Time to go Full PI?

[LI98GT]

I'm considering going Full PI swap from my PI cams and PI intake combo, so I re-read through "Truth about NPI vs. PI" thread but there are somethings that have changed since the thread had been started. Namely the cost of a decent set of used PI heads can be had for much less now - in the $250 range. Adding the headswap kit ~$120, about 15 hours in the garage and for <$400 an (I estimated) 10-20rwhp and maybe a better under. Not sure if all that work is going to be actually worth it.

My goal is a low 13 sec stang that can meet NY emissions and don't want to do it with any P/A i.e. NOS (only temp) or S/C (too costly). I would consider Stage II cams, but don't think they can pass emmissions plus would prob. need tune.

Anybody go from PI cams/intake combo to a full headswap and can share their experiences? Thanks!

 

[duff daddy]

pi heads, comp 270's and full bolt ons good driving and decent suspension.... youll be high 12's

 

[LI98GT]

pi heads, comp 270's and full bolt ons good driving and decent suspension.... youll be high 12's

Thanks, but it needs to say NY emmissions legal and I'm on a budget like everyone, so don't think that's an option. The cost of the PI heads/aftermarket cams and prob the tune it's going to need will put me in the $1,500 range and need to stay about $500. I just looking for advice on where I'm at now with current mods how I can drop ~another .5-.7 in the 1/4 mile.

 

[duff daddy]

The only power addeer you have are the cams really. SO you need to drop weight, and get better tires, use either slicks 26x 8.5 or get some drag radials (I suggest slicks) then work on your suspension. If you can get the car light enough, and get good suspension in there, youll drop et.

 

[98GTnSC]

low e.t's are gonna cost money man. especially in the 4.6s. unless you go with duff and drop an ass of weight ur gonna need to spend that extra money here and there to get where u wanna go. its gonna take more research and all on you and prolly be harder since ur wanting to do it and make sure ur still legal instead of people in states like SC(where im from) and dont have to worry about the parts we put on

 

[sneakypete_ftw!]

my buddies full bolt on, pi heads, cams, and intake mani with 4.10 gears on a npi block, in a 98 gt went 13.2 on street tires. that was without a tune and with 150k miles on the npi block.

 

[duff daddy]

my buddies full bolt on, pi heads, cams, and intake mani with 4.10 gears on a npi block, in a 98 gt went 13.2 on street tires. that was without a tune and with 150k miles on the npi block.

you are aware the pi and npi blocks are the same right...

 

[sneakypete_ftw!]

you are aware that when you put pi heads on a npi block it bumps the compression to somwhere in the low 10's. if they were exactly the same that wouldn't happen. also putting new heads on a 150k mileage short block would usually be bad on the rings but his handled it like a beast. he now has a full pi longblock though. he found a 50k longblock for the low so he bought it.

 

[duff daddy]

you are aware that when you put pi heads on a npi block it bumps the compression to somwhere in the low 10's. if they were exactly the same that wouldn't happen. also putting new heads on a 150k mileage short block would usually be bad on the rings but his handled it like a beast. he now has a full pi longblock though. he found a 50k longblock for the low so he bought it.

Look before you get mouthy get your facts straight, the reason its different is combustion chamber size.

42cc: 1999-2004 Mustang GT (PI)
51cc: 1996-1998 Mustang GT (Non PI)
52cc: 1996-2004 Mustang Cobra

that cylinder head difference is a larger factor then the 11cc (npi)-17cc(pi) difference in the piston dish.

But to begin with I was stating the BLOCKS were the same. (never said short block or rotating assy's

 

[LI98GT]

PI longblock comes with dished pistons and NPI longblock has flattop pistons that accounts for the difference in compression when you install the PI heads on an NPI stang. As far as suspension goes, I do have LCAs that's ot in my sig which I installed after my previous runs. So, really what I'm concluding here is that the full PI swap can get me there over what I have - just a matter of if I've got the drive to do the work eh?

 

[duff daddy]

nps do no have a flat top piston, tey have an 11cc dish as posted above.

A stock pi car with d/r's can run 13.7 ish, your going to have to hustle that car, AND get some weight out fo it for you to see another half second drop consistantly.

 

[sneakypete_ftw!]

You made it sound like the whole block is entirely the same, pistons, and all. I simply stated there was a difference between the npi block and pi block. Man I've been into stangs my whole life I know a bit about them and have many friends who pretty much know everything about the motors internally. I know the npi bare shortblock are the same as a pi but the internals are where they slightly differ. Not getting mouthy man just telling you there's a slight difference. Don't be mad because I 19 year old nOOb knows a little lol.

 

[Willis_98GT]

pi heads, comp 270's and full bolt ons good driving and decent suspension.... youll be high 12's

im living proof!

bro, go pi and do the cams, i was in your same position.. actually same exact mods. (and sexy color) a while back.. hell you could even find the thread that i even typed out the same things. you wont be sorry man. and you will love the car. not only that but you'll get compliments from tons of people about how it sounds like i do on a daily basis. i promise.

