Ralf,

 

If you think the high CHT is being caused by lean mixture at 32” MP with the mixture full rich, try this; turn on the high boost fuel pump. This will normally increase the fuel flow by 4 to 5 GPH. If this keeps your #4 CHT down your have validated your suspicion.

 

If you have GAMI injectors you can try replacing the current injector with one that allows more fuel to that cylinder.   

 

Turning on the high boost for a temporary condition it an inexpensive remedy. 

 

Just a thought.

 

Lynn      

 

 

Ralf,

 

I had the exact same situation on my IV-P.  At full power (2700 rpm; 38 inHg; 43 gph) my engine ran nice and cool.  At all LOP conditions, my engine ran nice and cool.  I define nice and cool as below 380 degF.  At full rich and 65% to 95% power, my engine ran hot because it was “too lean” at full rich.  I went out and fuel mapped my engine from 2200 rpm to 2700 rpm and 22 inHg to 38 inHg. I didn’t fill in all the boxes but most of them.  I did not run high MAP at the lower rpm’s.  When I plotted out the data, using my best estimate for power at each setting, my suspicion was confirmed.  The fuel system was running about 3-4 gph lean at the reduced power settings when full rich.  The solution was a bit radical.  I worked with Dave Dewell at Great Planes Fuel Metering and he modified my fuel cam to fix the problem.  In the process, we correlated my flight data to his test stand data.  This process is not for the weak of heart but my engine now runs cool at all power settings.

 

Dave Dewell

Great Planes Fuel Metering

ddgpfm@tulsacoxmail.com

918 695 4356

 

Craig Berland

N7VG

 

 

Dear subscribers,

 

Since we are talking about hot cylinders I got one question that bothers me:

I have a plenum and I tried to do a very anal job in sealing all the leaks around the engine – I followed Fred Moreno’s instructions there.

I have different temperature patterns amongst the cylinders for different situations.

LOP cruise: #2 is the warmest and is usually between 330 and 370 depending on altitude, humidity, fuel flow etc. – always very cool no issue at all

Climb 32” MAP, 2500 1/min, full rich : cylinder 4 wants to get warm and I keep the airspeed around 180 in order to stay below 400F. This is the situation I am not really happy about – if I don’t pay attention on a warm day the #4 will get above 400F

Climb 2500 1/min, full rich, full throttle: even temperature profile amongst the cylinders. Engine runs generally cooler and airplane climbs faster.

 

I tried to watch the EGTs and see if #4 is running lean but I could not tell a difference in the EGT. #4 has the dip stick pipe and more hoses that could influence airflow.

 

Any idea why #4 is warmer at 32”?

 

Thanks for your help

 

Ralf