I recently got a infared thermometer for Christmas and tried it out yesterday for the first time on all the header tubes while the car was running. I figured a few cylinders were running hotter than others due to Dual plane intake, and history of plug readings.

Readings were taken a few inches from the port.

My question is how critical are these temps in comparision to each other?

I figured that #8 was the hottest and this was true, temps are not exact since I didn't think to note them but, #8 was 365*F and #2 was 280 or so. 4 and 6 were higher than 2 which is not a suprise.

I guess there are several factors that could play into this;

Vacuum port on #8.

Header coating was partially burnt off during cam break in and only has a thin coat of ceramic header paint where the temp reading was taken on 8.

Airflow around #2 and coating is 100% etc...

The narrow band A/F meter doesn't show the passenger bank as being lean!

I don't really even know if this is a problem but, how would you fix it or?

Staggered Jetting?

plug heat range?

Thanks for any replies, SS.

If you did this while the engine was idling, all you comparisons will go right out the window when normal rpms are achieved.
Fuel distribution and spark advance will change considerably.

For exhaust temps, you really need thermocouples (and a data recorder).

Great tool though. I want one!

Thanks for the info, I wasn't sure how relative the readings were. SS

they are a sweet tuning tool. steves right about running temps, but they will show a dead cylinder quickly, and help with you idle tuning.
another thing they do is help you appreciate coated headers, as soon as i saw your number i thought "coated headers", on uncoated your temps would probably nearly double.

In a race car, particularly in an endurance application, you will see head temp gauges, and O2 sensors so they can monitor any fuel distribution problem before it destroys the engine. As a tuning tool a pyrometer (or thermocouples) and wide band O2 are also essential, and any carb shop or dyno should have them.

I don't think the fuel distribution is the fault of the manifold; though I don't know what you have. I would suspect the carb needs fine tuning.

Your system plus reading plugs should help you get all your "ducks in a row" (tube temps) provided your carb has adjustments at all four corners. The newer street avenger/pro series have screw in air bleeds, and four corner idle circuits; but if you have an older 4160 carb I would accept what you have.


Larger Dave

Yes, the temp gun is a great toy, er, tool, right next to cordless drill. Your dog will appreciate the temp gun as you don't have to use a rectal thermometer.

As said earlier, I agree, temps are fine and yes, lack of coating and the fan have alot to do with localized heat.

The I.R Guns are a great tuning/pit tool :thumbsup:
They can give very accurate readings if they are set to the correct Emissivity for the material they're reading and there is a simular spot at each point to take each reading.
Most guns are adjustable but, they are usually set at @.095E as a default setting.
This is a good base number for most darkly painted surfaces, such as normal headers. Where you noted 'peeling paint', the 'E' may be much lower and causing a different reading.
"New" steel will have base 'E' of @0.8_(+) - where oxidized (rusty) steel will be closer to 0.7_ depending on the amount of rust.
If you provide a common shaped and colored area to that your readings you will get very accurate numbers for each location.
I often weld a small pad to the tube near where it meets the flange but, before the first bend, and take my readings at that spot after the car returns to the pits from the track.
If your header tubes are "Jet-Hot" coated in a bright finish, note that the 'E' can be as low as 0.1_(-) or lower. The readings you will get without adjusting your meter will be way off.

They are also a great tool for getting accurate tire readings very quickly.

btw - my I.R. meters have become one of my wifes favorite cooking tools :D
She has found that they are great for getting candy batches exactly the same and you don't have to scrape hardened gunk off things...
I finally just gave her one... ;)

Thankfully I don't have a dog... :eek:

Hope this helps some;
John