NPI Upgrades

[sneaky98gt]

I have a bone stock 98 GT auto, and am going to start doing a few mods here and there. I think that i want to put on a PI intake as one of my first mods, after my CAI (already have it on) and exhaust (coming soon.) I have read that the PI intake will fit on NPI heads, but I'm not sure if you HAVE to have the adapter plates, alternator bracket, etc. in order to do it. What exactly do I HAVE to have, and what can I do without?

Second, I'm gonna put on plain ole PI cams in with the NPI heads. I've read that they work fine, and I'm on a very tight budget, so that's probably what's gonna happen.

Then, a while into the future, I want to port and polish my NPI heads. What is a good company/shop to get this done at? Also, will porting and polishing my NPI heads lower the compression? Cause I don't really want much lower compression. I guess I could sacrifice just a little to get some better flow numbers, but overall I want to keep it like it is. And before you ask, I do not want PI heads, because one day, probably well into the future, I want a supercharger, and the bottom end just wouldn't hold the extra compression, so I'm gonna stick with the NPI heads.

And just about how much horsepower and torque would I be looking at when all of this except the supercharger is done? Thanks.

 

[Winters98GT]

PI intake is worth 2 tenths. Just got done doing it, you can look for my build/et gain thread in the talk section

Ive done 2 entire PI headswaps, and it was great. PI cams will proboly get you another .1-.2. It just depends on your goal for the car. If you doing the labor, great, PI cams/intake is great. If your not, do the entire swap, or at least get a set of used aftermarket cams. If your going to pay somebody to tear in the motor, get good parts off the start, not worth 400-500 bucks to have somebody put in stock cams in your car.

Depending on the port work, and what you have done, yes it can lower the compresssion, but less than half a point. NO, its not worth having your stock NPI heads ported if staying NA and your are not doing the labor. LABOR+PORT WORK=$1000 minimum, proboly close to $2000 dollars for 10-20hp NA.

PI intake and cams is proboly worth 30hp. Add a set of LT headers and you have a bit more, and stay away from a cold air intake.

 

[forum155pl]

you can get pi heads cut to make the compression very close to stock.. i would save my port and polish money for when you get the PI heads

 

[blackink00]

what would he cut? the combustion chamber? i wouldnt recomend that cuz the pi head have a quench area fot the combustion. he would have to change pistions. but i would do the pi swap and throw in dished piston. the exhaust flow on npi head suck and even with it ported still dowsnt flow well at at.

 

[98COBRA281]

i have pi cams and pi intake, great bang for the buck, pi heads arent much better then npi heads, they only flow 15cfm more on the intake then the npi's, and the same on the exhaust, but they raise compression 1 point, most of the power is from the intake and cams, im on a tight budget to, cause im only 16 years old, so i just did the intake and cams, well worth it, cost me about 400$ look it to other simple bolt ons to, like, GEARS, ud pullys, timing adjuster, npi's can go high 13s with a good driver

 

[Winters98GT]

i have pi cams and pi intake, great bang for the buck, pi heads arent much better then npi heads, they only flow 15cfm more on the intake then the npi's, and the same on the exhaust, but they raise compression 1 point, most of the power is from the intake and cams, im on a tight budget to, cause im only 16 years old, so i just did the intake and cams, well worth it, cost me about 400$ look it to other simple bolt ons to, like, GEARS, ud pullys, timing adjuster, npi's can go high 13s with a good driver

check your PM's

 

[TGJ]

I have a bone stock 98 GT auto, and am going to start doing a few mods here and there. I think that i want to put on a PI intake as one of my first mods, after my CAI (already have it on) and exhaust (coming soon.) I have read that the PI intake will fit on NPI heads, but I'm not sure if you HAVE to have the adapter plates, alternator bracket, etc. in order to do it. What exactly do I HAVE to have, and what can I do without?

Second, I'm gonna put on plain ole PI cams in with the NPI heads. I've read that they work fine, and I'm on a very tight budget, so that's probably what's gonna happen.

Then, a while into the future, I want to port and polish my NPI heads. What is a good company/shop to get this done at? Also, will porting and polishing my NPI heads lower the compression? Cause I don't really want much lower compression. I guess I could sacrifice just a little to get some better flow numbers, but overall I want to keep it like it is. And before you ask, I do not want PI heads, because one day, probably well into the future, I want a supercharger, and the bottom end just wouldn't hold the extra compression, so I'm gonna stick with the NPI heads.

