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Increased cooling by blocking front two cylinders

Ed_Wischmeyer

Well Known Member
Thought I had the RV-9A cooling tolerable, but yesterday cylinder #3 ran way hot for no apparent reason.

On Saturday, I saw an RV-7 under construction with relatively small pieces of aluminum to block airflow directly into the #1 and #2 cylinders, more or less where the head and the barrel meet.

How well do those actually work? I kind of understand the theory...
 
it forces the air up and around instead of through that barrel. it will lower the temp of the back cyls but will raise the temp of the front cyls. #1 normally runs colder than the others so the dam raises that cyls temp and helps lower #3 which is normally the hottest running cyl.


by playing with the size of the dam you can balance the cyl temps pretty well.



bob burns
rv-4 N82RB
 
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Foil tape works too - simple approach to test different sizes at least, before doing anything permanent.
 
Foil tape works too - simple approach to test different sizes at least, before doing anything permanent.

Good idea, I will try that. I have made removable ones and now need to trim to right size. Your idea will save me the time of removing top cowl.
 
Don?t forget that adding a washer between the rear baffle and # 3 cylinder at the # 8 screw attachment is a huge help. This allows air to flow down behind #3 cylinder where as stock it has no path. This has been discussed many times on this site and it works. A .032 washer lowered my #3 cylinder 20+ degrees if memory serves me correctly.

As suggested already install some tape 1inch wide to start on the front cylinders and see what happens to the temps. Adjust until the front and rear are the same, then if you want replace with metal.

Put the space between the #3 cyl and baffle first, It maybe all you need to do??

Larry
 
It's funny how things from vary from engine to engine and geographic location.

My hottest cylinders have always been 1&2 and over time, I've been cutting down the air dams. I've ALMOST got it where it needs to be but it's a little difficult in the upper midwest where the flying temperatures can vary by as much as 100 degrees over the course of the year.
 
My CHT balance on #1 and #3 is pretty good. I cut down the air dam about 1/2". The balance on #2 and #4 is still +20 degrees with #2 being the hottest and #4 being the coolest. I've cut down the air dam on #2 even more and it really hasn't done much. Both of the front cylinders (#1 and #2) are the hotter ones, even with all of that cool air hitting them first. It would be nice to have some better way to direct that air down through the front cylinders rather than up and over.
 
A strip of adhesive backed foil ('Speedtape') works well as a temporary dam whilst you are working out how high to make the dams. In fact so well, some years later, it is still there, just punctured by a few flies :eek:
 
Found more to the story today. Three cylinders had massive leaks due to failed intake manifold gaskets - the other cylinder had a new gasket. High EGTs don't help the CHTs. Along with redoing the panel, we're doing so much work that we're going to go ahead and annual the plane.
 
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