Another Powerflow exhaust question-cooling

[Tim Jodice]

Reading everything I could on find MS about Powerflow exhausts naturally most people that buy Powerflow exhausts buy them for the performance gain and some are happy some are not. They claim on there website that the lower CHTs.  I am interested in one solely for the help with lowering CHT. Those of you that own one even if your not happy with the performance did you see a reduction in CHT? 

[carusoam]

Most PF exhaust systems around here get purchased because their existing one has worn out...

Then the choice is PF or replacement...

The most performance gains are for pre-J exhaust systems...

The J, went through a modernization step to improve flow into and out of the engine...

So getting a PF on the newer J, doesn’t have a lot of improvement left in it...

CHTs do go lower when the back pressure is dropped... power increases...

How many °F are you hoping to lose?

Wait for somebody with a J to get more info...

Best regards,

-a-

 

[PTK]

18 hours ago, airtim said:

naturally most people that buy Powerflow exhausts buy them for the performance gain

What performance gains?

18 hours ago, airtim said:

I am interested in one solely for the help with lowering CHT

Why do you feel you want to lower CHT’s? How high are your CHT’s? There are certainly better and appropriate ways to deal with engine cooling.

[Tim Jodice]

29 minutes ago, PTK said:

Why do you feel you want to lower CHT’s? How high are your CHT’s? There are certainly better and appropriate ways to deal with engine cooling.

About 20-30 degrees. I did what I thought was the easy things. New baffles, checked timing checked fuel flow. Am I missing anything? 

I climb at 105-110 ias, full rich, 2700 rpm, cowl flaps open. Thats what it takes to keep them below 400 in the summer. If I climb at vy it will sail right past 400. Cruise 25-50 LOP WOT 7000' I need to keep the cowl flaps in trail to keep them below 380. 

My instructor has a 78 201 with no cooling issues. The only difference is he has removed the dual mag engine and my mechanic said his calls for 20 degrees on the timing where mine is 25. Could that make that much of a difference? 

Since the day I bought it I have compared it to my friends 67 F and his out performs mine in take off and climb and a little in cruise. That is at gross weight both having a gross weight of 2740. Is the anything that might result in low power and excessive heat?

[PTK]

Cooling in our engines depends on airflow through the cylinder fins. This airflow requires energy which is provided by a differential in air pressure above and below the cylinders. Higher pressure above. This higher pressure above must be maintained and not allowed to drop. It can drop if you have leakages between the top and the bottom. Controlling leakages is all a function of baffling. When baffled properly there’s very little space between the cylinder barrels and fins. It doesn’t take much leakage to throw this off. i.e. to bypass the fins rather than go through them. Based on your description I would say a major contributing factor is leakages. Granted it’s not uncommon to need cowl flaps in the summer in climb at or near gross. But cowl flaps are there to improve the air flow and carry heat down and out. They cannot recreate nor can they optimize proper air flow. (i.e. through the fins) if its not there because it is compromised by baffle leaks. In other words that pressure above the cylinders needs to be maintained higher than below and the airflow needs to be going through the fins. That’s optimal and efficient cooling.
I would really have someone look at your baffles carefully. Both flexible and inter-cylinder baffles.

 

[philiplane]

25 degree timing will definitely increase the CHTs. From 10-30 degrees. If your muffler is restricted, that will add to this number. A borescope inspection of the muffler will tell you if it's bad. 

[Tim Jodice]

20 minutes ago, PTK said:

I would really have someone look at your baffles carefully. Both flexible and inter-cylinder baffles.

 

They are new, installed in February. I used Gee Bee and they fit like a glove, no rinkles few cuts (like 3) no light makes it through.

[Tim Jodice]

16 minutes ago, philiplane said:

25 degree timing will definitely increase the CHTs. From 10-30 degrees. If your muffler is restricted, that will add to this number. A borescope inspection of the muffler will tell you if it's bad. 

I replaced the original muffler in January because it cracked. I installed a new regular replacement one.

Any idea why the dual mag calls for 25 degrees and regular mags call for 20?

[adverseyaw]

Most (all?) IO-360s were set to 25 degrees prior to the 1970s, even those with regular mags. Duplex mags came out during this period, and also got the 25-degree timing. Later on, traditional mags and 20-degree timing were in style, and Lycoming issued a SB on how to change the older engines with traditional mags to 20 degrees as well. I've heard the service instructions do not apply to engines with dual mags, but I haven't looked closely into it.

My M20J has an IO-360 with the duplex mags, and it runs on the hotter side. When I got the plane, the mags were (poorly) timed to 21/22 degrees. I've had it timed to both 20 and 25 degrees, and it did not make any difference in the CHTs. This bucks the conventional wisdom, but it's what I've experienced. I've got the plane timed back to 25 degrees, what's on the data plate, and just monitor temps in climbs.

Edited June 24, 2020 by adverseyaw

[Tim Jodice]

As it turns out I simply had the cowl flaps rigged flush with the cowl. Made it so there is a half an inch gap when the cowl flaps are closed.