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07-09-2015, 04:43 PM
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Join Date: Sep 2006
Location: Locust Grove, GA
Posts: 97
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One approach to lower CHTs
Ever since first flight, I've been struggling with high CHTs on my back two cylinders (#5 & #6). With WOT and full rich, I'd see #6 climb through 400 degrees pretty quick if it was any hotter than 65 OAT. By the time I would notice, and react, it'd usually make it to 405-410 range. Usually, I'd pull the throttle back to about 23" or so, sometimes lower.
The first thing I found that helped was the washer behind the back cylinders (between the baffle and the cylinder). That helped, but only by slowing down the progression to 400+ during climb out. It also helped in cruise.
Last week, I went to Spartanburg to visit AirFlow Performance for injector tuning. After the first flight with Don, the analysis showed that #3 & #4 were running rich and #5 & #6 were lean.
Cue to me smacking my head and wishing I had a V8 (the drink, not the engine). Why didn't I make that connection before? Anyway, Don makes some injector adjustments and we go fly again, climbing up to 8500'. I was able to leave it WOT all the way up, and even was able to start leaning a bit in the climb too, and never did I get close to 400CHT.
After one last injector adjustment (#1 was showing slightly rich), I left for home. Oh boy, what a difference. Again, WOT climb out to 8000' (OAT on the ground was 84F). Highest CHT observed was 387! This is easily 20 degrees cooler than the previous setup.
This may or may not be a solution for everyone, but wanted to throw it out there as another potential solution for high CHTs. Don at Airflow Performance was fantastic to deal with and has a wealth of knowledge he's very willing to share. Well worth the trip up there to have this done.
Oh, for the record, my engine is a stock IO-540 from Van's with two mags and Silverhawk throttle body.
__________________
Aaron Sims
RV-10 (2015 Bronze Lindy)
RV-6A (sold)
Home Field: Mallards Landing (GA04)
Locust Grove, GA
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07-09-2015, 08:17 PM
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Join Date: Aug 2006
Location: Taylor Texas
Posts: 811
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Yay!
Atta boy, Aaron!
Carry on!
Mark
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07-10-2015, 03:36 AM
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Join Date: Jan 2005
Location: Tampa, FL
Posts: 2,861
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Aaron,
What kind of tests did you and Don run - something like the Gami lean test? Also what size injectors did you start with on 5 & 6 and what did you end up with?
I'm having basically the same issues you had and plan to run the Gami test this weekend to gather some data, but any other suggestions would be greatly appreciated.
__________________
Todd "I drink and know things" Stovall
PP ASEL-IA
RV-10 N728TT - Flying!
WAR EAGLE!
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07-10-2015, 05:05 AM
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Join Date: Sep 2006
Location: Locust Grove, GA
Posts: 97
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Yes, it was the GAMI lean test. My engine came with stock .028 injectors. When I got there, Don swapped them all out with .025 injectors and we went flying to do the lean tests. The tests were done at 3500' and 8500' and at different MP settings. I think we wound up going to .0245 on 1, 5 & 6, and .0255 on 3 & 4 when we were all done.
As close to South Carolina as you are, I'd really consider just taking your plane down to Spartanburg and have Don work his magic. That way, you're done in just one day. It's $450, and that includes the injectors.
__________________
Aaron Sims
RV-10 (2015 Bronze Lindy)
RV-6A (sold)
Home Field: Mallards Landing (GA04)
Locust Grove, GA
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07-10-2015, 05:14 AM
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Join Date: Jan 2005
Location: Tampa, FL
Posts: 2,861
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Thanks for the advice Aaron!
__________________
Todd "I drink and know things" Stovall
PP ASEL-IA
RV-10 N728TT - Flying!
WAR EAGLE!
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07-10-2015, 05:31 AM
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Join Date: Jul 2007
Location: Keller, TX
Posts: 1,553
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Looking for cause and effect
Quote:
Originally Posted by GTWreck
(from earlier post) After the first flight with Don, the analysis showed that #3 & #4 were running rich and #5 & #6 were lean? (from second post) ?My engine came with stock .028 injectors. When I got there, Don swapped them all out with .025 injectors ? I think we wound up going to .0245 on 1, 5 & 6, and .0255 on 3 & 4 when we were all done. ..
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This is a counterintuitive. The two cylinders that were lean are two of the three with the smallest injectors and the two that were rich now have the largest.
#2 .0250 #1 .0245
#4 .0255 #3 .0255
#6 .0245 #5 .0245
I?m not any kind of expert on fuel injection. I just automatically look for cause and effect and I expected either that #5 and #6 injectors would have gotten bigger or that the injectors for one or more of the other cylinders would have gotten smaller so they would be less rich and more fuel would be driven to #5 and #6.
Maybe I don?t understand how injectors are numbered. Are the numbers (.0250, .0255 etc.) the orifice size or the flow rate at some standard conditions?
__________________
RV-8 180 hp IO-360 N247TD with 10" SkyView!
VAF Donations Made 8/2019 and 12/2019
"Cum omni alio deficiente, ludere mortuis."
(When all else fails, play dead.)
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07-10-2015, 06:50 AM
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Join Date: Jun 2006
Posts: 316
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Nozzle set
On this installation the injector sizes ended up .0245 on cylinder 1, 3, & 4. .025 on cylinder 2 and .0255 on 5 & 6. That got the total spread to within 0.1 GPH or so. Couldn't really tell with the flow meter mounted in the tunnel the fuel flow readings were not really stable. Used the "bump" method on the vernier control.
Just as a caution. This set probably won't work on a different plane. We find they are all different. And a lot depends on the mission the plane is used for.
Don
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07-10-2015, 06:57 AM
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Join Date: Jan 2005
Location: Tampa, FL
Posts: 2,861
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Don,
Can you elaborate as to how a lower nozzle number (.028 to .0255) led to lower CHT's on #5 & 6 for Aaron?
__________________
Todd "I drink and know things" Stovall
PP ASEL-IA
RV-10 N728TT - Flying!
WAR EAGLE!
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07-10-2015, 07:27 AM
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Join Date: Sep 2006
Location: Locust Grove, GA
Posts: 97
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Quote:
Originally Posted by Bubblehead
This is a counterintuitive. The two cylinders that were lean are two of the three with the smallest injectors and the two that were rich now have the largest.
#2 .0250 #1 .0245
#4 .0255 #3 .0255
#6 .0245 #5 .0245
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Yep, my bad. I was going from memory, which isn't what it used to be. Don's post has the right numbers.
__________________
Aaron Sims
RV-10 (2015 Bronze Lindy)
RV-6A (sold)
Home Field: Mallards Landing (GA04)
Locust Grove, GA
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07-10-2015, 07:46 AM
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Join Date: Dec 2014
Location: Just Minutes from KBVI!
Posts: 1,039
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Quote:
Originally Posted by Auburntsts
Don,
Can you elaborate as to how a lower nozzle number (.028 to .0255) led to lower CHT's on #5 & 6 for Aaron?
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No expert here, but I i would think that it was a balancing act. The absolute orifice sizes would be less important than the relative change in size between the richer and leaner cylinders while maintaining total flow at a constant pressure drop.
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