Lowering CHT's, RV-6 IO360 180HP, AFP
 

This is a follow up on my CHT's and fixes to get them lowered. First off, they are not that bad, just could be better. (climb out 400, cruise 370 on the hottest cylinder) I decided to do one thing at a time and report on each. There are a lot of posts on this subject that where very helpful, so I am just adding to them.
The first and easiest step took ten minutes; cut off the lower cowling exit to be flush with the firewall. Did not even need to remove the cowling. I only cut off about 1".
The biggest challenge was how to compare data to see what it did. I am not a test pilot by any stretch, but I am learning a lot. My EDM930 is wonderfull at collecting the data and I am getting a handle on how to interpret.

My climb temps seemed to improve, however, my climb procedures are also better. I dont need to bust off the field at 2000fpm and sustain that, 1500fpm is fine at 140+ mph. So, not sure how much might have been affected by my poor techniques at first.
However, relative cruise temps improved, but differently for each cylinder. #1 and #2 where 30-35deg cooler for the same LOP operation, FF, HP, etc... #3 was only 10deg and #4 20deg. Still big improvements for shaving off an inch of plastic that you can't really see. Weird.
Now, off to work on #3 by opening up a gap on the back of the cylinder baffle with a washer or two. I also need to work on the cylinder baffling to ellimate some gaps that are allowing the air to leave the cooling fins before they reach the bottom of the cylinder. There is a big, maybe 1/8", gap on the lower back part of #4 about 45deg down from center.
At the same time, I am going to put an angle on #1 to block it off a little. I will fly and see where that puts me.
After that, I am going to tape off the 2" hole for the scat tube directly behind #3. That is upper plenum air being dumped directly into the lower plenum when the heat is off, or directly into the cabin when it is on. You can hear the pressure change in my Lightspeed ANR's when you open or close the heat. I will also tape off part of the oil cooler as a temporary fix as my oil temps are bit low. Maybe I can recover some air there.
And of course, continue to look for any baffle leaks out of that upper plenum. Seems pretty tight, but I will find them if they are there.
More to follow....

Jon,

Good info--sounds like you are getting some improvement.

I have some leakage around the curved portion of my rear cylinder baffles as well--let us know how you fix it (rtv or alum flanges on the bottom baffles??) and what change you see as a result.

BTW, I was told by several on this site that you should not completely close off that 2" hole from the rear baffle to the heat muff---it needs some flow to keep from burning out the muff. I have installed a couple of plate nuts to the rear baffle and have a "summer plate" that goes over the 2" hole and reduces it to about 3/4" to reduce cooling loss--although the effect on my plane was not measurable.

Best of luck.

Cheers,

db

Makes sense to not close that off and I appreciate the heads up. The RV6 plans called out to have the hole on the front baffle ramp, but the RV7 plans show it on the back. I put mine on the back as it was a lot easier. Maybe would have been better off having it on the front? Does not matter now.

I intend to try to recurve the cylinder baffle so it will naturally follow the curve, otherwise, RTV (not my first choice). I will keep you posted.

Cht's and cooling
 

I too have a 0-360 A1A with C/s prop.
I have to limit my climb in hot weather to control cht temps.
In searching cowling cooling, I came across the basic cooling formula that says the exit air area should be 125% of the inlet air to allow for expanding the air from heating it. I measured my inlet and exit and found them to be equal sq inches, roughly as I didn't actully account for thigs like the exhaust pipes taking up space.
I too trimmed my cowl not only flush with the firewall but actually angled it away from the firewall forward to create a larger opening if only by a tiny fraction. I didn't really see much difference.
I have followed many threads on cht cooling or cowling cooling in general and have tried the little tips without much success.
I wonder why so many RV's seem to not have a cooling problem and quite a few do. I'm thinking lots are 150/160 hp with FP props and arent really developing a lot of HP on takeoff, therefore helping the cooling. Another thought is maybe some aren't monitoring the chts on all cylinders or can't really tell what is going on by a analog gauge.
I have a JPI 700 and it flashes at me if the cht hits 450, I know it right now.
I'm considering Louvers in the lower cowl like Vans supplies for the -10 and sold by Alex on his website:
http://www.aviationtechproducts.com/louver.html
also thinking about a plenum to get rid of the baffeling cowl seal to avoid any leaking.
Is anybody else thinking like this?
Thanks for your input.

