Truth about NPI vs PI

quickstang_1994 · Mar 2, 2007

Adam said:
You guys still arguing about this? lol. You aren't going to get 65rwho with just a PI swap. Unless your 1st dyno was 100 degrees and your after dyno was -20 outside. I picked up 72 rwhp by doing a PI head/intake swap, but I also put in VT cams, and FRPP shorties. And for all you guys saying to go with a blower because its the same money are crazy. A blower is $4000 minimum, then another $4000 for a new motor when you obliterate your stock one. These motors were only designed to handle about 1000psi of cylinder pressure. A blown car produces about 2.65psi of cylinder pressure per hp. A typical blown 4.6 makes around 400hp(or more, i am being very liberal here) actually around 460hp (the blower takes hp to run also) so take 460x2.65=1219psi of cylinder pressure. The best tune in the world is not going to matter, the engine components simply were not engineered to handle that kind of cylinder pressure....period. It is not a matter of IF the motor will let go, it is WHEN, this is fact, not internet rumor. Hope this helps some people.

Adam

For a Vortech its $3350 from mustangs unlimited and it will put you in the 320-350rwhp on a stock npi.

98coupe_GT · Mar 5, 2007

Awesome post. thank you soooo much for taking your time to do so. its a great help when you have a noob such as myself trying to learn everything there is to know.

tooslow · Mar 11, 2007

awsome write-up. thanks for the time to do so. and many good posts from others in this thread also. this will be very usefull in the near future.

blackfang · Mar 12, 2007

Adam is good people folks and brings a ton of info to the table. I read his install on his Flowtechs on another site and he is why I got my Flowtechs and installed them in March 06.

Adam · Mar 13, 2007

blackfang said:
Adam is good people folks and brings a ton of info to the table. I read his install on his Flowtechs on another site and he is why I got my Flowtechs and installed them in March 06.

Thanks....yeah those headers get a lot of grief. I think they are as good as any other brand out there. I think a guy just has to be honest with other people on what it takes to make them work and they will be fine. How are they working out for you?

Adam

blackfang · Mar 13, 2007

Perfect. The X pipe was difficult as it didn't line up with the header, but I got them on. No issue at all, car makers noticable power in the lo and midrange and the sound is killer.

voidfinger · Mar 13, 2007

stngmn96 · Mar 15, 2007

To be honest, I have the whole swap on my 96 GT and I have a hell of a time with the compression spike the heads caused and the increased compression from the forged flat tops. Therefore, running an 11:8-1 compression has not yielded me the results I had hoped for in hp even with a full exhaust, headers and the works. I am 6 months into this new motor and with the whole thing being bored over, completely hardend and gear changed, I am about to throw in stage 2 low lift cams in it to maximize the air coming in and out of the motor.

Adam · Mar 15, 2007

You need to find yourself a tuner....the end. ^-^

96gt226410 · Apr 9, 2007

I'm in the middle of doing a PI swap. I have the engine all back together and I finally got it back in the car onto the mounts. It's a lot of work. The next time I do a PI swap, I'm just doing a whole engine. It'll be so much easier. I'm very excited about the gains, though! This swap had better be worth it! 3 weeks with no Mustang and I'm still not done!!!

voidfinger · Apr 9, 2007

wow i'm hoping to get the thing done within 2 days..... so how did that guide thing work out???

Boomer! · Jul 11, 2007

Wow, I have read this entire thread thinking when is the real point going to come out. Everyone assumes the larger runner of the P.I will make more power, truth be told the P.I actually have a huge flaw which is why they do not make more than the average of 10 rwhp when bolted on to a NPI block.

1. Throw away the numbers in CFM, they are a gimmick to sell you something and are only the basics of airflow dynamics.
2. The shortside radius on the P.I head intake runner is horrible and is a restriction
3. Yes, the P.I heads flow higher rates of cfm. The airflow reaches it's chokepoint faster as the higher lift numbers approachon the P.I head. I saw a flow chart posted earlier in this thread that shows this happening.

"If" and I say if, the P.I head design was so great why did they not opt. for its runners on the SVO heads ? The SVO heads flow ported better than some of the 4 valve heads do. Out of the box they outflow most any port 2 valve head.

Believe what you wish, if you want to take CFM as your only data when puchasing a head let you be the one to get burned.

Dalamar · Jul 11, 2007

That's good info, thanks for the reply Boomer.

Jrgunn5150 · Jul 11, 2007

Boomer! said:
Wow, I have read this entire thread thinking when is the real point going to come out. Everyone assumes the larger runner of the P.I will make more power, truth be told the P.I actually have a huge flaw which is why they do not make more than the average of 10 rwhp when bolted on to a NPI block.

