info Noel!

Yeah, understood I intentionally have the wrong prop on so I have to take everything with a grain of salt here. I'm just trying to get everything as close as I can to correct so hopefully when my prop shows up I'll just need some final tweaks.

Is there a good way to test for intake leaks? I looked everything over and didn't see any signs of exhaust leakage, which I think would be pretty visible. Intake seems trickier... I've done it on cars by spraying starting fluid on connections and listening for the RPMs to change momentarily, but that's a little easier without a spinning prop nearby! Plus I'm almost always working by myself.

Anyway I will check as best I can for intake and exhaust leakage, and then look at the wastegate actuator. I remember setting up the arm with no preload according to the aerovee manual (page 46). However on the Kinugawa website they recommend starting with 3 turns worth of preload. I'll try that and see if it helps.

The springs are on Amazon if you search for "Kinugawa spring." I saw the bad reviews but I ordered a 0.3 and 0.5 bar spring anyway just in case I want to experiment later. I'll start with the pushrod adjustment first though!!

I also don't want to do too many of these high power ground runs though, the engine seems to really heat up in a hurry which I don't enjoy watching. I just want to get it close enough to fly, then do some breaking in, then perfect it later. My home runway is 7200' long at 1800 MSL, so I'm not super worried about slightly less than 100% takeoff performance initially.