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High CHT's On Climb

flickroll

Well Known Member
I am experiencing high CHT's on climb. Density Altitude the last few flights has been around 1500' - 2000', and mixture is full rich against the stop on the carb. This is on an airplane (RV-8) I bought with ~300 hours. Cruise CHT's are fine. If I don't climb at less than 110 kts, the CHT's will start climbing. My goal is to always keep CHT's at 400 or less, 415 an absolute limit for me. When I first started flying the airplane I'd see 435 which is way too high, and it's not even hot yet (~ 80 - 85 deg). My engine is an O-360 A1A turning a Whirlwind 200RV. The carb is a brand new Avstar 10-3878. I have looked in the air intake of the cowl with a flashlight and can see no gaps that would allow air leakage, and the baffles look to be in good condition. High temp RTV is used for a sealant where there is metal to metal contact on the baffle system. EGT's are 1300 to 1325. Timing is set at 25 deg (Slicks), and the plugs are cleaned and gapped. Take off fuel flow runs 15 - 16 gph. I have considered two options to help: 1. resize the carb jet to a little larger. And/or 2. retard the timing a degree or two.

Any thoughts and suggestions would be greatly appreciated. Thanks
 
Normal ops Jim. I think you meant, you need to climb faster than 110 knots to lower the CHT's. If that is the case, thats exactly what I do. My RV8 has a 3878 carb, and I accept the Lycoming recommendation of 500 deg. redline and 400 degrees continuous as my limit. I lower the nose and climb at a faster speed to regulate my temps to stay under 425 for climb( still over 1000fpm). I do not view 5-10 minutes in climb as continuous! A 4164 carb. might help slightly, but if you expect to be able to achieve Van's rate of climb #'s and remain within your CHT limitations as opposed to Lycoming's, well good luck!
Best regards,
 
More exit area will help almost for sure.

In a full power climb to 8500', I see 375F CHT. Oil temp 170 with a RV-10 cooling set up on the firewall.

Not many guys want to mess with the Van's cowl. But I think they cut it a bit too close on intake vrs exit area to keep drag to minimum. The ratio is about 108%. If it is 120%, cooling is better.
 
I accept the Lycoming recommendation of 500 deg. redline and 400 degrees continuous as my limit.

Jon, it's been a while since I have flown a Lyc, but on a big bore Cont, if the CHT's are allowed to go to 500 you'll see dramatically lower cylinder life. Aluminum does not care if it's on a Lyc or Cont, a cylinder will not last as long if it's allowed to get hot on a regular basis. I went to the Avanced Pilot Seminar put on by the GAMI folks (Braly, Atkinson, Deakin) at Ada, OK, and they say keep em under 400. They preach keeping them under 380, but that is not totally practical so their limit is 400, even in a climb. On a big bore injected Cont, you jack up the take off fuel flow to somewhere around 28 GPH to keep em cool. They excess fuel cools everything. Heat kills cylinders which is why I'm concerned about what I'm seeing. Thanks

Jim
 
One thing I don't see mentioned here is the cowling inlet eyebrows inside the cowling. If your cruising temps are good and the problem is only in climb, you might take a look here. If the internal eyebrows are not sealed properly you can get turbulence during high AOAs, thereby increasing CHTs.
 
And you're climbing with full throttle open all the way up for the enrichment circuit? Full throttle for fuel cooling, and slow the prop down some (2500 or so) in the climb to reduce power output. This is working great for us.
 
One thing I don't see mentioned here is the cowling inlet eyebrows inside the cowling.

Mel - checked that too. The rubber baffle material is sealing the inboard and the outboard portions of the eyebrows, both left and right/
 
If I look hard, I can find it, but that involves work. I have read what Mel refers to before. The inlet ramps on the top cowl half, at least one end needs to be sealed off. I am told the air will bypass the cylinders if it is not sealed.

Two things I plan on doing with my cowl
1. Cut the exit area back at least one additional inch.
2. Seal the inlet ramps on the top cowl.

From all of the experience I have read here, these seem to be the biggest bang for the buck to lower cylinder head temps.
 
And you're climbing with full throttle open all the way up for the enrichment circuit? Full throttle for fuel cooling, and slow the prop down some (2500 or so) in the climb to reduce power output. This is working great for us.

I've been bringing them both back to 2500/25". Guess I can try WOT and 2500 next time and see what I get. Mixture is staying full rich.
 
