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But what about #2?

rjcthree

Well Known Member
RV-9A. O-320, FP. I would like to stay below CHT 400F on extended climbs, but #2 is my challenge. I have the dam cut down to about 1” and bent a smidge forward to even cruise CHT which is good, and I’ve got a one washer gap in place with RTV blocking the wasted area. While the three other cylinders climb at Vy below 400F, #2 runs 20F to 30F hotter. At Vy + 10kts, it’s a pretty consistently 15F higher than the other three. For all I know it could be mixture distribution. In cruise #2 peaks second when going LOP.

I’m not sure this is really a problem, as I’ve never seen higher than 420F on #2 in extended climbs, but this is a pretty experienced group. I’d appreciate the feedback.
 
Are you climbing at Vy+10? If I do an extended climb at Vy+10, I might get a little hot too. My Vy is 96K. I typically climb at 115 (minimum) to 135 KIAS. I have a fixed pitch prop on my O-360 powered RV4. A little extra airspeed might help a lot. Actual trip time vs fuel burn on a cross country may actually be better, or about the same, with a higher speed climb, depending on winds and time enroute. Shaving off a couple minutes because of higher climb ground speeds can make up for the extra fuel burn from using climb power for a marginally increased time at that power setting. And don’t forget to lean during your climb to maintain takeoff EGT’s until level off.
 
Vy + 10 kt

Yes, I normally climb at Vy transitioning to Vy + 10 kt at about 500’ agl, depending on my mood and how TO trim was set at that moment ;). I have play nice with spam locally and Pax seem to prefer the deck angle of +10. My Vy is 95kt. My rate of climb is pretty stable Vy -5 kt to Vy + 10 kt based on testing, so not a lot of penalty. If I go to +20 to +30, I get more balanced numbers, cruise-like, but somehow that feels like cheating. Maybe I’m asking too much?

I wonder how much I didn’t know about how I was flying spam at Vy on hot summer days...is our advanced instrumentation making causing us to obsess?
 
RV-9A. O-320, FP. I would like to stay below CHT 400F on extended climbs, but #2 is my challenge. In cruise #2 peaks second when going LOP.
.

You go LOP with a carbed O-320? I’m not familiar with Ellison carbs.
 
o-320

You go LOP with a carbed O-320? I’m not familiar with Ellison carbs.

It seems the Lycoming o-320 (carb'd) can be run lean of peak; Lycoming hit the sweat spot with that design. I have not done it, but others have suggested a little carb heat helps.

Maybe those in the know will chime in.
 
Rick, you know #2 has the same fin blocking challenge that #3 has. I made a chute for my M1B, in the baffle stage, but my 10Friend did not and cleverly just added 3 (maybe 4?) #30 holes in the corner of the cross angle to give it a little air. It dropped a few degrees, and although I can not recall how much, there is a memory of surprise it was that good.

I don't have a clever DanH drawing to show, but the drill angle was such that it fed air matched to the fin openings as it can be tight in that area. Maybe 45 deg angle. 500 hrs and no issues in that region.

15F is not much, I have a 20F issue with #4, and finally tracked it to the baffle gap under the head being smaller than others. It is on the improvement list to curl back the exits about 1/8".
 
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You can remove the dam to bring down the #2 temps in climb and accept a lower CHT in cruise, which may not really be much lower without it. You could also build a little box under the #2 inlet ramp with holes in the ramp to feed it. Several posts on this issue and I have done it. But I would start with removing the ramp. Lot of religious discussion about this 400 limit. Definitely not a problem to climb at 410 for a few minutes IMHO. Sure, 400 is better and 350 even better still. But you must introduce reality somewhere in the equation. Lots of planes without CHT gauges made it to TBO and suspect many were climbing Vy with CHTs well above 400.

Larry
 
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My o320

New rebuilt engine last year,superior cylinders, upgrade to 160 hp, #2 was hot from the beginning. Had already install a cowl flap. Made a “bump out” for that cylinder. My procedure is to climb at 5-600 fpm with power back to about 2500 rpm. Can keep the cht about 400-410
 
. . . I wonder how much I didn’t know about how I was flying spam at Vy on hot summer days...is our advanced instrumentation making causing us to obsess?
I vote for this observation! Your numbers are not that far off to worry too much about. If it concerns you to look at those fancy gauges then climb faster and you should see numbers come down.
 
+1 for what Larry (lr172) said. Lose the dam. If temp is still high, increase climb to 115-120 KIAS.
 
I wonder how much I didn’t know about how I was flying spam at Vy on hot summer days...is our advanced instrumentation making causing us to obsess?

So, one of our core engines was from a flying club Cessna 172. 800 hours when removed from service due to a cam / lifter problem. Pulled the jugs for potential re-use or overhaul. NONE usable as every one of them had cylinder head cracks.

My opinion - without good 4 point engine instrumentation there was a lot of unknowing engine abuse going on.

Check for an intake leak at #2.
 
Also, check out the Engine Cooling sticky under the Traditional Aircraft Engines subforum....also post #15. It shows a photo of the extra channel on the #2 baffle.

I did baffle mods on both #2 and #3 (#2 was my hottest as well) and it brought the temp down by 20-25 degrees F. It was actually too cool after this fix, and I restricted the intake slot a little with some aluminum tape to even out the temperatures.
 
https://vansairforce.net/community/showthread.php?t=93949&page=2

Post 15 shows the bypass duct.

Another potential issue is the presence of casting flash between the fins in the spark plug area.

Mike refers to the aft of #3 for post 15 but is spot on about the spark plug. I found a really cool file to do between the fins. 0-10F benefit.

Here is the front of #2 chute, but as I said, you can drill 4 #30 holes in the angle to get past the casting dam.

No 2 Baffle Detail.jpg
 
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Mike refers to the aft of #3 for post 15

I was posting a photo just to give a general idea of what the duct looks like. For #2, the shape will be different due to the horizontal shelf of the cooling tin, vs. the vertical wall behind #3

but is spot on about the spark plug. I found a really cool file to do between the fins. 0-10F benefit.

Any details on the file??
 
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