PI Heads or NPI Ported?

97woodward · Mar 1, 2008

Hey everyone, Just wondering what the general consensus is on this. My 97 Gt (auto) is in the shop right now getting suspension work done as well as 4.10 gear install and dyno tune. Once it gets returned to me I will begin purchasing parts to do the PI Swap. I have talked to many people and have recieved plenty of perspectives, but I would like to get some more ideas from you guys.

Heres what my plan is, I am going to probably purchase a NEW Pi Intake manifold. Then either PI cams or Comp cams, whatever would be a better bet. I dont have a ton of mechanical knowledge so all of this work is going to have to be done by my mechanic. I am willing to learn but I also live in the city and have no access to anywhere to work on it.

The heads are the one area I am trying to figure out. Many people have mentioned getting the NPI heads ported since it will be much less labor costs. Is this the best route? I may supercharge in the future but not anytime real soon. Any help is appreciated.

rocknroll · Mar 3, 2008

You pretty much need to decide now if you're going to supercharge in the future.

If you plan on staying normally-aspirated the PI heads are 100% worth it because they raise your compression ratio from 9.0:1 to ~10.5:1. If you plan on running boost in the future port the NPI heads so you keep your stock compression ratio. 10.5:1 is way too high for forced induction. Compression ratios aside, I've read a lot that says a ported NPI head will flow as well or better than a PI head.

If you end up doing the PI swap a nice set of aftermarket cams will give you noticable gains, but they're not cheap. If it were me I'd use them over stock PI cams so you don't end up taking the motor apart twice if you decide PI cams aren't cutting it.

Red96GT · Mar 3, 2008

I too have heard ported NPI's flowed better than stock PIs from some pretty reputable people but haven't ever seen flowcharts or a dyno sheet to prove it.

rick focks · Mar 3, 2008

rocknroll said:
You pretty much need to decide now if you're going to supercharge in the future.

If you plan on staying normally-aspirated the PI heads are 100% worth it because they raise your compression ratio from 9.0:1 to ~10.5:1. If you plan on running boost in the future port the NPI heads so you keep your stock compression ratio. 10.5:1 is way too high for forced induction. Compression ratios aside, I've read a lot that says a ported NPI head will flow as well or better than a PI head.

If you end up doing the PI swap a nice set of aftermarket cams will give you noticable gains, but they're not cheap. If it were me I'd use them over stock PI cams so you don't end up taking the motor apart twice if you decide PI cams aren't cutting it.

word...

Jrgunn5150 · Mar 3, 2008

:wall: 10.5:1 is NOT too high, and it's actually 10.3 if you want to nitpick.

The higher your C/R is, the less boost you'll be able to run on pump gas, and the less boost you'll NEED to run in order to hit your power goal. In addition, a higher C/R will get you better mileage, better throttle response and an all around better car.

The one thing you really need to decide is how much money you really want to sink into a car, that at best, even if you go all out, will be hard to get 10k for.

97woodward · Mar 3, 2008

thanks for the replys. I am still deciding on supercharging or not, but as it looks now im thinking I will stay n/a. That being said Ive read on here that its fine to just replace cams and intake manifold. I am paying for all the installations so im thinking thats my best bet seeing as a head install or port would be real expensive.

Im trying to decide what cams to go for now. Ive been told that if i dont get the PI cams to get Comp Cams XE268H. Are there any other cams you guys would recommend? Thanks!

Jrgunn5150 · Mar 3, 2008

Cower's stage II N/A NPI cams are about the best NPI off the shelf grind.

9psi 98 · Mar 3, 2008

Red said:
I too have heard ported NPI's flowed better than stock PIs from some pretty reputable people but haven't ever seen flowcharts or a dyno sheet to prove it.

I actually have a flow chart from Steen Racing for my Ported NPI's that shows that they flow just as good as the PI heads (+/- 5cfm which is nothing). I'm at work right now, but I'll see about scanning it and posting it up as proof.

Red96GT · Mar 3, 2008

9psi 98 said:
Red said:

I too have heard ported NPI's flowed better than stock PIs from some pretty reputable people but haven't ever seen flowcharts or a dyno sheet to prove it.

Click to expand...

I actually have a flow chart from Steen Racing for my Ported NPI's that shows that they flow just as good as the PI heads (+/- 5cfm which is nothing). I'm at work right now, but I'll see about scanning it and posting it up as proof.

That'd be awesome! :thumb:

rick focks · Mar 3, 2008

i'd rather have lower compression and run more boost w/forged innards

Jrgunn5150 · Mar 3, 2008

But this is what you guy's don't seem to understand. Lower compression with more boost equals the same power, except under the curve, when you aren't in boost, you are giving up power. And you won't see full boost until 3k-3500, so for a driver, you would have an inferior combo. On the track it would be a different story, but most of us still street drive these things.

rick focks · Mar 3, 2008

i'm thinkin' 15 psi + :crazy2: :crazy2: :crazy2:

Jrgunn5150 · Mar 3, 2008

But you still don't see the benefits of full boost until higher in the rpm range. With a forged lower end, you could run 12 psi on 10.5:1, still be plenty safe, and have a better driving car.

Now if you wanna go all out for a track number, then drop compression to about 8:1 and run 18-22 psi, then yeah, that'll do it, lol.

rick focks · Mar 3, 2008

J.R. said:
But you still don't see the benefits of full boost until higher in the rpm range. With a forged lower end, you could run 12 psi on 10.5:1, still be plenty safe, and have a better driving car.

Now if you wanna go all out for a track number, then drop compression to about 8:1 and run 18-22 psi, then yeah, that'll do it, lol.

12 PSI ON 10.5:1????? SOLD!!!

Jrgunn5150 · Mar 3, 2008

I ran 10 on 10.5:1, but that was because I was worried about California's crap 91 octane and the 100+ plus days out there in the desert. I left everything super safe, since it was my main mode of transportation at the time.

rick focks · Mar 3, 2008

so you do how much to the wheels?
sorry for jackin' teh thread, i'm learnding and this is supa' important....the most important thing you'll ever read....

Jrgunn5150 · Mar 3, 2008

lol, my final number's with Foxlake Stage II heads, MPH custom cams, longtubes, etc, was 498 to the wheels, through a T56. My injector's were near 90% duty cycle, so I didn't try to take it any farther than that. Plus was paying 100 an hour for dyno time and I kept effing up, so it got expensive fast.

rick focks · Mar 3, 2008

J.R. said:
lol, my final number's with Foxlake Stage II heads, MPH custom cams, longtubes, etc, was 498 to the wheels, through a T56. My injector's were near 90% duty cycle, so I didn't try to take it any farther than that. Plus was paying 100 an hour for dyno time and I kept effing up, so it got expensive fast.

GGGGGOOOAAAALLLLLLL!!!!! 500 HP!!!! daily driver...that my friends ... is the promised land

Red96GT · Mar 5, 2008

9psi98 I hope you haven't forgotten about the flow chart have you?

Jrgunn5150 · Mar 5, 2008

Steen is out of business, but these are their number's, not all that great, but for 750, what do you expect?

Street Port Package: Probably the best deal out there!!! No switching intakes and all the other stuff that goes along with the '99+ PI headswap. These heads are worth it!

Includes: '96-'98 NON PI heads, ported (core), '99+ Larger exhaust valves installed, Competition 3 angle valve job, Full port work on intake and exhaust, New OEM valve springs and seals.

Flow:
Intake: 190 cfm @ .550
Exhaust : 165 cfm @ .550

'01+ PI cams (adds 10hp) - Add $235.00
ModMax valves are available!
Race Port packages are available for these heads