If the internal eyebrows are not sealed properly you can get turbulence during high AOAs, thereby increasing CHTs.

Mel - Reread your post. Even though the eyebrows are sealed by rubber gasket material, I suppose under certain conditions they could 'unseal' and provide a bypass for the air. Any ideas on how to insure a good seal? I suppose plugging the tunnel between the two ends is one idea.
 
I've been bringing them both back to 2500/25". Guess I can try WOT and 2500 next time and see what I get. Mixture is staying full rich.

I bet you'll see a big difference by keeping the throttle all the way in, and the prop slowed down. I used to (until a few months ago) do the same thing you're doing and would always see the CHTs headed through 400 deg. by pattern altitude on a 90 degree day. We've had a few 95-98 degree days so far and with the my new procedure, I can climb almost as slow and as long as I want and see a max of about 385.
 
Cooling ramps/eyebrows

Inside the upper colw.

This has come up numerous times before and folks with similar issues have announced dramatic improvements by glassing in one or both sides of the cooling ramps.

Definately do this before you do anything else.

Frank
 
This has come up numerous times before and folks with similar issues have announced dramatic improvements by glassing in one or both sides of the cooling ramps.

Wonder how an aluminum plate RTV'd in the tunnel would do? I HATE glass work.......
 
Hehe

Probably a rolled up sock would do it but is half an hours worth of rough glass work really that big of a deal?..I mean its not like it has to look pretty..:)

And if it solves the problem (and thee is high likleyhood it will) then surely its a small price to pay..:)

Cheers

Frank
 
It's probably not a recommended procedure, but I sealed the eyebrow tunnels with foam-in-place insulation. Easier than fiberglass and just as effective. Takes about two minutes and costs about $5. Works great and it DOES lower CHTs.

Bob Kelly
 
Smiling

Wow, if you set 400 or 415 as your absolute here, you wouldn't fly between May and October in AZ. This had me smiling. I use 425 as my climb limit on a hot day. Set the airspeed to not go over 425. I also lean with the climb.

I fly to work everyday. Yesterday coming home at 1930 hours (7:30 pm) it was still 102 outside. (That isn't considered hot yet!!!) I only climb to 2900 feet to avoid the Class Bravo airspace in Phoenix. Power was 24" x 2450 rpm. Temps, #1 385, #2 397, #3 416, #4 421. Oil temp 202.

I use Phillips XC 20-50 on a 25 hour change schedule. I talked with the engineers at ECI about temps in general. They said anything below 450 as a transient number is fine. They told me 425 is also fine and that people get too worked up over temperatures. Obviously, cooler is better but hot can't always be avoided. He further told me they tested an engine at 500 degrees for over 24 hours.
 
Recently ran some theoretical cooling numbers for the RV8, and I do not think the exit area is too small. I think Van sized it just right for an average installed setup...and frankly, I think most of the guys with high temps have baffles in need of work.

The single most important variable (small change equals big difference) is heat transfer efficiency ratio, cooling air temperature change /(CHT - ambient temperature). Put another way, your goal is to raise air temperature as much as possible. Consider a 380 CHT on a 60 degree day. Raising outlet temperature by 20F (80 vs 100) is a bump from .25 to .3125. Doesn't sound like a big deal, but......

The RV8's exit area is between 0.4 and 0.45 sq ft, depending on how much area you squander on exhaust pipes. At .25 ER, the sample calcs say you should be able to cool 174 to 183 hp with 2.8 and 2.9 lbs/s at 100 mph. At .3125 ER, you should be able to cool 214 to 225 hp at the same speed. Or you could cut exit area to 0.3, still cool 180 hp, and lose some drag; required air is now about 2.35 lbs/s.

So how? First, make sure your baffles really fit, hugging the cylinders and heads at all points so every bit of air passes between fins with maximum surface contact for the maximum possible distance. A standard set of Van's kit baffles don't fit right from the box. Many builders are happy when they get them trimmed to fit on the engine, and stop working.

Below is the stock Lycoming intercylinder "baffle" supplied on my 390. It doesn't even touch the fins as delivered. Somebody placed a strip of orange RTV across the end of the baffle, but it doesn't do any good; a lot of the air will leak out the side gaps (small arrows). For sure this air never makes it to the vicinity of the fins inboard of the spark plug, where it should be exiting the baffle (big arrow).



Another view of the same spot, and the other wing of the same baffle. See the gaps?



