Preferred 'Stock' Cylinder Heads in Order Of Choice
1} ~ #2531894 'X-Head'.......................... July 1967 - thru - October 1970 'Casting'
Note; Called the 'X-Head'
Note; Generally considered the 'best' 340 Cylinder Head. Consistent 'Port Measurements' of 160 CC's Intake and 70 CC's Exhaust.
Note; The 'tightest' Combustion Chambers with levels between {67.0 to 69.0 CC's}.
Note; The 'X-Head' has the best Intake CFM Flow at High RPM's.
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2} ~ #2531894 'X-Head'........................ October 1970 - thru - June 1971 'Casting'
Note; Also with consistent 'Port Measurements' of 160 CC's Intake and 70 CC's Exhaust.
Note; These later 'X-Head' Castings will have approximately +2.0 CC greater Combustion Chamber volume, usually between {69.0 to 72.0 CC's}.
Note; When these later Castings were machined by the Factory, less material was removed from the Head Deck Surface than early Castings.
Note; This was done to lower the 340 Engine's Compression Ratio from 10.5-1 to 10.3-1 to meet the EPA's Emissions at lower RPM's.
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3} ~ #3418915 '1970 340 T/A Head'.... October 1969 - thru - April 1970 'Casting'
Note; Called the '1970 T/A Heads'.
Note; Specifically cast for the 1970 Dodge Challenger T/A 340 'Six-Pack' and 1970 Plymouth AAR Cuda 340 'Six-Barrel' engines.
Note; The Intake Push-Rod Guide holes were bored further away from the 'outer' Side-Wall of the Intake Ports.
Note; This was done to allow for Racer Modifications, to allow for more material to be removed from of the 'outer' Side-Wall sections, which will increase Port Volume and CFM Flow.
Note; Special 'Off-Set' Rocker Arms were required for these 'T/A Castings'.
Note: The Combustion Chambers of these 'T/A Castings' usually came in at {69.0 to 71.0 CC's}.
Note; The Intake Ports on the '1970 340 T/A Heads' are a miniscule amount tighter @ {158 CC's} than the 'X-Heads' @ {160 CC's}.
Note; But, the Intake Port floors of the 'T/A Casting' have a slight improvement between the Bowl and short-turn Radius.
Note; This allows for an improved Flow {approximately +10%} at very low RPM's.
Note; The Exhaust Ports on the 'T/A Head' are a tad larger in Volume at {72 CC's} than the 'X-Head' at {70 CC's}.
Note; The Exhaust Ports on the '1970 340 T/A Head' also do have a slightly better Flow-Rate than the 'X-Heads', at approximately {+5%} across the full RPM Range.
Note; Despite the slightly minor differences between the 1970 'T/A Head' and the 1968-thru-1971 'X-Head', both Cylinder Heads delivered similar Flow-Rates.
Misconception; It was thought at one time, that the '1970 340 T/A' Heads left the Factory with larger Intake Ports. Which is incorrect.
Note; The 1970 Dodge Challenger T/A and 1970 Plymouth Cuda AAR were built between March 10, 1970 and April 17, 1970.
Productions Numbers; Challenger T/A {2399} and Cuda AAR {2724}
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4} ~ #3418915 'J-Head'.......... {w/2.02" Intake Valve} ..... July 1970 - thru - May 1971 'Casting'
Note; Called the 'J-Head'.
Note; Primarily found on the 1971 '340 Engine'.
Note; These 'J-Heads' were cast at the Foundry with 1.88" Intake Valves and 1.60' Exhaust Valves.
Note; The Heads were then re-machined at the Machining Division, and the Intake Seats were bored and reamed to accept 2.02" Intake Valves.
Note; The Combustion Chambers of these 'J-Heads' came in at {69.0 to 73.0 CC's).
Note; The Intake Ports of these 'J-Heads' did flow at approximately {-4%} less than the 'X-Heads' @ Optimal Lift.
Note: The Exhaust Ports did flow at a near identical CFM Rate as the 'X-Heads' {140 CFM @ .500" Lift}.
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5} ~ #3418915 'J-Head' ............ {w/1.88" Intake Valve} ......... July 1970 - thru - June 1972 'Casting'
Note; Also called the 'J-Head'.
Note; Cast at the Foundry with a 1.88" Intake and 1.60" Exhaust.
Note; Cast with a {69.0 CC to 73.0 CC} Combustion Chamber.
Note; These 'J-Heads' were found on the {1971 - 360}, the {1972 - 360} and {1972 - 340 'Low-Compression'}.
Note; Regarded as an 'Intermediate Performance Head'.
Note; The Intake Port with the 1.88" Valve did flow at approximately {-2%} less than the 'J-Head' with the 2.02" Intake Valve @ Optimal Lift.
Note; But at Low-to-Mid RPM Ranges, this Head actually out-performed the bigger Intake Valve Head by {+3%}.
Note; The Exhaust Port is found to Flow at {-6%} less on this Head than the 'X-Head' or 1971 340 'J-Head' @ Optimal Lift.
Note; Though 'not' the Optimal Flowing Head @ High-Lift or High RPM's, but for 'Street Performance' it is more than capable of performing well.
