906 or 915 ?

I’ve owned a flow bench for 30 years.
That’s back when there were hardly any aftermarket aluminum heads for BBM available.
Long before RPM heads, and all the Chinese copies.

Back then porting factory heads was pretty common.

Thru the years I had many people send me their “home ported”(or heads reworked by a shop that didn’t specialize in porting and had no flow bench) to flow test them.

A typical ootb Stealth head flows 260-265.
With the seats recut and a proper bowl blend they’ll flow 280.

The heads people sent me to test were often in the 230-240cfm range.
On the very rare occasion I’d see something touch 260.
None were even close to 280.

I can tell you one thing for certain........ how pretty the porting might be........ is really not a good indicator of what they’ll flow.

Also, since MP always preached “don’t touch the SSR”, and most people took that to heart...... with regards to the 906/915 intake port in particular........ if you don’t address the SSR....... you’re never going to see big flow numbers from those heads.

That’s a long way to say........ if you don’t have the 915’s tested........ you don’t really know what you’re getting.

That being said, even if they only flowed 230’s-240’s....... if the overall curve was decent....... they’d still be fine for a 450hp type combo.

I did what I would consider an actual “porting” job(not just the bowls) on a set of big valve 906’s in 1990. That was the first set I spent that much time on porting some heads.
They made 535hp on a 448 with a RB SSH-44 cam.

A couple years later after I had my first flow bench I had the heads off and flowed all the ports.
They looked pretty........ but the 8 cylinder average was only 239cfm.

Like with many skills......”once you know” how to do it, it gets much easier.
Nowadays, I can get 260-ish out of a nice bowl blend, bull nose the guide a bit, and a SSR tweak.

Those 239cfm ports had the whole port reworked, all polished up, etc.
A lot of time for 239cfm.