I posted this in LT1 tech and not one response so Ill try here where I thought it should have went anyway. I pulled the intake off my car as I like to do in the off season and discovered #5,7,8 intake runners of the heads have a burnt black look to them all the other ports look fine, nice and clean. Any idea's as to what would cause this? Doesn't look like valve seals, no smoke on start up and no deposits on valve stem. I"m running the GM 847 cam and AFR 190's stock bottom end 40 k on it.
thanks for any help
Mike

 

Not sure, but most of my runners were black when I took the top of the motor off for heads/cam swap. They were more streaked though, almost like some carbon deposits had been sucked in, and streaked some of the intake ports black as the carbon went through.

 

Superfluous posts deleted to keep it on topic.

I think that the EGR system may contribute. Did the black go all the way through the runner in the intake as well, or did it start after the little pinhole in the runner in the intake?

Or... any chance you had piston ring blowby, and hence a heavy/oily vapor load through the vent line from the passenger side valve cover to the throttle body?

 

The black seamed to go all the way up into the intake as well. Maybe ring blow by could have been the reason, I remember when I first started it after the heads and cam install it smoked for the first 15mins . I thought at that time that a ring could have been stuck after sitting for the winter. If thats the case why only on the back three ports of the engine 5,7,8 ??

thanks
mike