The Chapman heads used specially machined castings and used longer valves than std stage6’s.
The main hurdle for big power with stage 6’s and bigger cubes is the lack of port area at the short turn under the valve spring.
The head is very thin there.
So, the smallish csa coupled with larger displacement means the motor is going to peak at a low-ish rpm.
It’s easier to make hp when there’s enough port area to allow the torque curve to carry well into the upper rpms.
If the OP’s heads are std port size, then there would(should) be a rather large increase in power going to a TF270 head and appropriately sized manifold.
If the current combo has MW sized heads and manifold already, then the gains would be less........ and would depend on exactly how well the current heads are working.
I can add this......... from an airflow standpoint........ I was involved with those heavily modded stage 6’s in the pics in this thread.
Those were the best non-Chapman stage 6’s I’ve tested.
The TF270’s outflow those.
Re-read the first post-
My heads and intake have been ported but are still the standard ports.
The std port heads can have the opening made into MW size, but they won’t quite be the same as the actual MW stage 6’s.
Those had relocated intake pushrod holes and used offset intake rockers(like what’s done with W2 and Victor heads) to allow the removal of the pinch.
Trying to get a set of std stage 6’s to be “comparable” to TF270’s will cost more than buying the TF’s.