Here we have a Vans baffle wrap on the left rear cylinder. Lycoming puts a rubber comb on the fins so they won't vibrate. The baffle wrap rests against the rubber comb, rather than the tips of the fins:



However, look what happens to the baffle wrap. Again you get a big 'ole gap along the sides. You figure the air is continuing straight ahead between the fins, over the rubber comb, and exiting the end of the wrap, or going out the sides?

BTW, this is after the wrap was bent to conform with the sharp corner on the cylinder head fins (big arrow). We've all seen lots of these which were simply pulled around the head with no forming, and the gaps are huge.



Air not in in contact with a fin surface doesn't pick up any heat. The really sad thing is that the above baffle wrap is the one near the exhaust port.....the hottest part of the cylinder head. Remember delta-t? This is the area with the most potential for heat transfer.

Ok, so much for fixing stock baffles to work better. Now consider some of the work done by the canard guys, the sho'nuff fanatics of drag reduction. The fast guys don't use baffles like ours. Ours wrap only 60 or 70 degrees of cylinder on each side. Some of theirs wrap 120-130 degrees.....and are often formed from glass and RTV so as to not leak anywhere along that wrap.
 
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What Darwin says

I echo what RVGUY says. In many cases I think we're victoms of too much information. I went through the same consternations durring my phase one with high chts on climbout. Did all the usual fixes and finally listened to an old sage and just powered back a little, and dropped the nose a bit when chts got to >400. They stablized and I was still climbing like mad (compaired to the old Piper). If cruise temps are OK, don't sweat those climb temps (within reason).
 
Hey Dan

So how? First, make sure your baffles really fit, hugging the cylinders and heads at all points so every bit of air passes between fins with maximum surface contact for the maximum possible distance. A standard set of Van's kit baffles don't fit right from the box. Many builders are happy when they get them trimmed to fit on the engine, and stop working.

Air not in in contact with a fin surface doesn't pick up any heat. The really sad thing is that the above baffle wrap is the one near the exhaust port.....the hottest part of the cylinder head. Remember delta-t? This is the area with the most potential for heat transfer.

Ok, so much for fixing stock baffles to work better. Now consider some of the work done by the canard guys, the sho'nuff fanatics of drag reduction. The fast guys don't use baffles like ours. Ours wrap only 60 or 70 degrees of cylinder. Some of theirs wrap 120-130 degrees.....and are often formed from glass and RTV so as to not leak anywhere along that wrap.

I was just thinking about this....We have the plenum (or top of the cowl) but the air reallly is not going through the cylinder fins..its bascially short circuiting the top fins apart from those that are in the direct blast of incomming air..and we usually put temp raising sheilds in front of those to balance the front and back cylinder head temps.

Seems the Long Ezy guys are onto something by covering a larger part of the circumference on top of the heads and barrels.

I woundered if we could do some experiments with aluminium tape stuck directly to the heads/barrels to improve cooling.

of course this would also make the total cooling path longer which will add more pressure drop, but then the pressure in the top cowl would be larger anyway.

Any thoughts?

Frank
 
Think what I'll do, BEFORE the dreaded fiberglass work, is stuff some foam in the tunnel of the eyebrow and see if that helps. I THINK my baffle material is sealing well here. The 'foam test' will tell for sure.
 
Bill Woods, you out there buddy? Post some pictures of your baffles seals, in particular the intake area.

Frank, it is an easy experiment...go for it and report.
 
Yes I might

Sounds like a project for the next annual...Do it one day so the OAT's remain fairly consistent.

Frank
 
I did

Wonder how an aluminum plate RTV'd in the tunnel would do? I HATE glass work.......

Make a kidney shaped piece out of .020, bead of RTV, and pop rivet in place. Ten minute job, perfect seal.... I hate fiberglas work...
 
I did something similar to what Kent is suggesting when I reapplied my baffles to new ECi tapered fin cylinders. I did not want to rebuild the whole baffle system so I used hi temp rtv and made adapters to go between the baffle and the cylinders. For instance, for the front two cylinders I put a layer of duct tape on the front of the cylinder fins, then a layer of packaging tape. I wanted the tape to come off the cylinders without removing paint and for the tape to come loose from the RTV without pulling the RTV off the aluminum.

Once I had everything ready I gooped up the tape and the left and right front baffle halves with hi-temp RTV then assembled them to the side baffle plates and the engine. The next day I carefully pulled the front baffle halves off the engine. The RTV had set up nicely and made a tapered spacer for the cylinder. There were some voids and gaps but the basic contour and dimensions were there so I added more RTV and smoothed it out. I was worried that the second layer would not hold but it did!

