Cylinder Head Temp Variation
Posted: Tue Jan 12, 2016 11:30 am
by Craig Hoskins
I have been working on reducing the cylinder head temperature right to left variation. Have made lots of changes to cooling air flow and improving mixture distribution to all cylinders, but not achieved reducing the right to left spread. The right side runs around 25-30 deg F hotter during normal cruise (23.0 in manifold pressured and 3150 rpm).
I was wondering what others are getting for temperature spread left to right in their Aervee or VW engines at cruise power?
Happy flying,
Craig Hoskins
Sonex 1537, Tri Gear, 85 hrs
GPAS 2276cc VW, Rotec TBI, Prince P-tip
Re: Cylinder Head Temp Variation
Posted: Tue Jan 12, 2016 12:40 pm
by gammaxy
My right cylinders are typically 10-15 degrees warmer than my back left one in cruise. The spread is significantly greater during climb. I think at higher angles of attack the direction of the propeller spin allows the left cylinders to cool better.
My front left cylinder’s CHT is typically ~30 degrees cooler than the back left one. Its EGT is also significantly cooler than the rest, so I think it is running richer than the rest of the cylinders. At least one other builder has mentioned that cylinder being significantly cooler than the rest on his Aerovee also. I’ve been curious if there is something about the intake design that causes this cylinder to run richer than the rest. It’s mostly a curiosity, since I don’t think it’s reducing power by a noticeable amount.
Re: Cylinder Head Temp Variation
Posted: Tue Jan 12, 2016 8:00 pm
by MichaelFarley56
Hi Craig,
I hate to ask you, but are you sure you have the CHT probes connected properly? The only reason I ask is that it’s very common for VW’s to have the front two cylinders run 30ish degrees cooler than the back two cylinders.
Otherwise balancing left and right cylinders can be challenging sometimes. The Y pipe intake system can make things difficult to tune. As options, you can check the cowling air inlets to make sure the right side is opened up enough, or you may be able to twist the TBI to make the right cylinders run a little richer.
Of course if the engine is running well and all temperatures are “in the green”, you could also just fly and have fun! 
Re: Cylinder Head Temp Variation
Posted: Tue Jan 12, 2016 9:19 pm
by mike.smith
My #1 cylinder (left rear) is always about 30 deg hotter than the #2, and the EGT is also always hotter. If it were simply an air cooling issue then the EGT would be similar to the other cylinders. After spending a lot of time working on my AV, and rebuilding once, I’m personally absolutely convinced that it’s the fault of the intake system. It’s very simple and just sends a leaner mixture to the rear cylinder and a richer mixture to the front. That goes for both sides of the engine. But my hot cylinder (#1) is usually cruising at 350-360 F, so it’s generally not an issue except on climb out on a warm day. I can control the EGT with the mixture.
Unless you’re running fuel injection with GAMI injectors you are going to have a hard time tuning cylinders to match. You’ll often just be chasing your tail. As long as the temps are all in the green, I don’t see the need to worry about a whole lot about getting them to match. If they are not running in the green, or running close to the red, then that is something else.
I sometimes fantasize about having a second complete engine, and making all kinds of changes and tests on a test stand, then swapping out engines, where I can do it all over again to the second engine. That would be the ultimate way to test changes to the intake and the engine. Maybe when I win the lottery!
Re: Cylinder Head Temp Variation
Posted: Tue Jan 12, 2016 9:32 pm
by MichaelFarley56
mike.smith wrote:Unless you’re running fuel injection with GAMI injectors you are going to have a hard time tuning cylinders to match.
You’re absolutely right Mike, although there is one more option that really balances EGT and CHTs; add the turbo! Adding forced induction virtually eliminates any intake system limitations and I normally see my CHT spread within 5 degrees and EGT spread within 10-15 degrees between all 4 cylinders.
And I like your lottery idea!
Re: Cylinder Head Temp Variation
Posted: Wed Jan 13, 2016 1:24 am
by mike.smith
MichaelFarley56 wrote:
mike.smith wrote:Unless you’re running fuel injection with GAMI injectors you are going to have a hard time tuning cylinders to match.
You’re absolutely right Mike, although there is one more option that really balances EGT and CHTs; add the turbo! Adding forced induction virtually eliminates any intake system limitations and I normally see my CHT spread within 5 degrees and EGT spread within 10-15 degrees between all 4 cylinders.
And I like your lottery idea!
I like your turbo
Re: Cylinder Head Temp Variation
Posted: Wed Jan 13, 2016 1:41 am
by nwyooper
My CHT’s have been pretty consistent. Just looked at a screen shot of my Dynon
OAT 73 deg F- 3060 rpms @3800 ft msl
#1-325 F
#2-316 F
#3-328. F
#4-326. F
EGT’s 1351 to 1369 F
One of my biggest problems has been factory defective spark plugs-one Autolite so I replaced all with NGKs and then I had one bad NGK. The bad NGK had broken porcelain on the electrode so it was not firing at the gap like it should but arcing down inside. Only saw that when plug was put in tester with air pressure. Valve adjustment is crucial too.
Non turbo AeroVee with Rotech MKII TBI
Loren
Onex33
N331EX
Re: Cylinder Head Temp Variation
Posted: Wed Jan 13, 2016 3:10 pm
by Craig Hoskins
Thanks for the great feedback. I have been thinking my cylinder temperature variation is a lot to do with uniform mixture, than cooling. After lots of changs to try to improve mixture balance to all cylinders using the standard “Y” and 1:2 cylinder intake manifolds, I decided to try a major change to more uniformly deliver fuel and air to each cylinder. I built a distribution manifold to blend the “Y” manifold flows to a common point, then have an equal distance to each cylinder. I have only had one test flight and did not get the changed I had hoped. Front to back CHT’s are within 2 and 9 deg F, but the right side still averages 25 deg F hotter. I need to do some more test flights looking at ram air vs carb heat, ROP leaned vs. LOP and test at higher altitude. Won’t get to flying again till March, but if I get any interesting results I will share them.
