I just finished putting in 8mm wires and new plugs. When I shut the car off it hissed for about 5 seconds. I think that a cylinder is bleeding off compression, but am worried as to how tight to tighten the plugs down. Would would you recomend for me to do?

 

It sounds like it's your Air condioning system equalizing pressure.. Normal thing if it is

 

Tapered seat plugs should usually be torqued to 18-20 ft/lb in iron heads, 12-15 ft/lb in aluminum heads.

 

I thought I turned the A/C off, but didn't and didn't think to check it either All is fine, just a false alarm.

 

heh heh Well for future reference minor damage to the plug sealing surface is common on aluminium heads and can be corrected with a little GM Black Hi tack sealer.