The back baffle halves were harder but I was able to take some measurements of the gap between the bafle and the cylinders and use RTV and bid fiberglass to create a contour that matched the cylinder pretty well.

Here is a posting from Groucho that gave me the idea. I'd seen this on EZs years ago but had forgotten all about it until this post showed up. I did not apply the RTV/FG in a way that it would stick to the cylinders though. My baffles can be removed without peeling RTV off the cylinders.

http://www.vansairforce.com/community/showthread.php?t=26988
 
I was planning to saturate fiberglass cloth with high temp RTV to line the inner surface of the baffle wraps (additional plies for thickness where needed). John's method sounds good too....and there are probably 3 or 4 more ways to skin this cat.
 
Yes

I now remember Groucho's (Bryan's) post...I think this is definately an experiment coming on.

I do have a roll of very sticky aluminium tape that will conform well to the fins..so I expect to be able to run a few test cases (assuming the lower baffles already fit well ..I think they do).

So hopefully just the uppers will recieve the tape...fly adjust, rinse ,lather, repeat until the lowest cylinder head temps are seen for the same power settings assuming the same OAT.

Once i have have baffles that give me the best temps I simply replicate the alu tape with the RTV/BID layup, marking the edges of the required layups with a sharpie.

I just hope the openings in the lower baffles would not need to be opened up to reduce the pressure drop.

This could be cool!

Frank
 
Problem Solved......

Bought parts from Avstar and converted my carb from a 10-3878 to a 10-4164-1. T/O EGT's went from mid to upper 1300's to lower 1400's with the 3878 to lower 1200's with the 4164 (DA today about 1500' at airport), and T/O CHT's went from 425+ with a 130 kt climb to 385 or so with a 100 kt climb.

Throttle response is much smoother. Before I had a dead band in the mid range which made it a little difficult to find 1700 RPM for a run-up. Also, with the 3878 and at about 70% power, the engine would 'surge' (for lack of better words) when I would lean it out. Sounded to me like it was starving for fuel. I could not see it on the engine instrumentation but could definitely feel it and hear it. Also, T/O fuel flow went from about 16 to 19+ gph.

Overall the engine responds much more smoothly than before. This is an O-360-A1A swinging a WW RV200 prop on an RV-8. The only thing I did different from a stock 4164 on the conversion was to drill the new jet to 30. It came drilled between 31 and 30, so I did not change the orifice very much. I may buy a new jet and install it undrilled and see if there's much of a difference.

But for now I am a happy camper. The engine is now performing like it should. :D

I do have a question: what T/O EGT's (sea level or thereabouts) are you guys seeing with this engine? Thanks
 
<<Now how to fix it?>>

Kent, did the cylinder wrap "gaskets" today. Here's what I was talking about. These are Loctite 598 rolled into 9.66oz 14x16 plain weave between plastic sheets. Cut to size through the plastic, peel one side, stick on place, wait two hours, peel the other plastic sheet. These cylinder wraps won't leak; all air stays between the fins. And the aluminum baffles shouldn't wear on the fins.

As for the rubber combs, I adjusted the baffle bends so the wraps end just short of them and lay flat on the gasket and fins.

The low drag cooling scheme I'm working requires maximum heat transfer. Probably overkill for a standard setup with properly fitted and otherwise sealed baffles, but it can't hurt.



 
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<<Now how to fix it?>>

Kent, did the cylinder wrap "gaskets" today. Here's what I was talking about. These are Loctite 598 rolled into 9.66oz 14x16 plain weave between plastic sheets. Cut to size through the plastic, peel one side, stick on place, wait two hours, peel the other plastic sheet. These cylinder wraps won't leak; all air stays between the fins. And the aluminum baffles shouldn't wear on the fins.

As for the rubber combs, I adjusted the baffle bends so the wraps end just short of them and lay flat on the gasket and fins.

The low drag cooling scheme I'm working requires maximum heat transfer. Probably overkill for a standard setup with properly fitted and otherwise sealed baffles, but it can't hurt.


I must say that I'll be interested in the results. My mind says it won't work as well as expected. But then I'm not an engineer either. Just nearly 40 years in the HVAC business. Just seems to me, that if heat transfer was that effective by tightening up the gap; that heating/cooling manufacturers would have caught on years ago. I think the airflow is going to become somewhat restrictive. But that's what testing of this type is for! :)

L.Adamson
 
Or you could just drill out the main jet in the carb.

