Cowl mod

[dfcpac]

Do they make a cowl mod kit for the Onex? I think the opening on the bottom of the cowl is to small and not enough air coming out I have a Revmaster 2300 and the egt are running very high

Thanks
Danny
127nx

[gammaxy]

Danny, did you ever get another propeller to try?

On the Sonex, some builders cut a larger exit. I've never seen a need to and I regularly fly when it's hot in Alabama. This experience causes me to question whether a larger opening will solve whatever issue you're experiencing. I don't think egt would be affected much by cooling. Are your chts fine? Mixture and timing have a very large and immediate affect on egts. Personally, I wouldn't read much into the exact egt number unless the engine was also not running smooth or generating good power.

[dfcpac]

The cht is pretty much normal around 350 degrees and the engine has good
Power high end it runs a little rough

Danny
N127nx

[MichaelFarley56]

Hi Danny,

EGT has a pretty direct relation to your mixture setting, not the cooling airflow into the cowling. If you were running low EGTs yet have high CHTs that could indicate a lack of airflow into or out of the cowling (along with an advanced secondary ignition, bad baffling seals, etc).

In your case, if your CHTs are in the 350 range, that would indicate you are getting proper cooling air through the cowling. If your EGTs are high and you're experiencing some roughness at wide open throttle, I would recommend you start with adjusting your AeroInjector needle a little bit more rich and see if that drops your EGTs. Hopefully you'll be able to accomplish two things; first, your EGTs will drop a little, and secondly, your engine will run more smoothly.

What EGT readings are you seeing at full throttle?

[mike.smith]

Hi Danny,

EGT has a pretty direct relation to your mixture setting, not the cooling airflow into the cowling. If you were running low EGTs yet have high CHTs that could indicate a lack of airflow into or out of the cowling (along with an advanced secondary ignition, bad baffling seals, etc).

In your case, if your CHTs are in the 350 range, that would indicate you are getting proper cooling air through the cowling. If your EGTs are high and you're experiencing some roughness at wide open throttle, I would recommend you start with adjusting your AeroInjector needle a little bit more rich and see if that drops your EGTs. Hopefully you'll be able to accomplish two things; first, your EGTs will drop a little, and secondly, your engine will run more smoothly.

Also keep in mind the EGTs are relevant numbers, not absolute. The numbers depend greatly on where the sensors are located. Closer to the exhaust flange, the hotter readings. Further from the exhaust flange, the cooler the readings. I think CHTs are the most important numbers as those are more directly related to the health of the engine and the cylinders. If the engine is running rough, though, then testing changes in the needle are probably warranted.

[dfcpac]

Highest reading 1425 egt that is on the ground

[MichaelFarley56]

Highest reading 1425 egt that is on the ground

This is just my opinion but that seems pretty lean. I’m normally happy with a smooth running engine at full power (on climb for example) and when I see maximum EGT readings around 1200-1300. Any higher than that and my CHTs will go pretty high.

Consider richening the needle 1/8 turn at a time until it’s running smooth at full power and the EGTs drop a little. Up to you of course.

[mike.smith]

Highest reading 1425 egt that is on the ground

This is just my opinion but that seems pretty lean. I’m normally happy with a smooth running engine at full power (on climb for example) and when I see maximum EGT readings around 1200-1300. Any higher than that and my CHTs will go pretty high.

Consider richening the needle 1/8 turn at a time until it’s running smooth at full power and the EGTs drop a little. Up to you of course.

I agree. Even being "relative," 1425 on the ground is pretty high.

[Gordon]

In regard to the Onex "cowl mod" to get better cooling and lower CHT's.... here is my 2 cents worth.

I think it may be a case of "hitting the bull's eye......but it was the wrong target" by simply cutting a large hole in the bottom of the cowl. I have yet to do my baffling on my Hummel 2400 but I WILL NOT be using the stock rubber seal Sonex supplies with the baffle kit. I think at high speed the cowl "blows up" slightly and thus loses the seal and loses effective cooling pressure. I think this is aggravated further on the Onex as the plans show NO hold down screws along the back side of the top cowl thus allowing more of a 'blow up' situation. I will be fastening mine down tight.

On both my RV-6 and 7 at 180 mph you could see a slight ballooning of the cowl from that cooling pressure. I will be using the same rubber sealing material that I used on the RV's and most certified airplanes use as well. Then as the cowl balloon's the rubber seal will still stay in tight contact with the top of the cowl and make for good pressurized cooling.

Any one looking at excessive high temps should maybe re-visit their cowling seals before chopping a larger hole in the lower cowl...........some food for thought.

Gordon.......Onex....Hummel 2400