NPI and PI engine questions??

[188slo50]

Im totally confused on this! Ive read that the npi motors are from 96-98 and the pi is 99-04 but have also been told the pi motors are from 00-04. My question is I have an early 99 and want to know if my engine is original. Wheres the engine ID plate and how do you read it? The reason Im wondering is when I got the car it was cosmetically in poor shape but the underside of hood/motor is very clean(its got 160k on it) no oil leaks or anything and Ive put 5k miles on it and still no hidden leaks. Thought maybe someone went through it prior cause the previous owner didnt know or could tell me anything.

 

[BigBore96]

If its ANY 99+ it is PI. You may have been reading about the differences in PI motors with the Windsor/Romeo builds. There is like a 0% chance the owner swapped it back to NPI. Most owners wouldn't dare tear into a 4.6 out of fear of timing chains.

If you want to know for sure. Take pictures of you engine, close ups of the Intake, especially it mounting on the front areas and a good entire intake pic and I'll tell you what it is.

 

[FrankenStang]

what side is ur oil fuiller on, a 99 Pi impretty shur its on the passengers side and you have 13bolt valve covers...and ur PI manifold should be ALL plastic..look on the drivers side valve cover or passengers maby for a manufactor date,always had them on that year..should be ?/??/1999

 

[cobra clone 98]

i have a 98 gt and it has the plastic intake.. but my oil filter is on the driver side..

 

[188slo50]

Yes oil filler is on the drivers but can you swap npi and pi valve covers? It does have a PI intake for sure, do the windsor/romeo motors only come after a certain time? Whats the benefit in those platforms? I also was wandering why if its in park and you rev it up is there a vibration at 2500rpm?

 

[sn95jones]

He said oil FILLER not FILTER. And all npi and pi motors have plastic intakes with the aluminum coolant crossover unless your sn95 hasnt had it replaced yet due to the faulty plastic crossover cracking.

PI motors will have the oil filler neck on the passenger side Frank is correct and for fawk sake Frank spell "shur" right!!!! Its sure, SURE!!!!

 

[sn95jones]

Yes oil filler is on the drivers but can you swap npi and pi valve covers? It does have a PI intake for sure, do the windsor/romeo motors only come after a certain time? Whats the benefit in those platforms? I also was wandering why if its in park and you rev it up is there a vibration at 2500rpm?

*sigh*

ALL 1999 - 2004 Mustang GT had the PI set up and no the valve covers wont work the heads are different. The difference in power is about 60hp the PI set up is called PI because its callrd Performance Improved. The heads are different, cams, and intake are all different.
The vibration at 2500rpms could be a bad harmonic balancer or you could have bad motor mounts

 

[188slo50]

I checked the mounts and they look good I also checked the harmonic and didnt see any rubber puling from it. I may just replace both eventually cause I want to start looking for another motor for it since this ones got 160k.

 

[cobra clone 98]

sorry i read that again and i thought he said filter lol... my bad. yea mine has the alumin cross over to.

 

[cobra clone 98]

by the way how much hp can u gain by swapping to the p.i heads, cam and intake???

 

[Ferocious]

by the way how much hp can u gain by swapping to the p.i heads, cam and intake???

About ~60hp. A Pi swapped npi car should be faster than a pi car due to the small bump in compression and tiny bit of added power by swapping on the heads.

 

[rz5.0]

I thought some early 99 models got npi...

 

[turion94]

Here is a article you might find helpful....

stock npi engine= 215hp
stock pi engine pi heads= 260hp

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.

 

[cobra clone 98]

so basically if i get 01 plus p.i cams and intake my car should run real good?? and i have already a bunch of bolt ons..
i thought i read somewhere that the 98 gt where sitting at 10.1 compression.

 

[sn95jones]

The '98 GT got a small HP bump to 225hp because of a refined exhaust

 

[cobra clone 98]

what would they be at with bbk long tubes with h-pipe and flowmasters

 

[cobra clone 98]

i went back to read that again and its 9.5.1 compression for the 98 gt. they said 225 hp for the more aggresive computer and exhaust
flow.

 

[sn95jones]

i went back to read that again and its 9.5.1 compression for the 98 gt. they said 225 hp for the more aggresive computer and exhaust
flow.

Yup, I've got Flows,tune, and 3.73's on my car and it definitely is quicker, I'd love to get a dyno on it but if I could guess I'd probably say 235-240hp to the flywheel on my car, some might laugh at me but that to me sounds pretty realistic for a tune and exhaust and gears

 

[cobra clone 98]

i can believe it. my has bbk cold air, 90mm mass air meter, 73mm bbk t/b, 73mm trick flow pletum, bbk long tubes h pipe flow masters, msd coils, msd wires and ngk plugs. mine runs real good. it has 4.10 gears to. i would like to have mine dyno tune also. it would help it out to. the car is also a 5 speed.

 

[cobra clone 98]

i thought about changing to a x pipe. i heard it gives more hp then h-pipe.