1968 #16 heads question of HP rating
 

I have a pair of #16 heads dated 1968 and am wanting to know what codes determine what horse power rating.

The dot clock in the rocker valley is at the 9 position, to continue. . . .
I have decoded:

9 pm on January 22nd of 1968
General Motors #16

The arrow to the 3 and the number 7 above the last exhaust port are my curiosity.

I found two #16 head codes for '68

1st code is for a 400 engine at 330, 335, 350, 360
cc 72 High Output

2nd code is for a 428 engine at 375, 390
cc 72

Thumbnail preview attached
Thanks for the insight
Alex

The heads are the same- the HP differences come from cam and exhaust differences.

Yes.. All the same heads ... just the chassis and options, etc.... for the difference.

Firebird 400's (330-335hp)had the restricted carburetor linkage to cheat a lower advertised HP
GTO 400's (350-360hp) were the same as the Firebird exept the four barrels opened fully..
FullSize models 390 HP 428 HO had the better exhaust manifolds than the GTO HO 400 and yielded the highest HP rating with the bigger engine , fully open carb and the great exhaust...