Hot right rear cylinder in RV-8A Lycoming

[Wolf Aviation]

The number 3 cylinder head temp is always twenty to thirty degrees hotter than the nearest other cylinder, but a guy who has built two RV-8s tells me that the inlet is built correctly and that this is a common problem with the 8. Any suggestions on how to bring the temp in line with the others and to keep the temp below 400 without excessive fuel flow?
Thanks
jim

[Mike S]

Jim, welcome aboard the good ship VAF

There is a little trick of spacing out the rear baffle with a washer, has been discussed many times here-----------try doing a search.

The cylinder head has virtually zero depth of fins in one area, and the baffling so the air flow is not adequate-------see the link below.

http://www.vansairforce.com/communit...ad.php?t=93949

[rscooter]

Jim
I have the exact same thing. A friend and I both built our planes and have flown the 40 hours off. His is a 9A and mine is a 8A. We have fought off the hot #3 cylinder for so long I'm waiting to see what gives. Ours both have plenums, my engine is a Superior XPIO360 and slicks his is a Lycoming 0320 with duel electronic ignitions. My buddy modified the rear baffle around #3 and has dropped it he says by 15-20 degrees. His oil temp still goes up to 210 degrees. I on the other hand have been able to manage mine by flying at 115-120 knots climbing around 5-700 ft. My oil temps never gets above 185 even on a hot day like 98 degrees ground temp. I can manage all the temps at 55% power in the 325-370 degree range LOP. I have sealed all of my system to no avail. I have to big of a space to use the washer method but it would be nice to lower it down.
I flew my Citabria for years at 50degrees ROP CHT 425-430 and since no EFIS and no other sensors all was good. Book said to run engine that way.
I get jeallous about how all the others guys say that they have so low of cylinders, I can hit 430-450 on a steep climb at 2000-3000 ft a minute but try to keep it all lower than 400. Superior book says red line 500 with longest life 400-430 and at cruise setting best to run 300-400.

[Larco]

Originally Posted by Mike S

Jim, welcome aboard the good ship VAF

There is a little trick of spacing out the rear baffle with a washer, has been discussed many times here-----------try doing a search.

The cylinder head has virtually zero depth of fins in one area, and the baffling so the air flow is not adequate-------see the link below.

http://www.vansairforce.com/communit...ad.php?t=93949

The washer install on my 7 did the trick. About 25 degrees if I remember correctly. I was very surprised and very happy. Thanks to the input on this forum. Larry

[JohnInReno]

Originally Posted by LARCO

The washer install on my 7 did the trick. About 25 degrees if I remember correctly. I was very surprised and very happy. Thanks to the input on this forum. Larry

The washer helped on my 9A and I ended up fabricating an "L" shape from .125 stock to replace the washer. Temps on #1 are now the highest on climb but everything settles down in cruise.

[DanH]

A washer is quick. A bypass duct is arguably a little better.



I recently flew an unrelated experiment, which involved a climb to 15,000 feet while holding pitch at 125 knots true, all knobs forward. It's not best power mixture, or best rate speed, but since I recorded it, here are two lines from the datalog...liftoff and 15K later. Temperatures ain't too bad. Note this is an angle valve 390, so CHT will be lower and oil temp higher than a parallel valve.

[David-aviator]

Yes your airplane climbs well.
I cannot maintain that rate to 10,000.
FP vrs CS
180 vrs 200+
....makes a difference.

[BillL]

Note how far down the head DanH carries the increased gap. Nearly to the port line. That is very important as the fin depth is still increasing all the way down. The washer works somewhat, but is indiscriminate for directing air where it is needed.

[DanH]

Originally Posted by David-aviator

Yes your airplane climbs well.

Sorry, didn't mean to suggest a focus on climb rate. That's a given with more cubic inches and a CS prop, two things anybody can buy.

I do admit to pride in the cooling numbers, which are the product of considerable work. Here climb is at 2700 RPM, a more difficult case than the lower RPM of a fixed pitch. Specific to this thread, #3 is not warmer than the other cylinders. I wanted a system in line with Mr. V's "balanced performance" manta, one that worked as well at slower speeds as it does when going fast. A bit of additional ducting is a detail for #2 and #3, both of which have blocked fins with the standard kit baffle tin.

Good thread below. And note the Grumman baffles at post 29:

http://www.vansairforce.com/communit...d.php?t=113134

[DanH]

Just rattling around a hangar, and noticed this bypass duct, apparently OEM on this old Mooney. Much better than a washer spacing out the baffle, but I hope he has not been flying around with the scat hose off that heater feed.