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>> soon as throttle pushed in, cyl's 5 and 6 climb at about 1 degree per second - power always retarded not to exceed 390 and cool down in the 350-360 range before trying to push up power again.<<

Bob,

When I read that statement - - I stopped what I was doing (preparing a presentation for the ASTM in connection with the approval of the G100UL™ avgas ) - -

In order to follow up.

THIS IS IMPORTANT: There are VERY FEW THINGS IN AN AIRCRAFT PISTON ENGINE THAT CAN CAUSE AN OPERATING CYLINDER CHT TO SUDDENLY BEGIN TO INCREASE AT A RATE OF 1 DEGREE / SECOND ( 360 TO 390 IN 30 SECONDS, FOR EXAMPLE ) - - - except:

1) Outright pre-ignition; or,

2) Simulated outright-pre-ignition due to improperly advanced timing.

MERE DETONATION - - EVEN MEDIUM TO HEAVY DETONATION - - will not do that.

Amazingly, if you have caught and limited the CHT rise and managed that at levels under about 420 dF, as you appear to have done - - then you have likely NOT done any harm to the cylinders. But a borescope is in order. And change the spark plugs in those two cylinders. The plugs can be damaged from those kinds of combustion events.

I have a lot of old and a lot of more recent data that documents all of the statements made, above.

If you will forward to me the engine data downloads from those flights I will try to take a look at them and I can tell you what was going on.

Call me if you want to. I might have some suggestions for you to allow you to proceed to get your aircraft flying again comfortably. However - - getting me the engine download data is the most important thing you can do.

Regards, George

George W. Braly

Head of Engineering

GAMI

gwbraly@gami.com

toll-free: 888-359-4264

ph: 580-436-4833 x1009

cell:580-421-5645

fx: 580-436-6622

www.gami.com

On Jun 20, 2012, at 7:15 PM, Bob Rickard wrote:

IV-P non turbine Fellow Pilots:

First flight - one pattern only - Max MAP was set too low, low fuel flow - fixed.

Next flight - 10 minutes - Cylinders 5 and 6 temps run away hot at 38.5 MAP and 45gph. Must retard throttle to less than 25gph (25ish MAP) to keep under control.

Third flight - after checking baffling for hours and scratching head - same deal. Fly for 1 hour full rich at low power settings. Motor very smooth and happy at low settings, but as soon as throttle pushed in, cyl's 5 and 6 climb at about 1 degree per second - power always retarded not to exceed 390 and cool down in the 350-360 range before trying to push up power again.

Fourth flight - today - a 2.3. Takeoff WOT and full rich. Can't get above 3000' agl before having to pull power for cal 5 and 6. Pull power to 25gph/25 MAP/Full rich and slowly climb to 10.5k MSL. Fly there for a while, cylinders all look great in the 340-350 range. After an hour, try full power climb, have to stop within 1500' of climb. So then I leveled out, and set my typical speed cruise LOP mode to try something different - 34MAP, 2500 RPM, 18-19 gph. Motor is very happy. All EGT's normal (actually less than previous engine by almost 100 deg), CHT's all between 340-365. I climb with this setting to 16.5 and cruise for another hour, no problem. Return to base, set full rich/2700 rpm, and land normally. At retarded power settings in the pattern, motor stays cool and happy.

So what to look at? New motor mounts make the engine sit noticeably lower in the cowl, and we are checking the rear baffling to make sure there is a good seal, but would that affect the front 2 cylinders (5 and 6)? Every other indication (including the other 4 cylinder temps) are totally normal. Any other suggestions out there to look for?

Appreciate your experience

Bob Rickard