HELP

HELP!I bought my '68-400 last fall, it has good power and I was sure it was A-400 but I knew it wasn't the orginal engine (I'am experienced with pontiacs from that era).
I've driven aprox. 500 miles in it.trying to tune
it up for spring & indentifying exactly what I have I'am confused!!! the engine block has a code
of "YH" stamped on it. Where do I fine the head stamped codes? It has a regular distributor and the points&rotor look fine, but the plugs are old
& fouled & are motorcraft #ASF52C any sugestions
on what plugs to use?

If it's a '68 engine, it's a 375hp 428! Look on the side of the block and look for the #'s 428 between the freeze plugs. Also check the block part # on the driver's side behind the head. A 400 would be 9790071, 428 is 9792968. Specs for tune-up are as follows:

timing- 9 degrees for all V-8
dwell- 28-32
Steve

Yep, it looks like it's a 428. I don't think that they were originally offered in the Firebirds but who cares becuase it's a Pontiac big block! As far as plugs, I've tried 'em all and haven't seen a noticable diference in performance. You may as well go with the AC delco 44S and gap them to .035". They are cheaper than most others and do just fine. Also, I've seen torque specs for plugs range from 23 to 25 ft-lbs.