I did mine on my 1800E. I think as was said the head studs conduct heat to the manifold and it does not dissapate the heat I beleive. It looks good. The guy from www.performancecoatings.com explained it more like if you leave some thing in an oven it will go to the temp of the oven after long enough. I have an uncoated manifold but did not put on and to a side by side comparison of temp absorbsion/heat retension when under good cold ram air to see what the inside is like. It was done both inside and out. I did not have any throttle plate issues after the coating like I was afraid of. I did ceramic coat the header also. .

Greg Bodner
1970 1800E

1970 1800E

It can be worthwhile if you have a modified B30 mainly from keeping the engine bay cooler rather that better flow. I'd only bother getting the exhaust done (unless you hace the intake and exhaust manifolds joined). If it's just a stock engine and you don't drive very hard then It won't gain anything for you apart from looks.
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Alex Shevlin (Sydney): '71 142S, '72 144S, '81 244GLE, '81 244GL, '01 V70XC

Viper mentioned to me that inlet did not dissipate heat as well due to heatsink from head, this does not cool inlet air properly which is not what you want, looks great though.

One benefit: Coating the outside of the manifold will help reduce underhood temps.

Best,

Cameron
Rose City

If you coat it on the outside it won't rust but you might chip it and it
will be very pretty except where it is chipped.

If you coat it on the inside, that portion of the exhaust heat that normally
dissipates through the manifold will go on to the headpipe and it will
run hotter than normal. Since it is much thinner than the manifold you may
shorten its life. It might give freer flow for a while but it will get dirty
before long, just like your exhaust ports so you probably will only have a
temporary gain if any.
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George Downs, The "original" Walrus3, Bartlesville, Oklahoma