I struggled with this for a year.

Changing baffles, opening the rear exit.

Nothing improved very much until I enriched the carb mixture.


Now its much better.
 
Very nice look to the change.

<<Now how to fix it?>>

Kent, did the cylinder wrap "gaskets" today. Here's what I was talking about. These are Loctite 598 rolled into 9.66oz 14x16 plain weave between plastic sheets. Cut to size through the plastic, peel one side, stick on place, wait two hours, peel the other plastic sheet. These cylinder wraps won't leak; all air stays between the fins. And the aluminum baffles shouldn't wear on the fins.

As for the rubber combs, I adjusted the baffle bends so the wraps end just short of them and lay flat on the gasket and fins.

The low drag cooling scheme I'm working requires maximum heat transfer. Probably overkill for a standard setup with properly fitted and otherwise sealed baffles, but it can't hurt.


I will look forward to seeing your test results.
Also will the wraps hold up with the pressure inside them. IE will they blow off/up.

Kent
 
RTV the edges...

...it is very easy to RTV the gaps on the edges of the aluminum cylinder baffle keeping the air from escaping through the sides. Find every nook, cranny, and hole that the air can escape and RTV it. Simple, quick, and very effective...
 
<<Also will the wraps hold up with the pressure inside them. IE will they blow off/up.>>

The wrap sections you see (from below) in the photo are little more than gaskets sandwiched between the aluminum baffle wraps and the edges of the cylinder fins. They can't go anywhere, period.

These wraps do extend about an inch above the cylinder midline, so there's about an inch unsupported at the front of the front cylinders and about 4" unsupported between the front and rear cylinders. However, I don't think those sections are going anywhere either. Discount the adhesive entirely; consider the upper and lower plenum pressure differential, as well as Bernoulli.

<<...it is very easy to RTV the gaps on the edges of the aluminum cylinder baffle keeping the air from escaping through the sides. Find every nook, cranny, and hole that the air can escape and RTV it.>>

Right on brother.

FAST FORWARD, DECEMBER 2014 The wraps are at 415 hours now. Just finished the annual; they're all as good as brand new, fully adhered to the fins. I have excellent cylinder cooling, and compressions are all high 70's over 80.
 
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Or you could just drill out the main jet in the carb.

A lot of people have drilled out the jet, nothing more, with acceptable results. I chose to convert to the 4164 as there are other parts that change, as well as an adjustment to the economizer. I'm happy with my results including what appears to be a fairly linear throttle response, something I did not have before. My friend Bob Martin is very knowledgeable about carb work, much more than I, so perhaps he will chime in. Bob put a 'Mooney' kit in his 3878, Precision part no. 666-660-F, which essentially converted his carb to a 4164, although the full conversion includes a few additional parts that the Mooney kit does not have. One new part is the accelerator pump, but for the life of me I can see no difference in the one for the 3878 and the one for the 4164.
 
I am slow some times....

<<Also will the wraps hold up with the pressure inside them. IE will they blow off/up.>>

The wrap sections you see (from below) in the photo are little more than gaskets sandwiched between the aluminum baffle wraps and the edges of the cylinder fins. They can't go anywhere, period.

These wraps do extend about an inch above the cylinder midline, so there's about an inch unsupported at the front of the front cylinders and about 4" unsupported between the front and rear cylinders. However, I don't think those sections are going anywhere either. Discount the adhesive entirely; consider the upper and lower plenum pressure differential, as well as Bernoulli.

.

I thought that you were not using the AL baffle, but just the new seals that you made.:eek:

Kent
 
Increasing WOT fuel flow is certainly a practical CHT fix. A carb mod is an easy single point solution, and some carbs are indeed delivered too lean.

Increasing cooling capacity has no operating cost but requires more work initially. The baffle wrap sealing example is not a single point cure; it's just one tweak among many.

Let's face it, we've all seen marginal baffle and seal craftsmanship. Maybe your carb needs fattened...or maybe not. Better to make sure your cooling installation is top notch before assuming a need to waste fuel and produce less power.
 
Increasing WOT fuel flow is certainly a practical CHT fix.

Especially, as in my case, when the t/o ff was around 15.5 gph which I firmly believe is way too low for a carbureted O-360. Should be closer to 18 or so at sea level.
 
