head comparison

rod7515 said

I know the bottle neck in the motor I will be running in my dart is going to be the 915 J heads. I did step up the valve size when I had them redone.
So heres my question:
What does a 915 J head flow stock? how much more with the larger valves. And how much would I improve the flow if I swapped them out for a set of x-heads? What do X-heads flow?
Thanks
Rodney

Click to expand...

Measured Stock Cylinder Head w/Competition Valve Job

#3418915 'J' Cylinder Head

........................{1970 and 1971 Casting} ............ {1972 Casting}

Intake Valve..................... 2.02" .................................. 1.88"
Intake Bowl Size................ 1.75" {86.6% of Valve}

Exhaust Valve.................... 1.60"

Intake Port Volume............ 157 to 160 CC .................... 150 to 152 CC
Exhaust Port Volume.......... 71 to 73 CC

Intake Flow @ .450" Lift...... 213 CFM ........................... 190 CFM
Exhaust Flow @ .450" Lift.... 146 CFM

Intake Flow @ .500" Lift...... 220 CFM ........................... 196 CFM
Exhaust Flow @ .500" Lift.... 148 CFM