ok i got a 1966 Pontiac GTO With a 389 tri power the moter rebuilt and bored .30 over and had a 3 angle valve job do i need to use lead substitute? And what happenes if i dont will it cause a prob and what if i didnt use some for a lillte while like 100 miles.


thanks

 

Check with the rebuilder, see if hardened seats were installed...most likely they were on a fresh rebuild. If not, well, FWIW I've put on about 18K miles on my '59's stock 235 head that was last touched in '62...so it definitely doesn't have hardened seats...up to this point I've no ill effects.

 

Just sold my 66 pontiac last year. 325 HP 389.
10-1/2 to 1 CR.
Didn't have any problems with the valve seats, but detonation from 92 Octane Unleaded and hi compression ratio wasted a piston.I'd add a lead substitute as often as possible.
Anything to get the octane up and cool the seats.
A hundred miles without,here and there probably won't matter.

Guy who owned the car before me drove it hard on crappy gas
and the constant hammering it got from the hi compression and bad gas eventually took it's toll. Piston #7 had a hole in it and half the top ring was gone.Amazingly enough, the bore was fine and so were the valves, so I replaced the one piston (std bore)
and it was fine.

Pontiac Motors are beefy!Mine had a ton of hard miles on it and internally it was cherry!

-Rich-