 

[Lee12609]

from what you have now to just adding PI heads you will see 2/10ths maybe.....

only thing you can do to get low 13s for under $500 w/ what you have now is a bottle, and even then on street tires it wont be as easy as you think.

slicks or DR's and a big set of balls will get you 2-3 tenths atleast, if you're drivetrain is up to the launch.

NPI heads arent as horrible as people think unless you're boosted.

my vote is tires and driver mod, cheapest mod per ET drop there is, unless you're all about street racing.....

 

[Marvin97]

You made it sound like the whole block is entirely the same, pistons, and all. I simply stated there was a difference between the npi block and pi block. Man I've been into stangs my whole life I know a bit about them and have many friends who pretty much know everything about the motors internally. I know the npi bare shortblock are the same as a pi but the internals are where they slightly differ. Not getting mouthy man just telling you there's a slight difference. Don't be mad because I 19 year old nOOb knows a little lol.

lol you're not getting it. Its your wording that making it sound like you don't know what you're talking about. The whole BLOCK is the same. The block is just that, the block. Nothing else.
The SHORTBLOCK consists of the block, crank, rods, pistons, and bearings.

As Duff said, the only real difference in a pi and npi shortblock is the size of the dish in the piston. Both are dished, but one is deeper. Cobra's have flattop pistons.

 

[LI98GT]

nps do no have a flat top piston, tey have an 11cc dish as posted above.

A stock pi car with d/r's can run 13.7 ish, your going to have to hustle that car, AND get some weight out fo it for you to see another half second drop consistantly.

Appreciate the input so far - I want this to be a healthy discussion. So that is what I ran the last time out with DRs with mod list (again minus LCAs). Sorry, guess I used the wrong words as you are correct, the NPI pistons are not flat, but do have less of a dish than the PI pistons. From where I was at last time out, I'm trying to drop ~.5. Willis, I discounted the stage II cams due to cost an emissions issues .
Maybe it's too much for me hope for, which is why I was asking if anyone did just the heads on top of PI cams and PI intake with the increased flow and compression that they bring. Hoping that not just the extra 10-20 rwhp peak but additional improvements under the curve (if they exist?) might get me down to low 13s. I do have some mods to go along with this setup i.e. gears, upper intake, 70mm TB, pulleys, catted X and catback, DRs plus the aformentioned LCAs. Unfortunately, being on L.I., doesn't afford me the luxury of going to a track that often to improve on driver mod that much as there are none on L.I. and the closest track is several hours away. Maybe the heads plus a tune? I'm still on stock tune.

 

[Lee12609]

i think you're being a little optimistic for the heads. from what i've seen the curve of a PI car is worse than a NPI headed car.

you say that you plan to get gears etc, but the "mods" in your sig states gears already.... so you're still basically just swapping heads which is worth 10-20whp, or .1-.2 tenths max.

a tune with your mods wont make a huge difference, not enough to justify the money spent at this time IMHO....

can you post your timeslip or atleast details about it, wondering what your 60' and trap speed etc are currently.

 

[DropTopPony]

I've done the PI parts in phases like you are. First I had the Intake, then added the cams and a few months later found heads cheap and popped them on until I went with the Fox Lake PI's and a few sets of Comp Cams.

The Intake was the single biggest difference to me just because the usable RPM range was extended. The cams also were a nice kick compared to stock. When I switched to the stock PI heads I did not notice a big gain but the premium fuel at the pump was difference in my wallet

If I had it to do it all over again I would have bought some NPI's that were ported by Renegade and stayed N/A with a 150 shot of Nitrous.
My opinion is if you are going to go through the effort of swapping heads save up for some P&P'd with better valves/springs etc and a set of mild street cams so you can still pass emissions if needed.

 

[LI98GT]

i think you're being a little optimistic for the heads. from what i've seen the curve of a PI car is worse than a NPI headed car.

you say that you plan to get gears etc, but the "mods" in your sig states gears already.... so you're still basically just swapping heads which is worth 10-20whp, or .1-.2 tenths max.

a tune with your mods wont make a huge difference, not enough to justify the money spent at this time IMHO....

can you post your timeslip or atleast details about it, wondering what your 60' and trap speed etc are currently.

To be clear, I do have gears already as stated above and in my sig, sorry if I wasn't clear about that. Tune would be post PI heads.
Here's the slip. I granny shifted (too far from home to take chance) and left abut 2000-2500rpm and shifting ~5500rpm Thanks.

 

[Lee12609]

101mph is good for LOW LOW 13s if not a 12.99... you have the power just need the balls to get it out the hole. what drag radials are you running???

is it your daily driver, are you scared to break? if not you should be leaving the line at atleast 4000rpm. i dont see how you leave the line at 2500rpm on radials without MAJOR bog unless you are slipping the hell out of the clutch. track time would do wonders for your times in my opinion.

get that 60' down to a 1.6 or 1.7 and you would be low 13s, very doable on the right tire.

also, shifting at 5500rpm is not short shifting with your mods, peak power is probably around 5400rpm, from what i've seen shifting at 5500-5700 works best with a bolt on car, after 5500rpm you are just wasting valuable time that could be used in the powerband if you had shifted. <--- especially true on an NPI car.