NPI and PI heads question

avexhype · Dec 25, 2007

Looking to get ported heads for my car very soon. I dont have $1300 to just get ported stock heads so i found this guy in my area that can do it for around 400 (very reputable and experienced person, 3 stang guys recommended him).

Now, i have ZERO down time available for my car since its my DD so i must buy heads seperately then put them on later when i have a day or weekend off. Now heres my Q's

1. PI heads are just ported NPI from the factory right?

2. If yes, does that mean i can buy NPI heads and let the guy port those instead of PI heads and get equal flow and power than if i would PI heads? (since its just like a NPI skipping a PI swap and just porting his NPI heads) This yeilds the same results right? (NPI will need more porting than PI heads)

3. If no, then whats the difference between the two heads?

Thanks so much and happy holidays

Winters98GT · Dec 25, 2007

no, you shouldnt put NPI heads on your already PI car, its not gonna work. The heads/cams/ and intake required are completely different. You have PI heads already on your car. The compression will be low, low, low, with NPI heads and they dont flow as well as PI heads. Ported NPI heads will work on 96-98 cars.

Zero down time? Its not gonna happen. Unless you have the funds to buy new/used PI heads to have them ported, your not going to be able to do this.

When doing serious head work on your car, its always a safe bet to have a backup mode of transportation until you make sure that everything is running properly. Ive had two headswaps done on my 98 car, both with no problems and it was my daily driver, but it is not without risk.

The two heads are different. NPI heads came on the 96-98cars, 99-04 were PI heads. Putting PI heads on an 96-98 motor raises the compression, because the 96-98, and 99-04 cars have different pistons.

My recommendation is to do a ton of researching here and the other sites by using the search button. It sounds like you have a lot of information that you need to the gather before considering doing this swap.

Good luck and Happy Holidays as well!

Mark

COramprat · Dec 26, 2007

avexhype said:
Looking to get ported heads for my car very soon. I dont have $1300 to just get ported stock heads so i found this guy in my area that can do it for around 400 (very reputable and experienced person, 3 stang guys recommended him).

Just a P&P? Not worth it. You won't see much of a gain so don't waste your money. For the 400 I'd look to get cams...even a mild cam will net you 25-30HP tuned. If you look you can find low mile used cams for about half of what they cost new.

Now, i have ZERO down time available for my car since its my DD so i must buy heads seperately then put them on later when i have a day or weekend off.

See cam swap above. Can be done in a day.

Now heres my Q's

PI heads are just ported NPI from the factory right?
...etc

No...they are completely different. The ports are shaped different as well as the combustion chamber volume. The reason you see a lot of swapping between NPI to PI is the ease of bolting the heads and cams and the increase in HP. Since the ports are different the intake manifold is also different and the NPI manifold is crap. You would be going backwards. You see quite a few intake only swaps in the NPI cars by installing the PI intake and sealing the port differences with RTV and getting better flow. If you installed your intake on ported NPI's you would lose any advantage to porting the NPI heads due to airflow turbulence between the PI intake and NPI heads. Although the loss is minute so is the gain from the P&P.

That said the loss in the NPI cars is more in the intake design and cam specs than in the heads.

avexhype · Dec 26, 2007

wow the replies really opened my eyes. Thanks guys im just going to have to put off messing with the heads for a long time. Ill stick to bolt on for a bit and will get back to this later... it can get stressful

COramprat · Dec 26, 2007

If you really want to get some gitty-up install new gears. 3.73's or 4.10's will hit the spot. That can be done for about 600 tops with labor.

screamin gt · Dec 27, 2007

when you do have the heads done, have them do a valve job as well as the polish. just the valve job alone is worth more than the polish. the stage II patriot heads are just pi heads with a valve job and polish as far as I know.

avexhype · Dec 27, 2007

thanks for the advice guys will deffinetly look into it.

Oh i guess i forgot to update the sig, i had 3.73's installed 2 weeks ago =)

NPI and PI heads question

avexhype

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Winters98GT

Whoop...whoop-whoop-whoop-whoop...GANGNAM STYLE!!!

COramprat

...I can take it. I think.

avexhype

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COramprat

...I can take it. I think.

screamin gt

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NPI and PI heads question

avexhype

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Whoop...whoop-whoop-whoop-whoop...GANGNAM STYLE!!!

COramprat

...I can take it. I think.

avexhype

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COramprat

...I can take it. I think.

screamin gt

avexhype

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