Does anyone have an opinion on SL6 heads, which is better 1969-1974 head...lighter and I think the exh and int ports are a little bigger but exh seats not hardend for unleaded...or the 1975-1977 head before they drilled a hole for air injection in the rear of the head with a conection to the air filter.....which is better to shave and install oversize valves......

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I has a 225 with overdrive....my plate is a vetrains plate from MAASACHUSETTS it is
198 S I might want to put a 198 overbored and stroke to come up with 213 cubic inches!!!!!!!!

Air injection port was standard as far back as 1976, only certain vehicles got the "600" non-port head, most of them got the 447 port head, and it will be the most common find in junkyards especially if you are located near an area that tests. Also the late heads have less variation in their manufacturing and tend to have a 53-54 cc chamber stock vs. the drool tube heads that could be 58 cc in 1967, to 54 cc in 1974...(and more if an earlier 60's head). I've yet to see a performance difference between the 447 or the 600 head on any of my builds.

The drool tube head is preferred due to weight and larger spark plug selection. If you are going to O/S valves and porting/blending for better flow you are going to replace the exhaust seats anyway.

The 1975-1987 heads are more common as the 80's trucks/vans are dumped at junkyards now, you may have an old mom and pop junkyard nearby that still has some early 70's mopars that you can get the drool tube head from. Make sure when pulling it to check for the lack of a 'dime spot' casting in the chamber.

http://www.slantsix.org/articles/combus ... hamber.htm

-D.Idiot