Why there is a differences in headers temperature ?

[Schulmann]

I am trying to really fine tune my Viper with the VEC2 and I was checking the header's temperatures. I performed this verification after an extended drive(150mi) on highway under vacuum (no racing, just regular driving).

AFR is around 15 on all cylinders.
Compression is also perfect.

The average temperature of my headers is 250F.
However there is two headers which run hotter 300F.
And header at cylinder #9 is just 170F.


What might cause this difference ?
Ignition ?!

I read about ingition systems where it is possible to add little advance/retard adjustment to each cylinder.

 

[LETHAL GTS]

Very interesting. Would plugs cause this variation?
Have you changed your plugs lately?
Is #9 firing? Seems pretty cool. You using an infra temp gauge? Are you checking all header pipes in the Exact same place? Just some thoughts.
Let's see if any of the tuners here can shed some light.

 

[Schulmann]

Plugs are new: NGK FR-4
All cylinders are firing.
I used an infra rayed tool.
But I couldn`t check the temperature exactly at the same location. However I think the way I mesured the temperature would not introduce an error.

 

[LETHAL GTS]

Do you have your heat shields on?
Do you have factory headers?
Was 9 (being a bit of a pain to get to) the one you had to test in a different location on the pipe?

 

[LETHAL GTS]

Just a thought, but maybe try checking the temp of the head near each cylinder. See what kind of temp readings you get there.