Happy flying,
Craig Hoskins
Sonex 1537, Tri Gear, 85 hrs
GPAS 2276cc VW, Rotec 34-2 TBI, Prince P-tip
Re: Cylinder Head Temp Variation
Posted: Wed Jan 13, 2016 4:10 pm
by gammaxy
That’s a pretty neat experiment. I guess there’s a chance that the heads are still more directly connected to the same side of the Y manifold as before. If you could somehow swap it so the heads get air from opposite ends of the Y, it would be pretty interesting.
What is the orientation of the spray bar in your Rotec relative to the Y? Any chance it deflects fuel to one side?
MichaelFarley56 wrote:You’re absolutely right Mike, although there is one more option that really balances EGT and CHTs; add the turbo! Adding forced induction virtually eliminates any intake system limitations and I normally see my CHT spread within 5 degrees and EGT spread within 10-15 degrees between all 4 cylinders.
Mike, do you see increased spread when in a climb/higher angles of attack? I’ve been assuming slip stream from the propeller causes one side to run warmer than the other, but it would be interesting if this is not the case with the turbo.
Re: Cylinder Head Temp Variation
Posted: Wed Jan 13, 2016 4:36 pm
by SonexN76ET
I am not sure you can make a fair comparison with the turbo on CHT’s. I believe the turbo set up with the dual oil pump pumps additional oil to the heads which is greatly responsible for the cooler CHT’s.
Jake
Re: Cylinder Head Temp Variation
Posted: Wed Jan 13, 2016 6:08 pm
by Craig Hoskins
Chris,
My Rotec TBI is installed the spray bar to the left. This could be the root cause of the left more rich and cooler, and the right more lean and hotter. When I run cowl air or carb heat, I also get the EGT’s hotter on the right side along with higher CHT’s. One test variation in my new distribution manifold setup will be to block the right supply side and record the performance, then block the left side and compare.
I’m also running a air flow straightener between the air filter and the Rotec TBI. It is made from 3/16-in hex cell by 3/4-in thick and made from aluminum. Rotec makes a big deal about straight flow air into the TBI to make sure the sensor works properly. I have seen several others have done the same thing.
Happy flying,
Craig Hoskins
Sonex 1537, Tri Gear, 85 hrs
GPAS 2276cc VW, Rotec 34-2 TBI, Prince P-tip
Re: Cylinder Head Temp Variation
Posted: Wed Jan 13, 2016 6:21 pm
by WaiexN143NM
Hi All,
Don’t know if it will help , but on our jab 3300 waiex we are using a stainless flow straightener from aircraft spruce ($100) , was designed for Ellison Tbi , but we are using on our rotec tbi , works great, very even cht/egt’s.
WaiexN143NM
Michael Radtke
Re: Cylinder Head Temp Variation
Posted: Wed Jan 13, 2016 7:35 pm
by Johns
Hi Guys, I purchased my plane from someone who was a auto mechanic and he had the same problem of the two front cylinders being cooler than the rear two. He also thought it was a fuel mixing problem. To quote the log book “I suspect due to the air pipes going 2 into one that the momentum of pulsing fuel in the intake rams against the end of the manifold and a lot of extra fuel bounces from that end into the front cylinder.”
So what he did was to use the stock VW metal intake gasket and cut out the center between the ports and that equalized the fuel problem.
Hope this helps, it is inexpensive if you want to try it.
John
Re: Cylinder Head Temp Variation
Posted: Thu Jan 14, 2016 12:35 am
by tom0nex74
Been flying 0nex0074 for 130 hrs with usual cylinder temp problems,went to 2.5 needle in Aeroinjector, richened mixture, opened lower cowl,etc. I have found that, in my particular aircraft that minimizing prop loading keeps temps at an acceptable level.I let the speed and rpms build on climb out 3200 rpms 95 mph 400fpm keeps my cylinder temps below 350 and egt in the low 1200’s. I cruise climb at 110 mph from there letting the rpms build slowly. It seems to be a low torque system, steep turns load the prop quickly, decreasing rpms and added back pressure deceases airspeed quickly. Any increase in temps disappear on return to level flight. Should have built it lighter and cleaner, I reckon. At 5000 ft 3350 rpms I get the advertised 150mph true. The engine and prop seem smooth and temps are at an acceptable range.
nwyooper…How do you like the TB MarkII? Improved performance? The mixture system seem more precise than the Aeroinjector system.
Happy and safe flying boys…Tom Ryan 0nex 0074
Re: Cylinder Head Temp Variation
Posted: Thu Jan 14, 2016 1:19 am
by nwyooper
Hi Tom,
The Mark II is great-I had issues with the Mark I and Rotec replaced it which I thought was great. I am at sea level and never run full rich except on startup and then I go to full lean while warming up and taxiing(Check list item on run up to richen mixture and fuel pump on). It idles better than the AeroInjector my hangar mate has on his Onex. No airflow straighteners and I am running 92 octane non-ethanol mogas. BTW we have 3 planes(two Onex’s and a RV4) in one hangar-advantage Onex’s and they fly great!! Also I have gotten 150 mph TAS at about the same rpm and altitude as you state.
Loren
Onex33