A question about CHTs in a new RV-7

[Tango Mike]

I'm a non-builder who has owned three RVs and still has an RV-4 and -6, and I need some perspective on an engine issue. Here are the particulars:

1. RV-7 with factory new IO-360, dual P-mag ignition with 30 hours total time airframe and engine.

2. During one-hour flight at various altitudes up to 7500? including climbs and descents, front cylinders consistently indicated about 20+ degrees higher CHTs than the rear, 400-plus versus 380-plus.

3. Attempts to lean to peak EGT resulted in CHTs too high for my personal comfort based on Lycoming?s recommendation to use 400 as the max during economy cruise and 425 for high-perfomance cruise. In addition, I?ve read and always followed the guideline that says, ?For extended service life, limit CHTs to at or below 400 degrees.? Seems like a good idea, as does not riding the limit in continuous operation.

4. My 13 and 7 years? experience with the RV-4 and -6, respectively, and their IO-360s, both with about 580 hrs SMOH and dual Electroair ignitions, has never encountered CHTs anywhere near 400 degrees at cruise. I typically see mid-300s. I appreciate the potential for various engine analyzers to measure engine temperatures differently, but it seems reasonable to expect that a new system using the Garmin G3X?s engine displays in the RV-7 would be more accurate than my old VM-1000 in the RV-4 and the EI in the -6.

5. This raises some questions. Why the difference between the front and rear CHTs? Why is the overall CHT range higher in the RV-7? Is it because it's still using mineral oil, and that new and newly-overhauled engines run hotter at first? The P-Mag folks say that relative to magnetos, their system will result in higher CHTs and lower EGTs because the hotter/longer duration spark burns more fuel in the cylinders and puts less unburned/still burning fuel into the exhaust. That said, my Electroair systems do the same.

6. None of the three RVs I?ve owned have a cooling system like this RV-7.

7. First, there are two metal plates positioned vertically in the intakes that appear to block about 20-25% (and that?s a very rough guess) of the surface area of the front cylinders. It?s hard to believe this isn?t reducing airflow over them.

8. Second, the baffle material is much thinner and more flexible than the thicker/stiffer blue or red baffling in my other RVs.

9. I looked through the oil door after the flight and discovered that the baffling at the top rear of the engine had been shoved aft, leaving a gap between it and the cowl as an exit route at the top of the engine rather than forcing the cooling airflow down and out at the bottom rear. That can't be right, can it?

I'm trying to make sense of this and would appreciate any comments/suggestions from the experts.

Thank you.

[flyinga]

I'd fix #9 first. This is not right. The flexible material should be toward the higher pressure air.

The vertical pieces of baffle can be trimmed to equalize temperatures.. Try taking off 1/4 inch at a time until you are happy with the balance.

[Sig600]

#6-9, I think you've already diagnosed it.

[DanH]

Originally Posted by Tango Mike

9. I looked through the oil door after the flight and discovered that the baffling at the top rear of the engine had been shoved aft, leaving a gap between it and the cowl as an exit route at the top of the engine rather than forcing the cooling airflow down and out at the bottom rear. That can't be right, can it?

It is wrong as a soup sandwich.

[kiwipete]

#7. You need to reduce the plates until each cylinder on the same side are equal.
ie 1=3, and 2=4.
The engine will run hotter until the cylinders are fully broken in.

Cheers

Peter

[hydroguy2]

as othres have pointed out #9...until you fix that the rest of the stuff is just guessing. Fix all the leaky paths and I'll bet you get your 20*+ drop. THEN you can fine tune the balance.

[Brantel]

I found that my seals would flip back when I had them too long. I trimmed them shorter and they never did this again.

When they flipped back, I would get an instant increase in CHT's.

Fix that and you will be headed in the right direction.

For us mere mortals, cooling these things can be a challenge!

[Tango Mike]

Great advice, fellas, thanks.

To confirm: the plates should be there and are a CHT equalization device, and no one has said this specifically for the dummy =;-), but the thinner/more flexible baffle material is not a design/plans characteristic of the -7, correct?

Baffle material needs to stand up to the pressures inside the cooling area, resist deforming, and move only enough to press outward against the cowl so that the pressure helps seal them tighter, prevent leaks, and make cooling more efficient?

[DanH]

Originally Posted by Tango Mike

To confirm: the plates should be there and are a CHT equalization device, and no one has said this specifically for the dummy =;-), but the thinner/more flexible baffle material is not a design/plans characteristic of the -7, correct?

They are standard components included in a Vans baffle kit, to be used as necessary...whole, trimmed, or removed entirely.

Baffle material needs to stand up to the pressures inside the cooling area, resist deforming, and move only enough to press outward against the cowl so that the pressure helps seal them tighter, prevent leaks, and make cooling more efficient?

Exactly right.

[RV10inOz]

Check your PM's