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Old 03-04-2018, 07:09 PM
jacksel jacksel is offline
Join Date: Jul 2005
Posts: 108
Default High CHT

My RV-7 now has about 50 hours on it so I'm assuming the engine break-in is complete (it consumes very little oil). However, it still has CHT's ~ 20-30 deg higher than I see on my RV-6 (13 years and 800+ hours). My RV-6 has dual UNISON LASAR ignition and my RV-7 has Slick impulse mag powering the bottom and LSE Plasma 3 powering the top. Other than that the power plants are identical (Lycoming O-360 on the 6 and Superior XP-360 on the 7). If anything, I would say the baffle installation is better on the 7. As far as I know the cowlings are identical. So I am at a complete loss to understand why the difference in temperature. The 6 maintains ~ 300 deg in cruise and perhaps 350-380 in climb, depending on OAT. The 7 is 370-400 in climb and 320-350 in cruise, but temps seem heavily dependent on whether I lean and how much. I've been running the FF higher just to keep the CHT's down. Also, the 7 CHT's are very balanced and moderate on the ground and the imbalance and significant increase occur after T/O. Generally #2 runs 30-40 deg hotter then #3 and 4, and #1 runs 10-20 degrees hotter than 3 and 4. 3 and 4 run the coolest and are generally within 10 degrees of each other. I have a small baffle dam in front of #1 cylinder and none in front of #2. I started with fairly significant dams in front of both, with my modifications making little difference. At this point the baffle systems of both airplanes are essentially identical.
Any thoughts or other input would be greatly appreciated.
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Old 03-04-2018, 07:20 PM
Marc Bourget Marc Bourget is offline
Join Date: Apr 2009
Location: Stockton, California
Posts: 184

I think it is easy to assume the baffles are identical by appearance, but are they identical in Delta-P?

Hook up a manometer to each and verify they perform the same.
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Old 03-04-2018, 08:31 PM
RVbySDI's Avatar
RVbySDI RVbySDI is offline
Join Date: May 2005
Location: Tuttle, Oklahoma
Posts: 2,497

Well, I am no expert engine guru but here are my thoughts. The temps you mentioned are well within the "good operating temps" for the engine. So I am not sure it is necessary that you worry too much about the differences just yet. I personally would not worry too much about the differences in the two airplanes. 800 hours on the RV6, 50 hours on the RV7. As long as the temps remain within acceptable limits for the RV7, I would say, re-visit the question when the RV7 has 800 hours on it. At that point you could see how it compares then to how the RV6 is doing now.

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Old 03-04-2018, 10:14 PM
jacksel jacksel is offline
Join Date: Jul 2005
Posts: 108

I have to plea complete ignorance here. I honestly don't know what a "Delta-P" or a manometer are.....But I will look into it:confused
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Old 03-04-2018, 10:29 PM
Kyle Boatright Kyle Boatright is offline
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 3,406

Originally Posted by jacksel View Post
I have to plea complete ignorance here. I honestly don't know what a "Delta-P" or a manometer are.....But I will look into it:confused
"Delta P" is the difference in pressure from the high pressure side of the baffles to the low pressure side of the baffles. In other words, the difference from the top side (high pressure side) of the engine to the bottom (low pressure side).

A manometer is a tool to measure the difference.
Kyle Boatright
Atlanta, GA
2001 RV-6 N46KB
2019(?) RV-10
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Old 03-05-2018, 04:13 AM
mike newall's Avatar
mike newall mike newall is offline
Join Date: Jan 2005
Location: Yorkshire, England
Posts: 1,681

Basic check-list

1. Check timing accurately
2. Run tops on auto plugs if you can - NGK BR9EIX work well
3. Check and fix any - I mean any, gaps in solid baffles with silicone
4. Check ramps and nose silicone flexi baffles for seating
5. Check and increase if nec the exit area at the lower edge of the cowl

We dropped our cht's by doing the above. We run mid 300's now most of the time.
"I add a little excitement, a little spice to your lives, and all you do is complain!" - Q

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Old 03-05-2018, 04:48 AM
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RV10inOz RV10inOz is offline
Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,131

I wonder what the spark advance difference is between your old and new?

The old Unison system may still have had less advance than the LSE.

Especially when ROP, this drives CHT up but even LOP it does, however a bit of advance when LOP helps.

The big problem with all these things is finding the balance. Theta PP is what matters and unless you measure that it is a bit hard to control.

Perhaps you need to dial out a couple of degrees on your LSE system. Easy to do with the magneto replacement unit and a bit harder with the flywheel sensor, but it can be done.

David Brown

The two best investments you can make, by any financial test, an EMS and APS!
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