<<t/o ff was around 15.5 gph which I firmly believe is way too low for a carbureted O-360. Should be closer to 18 or so at sea level.>>

Serious question Jim...would you explain why? Strictly a case of cooling with fuel, or some other reason?
 
Good CHT'S

How many of you are out there with O-360's with the 3878 that have good CHT's? Was there a problem and if yes what did you do? Also how many of you have drilled main jet or conversion of the 3878?
 
How many of you are out there with O-360's with the 3878 that have good CHT's? Was there a problem and if yes what did you do? Also how many of you have drilled main jet or conversion of the 3878?

I have and 0-360-A1D with the 3878 carb. I drilled the main jet to .125 before first flight due to info on this site. I see CHT's of around 410 on a hard climb in 90 degree temps.

I think another factor is piston cooling nozzles. My engine doesn't have them.
Most of the newer engines do (I think). By spraying oil on the back of the piston this has to help cool the cylinder. But a side effect is higher oil temps.

My oil temp will reach 205 on a hard climb and I DON'T have the (better) Stewart Warner cooler. I also have about 2/3rd's of the oil cooler blocked off!

Mark
 
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proper fuel flow

According to Mike Busch, the "Savy Aviator" on the Avweb site:

"For a normally aspirated fuel injected engine designed to run on 100-octane fuel (8.5-to-1 compression ratio), takeoff power fuel flow in GPH should be roughly 9% of the engine's maximum rated horsepower."

For 180 HP, that equates to 16.2 gph

erich
 
John Deakin

John Deakin from AVWeb has a great column that I've read and learned a lot from. I cut a pasted parts here, but go read the entire article for the full effect on the subject. I know this info is not about gallons per hours flow, but for those of us with a flow meter, it is good info.

Pelican's Perch #63:
Where Should I Run My Engine? (Part 1) by John Deakin
http://www.avweb.com/news/pelican/182179-1.html
"The Takeoff"

IT IS ABSOLUTELY CRUCIAL THAT YOU ATTAIN THE FULL REDLINE FUEL FLOW AT TAKEOFF, AT SEA LEVEL!

If you take nothing else from this column, pay attention to that statement. That fuel flow is vital for cooling, and that redline is a minimum, not a maximum. The vast majority of all these engines are set too lean by the manufacturer's recommendation! Almost all mechanics will resist this idea, and they seem to think that if the book specifies a fuel flow redline, then a little less than redline is somehow "better." If you cannot get your mechanic to set this up properly, find a mechanic who will. If your full-power fuel flow is a bit over redline, so much the better! You can always manually lean it back to redline if you wish, but you can't do much with a fuel flow that is less than redline. Even half a gallon per hour can make a large difference in CHTs right after takeoff, and during climb. Normal climb CHT in a well-baffled normally aspirated engine is around 330?F at full power and sea level, at any decent climb airspeed. CHT might be higher if you insist on low climb airspeeds. If you see higher CHTs on your engine monitor, your fuel flow is too low. A lot of these fuel flow indicators are not very accurate at all, and most are not even true fuel flow gauges at all. They're pressure gauges, marked in flow. We really like digital fuel flow systems that have been calibrated by actual tests for this reason. If your redline is 27.0 GPH, and you get only 26.5, have it set higher.

Pelican's Perch #64
Where Should I Run My Engine?
(Part 2 ? The Climb)
http://www.avweb.com/news/pelican/182176-1.html
In general, and speaking very roughly, if you see EGTs anywhere over about 1,300?F (lower will not hurt a thing and is probably ?better?) during a sea-level takeoff, or CHTs above about 360?F right after takeoff, YOUR FUEL FLOW IS TOO LOW. Having a good understanding of the proper relationship between the EGTs and the fuel flow at very rich mixture settings will always give you a good cross-check on whether or not you are getting adequate fuel flow -- even if your fuel flow needle breaks off and falls to the bottom of the instrument!
 
Jim,
Try this: After takeoff when your get to about 400 or so, level off for about 5 minutes, let your speed build up (for cooling), and when it gets down to about 360 or lower, continue your climb. When I did this with my RV-6, it worked every time. I haven't tried it yet with my RV-8 (haven't gone anywhere but local formation yet), but once the CHT's cooled, they stayed cool for the rest of the flight, even in hot weather.

Scott
 
From John Deakin:

IT IS ABSOLUTELY CRUCIAL THAT YOU ATTAIN THE FULL REDLINE FUEL FLOW AT TAKEOFF, AT SEA LEVEL!

