Aerovee Turbo High EGTs

[Spaceman]

Howdy gents,

I have about 5 hours in flight on my plane now, over the course of 8 flights I think. I've been mostly spending my time trying to get the secondary ignition timing dialed in, and I think I have it correct now or at least very close. Now that I have a few hours on the engine, and the weather is cooler here, I can finally keep my CHTs somewhat reasonable (~375°F average) at a 'gentle' cruise power setting (2900rpm / 30" MAP, which gives me 115 knots indicated).

Anyway, I think my most limiting factor now is EGT. At 2900rpm, my hottest EGT (#1) sits around 1350°F at full rich. If I push the power up much at all it hits 1400 pretty much right away. Even with some very mild leaning, turning one ignition or the other off for a few minutes causes enough EGT rise for it to hover around 1400.

Is my Aero Injector still just way too lean? My EGT rise from full rich to peak lean seems to be about 150. The manual says to adjust the mixture needle until you get a 90-100° rise, so that seems to tell me my adjustment is on the rich side of anything. But my EGTs are too hot! Does this make sense to anyone?

Thanks!
-Chris

[Bryan Cotton]

Mine are similar. You could try another quarter or half turn on the carrier, in the name of science. I'm pretty happy with how mine runs.

[pappas]

Please go back and read all of Mike Busch's articles in Saavy Aviation on leaning an engine, normally aspirated or turbo. Besides being a lousy way to monitor the combustion process, the EGTs are nearly impossible to accurately measure and actually not very important in determining how to manage your engine. The CHTs are the thing you need to monitor and the best indicator to use for leaning.

With the turbo, the other critical temp is the turbo body temp. But that is very hard to get hot enough to worry about especially if you have the turbo cooling system installed.

[Spaceman]

Thanks for the info guys. I didn't know about all these Mike Busch articles; he has some good stuff here!

I've noticed in a couple of articles that he mentions EGT rise from full rich to peak lean should be around 250° or more for most engines. The AeroInjector manual says to tune for only 90-100° rise. Why such a big difference?

Mine is currently about 150°, which would be too rich by Sonex's standards but maybe way too lean by Mike Busch's...

[Spaceman]

Alright I richened the aero injector another 1/4 turn and gave it another try. It actually seemed like everything was a little hotter than last time! I wonder if it's possible that I'm just still too lean and I was way lean before when I thought I was in the ballpark? Pulling the mixture out causes the EGTs to start rising right away, so I don't think I'm lean of peak even at full rich, but I am a little confused why it ran hotter today with the carb set richer.

Here are a few data points. I didn't get good stable CHT checks at 35" and 40" because they were just increasing and I didn't want to keep at it too long. I'm trying to keep them below 420 as much as I can...

Anyway this is all at 1500' MSL and mixture pushed all the way in the whole time:

30" MAP - 2900 rpm - 5.1 gph
EGTs: 1405 / 1350 / 1395 / 1350
CHTs: 381 / 386 / 408 / 390

35" MAP - 3150 rpm - 6.0 gph
EGTs: 1490 / 1425 / 1475 / 1425

40" MAP - 3300 rpm - 6.9 gph
EGTs: 1525 / 1465 / 1515 / 1465

[pappas]

You mentioned that you only had about 5 hours on your engine. I should have reminded you that you will likely fight higher temps until you have closer to 25 hours and maybe up to 50 hours. That would be a completely normal experience for all of us that have flown new Aerovees. Keep temps under control by reducing power and angle of attack on your climb out. Look for a fuel burn in cruise closer to 6 or even 6.5 gals per hour at 2900-3100 and 30 inches during that first 25-50 hours.

But, the temps will get better over those hours. My suggested course of action would be that - IF - you can get 40 inches on take-off, the engine seems to run smoothly in climb and cruise, can idle around 900-1000 on the ground without stalling, and you can keep your CHTs limited to 425 for the first 2 minutes of climb and 400 or less in cruise, (per my correspondence with Sonex), ...then just fly it!

Get the hours on and like the rest of us you should find the temps come into the right range with that flight time. After it is completely broken in, that would be the time to tweak and final tune. Pay way less attention to EGTs. CHT is the critical reference. Keep the CHTs in line and the rest will take care of themselves.

What needle are you using in the Turbo? You might need to go one richer.
In my turbo engine at 30 inches and 2900 rpm, I was burning 5.5 - 5.9. after the break-in and truing out at 136 - 142 mph.

[Spaceman]

Hey Lou,

Thanks for all the info. I just hit 10 hours total on the engine, and about 6 actually in flight.

I'm using the #3 needle, but if you're burning 5.5-5.9 gph at 30", maybe I do still need to adjust a little richer. I'm at like 5 gph at that power setting. I'm using the Prince prop by the way, I can't remember if that's the same prop you had or not. Looking back at the data now, the highest fuel flow recorded during takeoff was 7.2 gph, at 39.5" for reference.

So far I haven't even left the pattern yet, since I'm not sure how much I trust this engine so far! It hasn't ever scared me yet, but I kind of wanted to be able to maintain like 35" max continuous without overheating before I moved on with my testing. Maybe I should just work with what I have and let the engine break in as I go.

Cruising around at 30" and 2900rpm it seems pretty happy, at least with minimal leaning. Only CHT 3 really concerns me; it's always about 20 degrees hotter than the other three. I'm pondering if I can redirect a bit of air from #1 since it is the coolest, and try to make them all a little more even.

[pappas]

The #3 needle is probably rich enough. I used it during the break-in and went back to either the 2.5 or 2, (can't recall right now). I used the Prince, Sensenich cruise and climb, and an Ed Sterba cruise. The prop didn't make a difference in temps for me.

I read somewhere that to get an estimate of the maximum fuel burn your engine should see is to divide the HP by 11.5. 100/11.5 = 8.69. I easily saw over 8 gph at max takeoff. The indications are that you are a bit lean. Leave the needle alone and adjust a bit richer. Regardless, you will still see higher temps in the first 25 hours. Only count the flight hours for this process and don't forget to lean some for smoothness above 3000 ft DA.

You might notice them a bit better after 15 flight hours. Ground running doesn't help you and should be minimized. Fly it. Circle the field at 2500agl until you feel comfortable. I was there for 3-5 hours before I ventured too far from home.

For some of us, #3 is the hottest and for others #1. Mine was #3. Go figure. A few outliers have 1 or 4 as the hottest CHT but that is less common. I don't think any of us get the CHTs closer than 20 degrees between the hottest and coldest. It is after all still a VW-based engine. In the 250,000 miles that could be put on a 1969 VW, not for one minute of that time did anyone know what their CHT or EGT was! Just a light for the OP. And that one would always flicker at idle!

Adjust a little richer, don't be afraid of the extra fuel burn during the first 50, fly it, and have fun near home until you have the confidence in it you will certainly find. Let us know when the temps come down. Everyone has the high temp, new engine blues. Then they go away.

[Spaceman]

That all makes sense I suppose. Yeah I will leave the #3 needle in and just try a bit richer for now!

[tps8903]

That all makes sense I suppose. Yeah I will leave the #3 needle in and just try a bit richer for now!

Hey Chris, I'm working through the same growing pains right now. I sent you a PM with my info if you want to chat and work on yhis together.