heated manifold helps you extract more from the gas. liquid gas/petrol doesn't burn. heated manifold helps evaporation of the liquid gas. you should get better mileage, better performance in cold climate, and more importantly, prevents carb icing, which is crucial in cold climate.

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This is for racing manifolds that do not have matching water galleries to the head. Usually twin DCOE manifolds are like this.

The factory twin hitachi SU type manifold is water heated and still gives good performance.

its common knowledge that cars normal perform better on cooler nights, when air is more dense and timing can be increased. people do away with water heated manifolds for this reason usually. For economy reasons, heating helps, not so much for performance.

Grub screws are in and cold tested. In the end I went for M8 (due to availability) and sealed with Loctite sealent.

http://i1212.photobucket.com/albums/cc444/tstorm1986/IMAG0150.jpg

Thanks for the help guys.

the picture for link above.