How to raise cylinder temps ?

I finally got all 4 cylinders about the same using foil tape. They run only in the high 200?s. Pmag timing is dead on, set at TDC. If I understand Dan H and others, my next task is to restrict cowl exit flow to raise it to 350F for good engine performance.

I would appreciate suggestions on how to restrict cowl exit flow for experimentation. For example foam and gorilla tape, aluminum taped to the inside of the cowl bottom, or ?

Once defined, I can fab a glass or carbon insert for permanent attachment.

Larry DeCamp said:

I finally got all 4 cylinders about the same using foil tape. They run only in the high 200’s. Pmag timing is dead on, set at TDC. If I understand Dan H and others, my next task is to restrict cowl exit flow to raise it to 350F for good engine performance.

I would appreciate suggestions on how to restrict cowl exit flow for experimentation. For example foam and gorilla tape, aluminum taped to the inside of the cowl bottom, or ?

Once defined, I can fab a glass or carbon insert for permanent attachment.

Click to expand...

Well done.

An insert is a poor choice, as it does not change frontal area, and the no-flow area behind it will have a low pressure wake, a miniature of the one you feel when driving close behind a big box trailer on the interstate. I suppose it would work for determining the necessary exit area for a more permanent change later. The CHT change should be accurate, but you won't see an airspeed performance difference.

Lots of builders have either removed the entire exit "coal shovel" from the bottom of the cowl and formed a new one, or sectioned out some of the sidewalls, raising the belly panel.

To work iteratively, I removed the entire coal shovel and built three exit panels I could swap via screw attachment. Flying them in various conditions
really helped tailor the final, fourth panel, which included an additional variable exit. The key was zeroing in on the exit area necessary to balance open vs closed around Standard Day temperature, 59F. At 65%, best power mixture, and OAT of 59F and above, the additional exit area is always open. At 50F and below, it is closed. If running LOP, the range shifts due to cooler CHTs.

Of course it is always open at full power.

I really like having a tool to control temps across a wide range of OATs.

See post #1, and post #145: http://www.vansairforce.com/community/showthread.php?t=68241&highlight=shrinking+exit

Larry DeCamp said:

I finally got all 4 cylinders about the same using foil tape. They run only in the high 200?s. Pmag timing is dead on, set at TDC. If I understand Dan H and others, my next task is to restrict cowl exit flow to raise it to 350F for good engine performance.

I would appreciate suggestions on how to restrict cowl exit flow for experimentation. For example foam and gorilla tape, aluminum taped to the inside of the cowl bottom, or ?

Once defined, I can fab a glass or carbon insert for permanent attachment.

Click to expand...

Can you give us some details or references on the use of foil tape?

Foil tape

There are many references on VAF where I learned the process. Foil tape from a big box , with release paper backing. I just covered the finned head (#1&#2) to varying heights til the left and right are about the same. Oddly enough, the original aluminum angle (per baffle plans) for #2/#4 side is fine with no tape.
Just a side note, I delayed restricting the #1/#3 side for 200 hours because #1 was 80degree low and didn't trust the CHT. Finally found the problem in a poor solder joint at the TC/extension wire junction. A crimp splice solved the problem.