Technical exhaust temps

SBC the exhaust temps from some exhaust ports are high.
I had a pop in exhaust for a couple of days and got to wondering if the engine was running rich. Today I used a temp gun at work and pointed it at each pipe coming out on the headers.
From the left front port to the left rear port they register 270, 230, 235, and 430 degrees
From the right front to the rear they register 410,290, 450, and 260 degrees.
Anyone know what I should check?

 

Compression first, as always. Dry then wet. but the plugs must come out too, so
while the plugs are out examine them for fouling.

Assuming all cyls have good compression dry, I'd do the propane torch test for vacuum leaks around the manifold.

 

yep....sounds like intake has a vacuum leak on the runners going to those cylinders.

 

I'm not sure what the temps should be considering the outer ports are farthest away from the carb/flow but I had a similar issue on the popping through the exhaust. I knew it was on the driver side and #8 plug was excessively oily. I could clean it up and a few days later it was coated again. It wound up being the valve seats and guides on that hole. Once repaired all was good. As stated earlier check out the plugs first.
Jim

 

Timing too retarded will increase exhaust temps also.

 

Thanks guys, I'll check the intake this weekend.

 

IR guns are great for a lot of things, but not for tuning. External header temps are hugely effected by the conduction and convection environment around the individual tubes. Shrouded tubes and the back tubes usually retain more heat. Also any silver surface can't be read with any accuracy at all. A TC at the exhaust port is the only
accurate representation.

 

Perhaps examination of the plugs will bear out what the heat gun saw.

 

That is good to know.. Thanks