4 different DOHC heads. 2nd gen 3N, 1st gen 3T, 3A from a 3.5 and then the MIVEC.
The 3N came from an NA 2nd gen GTO , unsure of year.
The 3T heads from a 1st gen GTO TT.
The 3A from a Pajero 3.5, 1995.
The mivec from a Diamante 30M, maybe '96 or '97?
In terms of stock performance, the 3N makes, 220 ish HP so 73 HP per litre.
The 3T makes 280 HP in a GTO and compensating for 0.5 bar of boost would make 185 HP or 62 HP per litre.
The 3A in the Pajero 3.5 makes maybe 220 HP or 62 HP per litre.
The mivec makes 270 ish HP in the Diamante, that's 90 HP per litre.
Well, so what? If you want to build the best engine, you start off with the best parts. Unfortunately most seem to think that all there is, is NA and TT.
OK so TT is the best (no it's the worst but makes the most money) You want to port it? That's $$$$$ and still inferior. What you've done is you've knife edged the divider and removed a lot of strength from the structure. Where the head gasket leaks is in the fire ring on the intake side and if you were to drill a hole there you'd go through the edge of the water jacket then when you keep going you end up at the divider which you've just removed. That's a fail. Zero out of 100. OK so next is the water jacket pinning job. That's even more $$$$$ and an even bigger fail. Because you cut it away between the ports. Then after the welding that softens the head you've got to reface it, that makes it thinner and weaker. End result, scrap metal. All you need to do is use 3N heads? But they're free and nobody makes gazillions of $$$$$.
As for the port shape of the 3T heads, the divider disrupts flow at high speed, the floor of the port is too low and needs lifting.
As for the port volume, I've got it written down somewhere but from memory the 3T is 129cc, the 3N, 130 cc, the mivec about the same and the 3A much less, just over 100cc.
The 3A if you do some googling, might be what's considered to be a "venturi port" for good low down torque but maybe not so good top end.www.3si.org/threads/ported-he... Go to the very last post. Then look at the pic in the previous post. On the way try not to laugh about the ozzy porting jobs.
Another www.3si.org/threads/do-i-need...
There's plenty of good forum links www.3si.org/threads/advice-an... Why would you start off with something so inferior when you could start with a far better head casting? And no need for porting.
I've seen pictures of ported 3A heads from 3SX. Ported 3T heads from 3SX and pictures of ported heads from DR that look just like stock 3N heads.