I purchased a spare tpi setup from someone in the classifieds with the intentions of polishing the outside , my cars running just fine so I'm in no hurry to get it polished right now , I've got a dremmel and a ton of bits so I decide to deburr the runners . The intake was filthy in the runners so it was really hard to see what I was doing in the begining but a quick pass with a flap sander brightened it up .
The intake runners on a stock TPI manifold are horrible ! , the first one I looked down had a big glob of aluminum where the casting mold had failed , it took me 20 minutes just to grind that out , I understand that GM made the castings that way to minimize defective units but wholly crap there's a pile of aluminum on my bench from just the first runner and I've got a whole lot more that can come out and I'm not even siamesing it .
I wish someone would have emphasized this modification , I honestly think this will make a big difference , more so than adding a k&n filter or a cold air intake .

 

I agree, the amount of crap in the lower intake is amazing. I have one I am wanting to get working on, and it fathoms me how bad some of the runner ports look. The plenum isn't bad, just small and could use a little opening up.

Cheers!!!