I have a procharged 502 efi that pops when getting on plain .It would idle fine and rev up good but when i tryed to get on plain it would pop in the intake it sounded like. Changed plugs no help i tryed all day and now it will not idle good at all.

Lean lean did I mention lean?

NEED TO CHECK YOUR a/f RATIOS. Pro chargers are an engine builders best friend!

Has it been running fine? Could be a valve spring etc..

If you just installed it yes I would be checking for a lean condition.

It has run fine for 3 years. i drained the oil last nite and had water in it not good i think a head gasket now

We really need to know more:

Fuel pressure?

How do the plugs look?

Any other mods?

The water is not a good thing

Just do a compression check - you'll find bad cylinder real fast.

Head gasket!

It could be a number of things if the engine and tune-up ran fine for three years it sounds like your head gasket was the problem. We just did a pro charged 502. Same problem blown head gasket was it. We built a nice package with his 502, pistons, custom cam,AFRs and a few other goodies made close to 800 hp on the Dyno.

Well the problem has been found.
THe original head gaskets let lose. More proof that the stock gaskets are not set up for supercharge applications. They were squirting into the intake and thin between all cylinders.
Its amazing the thing ran let alone ran as good as it did. No other damage what so ever.