Colyn,
Thank you for your input. I will turn up my fuel flow some more…
The temperature spread became smaller since I cranked up the fuel flow and used the boost pump (but maybe I just did not allow the temp spread to get bigger by using the boost pump).
My EGT from 1 to 4 are almost identical – only 5 and 6 are slightly lower.
I built a plenum for engine cooling and tried to do an anal job in following Fred Moreno’s guidelines. The only thing different about CHT 4 is that there is a lot installation congestion on top (3 hoses from the front to the back, the dip stick and spark plug cables). The bottom air guides look fine too.
When we did the annual inspection we paid special attention to the #4 injector – nothing there.
I cannot come up with an explanation why #4 is warmer with 32 MAP. Especially since LOP #1 and #2 are the warmest and with 38 MAP 2700 rpm the temp spread goes away.
Ralf
From: Colyn Case [mailto:colyncase@earthlink.net]
Sent: Saturday, May 26, 2012 3:35 PM
To: lml@lancaironline.net
Subject: Re: [LML] boost pump for engine cooling 4P
Ralf,
I actually have my fuel set at 45gph @2750/38. That is the extreme high end of the range.
..so one angle might be to add another 1.5 gph or so to your fuel flow.
However, from everything else you are saying, it seems like you would want to find out what is going on with cylinder #4.
Do you have the airguides that hold the flow through the fins until the very bottom of the cylinder?
Is that cylinder slightly leaner than the others?
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.