T/A heads

I work on a fair amount of stuff where any blending/porting/bowl work isn’t legal....... so I def don’t consider it as something that’s included as part of a “normal” head reconditioning.

On heads with fairly tall/steep short turns, if you don’t address the short turn to some degree as part of the bowl blending, you will often end up with less high lift flow than if you hadn’t done any porting.

If the bowl capacity exceeds the short turns capacity by enough, the air column starts skipping over the turn, and that effectively blocks off a portion of the bowl....... and the flow numbers start dropping as the lift increases.
On the stock port I tested, even the unblended bowl was overtaxing the stock short turn.

So, when I do the bowls...... I at least make some attempt at addressing the short turn to try and keep the flow backing up situation in check.

Sometimes there is still some minor flow regression though....... although it would be less than if the short turn hadn’t been tweaked.

One thing to keep in mind is, these stock heads can vary quite a bit in stock form.
I had a pair of factory 2.02 915’s off the same motor.......with only a fresh valve job, one flowed like 215....... the other only 196.
I’ve had some fairly low mile T/A heads here that still had the not-too-beat-up factory valves and valve job...... those were only 200cfm.

Also.....My experience has been that stock X heads typically outflow stock J heads.