valve seal vs leaky ring

heads need to be rebuilt, i had a tbird that would smoke on startup, but it would scoot down the road quick. one day i was going probably 115 for 5 minutes and i looked and smoke was everywhere but it was running fine. i started driving normal and it stopped.

fouled plug...............since you changed it things are fine................the cylinders should all be within 10% of each other if they are you need to put in new seals and that means it is time for those bigger heads you always wanted.

how where the wet vs dry compression numbers?

Faulty valve seals won't cause low compression, but they will allow oil to leak down around the valve stem into the combustion chamber; hence the smoke when the engine is started. It is possible that one of your valve seals/guides is totally shot and has allowed enough oil to leak into the cylinder to burn dirty and form deposites on your valve seats, the result would be low compression due to poor valve sealing.

An old trick to help determine the cause of low compression is to do a compression check normally, then squirt a small amount of motor oil into the cylinder through the spark plug hole and do the compression check again. If your compression in that cylinder is higher once the oil was added, you probably have worn compression rings (the oil added will help seal the rings and raise the compression reading).

Either way, if you're going to go through the trouble to tear down the engine for a new set of heads I would recommend pulling the motor and freshing it up. You'll save yourself a lot of headaches down the road by doing it right the first time. Assuming your engine isn't totally shot, you can clean up the cylinders with a quick hone, replace the rings, crankshaft bearings, timing set & oil pump, and then button it up with fresh gaskets. Get the flywheel resurfaced and throw in a fresh clutch and you'll be ready for action. (obviously this is just a quick overview and omits some parts/steps but you get the idea).

Rebuilding a mild motor isn't nearly as difficult as some people make it out to be, as long as you're just looking for 300hp or so spend your money in other areas. Personally I'd rather have a 302 with a fresh re-ring kit in my car and spend some money on upgraded brakes, new shocks, and all the other things that could stand to be replaced on a 15 yr old foxbody.

You should consult with some of the other members on this board to see what kind of fuel system upgrades (if any?) will be necessary to support those new heads.

Just my $.02, good luck.