Quote:
Originally posted by SteveC
There are two schools of thought on this. One says always replace them because they tend to eventually shrink with prolonged exposure to heat. The other school says that if they are visually okay, then they can be reused by applying a coat of hylomar to both sides. I also recommend using the hylomar even when you're installing new ones.
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I just had Extrude Hone do the intake manifolds for my CSi. The Manifolds are now being polished on the outside on the non-black surfaces, so I can't tell you what the effect on the is until I get them back and the car is together again. However, I can tell you that Extrude Hone quoted me a 20-30 HP gain. Of course, none of these guys quote HP gains at the rear wheels, including BMW's quotes for stock engine output. But Extrude Hone's HP increase quote was for "Stage One". I did "Stage II", where you send them a new set of manifold blocks and they match Hone them too. So, although my car only has 11,000 miles on it, it will be getting new blocks/gaskets, to match the very smooth interior of the intake manifolds. They only sharge $80 extra for the Stage II.