Measuring head temp with infrared thermometer

You can take my advice for what it is- free on the internet. But I'm in the "temperature" business, so at least there's that.

 

I'd like to take all infrared thermometer guns costing less than $500 and burn them in a sacrificial pyre.

 

They're perfectly adequate for aiming at an HVAC register you can't reach by any other means and registering a temp +/- 10% or so, and absolutely useless for what you (and most of the world) are trying to do with them. What you are finding is exactly the issue. If I could convince meat managers in supermarkets of this, I'd have a better quality of life.

 

There's one good way to measure surface temps: with a thermocouple. Getting an accurate head-temp reading means putting a thermocouple under the spark-plug. There's no short-cut. Anything else is just a vague approximation.

You can search for "emissivity tables" for your answer, but emissivity varies widely with material, surface conditions (rough, polished, oxidized, etc), and even the temperature of the material at the time. I agree that a thermocouple is a better choice for accurate temp measurements.

Hopefully Mike paid more than $499 for his.

 

Perhaps this one?

 

Here's a Fluke 66 for $594.

 

I still wouldn't use it to measure cylinder head temps.

I'd defer to Stan. The man is all about temperature, and is our resident expert.

Gee, I thought I was going for the expensive unit when I bought the $30 unit instead on the one for $17.

 

Different emissivity settings result in about a 200 degree difference in temperature readings.

 

I am going to paint the screw flat black so I will know what emissivity setting to use.

 

I realize I still may not get any useful information.

 

I have a VWarning device that turns on a light when the head reaches a certain temperature. 

 

This never came on with my 1776 and it is coming on after about 20 minutes with my new 2110.

 

This is why I am concerned about head temperature.

 

I drove the car until the light came on and then stopped and immediately checked the temperature.

 

I read on thesamba that peak head temps can drop Very fast, they can significantly change by the time it takes to stop the car, and get out to check the IR reading.

 

I am afraid to drive the car now. If I didn't have that warning light thing I would probably just be happily driving it.

 

Does anyone have any suggestions about why the heads are hot?

 

The next thing I am going to check is if I have a leak around the intake manifolds.

Do you have an A:F bung in the exhaust to check your mixture?

I do have a bung.

 

I think probably it is running rich right now, at least in the idle circuit.

 

I have Weber 42 DCNF (as modified by Berg) carbs with 34 mm venturis.

 

Idle Jets 60

 

Main Jets 140

 

Air Jets 180

 

The recommended size for the idle jets seems to be about 52.5 to 55.

I don't know, Mike. You may be right on the money. You'll only know once it is broken in and you check it with the wide band meter.

I have the exact same jet sizes, in a 2165 with 44 IDF. Eventually I settled on 57.5 idle, 55 are too small. The motor kind of fell on its face down low. A/F reads a little rich at idle, about 12 or 13:1, but plugs are perfect, and mileage is up with the 57.5. I think my O2 sensor is a little too close to the outlet. I'm calling it done,

Instead of messing around with the IR thermometer, why don't you just buy a thermocouple and gauge and put it under number three. Then you'll know if you're too hot.

If you're going to buy a CHT gauge I'd recommend either a Dakota digital gauge

 

http://www.dakotadigital.com/i...mode=prod/prd348.htm

 

or a gauge from Aircraft Spruce

 

http://www.aircraftspruce.com/...us/in/chtgauges.html

 

I have a Westach in my IM.  I was going to install a Dakota digital gauge, but thought the blue numbers might get 'washed out' in the sunlight, when the top was  down.

 

They are the only two that I know of that are fairly accurate.

I have this one. Works great:

 

http://www.aircraftspruce.com/...pages/CHT_gauges.php

I've got two of these to measure all four cylinders. Same gauge as Terry's, different flavor:

 

http://www.aircraftspruce.com/...1000/dualchtpyro.php

Stan, do you find much difference between cylinders?

Interesting question.

 

I've had this set-up on three different engines. It tells me more than you would think possible about carb jetting, sync, etc. I'd like to monitor exhaust temps as well, but they tell me that sometimes "more" is just "too much".

 

When everything is perfect the temps are pretty darned close to each other right across the board.

 

At idle, the 1-2 bank runs a bit cooler because that's the direction the bulk of the air is being thrown, and there isn't enough pressure for the diverters to function properly. That's with a DTM: I've got no idea about anything else.

 

However, with my present set-up I've got more gradiation than I've ever had at light cruise (on the idles only), so I know I need to keep playing with my tune, even though the car runs really, really well. When I was 1/2 idle jet fatter, temps were much more even and there was no lag just off extended cruise, but the A:F meter was on the chubby side of my ideal.

 

It's not for everybody, but I like it.

 

I'd love this one, but it's very expensive ($980).

Reads all four cylinders at the same time and can be set to change color at certain temperatures.

 

 

 

 

 

Bill,

 

One sensor under each (top) plug. If I'd have known I was going to twin plug it, I would've wired them into the bottom ones. I've got two of the gauges I linked to.