The TF intake port is the same diameter as a PI head but they are longer and this is where the port volume increases so to get the same port volume as a TF head you must port the PI heads a lot and that causes problems. Where and how makes a big difference and I sent 40 hours per set of PI heads and had lots of failures hence the 13 engine builds. I am the guy that has to pee on the fence wire to see what it feels like.
I have made good ported heads that failed over time slowly because as a cast product then the walls get thin but still pressure test fine they can weep and slowly hydrolock the cylinder. TF runs a long stock port with a bigger valve and a custom cam and unless you go BIG on a PI head you will not match a TF head for power and at the price in the long run it is cheap. One problem I found is the long tapered valve guide is high flow but easy to brake and they shattered junk bounces back into the manifold and goes to all the cylinders and did in one my engines. How?
When doing your clay check for VtP clearance if the valve gets deflected at all the guid will crack, cam locks help on install to keep the chain jump shock when doing a change.
After all is said and done a TF head change in the car with just head gaskets and new bolts is the fastest and cheapest way to get to 400 crank HP NA on a stock NPI engine.
That's really interesting. How much longer from the port face to the seat, say a line strung though the ports dead center? I'd tend to think thats more of a side effect of moving the intake valve, but ive not seen the cross section of how the TF heads are compared to Npi/Pi.
I tend to view this in terms of port length being only the first half of the total intake runner length. Paired with an aftermarket intake I bet it works well.
Runner volume is really only an approximation of average runner area (since that cant be done exactly due to the shape changing).
At least on the NPI heads Ive seen, this is one of the bigger limitations of the 2v head. The heads can be ported, but barely enough to be adequate for stock valves, unless its a max effort porting job. There's just not enough material to port out. The PI heads are a little better in this regard, but not amazingly so.
We've pushed the ford design way past what they designed it to handle. The emissions and mileage goals I believe forced the larger exhaust valves, which forced the smaller intake valves. It makes the exhaust/intake flow ratio like 80%, when pushrod heads like the GT40 heads are around 70%, and extreme heads like Pro Stock are close to 60%. It's also why these cars just love boost, the exhaust doesnt get bound up, and the intake shines with pressure.
What I'm getting at is that the TF heads would need to have a larger average cross section than the Ford heads to be better, and I'd bet thats the case The CCs is really only useful when the length is close to the same. Other than that it's really only good as a before/after.
I'd love to see (total CCs/runner length). That would be more telling.
All just IMO, of course.
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