And just about how much horsepower and torque would I be looking at when all of this except the supercharger is done? Thanks.

Having done a few PI Intake swaps, this is what you need for sure:

- PI Intake, prefer one with an aluminum cross-over( you may need to modify the aluminum crossover for you 2nd coolant sensor )
- PI Coolant tube that or make one your self
- Alternator bracket if your NPI intake does not have the aluminum crossover
- PI Intake Gaskets
- RTV to seal coolant ports, you don't need adapter plates
- PI Water pump nipple and o-ring

If you ever do decide to port yours or a set of NPI heads, contact me for Renegade Racing's contact info. Jim is the only person, I would have port NPI heads. The heads will be over $2000.00 but they move air very well. Renegade Racing P&P NPI heads do not lower the compression ratio.

Personally, I would look into a Torque Converter and a set of rear gears as well.

the exhaust flow on npi head suck and even with it ported still dowsnt flow well at at.

Really?

What do you consider good flow? I will say it right now, Fox Lake Stg 2 PI heads do not flow as well as my NPI heads at any lift point upto and including .600 lift. My intake flow is comparable to MPH Stg 2.5 PI heads, but my NPI's still have their swirl dam while those PI heads do not. My exhaust flow is far better than Fox Lake's Stg 2 PI head. My NPI's flow over 200 CFM exhaust @ .550 lift, while Fox Lake's heads are under 200 CFM exhaust at that lift point. To boot, my NPI heads cost about the same as those Fox Lake heads.

 

[blackink00]

Really?

What do you consider good flow? I will say it right now, Fox Lake Stg 2 PI heads do not flow as well as my NPI heads at any lift point upto and including .600 lift. My intake flow is comparable to MPH Stg 2.5 PI heads, but my NPI's still have their swirl dam while those PI heads do not. My exhaust flow is far better than Fox Lake's Stg 2 PI head. My NPI's flow over 200 CFM exhaust @ .550 lift, while Fox Lake's heads are under 200 CFM exhaust at that lift point. To boot, my NPI heads cost about the same as those Fox Lake heads.

are you sure the heads was flowed with a 3.55 bore size? cuz i have never seen a npi head able to flow 200 on the exhaust side except for the svo which is still barely getting there. ive wanted to keep my car npi cuz its the underdog but porting a pi just flows better all around.

 

[COramprat]

I too was on a budget...maybe not so much as some but I've bought everything on my car used except gears, PI intake and clutch. Search through site classifieds and you can lock up good deals. PI cams are cheap but I found my Comp 262's for $325 with 6K miles on them. Good deal cheaper than new and no issues whatsoever.

Brush up on the how-to's and do as much as you can yourself. I've done all of my mods (with help) except the gears.

 

[TGJ]

are you sure the heads was flowed with a 3.55 bore size? cuz i have never seen a npi head able to flow 200 on the exhaust side except for the svo which is still barely getting there. ive wanted to keep my car npi cuz its the underdog but porting a pi just flows better all around.

Yes, they were flowed at a 3.55 bore.

My NPI heads are over 3 years old and at that time, the only ported PI head that out flowed them was the MPH heads. The MPH heads barely out flowed them on the intake side, however the MPH heads had them beat on the exhaust side. Since I wanted to stay N/A, the best heads were either the set of SVO's I had or the ported NPI's I went with from the data I collected. If my car would have been more of a track car instead of a daily driver, I would have went with the ported SVO's.

 

[sneaky98gt]

Yea, I'm also only 18, and am on a really tight budget, so for now I want as cheap N/A horsepower as I can get. And I am planning on doing all of the work myself, my dad and a couple of my brothers are rather mechanically inclined, so I hope to save the install money. Concerning gears, my car currently has 3.27 and gets between 20 and 25 mpg. What is a good performance gear that still gets me pretty good mileage? I think 3.73 is about the highest I'm gonna go. I was thinking maybe 3.55s. What do yall think?

 

[98COBRA281]

373's FTW it a really good all around gear, but since you have an auto, every ones gonna tell you to get 410's, how about some pics of that gt?

I have some pics on my motor when i was doing the intake and cams, if you wanna see just to get an idea

 

[COramprat]

I get 22mpg with my 4.10's but if you want gears 3.73's would be fine. 3.55's wouldn't make a big difference than what you have now.