More high CHT's etc. Some test results

hlangebro · #1 08-22-2014, 07:07 PM

So, I have had high CHT's in climb since day 1 (410-425f). I was pondering about the fuel nozzle and wanted to check my egt's, fuel flow etc. So here are my test data from today. Cht's corrected for 100F day.

Engine is a O-320 D3G, 160hp, Whirlwind GA200, RV7A. Cowl flap.

On ground 1200rpm -60rpm increase from full rich to just before rough. Just about right.

Static; 2160rpm, 130hp, 81%, 12.8gal/hr. A little low for fuel flow...

Climb, cowl flap full open, full rich, 115kias:
cht: #1 393, #2 408, #3 391, #4 379
137hp, 85%, fuel flow 12.3gal/hr. Fuel flow seems low....

Cruise, 8500ft DA, WOT, full rich, cowl flap closed, no increase in rpm during leaning, 2730RPM, 77%, 124hp, fuel flow 13.2gal/hr
EGT's (from full rich to peak, delta F):
#1 88F, #2 96F, #3 127F, #4 151F

CHT (as indicated)
#1 352 #2 365 #3 354 #4 361

Conclusions....
Seems like it is running a bit lean, but not by much. I would say that an increase in fuel flow would definitely keep the cylinders cooler and I could potentially climb at a lower speed without hitting 400F. I'd like to stay below 380F.
I am pondering about re-jetting. One thing that I also need to double check is that the mixture lever actually opens fully. I have the James cowl with pressure plenum. I have sealed everything and checked for induction leaks, I have been modifying for about a year now, with some success, but I still haven't found the smoking gun... my guess is that the mixture is a bit too lean...

erikpmort · #2 08-22-2014, 07:35 PM

i almost did the jet drill. I had the carb off, ready to drill, and i was told not to by a guy on this forum and i also found more reading that said it isn't a good idea. But you know what? kinda thinking i should have. it has worked for others. Let us know your results if you do it. I started going full rich at take off instead of leaning to peak and then two turns rich- it helped a little but not sure. Again I was told to try to achieve 1250 egt and i can't get it that low.. my temps are pretty similar to yours except i have louvers not a cowl flap... cooler weather is almost here and i'm exhausted from fighting this problem this year. i've made good improvements but still not satisfied. good luck

DanBaier · #3 08-22-2014, 07:38 PM

I think that if, when you lean the mixture, you can get a 100 degree rise in EGT, you are not likely to be running too lean and I don't think I'd be inclined to re-jet. Also, the ground test at 1200 is likely still on the idle circuit and is probably not going to reveal much in terms of the jetting.

I think I'd look at #2 & #4 with an eye toward balancing the temps on climb - if you could get #2 down a little and #4 up (adjusting the dam at the front of #2), then the spread would be more uniform and the numbers don't look to be bad at all. You'd be at or just below 400 all the way around on a WOT climb.

I think if I could get the balance of those cylinders I'd declare victory.

Dan

Kyle Boatright · #4 08-22-2014, 07:47 PM

Quote:

Originally Posted by hlangebro

So, I have had high CHT's in climb since day 1 (410-425f). I was pondering about the fuel nozzle and wanted to check my egt's, fuel flow etc. So here are my test data from today. Cht's corrected for 100F day.

<snip>

Climb, cowl flap full open, full rich, 115kias:
cht: #1 393, #2 408, #3 391, #4 379

<snip>

CHT (as indicated)
#1 352 #2 365 #3 354 #4 361

<snip>

Your temperatures look fine to me. There is nothing wrong with cooler temperatures, but there is nothing wrong with where you are today.

hlangebro · #5 08-22-2014, 08:05 PM

I would like to be able to climb better, around 100kias, but there is no way I can do that without, in my opinion, running to hot on Cht's...
I've been trying to balance the temps, but some reason the left bank runs hotter...

ColoRv · #6 08-22-2014, 09:26 PM

Have you run the high MP, low MP test to assure you have no intake leaks?

Click Here

Toobuilder · #7 08-23-2014, 08:20 AM

Quote:

Originally Posted by hlangebro

....Climb, cowl flap full open, full rich, 115kias:
cht: #1 393, #2 408, #3 391, #4 379
137hp, 85%, fuel flow 12.3gal/hr. Fuel flow seems low....

Cruise, 8500ft DA, WOT, full rich, cowl flap closed, no increase in rpm during leaning, 2730RPM, 77%, 124hp, fuel flow 13.2gal/hr
EGT's (from full rich to peak, delta F):
#1 88F, #2 96F, #3 127F, #4 151F

CHT (as indicated)
#1 352 #2 365 #3 354 #4 361

... I have sealed everything and checked for induction leaks, I have been modifying for about a year now, with some success, but I still haven't found the smoking gun... my guess is that the mixture is a bit too lean...

Funny - I'm working cooling issues as well, but what you consider a "problem" is my "goal". Barely above 400 in the climb and mid 300's in cruise is the promised land for me... I don't think you have a problem at all. I'm not saying you should stop looking at the details- air cooled engines need a lot more attention to detail for localized airflow management, but as a gross figure you're in great shape.

hlangebro · #8 08-24-2014, 01:47 PM

Did another test today. I heard from Sam James that wrapping the inlet tubes with exhaust wrapping would cool the inlet air and thus lower CHT's. Don't think it did anything...
This time I climbed out at 110kias, so 5 kias slower than before. Temps compensated for a 100F day:

#1 403, #2 411, #3 399, #4 385

Ok I guess, but not great.

I also did the induction test. EGT deltas:

#1 38, #2 44, #3 50, #4 111

What does this really tell me? cyl 1-3 are reasonably close, but #4 is way more... Seems like 1-3 are running lean and #4 is rich...? Would this mean I have induction leaks on 1-3?

ColoRv · #9 08-24-2014, 02:38 PM

You can't diagnose induction leaks by doing a climb test versus temps. Run the test I linked earlier.

Also, what does 'Temps compensated for a 100F day' mean? Are you saying the temps listed are not your actual temps? 100F at what altitude?

hlangebro · #10 08-24-2014, 03:22 PM

Let me clarify.

Climb temps are compensated by the OAT and 100f delta, as it should be done. So, actual temps were lower since it was not a 100F day. The temps stabilize fairly quickly, so I would say about 1500ft or so. You should always normalize the cht temps to 100F.

As far as the induction leak test. I was a 8500ft DA and noted the full rich EGT, WOT. I then pulled back 10" and noted the EGT temps. Deltas as shown.