The vast majority of all these engines are set too lean by the manufacturer's recommendation!

If your full-power fuel flow is a bit over redline, so much the better! You can always manually lean it back to redline if you wish, but you can't do much with a fuel flow that is less than redline. Even half a gallon per hour can make a large difference in CHTs right after takeoff, and during climb.

Normal climb CHT in a well-baffled normally aspirated engine is around 330°F at full power and sea level, at any decent climb airspeed. CHT might be higher if you insist on low climb airspeeds.

In general, and speaking very roughly, if you see EGTs anywhere over about 1,300°F (lower will not hurt a thing and is probably “better”) during a sea-level takeoff, or CHTs above about 360°F right after takeoff, YOUR FUEL FLOW IS TOO LOW.
This reply is in response to Dan Horton's question of me, but I quoted Bob Martin since what he cut and pasted from John Deakin is right on the money.

John Deakin is one of the instructors at the Advanced Pilot Seminar put on by the GAMI folks in Ada, OK, which I attended a few years ago (well worth the money!). This was back when I was operating an A-36 Bonanza with an IO-520. Other instructors are Walter Atkinson (I know Walter well - he was my CFI for my Seaplane rating) and George Braly. The snippets of information from Bob Martin's quote are taught at the school. A LOT of time at the school is spent going over manufacturers engine performance data, a lot of which is WRONG! For example, Lycoming says that 500 deg F is a redline for CHT's. If you operate anywhere near this number you'll fry your cylinders and you will not get anywhere close to TBO. In fact, if you regularly operate your engine with CHT's much above 400 you'll see a decrease in TBO. Straight from the Lycoming Operator's Manual is "For maximum service life, cylinder head temperatures should be maintained below 435 deg F". 435 ain't good at all, if you regularly operate there you will significantly reduce your engine's life. This is straight from APS and they have the data to back this up. Also, Lycoming in one of their curves shows a full power fuel flow of around 15 for an O-360-A1A. But they also say CHT's 500 redline, and keep them below 435. Those temperature parameters will HURT your engine! If those numbers coincide with 15 gph t/o ff (which they do), then their quoted t/o fuel flow (15) HAS to be too low!

I agree good baffling is important, but tweaking every tiny leak will not make that big of a difference in CHT's. An increase in fuel flow, even slight, will however make a significant difference. In my case, my baffling is in good condition and does a good job sealing. I did wonder if the upper 'tunnels' provided a means for air to bypass, so I temporally stuffed them with foam rubber and went flying. That made no difference in my CHT's. As stated earlier in this thread, unless I used a very high climb speed, my CHT's would climb right on through 425 or so before I lowered the nose to get more cooling air. Even more telling was my take off EGT's at a DA of 1500': 1350 - 1400 on 1 2 and 3, and over 1400 on #4. Reread Deakin above: it ought to be 1300 or below, and that's at sea level. At the school they tell you 1250 is better.

Back to my Bonanza days. I was fighting high CHT's on climb, so I installed GAMI's Liquid Air baffling system. Even with a well designed baffling system, my CHT's would rise above 400 in a climb unless I kept the nose down. About that time I attended the APS. There I learned that a high enough t/o fuel flow is extremely important for engine cooling. While I don't remember my starting ff (guessing around 25), I went to about 28 GPH for t/o. I am lucky I had a shop that would work with me because many A&P's will not set it that high. This is what did it. My t/o CHT's were now well below 400, and I could lean as I climed to maintain CHT's at 385 or so, thereby reducing fuel flow and at the same time keeping my engine happy. If there's not enough fuel flow to begin with quite obviously you can't do this.

So to sum it up, my airplane has a baffling system in good condition. What I learned at the APS helped to convince me that the take off fuel flows in my -8 were way too low. Other hints were a non linear throttle response, and RPM surging when leaning at altitude. Now, with t/o ff at 19 (that's probably too high - remember I drilled the jet - probably should have tried it first with a stock jet), I have t/o EGT's in the low to mid 1200's, and CHT's well below 400 (actually around 350), even while climbing at 100 kts. The throttle response is now linear, and when I lean in cruise I no longer get the RPM surge. My engine is happy, and I am happy. I am going to install a stock jet in the 10-4164-1 and see what I get. I suspect that will be just right, and it will be around 18 gph. YMMV

Hope this helps.
 
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