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2&4 ported polished flowed, 1&3 not, huh?

C

CATPart

Well Known Member
Looking at a logbook and saw some history that made me curious. This is a high performance 360 lycoming that was overhauled with the log entry "heads ported, polished, and flowed". many years later the log says "removed and replaced #1 & #3 , installed complete assemblies". Now looking at the engine it is readily visible that the barrels/heads on the LHS look old while those on the RHS look newer (better paint, less corrosion). This leads me to believe that the LHS has the porting and polishing while the RHS does not.

Now this makes me wonder if this is a bad thing. I think about uneven power distribution, or power pulses, just a theory. I wonder if there are rules of thumb out there among you high performance folks about such a situation?
 
I've always been of the school of thought that port/polish/flow match/whatever can't really do all that much on a big bore / short stroke engine that never turns faster than 2700 rpms. Am I wrong ?
 
Neal@F14 said:
I've always been of the school of thought that port/polish/flow match/whatever can't really do all that much on a big bore / short stroke engine that never turns faster than 2700 rpms. Am I wrong ?
Click to expand...

Engines are simply air pumps. The easier you make it for the air to get in and out, the more efficient they operate (and produce more power).

When you talk to the different engine builders they pretty much all will tell you that it is easy to get an (I)O-360 parallel valve engine to produce over 200 HP. Of course, high compression pistons helps.

The one thing I have never heard anyone do with aviation engines is port match the intake and exhaust tubes. I would very much like to hear from someone who has done this.
 
Check EGT peak spread?

I had a flow divider with uneven flows to two cylinders. This was causing rough idle and vibration. After the flow divider was adjusted, not only did I idle better but cruise was much smoother.


I would assume having two cylinders with less flow would do the same thing though to what extent I do not know. Have you done a leaning test to see if those two cylinders peak much differently from the other two? While imperfect, a match up between the peak EGT points and their relative values may tell you the story.
 
JD your comments reflect my suspicions. I would assume the heads with polish are getting the air a bit easier, thus running a different mixture compared to the other 2. I agree this should show up in the EGTs, but, we don't have access to that anymore. I was just helping a friend decipher a logbook for a possible purchase, but the airplane sold already.
 
Not to hijack your thread but I assume from your screen name (CATPart) you spend a lot of your work day driving CATIA? ;)
 
ha! I always wonder how may people think I have a strange thing for cats. Yes I have been a V4 V5 catia driver for many many years. Yourself?
 
Neal@F14 said:
I've always been of the school of thought that port/polish/flow match/whatever can't really do all that much on a big bore / short stroke engine that never turns faster than 2700 rpms. Am I wrong ?
Click to expand...

Ly-Con dynos from 4-6 HP per cylinder. Is that much? ;)
 
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