273 commando heads vs. standard
As far as I know,
Not really any difference.
I used # 302 heads, which have hardened valve seats,
and have the small combustion chamber,
when I built my 318 to replace my tired 273. ;)
I used a 318 to rebuild while still driving my Valiant to car cruises,
I figured why do a 273, when for the same money I can have a little more power.{I did not want a 340/360, as I don't want to take a chance of
breaking the stock push button tranny, or the 7.25" factory sure grip.}
anyone know the differences of a standard 273 head 2536178 (66) and 273 commando heads 2658920
2465315 273 1964-65 1.78 1.50
2532080 273 1964-65 1.78 1.50
2536178 273 1966 1.78 1.50
2658234 273 1966 1.78 1.50
2658920 273/318 1966-67 1.78 1.50
2843675 273/318 1968-74 1.78 1.50
The 318-2bbl heads (4323302) used from 1985 on are a swirl port design with a closed (heart-shaped) combustion chamber design with a chamber volume of between 56 and 65 cc. The 4 heads I examined averaged 62cc in volume. The 302 head has 1.78"/1.50" valves and small ports averaging 54cc on the exhaust side and 118cc on the intake side. The intake ports have a more severe dogleg than earlier heads because the holes for the pushrods are larger - 11/16". Cars equipped with the 302 head have a dished piston to keep the compression ratio from being too high. Some cars left the factory with nail head exhaust valves in 302 heads, others with semi-tulip exhaust valves, which add 0.6-0.75 cc to the chamber volume. There is an interesting excerpt in "Mopar Engines", page 72, describing how such a head was ported and made to flow as well or better than other small block cylinder heads. Apparently, this experimentation resulted in the master for today's Mopar Performance P4452758 cylinder head
http://mopedia.org/2658920
