Ralf wrote:

 

Dear subscribers,

 

A while back I reported a warmer cylinder 4 during climb at 32 MAP and 2500 rpm. Lynn recommended I could test high boost during climb and see if it makes a difference.

 

In the mean time I cranked up my fuel pump by approx. 1 GPH. At take-off I see now 42.5 GPH at 38.4 MAP 2680 rpm (on a TSIO550 B which is rated for 38 MAP at 41…43GPH according to my manual).

 

In climb under full rpm/MAP engine stays very nice and cool.

 

Climb 2500 rpm with 32MAP: all EGTs show the same, after increasing the fuel flow all CHTs stay generally a bit cooler but CHT 4 is still the one that runs a little warmer. During climb when CHT4 approached 380 I turned the high boost on – the CHT went down by approx. 10 degrees back into the 360’s. During the climb to 18000 I had the boost pump on 3 times for may be 2 min each time. The Fuel flow increased from 30.5 to 33 GPH. I climbed with +-170 kts at 1000 fpm.  This is new: usually I was never able to get the CHT down in climb unless I decreased the climb rate.

 

Question: is it a reasonable practice to use the high boost for engine cooling? How long can it run in high boost without getting damaged?

 

Craig reported earlier that he had his fuel pump modified to feed more fuel under partial power – this sounds complicated and expensive and if I don’t have to I would rather not go there.

 

Thanks for you input

 

 

 

Ralf,
You are still at the lower level of recommended WOT fuel flow for the big Continental. I have increased my WOT fuel flow to 44 GPH and the engine runs very cool all the way up. BTW, cylinder head temps of 380 are not worrisome; start being concerned/taking action at 400+. Still, keeping the engine cool lengthens its life.

 

It’s surprising how much cooling just a little extra fuel provides…and that’s what you are seeing. The boost pump used on the IV-P is rated for continuous operation at low or high boost, but again, it will wear out sooner if used a lot…and it’s quite expensive. Better to open the fuel flow a bit more and use the mixture control to moderate it…with one exception/note: It is possible to feed too much fuel to the engine, which will cause it to choke/stall (as opposed to flooding—a ground operation issue). You want to be sure the engine will take full throttle on takeoff without choking/loading up. With that caveat, the main problems with feeding it too much fuel are fouling the plugs over time, and the cost of extra fuel used. For my money, the extra gas is cheap insurance for the engine during climb; you can economize when you get the power back in cruise.

Hope this helps.

Bob