Interesting diagnosis problem??

Was showing the kids some diagnostic tools today (compression test, vac*** gauge, leakdown tester, etc.) Shot the header tubes with a pyrometer and readings averaged about 108 degrees (hadnt run for very long) except for cylinder 1 and 8, they were showing about 92 degrees. This is a .040 sbc with offenhauser dual port intake, 600 cfm holley, headers, hei, small valve heads, cam advanced 4 degrees, .480 lift (forget the duration). Why are those two cylinders down???
In addition a cranking vacuum test showed about 4" steady, I attribute that to the cam being advanced - is that the case there???
Looks like maybe we ought to compression test and see if those cylinders are out of spec??? thanks-

 

Stay away from pyrometers and run it.

 

Those temp readings sound too cold. It probably just wasn't warmed up all the way.

 

1 and 8 are the furthest away from other firing cylinders which are in close range of other cylinders that fire immediatly after each other. It is like how #7 is the last one to get oil when priming a motor. It's just because Chuck Norris said thats the way it has to be.

 

If Chuck says so then I'm not f'ng with it....

 

We use one of those hand held pyrometers at work...the little laser beam kind.
We use it to check mold temp of which we send typicaly 285f oil through. We hold little faith in that reading unless temp going in and out is getting to be 50f difference.You can move the contact point of the beam slightly and the temp changes drasticaly. Also surface finish seems to play a huge role....Our molds have a polished/mirrored finish. With everything ok you can try to take the temp and it can range 75f different by moving 1/2" over. Doesn't stand to reason any possibility of accuracy. Now if the surface is a more non reflective surface it seems to work better.
What I am saying is they only hold faith in my eyes if there is a large temp discrepency

 

If you really want to use thermal readings to diagnose something, get a thermal imaging camera. Then let me be your best friend, so I can use it...

 

Was the engine itself cold, besides only being run a short time? I'd let it warm up to stabilize the temp throughout the block/heads and re-test. Either way, the variance is not enough to worry about.