To Plenum, Or Not........

[mike newall]

Installed a plenum on our 7.

We still have issues with high CHT's and am not sure if they are related.

Cracking on with the 8 and wondering.....

Do we plenum or baffle.

Let me have some thoughts please.

Mike & Mark

[aussieflyer1]

Hello
I have a Plenum on my RV6A with a NEW Lycoming 0360 A1A and although I only have 6hrs on her the CHT are 350 -360 degrees runniing the engine at 2400rpm and full mixture because I'm running it in.
If you send me your email I will send you pic. The guy who made the Plenum is Wayne miller at HWO 305 298-2603 does a nice job.
Hope this helps.
aussieflyer654@gmail.com

[William]

Hi Mike how about both. I installed a Sam James cowling on my RV6A and it is built with a baffling system and a plenum.

Bill

[N941WR]

I've done both and what I have realized is that they both work but you must seal every air leak, regardless if you have a plenum or not.

[RV8RIVETER]

I have two plenums, one for each side and it works very well so far. I made composite cylinder wraps that keep the air inside the fins until it exits the bottom of the cylinders. My inlet area is just about 50% of the stock cowl and the highest CHT on the first few flights was 390, Texas, September, 2 hours on a rebuilt engine. They were all within 20-30 degree of each other.

[Beancounter]

I have the James plenum and 90hrs on my 9:1 0-320. Its winter here with temps ranging 20-40*F. I am only getting 325* max in cruise, reducing to 250* when I throttle back for the circuit. I think the plenum cools too efficiently. Time to make a cooling air exit restriction.

[RV10inOz]

In 100% of cases with plenums on RV7's that I know of, they all have chronic CHT issues.

In 100% of cases of standard baffles (not the black rubber though the orange stuff) that I know of the CHT's are good, i.e. around 300 +/-10 when LOP and 330-360 ROP.

It is just my opinion......but based on the evidence so far the plenum is not working and while some folk with the will argue....I say show me the data.

It is ironic you are asking the question when I think you know the answer already, but just are not sure you want to accept it.

Just remember that no amount of science and data can overcome the warm fuzzy feeling of a closely held superstition.

[Bastien]

Originally Posted by RV10inOz

I say show me the data.

Here are my RV8's with the plenum.



I can't say anything on the RV7 but at least on (my) RV8 it works pretty well. Not too hot/cold and CHTs are really close.
Never had any issues for the moment from 90F to 10F OAT.

I am sure baffles work well if you pay attention to the leaks (as you would also do with a plenum)

Note: Mike do you have the ECI cylinders with the tapered fins? If you have them and did not do any mod on the cylinder baffle, it could be an issue resulting in high CHTs.

[f1rocket]

The biggest and most often cooling issue I see is restricted airflow into the plenum/baffle caused by the air ramps in the upper cowling. Often, these are glassed into the upper cowling without trimming them back to open up the airflow. I've solved several CHT/Oil temp issues by cutting this back.

Stick your fist into your cowl opening on the right side. If your fist won't fit, your opening is too small. Fix that first and you may be surprised by the results.

[RV10inOz]

Originally Posted by Bastien

Here are my RV8's with the plenum.

I can't say anything on the RV7 but at least on (my) RV8 it works pretty well. Not to hot/cold and CHTs are really close.
Never had any issues for the moment from 90F to 10F OAT.

I am sure baffles work well if you pay attention to the leaks (as you would also do with a plenum)

Note: Mike do you have the ECI cylinders with the tapered fins? If you have them and did not do any mod on the cylinder baffle, it could be an issue resulting in high CHTs.

Exactly my point. I would class that as a Plenum FAIL.

Sorry if you feel upset by that harsh comment but lets be real here folks, the OAT is -8 deg C and at 61% power and running LOP !!!!

That should be CHT of around 290 d F.

You have proven my point exactly.

You are confirming exactly what I see here. Try that in Australia or the southern USA.

Here is +8degC OAT, and 67% power LOP


or how about +2deg C at 63% LOP


How about -2dC at 61% power and before I fixed a few things


and last one for tonight, +13dC, 68% power and check out the CHT


I understand my post above and this one will hurt some feelings, but you can have 100 opinions and beliefs, all it takes is one shot of real data to shoot them down.

All the properly baffled -7 and -10 installations I have seen have had good results.