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Old 01-15-2016, 10:49 AM   #1
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Default monitoring cylinder head temperatures

Is it worth doing?

I know that it's done a lot on airplane engines, but a significant portion of those are air cooled and thus don't have coolant sensors.

But I was wondering if it might be a good way of indirectly keeping track of piston temperatures to run 4x CHT probes under the spark plugs with a 4 way gauge. That way if one cylinder is running lean, it will show higher temperatures than the others and you can go "oh **** I have a problem I need to address" instead of melting a piston. Or am I completely misunderstanding what CHT probes can be used for?
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Old 01-15-2016, 10:56 AM   #2
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Techsalvager?
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Old 01-15-2016, 11:51 AM   #3
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4 widebands. Or just 1 in the normal spot, and watching it.
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Old 01-15-2016, 11:52 AM   #4
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Monitoring watercooled cylinders with four oxygen sensors: "Oh ****, I'm about to have a problem I should address"

Monitoring watercooled cylinders with four EGT sensors: "Oh ****, I'm now having a problem I should address"

Monitoring watercooled cylinders with four CHT sensors: "Oh ****, I had a problem I should have addressed and now my motor is blown up"
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Old 01-15-2016, 12:22 PM   #5
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Lol
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Old 01-15-2016, 12:34 PM   #6
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Alrighty, so it's not a good idea. I can live with that.
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Old 01-15-2016, 12:40 PM   #7
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I would think EGT sensors would be easier to install and probably more reliable. I've never heard of anyone running multiple WBO2 sensors.
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Old 01-15-2016, 12:47 PM   #8
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Andrew is spot on. Both O2 and EGT sensors respond extremely rapidly to power and mixture changes.

CHT response is a damped, time-derivative type of reading. It would literally be tens of seconds to minutes before a mixture problem became evident on a CHT sensor.
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Old 01-15-2016, 12:54 PM   #9
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Quote:
Originally Posted by Itty View Post
I would think EGT sensors would be easier to install and probably more reliable. I've never heard of anyone running multiple WBO2 sensors.
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Old 01-15-2016, 01:02 PM   #10
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And now I have. Cool.
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Old 01-15-2016, 01:51 PM   #11
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CHT would only be useful for steady state operation anyway.
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Old 01-15-2016, 03:37 PM   #12
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Yup. EGT used to be common for this, but with widebands getting cheap youll start seeing ^ around more and more regularly.
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Old 01-15-2016, 03:42 PM   #13
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To be fair, the sensors don't last long sitting in a turbo manifold. It's really meant to dial in per-cylinder trims and then get removed afterwards. EGT sensors are a better option if you want something that lasts a while and still provides more data than a single sensor.
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Old 01-15-2016, 03:49 PM   #14
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Quote:
Originally Posted by Savington View Post
Monitoring watercooled cylinders with four oxygen sensors: "Oh ****, I'm about to have a problem I should address"

Monitoring watercooled cylinders with four EGT sensors: "Oh ****, I'm now having a problem I should address"

Monitoring watercooled cylinders with four CHT sensors: "Oh ****, I had a problem I should have addressed and now my motor is blown up"
This sums it up very well and accurately. If you want the best I'd do option 1.

Also if you're wanting it perfect, I'd put some higher-octane-than-normal fuel and get a well-established baseline for your knock sensor and set fairly tight buffer so that say, 8% to 10% more knock activity than the base the per-cylinder knock detection pulls timing. Of course you already have that if you think you need 4x O2's or EGTs.
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Old 01-15-2016, 04:35 PM   #15
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Word of warning. The output of a wideband is skewed by pressure. No idea by how much or in what direction, but something to read into if you persure this further.
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Old 01-15-2016, 05:10 PM   #16
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Quote:
Originally Posted by sparkybean View Post
Word of warning. The output of a wideband is skewed by pressure. No idea by how much or in what direction, but something to read into if you persure this further.
What the **** are you talking about?


I do miss techsalvager. He had the ugliest turbo setup. I remember that sea green silicone pipe.
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Old 01-15-2016, 06:59 PM   #17
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Google found some numbers




Source: https://www.rbracing-rsr.com/rsrgauge.htm

Megamanual mentions it too.
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Old 01-15-2016, 07:09 PM   #18
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Well, if you are using them to trim together it doesn't make a difference what the error is.
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Old 01-15-2016, 10:27 PM   #19
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That is actually a really good point.
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Old 01-16-2016, 07:56 AM   #20
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True, but why would you do that when you could do it for 1/5th cost with EGT sensors?

You can leave them permanatly fitted as they last forever, are cheap, and are simpler to wire. Drive one with an AD595 with no external parts, unlike an 02 which needs a complex controller.

02's per cylinder are only worth the effort if you are pressure compensating, thus getting absolute values.
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