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Old 07-28-2011, 09:05 PM   #1
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Default infared thermometer gun. help!!!

hi, just bought a home depot infared gun with laser beam. I tune my sc8 with .21 hyper engine with this. the engine pulls hard and smooth from idle to hi rpm but when I checked the temp its shows different readings in every area of the cylinder head: top cylinder 220/ middle 250/ buttom near the exhaust 300. I spit the top area no sign of boiling but the exhaust did. please explain this to me.thanks
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Old 07-28-2011, 09:39 PM   #2
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I use to use a temp gun like the o e you are using and I found that it was over 60 degrees off. The PE-1 temp guns are the best budget friendly temp guns. HPI also makes a version of the PE-1. As long as you have a good tune with smoke out of the pipe and no high revving, machine gun action, or lean bog you are good.
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Old 07-28-2011, 10:12 PM   #3
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Naturally the temps are different as the idea of the cooling head is to take heat away from the motor, the extremities of the cooling head will be colder as that is how it does its job.

Temping needs to be done on the head (not cooling head). The head is what the plug screws into so u need to ensure your readings are right next to the base of the plug. Move the beam around a bit to find the hottest temp.

The reason they vary in temp a lot between different brands of temp gun is basically the cheapo units don't work.
The temp gun needs to know what surface it is looking at as different things radiate (emit) heat differently - called 'emissivity'.
If you want to get a real temp you need a gun with adjustable emissibity values and set it for aluminium.
If anyone does not believe me, go heat up a whole bunch of things in your oven really hot for 20mins or so then measure them. Water and metals are particularly different.

That is why people say don't tune to a temp - firstly your motor may run at 220 and mine at 240, even with perfect tune. Then all the different temp guns work differently, and even then the gun may have the wrong emissivity value as it was designed to take temps off a certain substance.

The only value of a temp gun is once you have a perfect tune and are very familiar with your motor, then you can use the gun on different days just to make sure you accounted for humidity or hot weather or whatever and know you are fairly safe

People used the spit method on cooling heads for many years before all this flash stuff came about.... and they did just fine

Last edited by Mark_Australia; 07-29-2011 at 05:59 AM.
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Old 07-28-2011, 11:27 PM   #4
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The Best way to tell if your temp gun is working correctly is to boil a pot of water and temp it.
water boils at 100c or 212f.
you can get away with 2-4deg either side...

and mark Is correct temp straight down the cooling head aim at the glow plug for the best results...
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Old 07-28-2011, 11:36 PM   #5
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thanks for sharing it with us,we appreciate it very much ,you are so kindly,we will go on look your post ,welcome more new information from you ,thanks again.
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