carguy614

carguy614

Well Known Member
Hey folks.
I call opon the vast knowledge of the VAF group for some advice.
My RV-9A has a superior O-320 and a new Precision MA4-SPA carb.My issue is high EGT temps on climbout and operation over 2300 RPM on the back 2 cylinders. The spread is nearly 175 degrees at high cruise, and as much as 250 degrees during full power climbout at sea level. I am equipped with a Sensi fixed pitch prop. Slight nleaning in the climb produces slightly higher EGT on the front 2 cylinders, and does not effect the rear ones. Carb heat makes no difference either. I suspect an intake air leak of some sort, but cannot find one. I have replaced the tube gaskets and rubber connectors, and smoke checked the induction system. No leaks. No fuel leaks thru the primer system , and CHT temps are really well balanced in cruise and very good in the climb after some effort to adjust baffling to get the temps in line.
Engine runs great, and I have no reason to suspect the probes, as they read even at 2200, and display ambient temps perfectly on my Dynon D-120. The probes are exactly 2 inches from the head on all cylinders, But I have yet to swap cylinders, as the leads are too short to do that on my plane.
I will need to do a full throttle 8000 density wide open throttle check to see how much spread I have to peak, but ceilings have been extremely low around here forever. I suspect the main jet is a bit too small, as others have commented in the archives. some have commented on uneven fuel distribution with a carb equipped engine at less than WOT.
Thought I would see if anyone has had a similar issue, and what you did to resolve it.
Thanks a million,
Chris
 
carguy614 said:
Hey folks.
I call opon the vast knowledge of the VAF group for some advice.
My RV-9A has a superior O-320 and a new Precision MA4-SPA carb.My issue is high EGT temps on climbout and operation over 2300 RPM on the back 2 cylinders. The spread is nearly 175 degrees at high cruise, and as much as 250 degrees during full power climbout at sea level. I am equipped with a Sensi fixed pitch prop. Slight nleaning in the climb produces slightly higher EGT on the front 2 cylinders, and does not effect the rear ones. Carb heat makes no difference either. I suspect an intake air leak of some sort, but cannot find one. I have replaced the tube gaskets and rubber connectors, and smoke checked the induction system. No leaks. No fuel leaks thru the primer system , and CHT temps are really well balanced in cruise and very good in the climb after some effort to adjust baffling to get the temps in line.
Engine runs great, and I have no reason to suspect the probes, as they read even at 2200, and display ambient temps perfectly on my Dynon D-120. The probes are exactly 2 inches from the head on all cylinders, But I have yet to swap cylinders, as the leads are too short to do that on my plane.
I will need to do a full throttle 8000 density wide open throttle check to see how much spread I have to peak, but ceilings have been extremely low around here forever. I suspect the main jet is a bit too small, as others have commented in the archives. some have commented on uneven fuel distribution with a carb equipped engine at less than WOT.
Thought I would see if anyone has had a similar issue, and what you did to resolve it.
Thanks a million,
Chris
Click to expand...

Chris,
What type of exhaust system are you running with? Exhaust scavenging can have an effect on cylinder EGT temps. Type of ignition system? Also in flight, have you cycled to left and right ignitions to see if the EGT rise is consistent with all 4 cylinders when only running on one ignition?

Thomas Shpakow
www.g3ignition.com
 
I have a similar engine. I think the day we decided to go with a carb' wide spreads on the EGT became inevitable. I would be really interested to see a graph of a carb'd engine that does not have wide variation. I doubt I will. This is mine. It balances up nicely at one power setting but then you change something and it opens right up. I think I have similar spreads to what you describe.

Bart at Aerosport Power commented to me along the lines that it was a sad day for the engine manufacturers when multi cyl monitoring became comonplace!

I have ended up focusing on getting adequate fuel flow to keep the cyl temps under control. I would like warmer oil, it runs cool despite partial blanking of the cooler, though oil analysis indicates its dry.

While I would like to have graphs that show everything travelling together, if presented with the carb .v. injected decision again I would still go with the carb.

If you do get the EGT to travel together please let me know!
 
high temps EGT

Thanks for the replies.
I have slick mags, and Vetterman exhaust with no mufflers. Although I have not cycled the mags in flight, I have done it on ground runs, and the rise is equal on either mag. The high EGT condition on the rear 2 cylinders is repeatable with a hard runup on the ground. CHT's are fine, nice and even in the cruise, and slightly higher in the climb on 3 and 4 by about 15 degrees, which I think is pretty good. I have a full plenum on my bird. I had to add tabs in front of 1 and 2 to balance the head temps. Timing was checked at July CS, and mag drop is even at about 30 RPM. Adding carb heat makes no difference. There is a little over 100 Hrs. on the engine now.
I wonder if my concern is warranted??

Regards,
Chris
 
Add me for the exact problem. Can get the EGT temps even at 2100 rpm cruise but that's no fun. My motor has 1400 hrs. on it ( O320 E2D) and the plugs look fine.
Crossover exhaust.
 
I don't see absolute temps in any of these posts. Maybe y'all are running too cool! What's your metric for too hot? Depending on the airplane, I've seen 1000 to 1500+ degrees for EGTs and 250 spreads. There's going to be a spread and it varies with power setting.

CHTs are what's important. If they're where you want them, stop fretting.

John Siebold
 
lean

Chris,
You didn't mention actual temps (or I missed them) but I noticed that you said the rear EGT's don't rise (or rise much) on leaning. Sounds like your just running a bit too lean to me.

I had the same problem on my '9 when I started flying it. Bart's (Aerosport Power) comment was that about half of the 320's he sees run too lean and have to be opened up a bit to flow more fuel. Thats what I had him too and it helped a lot. Apparently the carbs are somewhat variable so its hard to predict which ones will have this problem.

Good luck
 
chart

My O-320, carb,fp, 3sec. interval Dynon 120. always looks the same. :eek:
28ckhg9.jpg
 
I get essentially what Frank's plot shows in real time on my GRT display, and the graph's look like that all the time. Before I lean things out in cruise, I have a wide separation of EGT's, but once I start leaning it out, they all come together and play like a team. the biggest spread is down low, full rich at climb power. I've often wondered about the physics behind it, but never had time to go explore the "why's". As long as I can lean past peak and have a smooth running engine (which I can, even with the Carb), I'm happy. I spend as little time in the "ugly" part of the graph as I can.

I think it is the nature of the Carb'ed beast.

Paul
 
I too run very similar to Frank's graph albeit a bit higher. I typically see around 1500 EGT @ peak. This could be due to probe placement. My EGTs run very close to each other when leaned.
I have O-320-E3D with 9.5:1 pistons.
 
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