Turbo Causing Detonation??

[WannaFly]

Been flying for about 30 hours with the turbo maxing out at about 33" map. I wanted to get flying and work on the map issue later when it dawned on me it was probably the waste gate. Sure enough the supplied .3bar (4.41)psi spring will never get to 40". Its funny that we monitor inches but the waste gate is listed in bar or psi----there is a bit of conversion there to get to inches of HG. The math gets you to 38.7" or something like that. And if I was the spring mfg I would go light....

Anyway FINALLY got more power!!! Wow what a difference from 33" to 35" or up. It feels like twice the engine after flying at 33" or less. It is soooo amazing at least thats my initial impression but I have not been able to run it very long at higher power settings. Now I have horrible detonation I think. If I"m over 35" for 20 seconds or more detonation kicks in and I have to reduce power down to where I'm use to. I read the stuff on this site https://www.onallcylinders.com/2015/09/ ... etonation/

Got cooler plugs went from Autolite 4163 to the 4162, retarded my coils but I did not do the CHT tests. Flew on a 60 F day. All this did not let me get over 35" map for any length of time. I'm sposed get 40" for 2 minutes!!!.

Any engines guys out there have tips? I finally get my $4K turbo operating properly and I can't use it. OH I've been putting TCP in my gas to decrease lead deposits maybe I'm lowering octane?

[pappas]

Generally, the first place that I would look to for a detonation problem is the secondary ignition being too far advanced. Detonation can be dangerous to the engine and you need to resolve it. The secondary ignition needs to fire just slightly after the primary ignition which is set at 28 deg BTDC and can not be changed. The factory says the secondary should be18 deg BTDC but that wasn't close enough for me and others on the forum. My secondary is set at 24 deg BTDC and the engine now performs in the flight tests as it is supposed to.

Advanced timing can also cause high CHT's. If you have high CHT's and lower EGT's that could be an indicator of too much advance. Low CHT's and high EGT's can be an indication of a retarded secondary.

The turbo in my Waiex B is finally....finally....running really well and I am becoming very happy with it. I have 60 hours on it now. Really look carefully into the timing set-up and make sure the wastegate is set correctly. The factory told me that they have their wastegate pop off at about 41-42 inches. I can see 42 inches on take-off but make a point of holding at 40 for 3-5 minutes then drop back to 30-35 depending on how far I want to fly that day and how much fuel I want to conserve during the climb.

Good luck on this. Although I did not have any problems producing boost from day one, I can also tell you that my turbo didn't really start running as expected until I had over 40-45 hours. Look over the timing again, fly the thing, and build the hours. I think the gestation period headaches are common to most of us but the factory is right, it sorts out with flight hours.

Lou Pappas
Waiex B Turbo N535D
Waiex Legacy 3300 N715B
RV-8 N231D
Hiperlight SNS-9
Falcon Ultralight

[WannaFly]

Generally, the first place that I would look to for a detonation problem is the secondary ignition being too far advanced.

I think thats it! I did a simple test - full power ground run with coils off. Got just over 41" with 1/4" throttle left then waste gate kicks in and it ran great. Did same test with just coils on and detonation kicks in. Thank goodness! After 35 hours I'm excited now. Can't wait to see if I can get 160mph cruise out of this. Almost 3200 static rpm with cruise prop. Thanks for the tip. With no one else reporting this problem it had to be something simple.

[Rynoth]

I'm curious, what is the sensation (physical, audible) that leads you to believe it's detonation? I've been flying for over 4000 hours (but only 13 in my Waiex) and honestly don't know what detonation feels/sounds like, despite all of the lessons and articles I have read and hours I've flown. Maybe it's because I've never actually experienced it.

