modmonster said:
Look dude im not trying to be a dick or nothing but the valves are so different in size that you can see it. Look around for pictures because I have seen one on here before that showed the size difference and that was obvious to the human eye. Those #s are off. PI heads really brought the sohc mod motors to life. Cam profile and lift is also different but PI heads flow a good bit more of air then NPIs.
I am not trying to be a dick either but the PI heads are not better than NPI. It was not the PI heads that brought the 4.6L SOHC to life. Kris Danner and Johnny Langton proved that.
Way back in 99, 00, 01, 02, people were looking to modify 4.6L Tbirds. The easiest thing was the PI HeadSwap. For the 94 - 95 TBird guys, it was hardly cost anymore to swap in a PI motor as those TBirds required a bunch of 96+ plus parts to do the headswap. Like I stated above, these "PI" powered birds are/were making 210 - 230 HP at the wheels. Big Scott or Dr.FrankenCougie depending on what forum you are on does a N/A PI buildup. He used Fox Lake P&Ped PI heads/PI cams/Intake/Forged internals in his 94 Cougar and put down 256 RWHP.
Along comes Johnny Langton, he is the first to swap "PI" Cams into NPI heads, gained 13 RWHP from it. He then gets his NPI Heads port and polished and is aiming to run 12's. He then finds out that his car runs out of air at around 4000 RPM. He thinks the NPI intake is the restriction, so him and Kris Danner modify a PI intake to fit his car. He then gains 17 RWHP and 39 RWHP at the peak. Johnny's 97 Tbird made 254 RWHP with this setup. 2 less HP than Scott did with similar all around mods. They had the same cams, intake, compression ratio and all around mods, ie. exhaust.
He took a lot of crap from people when he did the cams, he took a lot of crap from people when he did the intake. People were questioning the what Johnny had done.
Kris then went on to show by putting PI Cams and PI intake on a stock 96 Cougar, he made 217 RWHP, which is right on par with what PI Powered Tbird/Cougars were making. A few other people have gone out and did this as well and the numbers are ranging from 212 - 228 HP at the wheels. Identical to PI motor/head cars. All being equal, compression, cams, intake, the PI's are not making any more power than the NPI's and if they really flowed more on the intake side in an N/A application, they should be making more power but they are not making any more.
Anyway, I happen to know the valve sizes of both PI and NPI heads. I don't need to see pictures.
PI head valves:
Intake...1.75"
Exhaust...1.41"
NPI head valves:
Intake...1.75"
Exhaust...1.33"
The valve sizes came from a very trust worthy source. Head flow numbers are all dependant on how they are done. Everybody( Fox Lake, SHM, etc. ) has different flow #'s. The numbers I got also came from a very trust worthy source. Those NPI's #'s I posted are from the F5( 96 -98 ) casting, what did SHM use? Did they use the garbage F4( 91 - 95 ) casting?
I am not going to debate PI VS NPI any further, I am done with this. You can want to believe the PI head is better but it has been proven that the head itself is no better than the NPI.