CHT Cooling Fixes
 

Reporting back on the simple things I did that worked! (Thanks Alan). I did all of these at the same time.
1- Found every little hole that air could possibly find a way out of the plenum. This was primarily small holes and sliver sized gaps around the sheet metal baffling where it mates up to cylinders, engine block, etc..., anywhere there was light coming through, I plugged it up with RTV. I was surprised how many tiny spots, I mean tiny, there where that could be plugged up, especially where the inlet ramp sets against the corners of the barrel and head on Cylinder #1 and #2, and other small spots behind Cylinder #3.
2 - The wrap around Cylinder baffles where not tight against the cylinders. I used the safety wire technique, so I was able to push the baffle against the cylinder while putting a few more twists in the safety wire. I was not able to close the gap on Cylinder #4, so I used RTV and sealed that gap.
3 - The lower part of the Oil Cooler robs air directly from the back of Cyl. #4. I fabricated a 2" plate to seal off that part of the Oil Cooler and wedged it in place and cemented with RTV.
4 - Cylinder #1 was considerably cooler than other Cylinders. I installed a piece of angle on top of the inlet ramp in front of Cylinder #1 to block off some of that airflow and hopefully divert more air into the plenum.

The Results - CHT's are now considerably lower, at least 40deg.! I pushed my climb a little harder than normal and watched the CHT's carefully; climbing at 130, 2000'/min., no Cylinder exceeded 370, none under 350. Ceilings limited my climb, but things seemed very stable. Cylinder temps in cruise where very low 300's and high 200's, 40deg OAT. Spread between Cylinders temps averaged less than 4%.
The only negative side affect; my already cool 165 deg. oil temps are now 145 deg, thats with 2" blocked off. Time to block off more of that Oil Cooler now. Good evidence that my plenum is working much better.

These where simple fixes which took less than two hours and had amazing results. This simple attention to detail with the Cylinder baffling and leaks did the trick. I am not sure what affect installing the piece of angle on Cyl. #1 had in regard to overall CHT's, but it sure evened out #1 compared to the others.

I am very confident that I will be able to operate my airplane in high ambients with no concern regarding my CHT's now.

High CHT's
 

John,
You also will want to look down in between your cylinder finds by the valves. Some engines cylinders have a lot of sand casting in this area which happers airflow down through the cylinder fins. Asked Peter about the ones he had on his ECI cylinders. Also, you may want to think about making a small ramp on the outlet at teh bottom of the firewall. THe RV-6 has a bent angle unlike the RV-8 which has a rounded exit ramp. This smooths air as it exits the cowl. It also could make your plane slightly faster as it will cut down on cooling drag. You might want to get Vans oil cooler door to change your airflow through your cooler via a cable. Remember, summer is coming and 80 degree days are not far off. Your oil temps will climb fast and then you'll have to pull the cowl to take out the air dam. Hope you'll fly up one of these days. Aden.

Superior Cylinders are very clean, so not flashing or anything. I'll check out the damper. I fly over you all the time, just seem to be occupied with other things. Soon though. Want to see that Rocket project!

Wow
 

[quote]Just wanted to say thanks for the compliment. :) But there is still room for improvement :eek: 40F decrease is great! Keep searching and you might find another 10-20F. It's all about air management and using it where it needs to go......

Look at #2
 

If you look at the front of your #2 cylinder, you can see how well - or how badly - the cylinder fins were cast.

This picture is the #2 cylinder on my O-360 Tiger, with 1999 Lycoming factory cylinders...



The filing of the fins by the spark plugs removes the casting flash that shows as "lumps" on the cylinder center line in the picture, allowing more airflow down around the head area, where the CHT temperature probe is...

gil in Tucson

I see no mention of mixture in this thread. I (and many others who have written extensively in this forum) have found that mixture has a huge effect on cht's. The effect is so large that I don't know how one can really tell the effect of other changes, unless the testing is done at the exact same mixture relative to peak egt's each time, and with the same power settings and OAT.

How balanced are the injectors? Do you have one/two EI systems? If you have balanced injectors and EI, you can really cool that thing down by running LOP.

Running 50 to 100 ROP vs 50 LOP will increase cht's by at around 50F degrees. Dan C. will probably "check" in here...