Cylinder Head Temp Variation

[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

[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.

[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! :)

[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!

[MichaelFarley56]

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!

[mike.smith]

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 :-)

[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

[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

[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?

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.

[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