[RalliartRsX]

Originally Posted by jr_ss

I think the P12 head is just an expensive piece of hardware that doesn't benefit you in anyway shape or form over a P11 head with the same cams. I have yet to see flow numbers for a P12 head. The only thing that supports this claim are the components in the head and slight changes in the casting. They have weaker valve stems(smaller diameter), require custom spring retainers and are more expensive to acquire. The only benefit are the cams are much better than the P11's but that doesn't matter if you're swapping them anyway.

You will need to upgrade your valve springs. You can run the factory P12 springs with the P11 inners for a cheap upgrade. They experience valve float in the higher Roma without an upgrade.

Agreed for the most part. For example; P12 head has the 5.5mm exhaust valves vs the 6mm valve. Also, the casting for the P12 head seems to shroud the valves a bit more (it seems the P11 head is better in this regard, but it may still be hit or miss as sometimes the cast would shift during manufacturing).

However, all depends on what the owner wants to run.
P12 head comes with the CAS, coil packs and the valve cover (about $600 in value by themselves). So once you sell everything else off associated with the 6spd FWD and internals (pistons/rods, etc), if one wanted to keep it simple, all you would have to do is go Nismotronic and done. John with the Camo S14 made well over 1000WHP and ran deep into the 8s, used Nismotronic until this year, when he switch to Haltech.


Also, a gentleman did do a flow bench test of a P12 vs a P11 head as recently as of last week (I have the images and flow numbers somewhere). However, he switched out the 5.5mm exhaust valves for the 6mm (which anyone turbocharging this setup will do). As it turns out, the P11 did better up top but fell short a few cfm below .250. The gentleman mentioned the valve shrouding being an issue (and ofcourse, the thicker valves as a good amount of flow is gained from going to a skinnier valve).

Either way, you can't go wrong with either livelovesole. Just make sure you lay out your plan of action, as that can be a $500-$1000 different in prep work (I think the machine shop quoted me $125 + parts for new valve guides (it didn't matter if it was 5.5 or 6 as the work is the same) and redoing the seats). In addition, the P11s do have problems with exhaust valve guide leakage in particular, so I would address those if at the machine shop as cheap insurance.

EDIT 1: Inlet manifold should be the same cost throughout and you can run the P11 dual valve springs (from Supertech) and be just fine if you end up with a cheap P12 head.

EDIT 2: P12 has better cams than the P11.

EDIT 3: With the P12 swap, you will need the P11 oil pimp spacer (P12 is two piece, P11 is correct one piece shorter spacer)

In all honesty, if I was to do it again, I would buy a P12 full swap, sell everything not related to the RWD swap, drop in P11 supertech spring and 6mm exhaust valves, slight deshroud and run nismotronic.