Deflection Vanes to Reduce CHT

Recently I top overhauled my engine with 4 new ECI cylinders, port polished and flow balanced by Lycon. I also replaced the exhaust with the AD hot rod exhaust and added an insight G1 engine analyzer. I'm at about 25 hours tach time since installing the new cylinders and oil consumption stabilized a long time ago. I can't seem to get the #4 cht to run less than 400-430 in cruise. I have to step climb to keep the CHT less than 450 even on cool days.

I've replaced all the baffling, sealed it with RTV, changed the probes to verify accuracy, and installed ramps on the front two cylinders. My next move is to add some deflection vanes and maybe a husky or CC lower cowl lip extension. Open to suggestions here.

Does anyone have pictures of the deflection vanes? I've never seen them, I've only read about them and a quick search of the CHT threads didn't reveal any pics.

Did you raise compression when you replaced cylinders?
What are the rest of the cylinders doing tempwise?
Rear mounted oil cooler?
Whats your oil temp at cruise?

Lots of tips and tricks in previous posts to bring temps down, usually a combination of several little mods that add up to satisfactory results.
Id start with confirming youre not running too lean. been a common issue with Lycon's ported cylinders.
Rear mounted cooler robs alot of cooling air from #4, so if its way hotter than the rest, may be another place to start.

I'm not flying this yet. Lycon ported cylinders, Airform baffles with oil cooler behind number 4. Leading edge exhaust. Vans oil cooler dampener. Narrow deck 160 hp. I may have the same problem with number 4 cylinder as well?
I've also sealed up the fly wheel with custom baffles... hope the extra effort to obtain the greatest differential pressure between the top and bottom of the cowl will give good cooling and keep the oil temperature better than 180.

Mark if you do have high OT with that Vans shutter, go with the controllable box from Dans Aircraft. Both require field approval. With low airspeed cruise like a Cub, the Vans does find in the cold but not hot summer. It works fine on an RV cruising at 150 but not a cub doing 90. Might be OK with your Pacer & region you fly in. It's in mid 80s again here in Fairbanks. With my Dans box I can stay below 210 with flapper wide open. BTW, my CHT on No. 4, no issues with either one.


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I didn't raise the compressions, still 160hp.

I've added front air dams/ramps made by air forms. With these installed the #1 temp came up and the #3 temp went down and they are now about 380 in cruise and they are within a few degrees of each other. The #2 temp came up a lot and the #4 temp went down marginally. They are about 410 - 420 in cruise with the front cylinder being about 10F cooler than the rear. Without the air dams the #2 cylinder is about 380 in cruise and #4 is about 410-420 still. It has been in the 80s here in Fairbanks.

I do have a rear mounted oil cooler. I'm going to tape it up tomorrow and take a short flight to see what that does.

Oil temps are around 200-210F.

Whats the issue with the ported cylinders running lean? and whats the fix?

Thanks for the input and help!

You did remember to reinstall the inter cylinder baffle? The one from Lycoming that goes up between the cylinders held in place with a hook to a strap at the top of the cylinders.

I'd buy a $50 manometer and see what kind of pressure differential you have between the top and bottom of the engine. The front baffle seals that sit against the nose bowl tend to open up in flight.

What Steve said. Sounds like all your CHTs are higher than they ought to be for the conditions. I bet you're loosing high pressure air from the top of the cowl without it having to go though the engine fins. Or that you're introducing high pressure air into the lower part of the cowl from the outside air - like through a leak in the front.

I assume you ran this engine in its current configuration prior to new cylinders? did you have heat issues then? Besides cylinders what did you change?

The intercylinder baffles are installed. Unfortunately I didn't have a 4 place engine analyzer until the cylinders were replaced so I don't know what temps were occurring before the top overhaul. I also added an AD hot rod exhaust at overhaul.

I will take a good look at the front seals today too, maybe add some tape to make sure there is a good seal and try it again.

Re Ported cyls running leaner:

In simple terms:

The engine is basically an air pump, "Porting" is a way to clean up sharp edges and re contour intake and exhaust chambers, valve seats etc. if done correctly should increase volume of air/fuel flowing thru the engine at a given rpm. More air/fuel more horsepower.
Proper combustion requires fuel and air to be introduced to the combustion area at a precisely metered ratio. Ideal ratio is about 14.7 parts air to 1 part fuel.
This fuel/air mixture is controlled by the carburetor. As air is drawn thru the carb it interacts with a fuel metering device that introduces fuel to the air. At the base of the metering device is a small orifice often called a main jet, though not really a jet. Its job is to regulate the amount of fuel introduced at the carburetor.
The metering device does a pretty good job at maintaining a consistent f/a ratio thruout the rpm range of the (stock) engine.
Important to note: this is your default mixture, your fuel/air mixture at full rich setting on the panel. You can manually lean the mixture from here but you cant enrichen any more once the little red knob is all the way in.

By increasing the volume of air flowing thru the system you may create a situation where the main "jet" cannot deliver enough fuel to to incoming air to maintain a correct (14.7:1) f/a mixture. therefor creating a lean condition during combustion. Lycons porting process allows cylinders to move alot more air as evidenced by some pretty impressive (though questionable) dyno results.
To take it a step further: Its possible to create a situation where you have exceeded the design limit of carburetor to meet the airflow demand (CFM) of souped up engine, inspite of rejetting. Poor fuel atomization, uneven fuel delivery to cylinders etc result. I think thats what drove development Lycons "pepperbox" fuel nozzle on the T340


FA dodge hotrod muffler, should help cylinder cooling by scavanging burnt fuel and some intake charge better during valve overlap phase of exhaust stroke, may also aid moving more air thru the system further adding to the lean condition.

Every time high CHT issue comes up here, folks are quick to point out poor fitting baffling, cowl pressure etc. Sure, Baffling should be in good shape but typically not the issue or solution.
Bottom line, more horsepower makes more heat EXCEEDING the ability of original cub cowl design at cub speeds to eliminate excess heat.
To make matters worse, with this type of flying, when we add horsepower its generally mated to a longer coarser pitch prop that works the engine harder at REDUCED aircraft speed, further compounding cooling issues.
I have yet to see anyone chime in here with high CHT issues on a stock engine...

Your engine is still pretty fresh, temps should come down a bit over the next 100 hrs. But id start looking at other mods to help eliminate heat.
Ted Waltman has explored this issue at length and has offered some great advise on the topic

My 2 cents

.... To determine if you are too lean:

Set up for level fight 2400 rpm, full rich. record egt hottest cyl. start leaning to peak egt and record that number.
Lycoming recommends at least 150 deg leaning authority, better 200 at or near SL
Lycoming also recommends you do not lean to peak beyond 75% rated hp so 2400 is a safe place to fool with it.

To enrichen a lean fuel/air situation, ive heard it rumored that folks will drill out orifice in fuel emulsion tube a few # sizes larger.

Where are you measuring the temperature and with what?


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