Hot number four cylinder

I have a cub with a Bart 375 electronic fuel injected and ignition. All four cylinders were replaced in the eci warranty. a year or so later cyl 4 was replaced with a superior cylinder and new rings after eci cyl was damaged from ring flutter. After 120 hrs number 4 runs 30 to 35 deg hotter on average. On hot day cruise 1,2,3 350 and 4 385. Climb short time over 415 and no sign of backing off still maintaining 35 deg spread. Done baffling work till blue in face. Cowl pressure differential 4 inches at 85 90 mph. Calibrated all temp sensors. Egt 1250 or less. Cyl 4 has coolest egt. Leak down 78 or better. Snapon comp guage 195 200lbs all cyls. Dialed the cam and seem reasonable. Set the sky danamics rockrs at 060. Built baffle down tight down backside of 4. No change. Measured depth of cht probe holes and the superior cyl was.120 deeper. Switched probes from cyl to cyl no change. Put temp probes under valve cover bolts and under spark plug on 2 and 4 it showed 4 carried 30 deg hotter. I am at wits end left with only option of repairing an eci and changing out the superior. Ideas thoughts. By the way big stewart warner oil cooler stays under 205.

wheatjp,

Have you visited the Vans forum website, lots of good info on baffles there... Good Luck!

What is max temp supposed to be? isn't 385 still in the normal operating range? Maybe high, but still in green- don't sweat it. Lycoming says max of 500 for cht.

Whose injection? Can you have your injectors balanced to level the temps? Maybe call Don or Kyle at Airflow Performance and chat with them?

Edit: You said you have electronic fuel injection? Maybe talk to your injection sipplier for tuning advice. For mechanical injection? http://airflowperformance.com/wp-content/uploads/2015/12/Nozzle-Tuning-Instructions.pdf

Fly efi electronic injectors Egt 1 is hottest 4 is coolest by 50 deg. Iwas told by fly efi that the fuel is the same on all cylinders. Electronic injectors are very accurate. it has to do with which cyls get the most air are hotter. By all standards they are real close. The clue is 4 is the coolest egt yet hottest cht no matter how mixture is set. Have read all blogs vans shortwings sc.org already. My question is has anyone had this issue with superior cyls?

wheatjp said:

I was told by fly efi that the fuel is the same on all cylinders. Electronic injectors are very accurate. it has to do with which cyls get the most air are hotter. By all standards they are real close. The clue is 4 is the coolest egt yet hottest cht no matter how mixture is set. Have read all blogs vans shortwings sc.org already. My question is has anyone had this issue with superior cyls?

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First perform the test as described by Airflow performance. If the electronic injectors are all flowing the exact same amount of fuel your cylinders are operating with different mixtures at a given power setting. As a result your #4 cylinder could be operating at peak EGT while the remaining cylinders are operating at less than peak temperature, either rich or lean of peak. The idea is to get all of the cylinders to reach peak EGT temperatures as close to the same time as possible. This does not mean the same temperature. It means that the EGT temperatures stop rising at the same time. The actual numbers may or may not be the same and it is not important what those numbers are.

Most fuel injected air cooled opposed cylinder airplane engines require different sized fuel nozzles in order to balance the mixtures. When all of the nozzles are the same size as they do come from the factory, the engine does meet the temperature/mixture requirements. When we start to refine fuel flows and lean LOP with our fancy temperature instruments and electronic systems these issues arise.

Do the test if for no other reason than education.

I am familiar with airflows balancing process did one on a 360. The 375 egts all peak around 1400 when going lop and will run smooth up to 75 deg lop. Still maintaining 30 deg differential cht hot on 4. One heck of ignition sytem. Much better than plama 3. Not that it matters except to find 150 deg Rop a good climb setting. Again 4 is coolest egt 1250 1240 1230 1215 respectively. I think we are safe to say 4 is not at peak temp. The only change I can point to is the superior cylinder heat rejection or airflow problems. This all came about when the eci was changed out. The fins on superior are slightly different. Anyone with heat rejection problems on superior cylinders feel free to chime in. Thx

I’m confused. You say all the nozzles and flows are equal but then you say #4 is not at peak. Are you sure your compression ratio is identical? The warmer CHT and cooler EGT together sound related.

I hear you on the confused part. Could be the superior combustion chamber is different but the cranking compressions are so close I discounted that. As said before the only thing changed in the engine was the replacement superior cyl and rings. According to Robert Paisley (has looked at lots of engines) of flyefi the egts shown are indicative of intake runner differences. I took it to mean intake runner 1 flowed (air) the best 4 the worst,hence rich mixture and cooler egt on 4. Under that assumption 4 would have the lower effective comp ratio. I agree all things being equal higher comp and engine timing both lower egts and raise chts. These electronic injectors are batch fired (all fire at once connected together) so likely hood of fueling different is remote. I suppose I could change injectors around and see if it changes. I keep coming back to something is different with the superior cyl. Thanks for being a sounding board. Probably never know without changing out the superior for like eci...you don't know how many times I have heard you are the ‘only one’.

Is this the system which you are using? http://www.flyefii.com/products/efii-systems/
If so, how are you determining peak EGT if there is no mixture control? "Automatic mixture control (no mixture knob to fool with)."
Before you pull the cylinder move the baffle away from the backside enough to get the cool air all the way down to the lower part of the fins. Adjust it so that there is no gap at the bottom for the air to escape without passing through the lower fins.

There is a manual control that allows you to shift the whole fuel curve 50% lean or rich from current gphour flow used when goin lean of peak. All cyls peak close to 1400 deg at 2300 rpm 20 inches mp. Tried what you suggested already. No baffle close baffle close at bottom spaced at top. Thou have not changed ramp at cowl hole at #2. More ideas?

Fly efi is the system. It runs real well idles like a clock at 390 rpm easily programed fuel an timing curve

wheatjp said:

..... Thou have not changed ramp at cowl hole at #2. More ideas?

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You may have something here. What does your baffle do between the bottom of the nose cowl opening and the front of the cylinders? It ought to be sloped up to about the horizontal center of both front cylinders. This smooths the airflow up to the region above the cylinders where it can then proceed down unimpeded between all of the fins. You could temporarily tape a piece of aluminum in here to test it.
Piper's original design is not good for higher powered engines.


Also it sometimes helps if you can minimize any air leakage into the area behind the ring gear. Perhaps you've done this?

Your EFI sounds like a nice system.