Contour Enthusiasts Group Archives Forums Modifications Duratec Performance P&P heads

3L exhaust valves are 30mm and the 2.5L exhaust valves are 26mm.
The intakes are 35mm and 32mm on 3L and 2.5L respectively.

I played with my dyno simulation program many times on this and I also have practical experience on these motors both 2.5 and 3.0.
If you stay 2.5L my opinion would be to have new 30mm exhaust valves cut into the heads but stay with the 32mm intakes with heavy porting. This may cost you a tad torque below 3500 rpm, but it will give you the breathing capability you will need about 5500-6000 rpm where you will end up making your 200 fwHP. Then when you decide to put those heads on a 3L it will perform just as well as any 3L with 3.0 valves. I have already ran the simulations for the 3L with 32mm intakes and 30mm exhaust versus 35mm intakes and 30mm exhausts and it makes little difference in overall power. In fact the torque remains higher in the midrange with the 32mm intake valves on a 3L. This is all based upon indirect assumptions from many engine projects and the computer simulations, but it is a good enough assumption that I would use it if I were doing a two stage project later on. That includes 2.5L N/A -> 2.5L turbo or 2.5L N/A -> 3.0L N/A.
It would still work fine if you went three steps from 2.5L N/A -> 3.0L N/A -> 3.0L turbo.

war......