However, I have noticed something in my own Aerovee turbo that I didn't expect which I can best describe as a "chugging" sensation, and it actually happens when I turn my secondary ignition OFF. When I run on mags-only at a high power setting in-flight that is otherwise stable (in terms of mixture, MAP, CHT, and EGT with both ignitions on), if I switch the secondary ignition OFF and run mags only, I'll get some "chugging." I don't have any discernible loss in engine power but the sensation exists nonetheless. The issue does resolve if I enrich the mixture. EGT actually drops when I turn off secondary ignition, so I'm having a hard time diagnosing it as a too-lean mixture, detonation, too-retarded secondary ignition, too-advanced secondary ignition, a fouled spark plug (that runs fine at lower power settings) or a combination of these things. I'm also unsure if it's detonation because I'm not entirely sure what detonation feels/sounds like.

P.S. Just to add to the thread, I have never had an issue getting 40+" with my turbo except for stuck-turbo issues I've mentioned in other posts (that were all pre-flight), if the turbo is spinning for me I get all the boost I need and then some, I haven't had any wastegate issues.

[jeff0196]

It is my understanding that you should not use TCP with turbos, as it states:
“For use in Non-Turbocharged Continental, Lycoming and Franklin Aviation Engines.”
I’m glad you solved the detonation problems but wonder if you have any lead building up on the turbo (instead of in the engine, as tcp changes what form and what temperature the lead precipitates out of the exhaust at) that could cause future issues?

Rnoth, Even if it is not detonation, although it does sound like it might be and caused by too far advanced timing, it sounds to me as if it is leading to excessively high cylinder pressures while running that way. Hard to directly measure, but I would avoid as excessive cylinder pressure is very hard on an engine even with no detonation present.

[GordonTurner]

Detonation is indicated by decreasing rpm and increasing CHT. If you see these symptoms you are damaging your engine and need to take immediate action (reduce power/richen mixture). It may be a result of timing, possibly changing to the other ignition will restore normal, but do not let these indications persist.

[pappas]

WannaFly,

Glad it turned out to be simple. Now you just need to tune in the secondary ignition a tiny bit at a time until the flight test indications are right. Remember, when you get close..tiny adjustments.

[pappas]

Ryan,

When running on only the primary, (with the secondary off), if the timing is correct, it is normally expected to see the EGT's rise because the fuel burns less efficiently with only one plug firing. After the exhaust valve opens the fuel may still be burning into the exhaust header which causes a higher EGT reading. That is exactly what I see with my turbo.

(With that said, I do NOT get an EGT rise with the primary OFF running on only the secondary). (I wonder if that happens because the primary ignition fires earlier than the secondary) Someone smarter will have to answer that for me.

If you have higher CHT's across the board and lower EGT's during your mag check, (on the ground or in the air at cruise rpm), that could be an indicator of too much advance. Low CHT's and high EGT's can be an indication of a retarded secondary.

A fouled spark plug, or two, usually shows up as a CHT and EGT that is much lower in the cylinder with the fouled plug than the other 3 cylinders while running on only one of the 2 ignition systems because the fuel is NOT burning at all in that cylinder. Selecting one or the other ignition should tell you if it is the top or bottom plug that is fouled.

Now my head hurts.

Lou Pappas

[Rynoth]

Thanks for the replies, and I'm hope I'm not hijacking this thread. This does seem to be a discussion about secondary ignition timing though.

That said, I have a question about the experience I described above.... IF it turns out that my secondary ignition timing is too retarded in cruise, does the following make sense? 1) Mixture appears to be too lean when secondary is turned off. 2) EGT drops when secondary is turned off. 3) CHT rises when secondary is turned off. 4) no discernible change when primary is turned off and running on secondary only.

Another way to ask the question might be, if talking about mixture alone, would advanced timing need a more rich or more lean mixture for smooth running versus retarded timing.

[XenosN42]

Hi Ryan,

One method to verify your primary/secondary ignition timing is described in this video: https://www.youtube.com/watch?v=bMWfEA8s8so&feature=youtu.be Even if you don't use the same method it might suggest some options for you.