It depends on the application. If your staying NA you need to have all the supporting bolt ons to get the benefit. Like intakes/exhaust/cams etc. Maybe 30hp? I know another guy who put fox lake P&P heads and PI Intake on his blown car and picked up over 100rwhp. Its all about where you want to be at and how much money you want to spend.
i have done this, everyone is right you wont pick up much unless you get cams also. with the heads and cams i picked up 35rwhp and 20 rwtq, but im building this car for the blower. i got blower cams which dont make as much as if you were to get n/a cams. then you would might get 45rwhp.
gog i hope to see 100 additional hp once i put the blower on. that would be nice
I did a P'n'P to my '01 PI castings, as well as smoothing and polishing the combustion chamber and a fresh 5-angle valve job. I've got quite a bit of porting experience with the old E7TE Iron heads and intakes, so I chose to tackle the job myself. All in all, it cost a couple of long shank Carbide cutters, a few sanding rolls and about 40-hrs worth of blood and sweat. It was a lot of work, but well worth it to me in the end, when you consider what it would have cost to have them shipped out and professionally done.
You likely won't see much with a stock or near stock set up, but it's well worth it with a few heavy duty bolt-ons, or on a blown engine (like mine).
I'll post Dyno numbers next spring when I have a chance to get it to the tuner, but since my engine and blower combination is kind of a unique one and I have no previous baseline to compare it to.....It probably won’t do most of you a lot of good.
I knew someone was going to ask me this.....I really planned to, but didn't have my digital camera on me that day and needed to get the engine together......so, I can't say that I do. I pretty much did a gasket match of the intake and exhaust ports and necked them down as they reached the bowls. When I got to the bowl area, I essentially just polished them up and removed the casting flash. To really do it properly, you should have the old valve guides pressed out, in order to polish the bowl area to a mirror finish, but I didn’t feel like springing for new guides and wasn’t sure if I could just press them in again afterwards, or if there was a special method to install them, or the need to have head machined for oversized guides, so I was just careful and worked around my existing one. As for the chambers, I basically got rid of all of the hard edges where the valve seats were machined into the head, to improve flow around the valves and polished up the chamber itself. I left the air damn where it was, but I did take the hard sharp edges off of it.
If you're interested in seeing some, I did collect a few pictures of Ported PI, NPI and SVO heads before I attempted mine, for a little research. There are too many for me to post on Stangnet, but PM me with your Email address and I'll be happy to send them to you.