Small Block "Unported" Heads......Stock 308 vs X or J Castings???

[woody9512]

  Does anyone know from experience how unported "Stock" 308 small block castings with added 2.02 valves would be performance wise when compaired to the stock 340 X head or the "J" head with added 2.02's......I always hear of the 308's being very good performance wise when ported.....BUT....left stock and adding 2.02's would they be better or worse performance wise than the stock X head or the "J" head with the 2.02's?
   Thanks  "Tim"

[dimples]

The exhaust port holds the older heads back, and that is fixed on the newer 308 head, intake port, from what I remember seeing once, on the net, haha, flows about the same.
I really don't think you will see much of a gain from the bigger intake valve though, not without some shroud and bowl work.
Cam selection changes with the different heads too.

[Chryco Psycho]

not sure I always port them 

[moper]

The 308 is a "high velocity" port head. The exh side is quite a bit better than any X or J "as cast". But, but adding the 2.02 intakes, you will want to either have the vavle job done with 5 angles and cutters, not stones, or, have the bowls cleaned up. I've gotten 230-240cfm with porting from both, with 2.02 and/or 2.05 intakes. If I was concerned with overall flow, and having to run an iron head for street racing or class rules, I'd run the 308s long before I ran Xs or Js. I'd bet with 2.02s and a 5 angle job, they would outflow the factory 2.02 Xs or Js, but if the same valve job was done on the Xs or Js, they would be very close on the intake sides.