the picture for link above.

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.

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.

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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.

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.

from memory 4mm (mabee 5mm) tap and screw some plugs in there, i just got bolts cut off the heads slotted them and screwed them in.. with a bit of loctite pipe sealenat on them of course..

Will plugging these holes increase engine performance? My A15 head is not plugged at the moment.

Thanks guys this stuff really helped, ill have to hit the stores and track down some grub screws of a similiar size. knowing that its a process nissan suggests gives me piece of mind. I was worried about opening the hole a bit and cutting into something i shouldnt.

Found it in my 1984 Nissan Competition catalog:

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No photo but your description is clear.