Truth about NPI vs PI

blackfang

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Alot of people have gotten on the bandwagon by thinking you need PI heads with the PI cams and PI intake. You don't and there are some running 12.3's on NA NPI headed motors.

For the owners of the 1996 – 1998 Ford 4.6L 2V Mustang GT, the PI (Power Improvement) swap can provide an excellent power boost for these underpowered motors. The PI swap may consist of a complete head and intake swap for full power benefits or just a PI cam and intake swap for decent power gains and other considerations. The pros and cons of both are discussed below.

Note: 1996 – 1998 Mustang GT’s are non power improved (nPI) equipped cars. 1999 – 2004 Mustang GT’s are power improvement (PI) equipped cars.


The PI cam and intake swap also provides decent power gains absent the draw backs associated with the PI head and intake swap. Swapping PI cams and a PI intake on nPI Stangs results in a 30 – 35 RWHP gain. The cams alone result in a 13 – 16 RWHP gain and the intake results in a 15 -18 RWHP gain. The extra 10-15 on the PI head is the bump in compression with an added cost for the heads.

The benefits of this swap are lower costs, less labor, and the fact that you maintain stock compression ratios. PI cams can be purchased used from many parts forums (such as those found on Corral, Modular Depot, or Mustang World) for about $100. PI intakes can be purchased for $100 - $200 depending on condition and whether or not they have the aluminum cross-over (recommended). The install kit with all the gaskets, heater tube etc, is about another $50 - $60. Therefore, for about $300 or less you can obtain up to an extra 35 RWHP making this mod an excellent dollar for horsepower gain! In addition you can use the saved money to port the NPI heads that will have more hp than if you went the PI head route. Some of the common rebuttles is "well i will prot the PI heads then". However, the drawback is that you have introduced much more airflow that the Pi cams, which are oem btw, can't be used to their full potential resulting in no real gain, but possibly a loss of hp. Too much airflow for the cam setup isn't going to yield hp.

When swapping PI cams, I recommend that you purchase 2001 + cams. These cams are Romeo cams (manufactured in the Romeo plant) and they have bolt on sprockets. Since the sprockets can be unbolted, you can use the Anderson tool to swap the cams. This makes the job a snap since all you have to do is take off the valve covers, cam covers, use the tool to hold the timing chain in place and then swap cams. Conversely, to do the entire PI head swap, you will have to either pull the entire motor, or tear it down in place to remove the heads.


The PI intake is a considerable improvement over the nPI intake. With its increased port volume and improved runner design, this intake has been shown to give up to 18 RWHP increases to the nPI equipped Stang.

When swapping the PI intake on nPI heads, make sure you purchase nPI gaskets since these gaskets seal the water ports. Failure to seal the water ports can result in coolant leaking into the combustion chamber and subsequent engine failure, so be sure to use nPI gaskets. Although these gaskets effectively seal the water ports (a must), they do not completely seal the intake ports. You must use high temp silicone sealant (permatex) to seal these ports. AGAIN… only apply the permatex to the intake. Applying excessive amounts of sealant can cause it to ooze into the intake port and obstruct it resulting in hesitation and reduced power.

I hope this helps any future 96-98 GT owners that you do not need a PI head to make power with these cars. Johnny Langton pioneered the first PI cam and intake swap and his 4.6 2v NPI motor runs 12.3 so he is proof this can be done and on a budget.
 

215horsesbaby

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Good quality post man! Someone new to the 4.6 mustang world would have gained alot of knowledge plainly and easily right there! :thumb:
 

BlueStangGT

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Thanks for the useful information man. That covers about everything about it in one post.
 

JerZeyStangz

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Wow, thanks for the head knowledge man! Now i know why my new PI intake on my 96 GT is leaking a lil bit of coolant behind on the right side of the intake...The shop used a speacial kind of the sealant like you mentioned above around the intake manifold but tyme to tyme it will leak a few drops very unnoticable without a trained eye but i can smell it burning off the block sometimes! Thanks so much!

Honestly I thought my PI intake manifold was faulty (meaning it bad from the factory). Thanks! Is there anything I could do stop this little leak of coolant of I have to live with it for the rest of my life?!?

Nate
 

Dan95-5.0

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good post man. theres a local guy with a full PI swap in a auto.

thinking of challenging him off the juice.

with your article, i got a further understanging of what the PI swap is and does.

thanks
 

blackfang

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Ram000 said:
i'm too lazy to find sources for P=performance.  great post, nonetheless.
:banana:
Not me, that's why I research as much as I can before I post it;) :p
 

98GTSTANG

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Awesome information. I have been contemplating the swap for a long time. You just saved me a ton of money when the time comes.


[attachment deleted by admin] SORRY RAN OUT OF ROOM, RE-UPLOAD IF YOU WISH!
 

ALITL8

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great thread. thanks for the info, blackfang!

hey BlueStangGT, nice car man!!!
 

Dalamar

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Good info Blackfang.
Thanks for sharing.

It depends on how far you want to go power wise.
You can only force so much air through the stock headports.

Prices have definately come down since I did mine.
 

ALITL8

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hey guys, got a question... will my 97 cam gears bolt up to another set of 02 saleen cams for this budget swap. found some cams with 10K and springs but no gears :dunno: what do you think i should offer for them if they'll work??
 

Dalamar

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I dunno exactly,
My cam gears bolted onto my PI heads.
Theres a picture of it on the head in my
I'd call an engine tech at ford and ask them what you'd need.

You can see it on my PI head - picture in my member gallery.


If you do the cam's you should also do the PI intake, it's only a few hundred bucks.

The intake has Way better runners, less flow resistance = more power.
There's decient gains to be had from cams and the intake swap, if you don't do the Heads.

intakesfront.jpg
 

ALITL8

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ive already got my PI intake, just wanted to know if these cams would work with my gears. i think im gonna offer him $50, he said he really needed to get rid of them.
 

DropTopPony

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ALITL8 said:
hey guys, got a question... will my 97 cam gears bolt up to another set of 02 saleen cams for this budget swap. found some cams with 10K and springs but no gears :dunno: what do you think i should offer for them if they'll work??
I didn't know saleen made Modular Cams, are they just PI cams?
 

DropTopPony

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oh and your cam gears will swap right over, but you may need to get new cam gear bolts.
 

ALITL8

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DropTopPony said:
oh and your cam gears will swap right over, but you may need to get new cam gear bolts.

thanks man! guess i know where im getting cams now ;D
 

Dalamar

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Sonds fun.

What are the specs on the cam.
Do they have an overlap?

Let us know how it turns out.
 

ALITL8

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Dalamar said:
Sonds fun.

What are the specs on the cam.
Do they have an overlap?

Let us know how it turns out.

they are just the stock PI cams out of PI heads. once i get everything together and have it installed i'll run it up to the local dyno and post the results. im not a mechanic and really dont know the specs on these cams i just know they are better than the 97 stock cams :dunno:
 

myillwillinc

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when i still had the 4.6 in my gt i did the PI swap along with headers and off-road x-pipe. it felt like a whole new car when i stomped the gas. now i have a nonPI 5.4 and i'm trying to decide to drop the PI heads on it or try to get cobra heads for it...
 

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