I won't argue that. BUT, it's the radiant surface area that contributes to under hood heat. The flanges where the bolts are have very little surface area whereas the header tubes themselves have tons of surface area to let off heat. And I will argue that the flanges and the tubes may not be the same temperature within 5 degrees.
If I didn't have such darn good header shields I'd shoot some numbers tonight.
SHOOT 'EM!!!
DO 'EEET!!!
COME ON! THEY'RE RIGHT THERE! SHOOT 'EM!
(It's tough to do a wicked Austrian accent with a keyboard...)
I wasn't really going for actual tube temps, but more for a repeatable source for accurately measuring heat as close to the manifolds as possible.
I could have used the POS battery terminal post....but that really wouldn't have been a very good baseline.
With the cast iron OEM manifolds, I will argue that the temp on the flange is within 5-10 degrees of the tube, at idle, at normal operating temp.
On headers, it will probably be a slightly larger difference.
At WOT, neither header flange temps nor OEM manifold flange temps compare to their respective tube temps. There will be a drastic difference.
"
Why not get some headers instead of running the OEM cast iron stuff?"
A couple of reasons...
1. The OEM manifolds are basically shorty headers.
2. Casting has improved dramatically over the years, and the insides of my OEM manifolds were very VERY smooth. Even smoother after they got back from Jet-Hot.
3. The weight savings (about 20 lbs; 10 lbs. per side) simply didn't justify the cost ($3K+) to me. I can drop 20 lbs. much more economically. Ditching the cats alone is a quick 15 lbs! A carbon fiber driveshaft for the truck is about $1500, and that trims a quick 30 lbs!
Maybe someday I'll do a set of headers, but for now...the Jet-Hot-coated OEM manifolds do just fine.