1. Throw away the numbers in CFM, they are a gimmick to sell you something and are only the basics of airflow dynamics.
2. The shortside radius on the P.I head intake runner is horrible and is a restriction
3. Yes, the P.I heads flow higher rates of cfm. The airflow reaches it's chokepoint faster as the higher lift numbers approachon the P.I head. I saw a flow chart posted earlier in this thread that shows this happening.

"If" and I say if, the P.I head design was so great why did they not opt. for its runners on the SVO heads ? The SVO heads flow ported better than some of the 4 valve heads do. Out of the box they outflow most any port 2 valve head.

Believe what you wish, if you want to take CFM as your only data when puchasing a head let you be the one to get burned.

For a swap of under 1k, VS 2k plus for Renegade or SVO heads, bang for the buck swapping a full PI setup onto our NPI cars is still the hands down HP fpr dollar winner. Whether the other heads can squeeze out another 15 or even 30 rwhp is kind of irrelevent in this thread for what these guy's are looking for.

Boomer! · Jul 11, 2007

Jrgunn5150 said:
Boomer! said:

Wow, I have read this entire thread thinking when is the real point going to come out. Everyone assumes the larger runner of the P.I will make more power, truth be told the P.I actually have a huge flaw which is why they do not make more than the average of 10 rwhp when bolted on to a NPI block.

1. Throw away the numbers in CFM, they are a gimmick to sell you something and are only the basics of airflow dynamics.
2. The shortside radius on the P.I head intake runner is horrible and is a restriction
3. Yes, the P.I heads flow higher rates of cfm. The airflow reaches it's chokepoint faster as the higher lift numbers approachon the P.I head. I saw a flow chart posted earlier in this thread that shows this happening.

"If" and I say if, the P.I head design was so great why did they not opt. for its runners on the SVO heads ? The SVO heads flow ported better than some of the 4 valve heads do. Out of the box they outflow most any port 2 valve head.

Believe what you wish, if you want to take CFM as your only data when puchasing a head let you be the one to get burned.

Click to expand...

For a swap of under 1k, VS 2k plus for Renegade or SVO heads, bang for the buck swapping a full PI setup onto our NPI cars is still the hands down HP fpr dollar winner. Whether the other heads can squeeze out another 15 or even 30 rwhp is kind of irrelevent in this thread for what these guy's are looking for.

I think you missed my point, in relation to installing the P.I heads there is not enough gain to make a fair dollar to horsepower ratio. I was trying to put a technical aspect into the mix rather than a speculation.

Jrgunn5150 · Jul 11, 2007

The power gain on the heads comes from compression. I understand that. However the fact that you can easily bolt aftermarket cams in the stock heds (pi), and the intake actually matchs the ports is the main bonus from my POV. Now I do know the facts, ported NPI whoops ported PI in a NA contest, and SVO heads flat out own. But for the guy in his driveway, the simplest easiest thing is still to swap it all, get a nice 40-50 rwhp gain, save a few more weeks, through in some comp 262's or whateer, and be close to 300 rwhp with minimal effort, and with resorting to expensive porting, head work, or retainer's.

DropTopPony · Jul 11, 2007

Yo Boomer, welcome to our little home

You still building the 10sec NPI?

Boomer! · Jul 11, 2007

DropTopPony said:
Yo Boomer, welcome to our little home
You still building the 10sec NPI?

Maybe, the car is gutted and ready.... I am trying to do some major shop work right now, I really have no time for my own stuff. I have a few sets of Npi's finished and near where they need to be, however I'm not sure how people will feel about them on a Bigbore

.

voidfinger · Jul 11, 2007

wow, npi's on a bigbore... Cool. ???

Casper98gt · Jul 12, 2007

Jrgunn5150 said:
The power gain on the heads comes from compression. I understand that. However the fact that you can easily bolt aftermarket cams in the stock heds (pi), and the intake actually matchs the ports is the main bonus from my POV. Now I do know the facts, ported NPI whoops ported PI in a NA contest, and SVO heads flat out own. But for the guy in his driveway, the simplest easiest thing is still to swap it all, get a nice 40-50 rwhp gain, save a few more weeks, through in some comp 262's or whateer, and be close to 300 rwhp with minimal effort, and with resorting to expensive porting, head work, or retainer's.

Hmm.... i totally agree with you. Due to the fitment issues with the PI intake on NPI heads, silicone isnt a 100% fix and the adapters would need a tune for best. The cams can have coilbind. So the PI swap is the best for the money. That end i agree. But people who say Npi heads are junk, myself and Boomer have gotten into millions of forums arguments and end up making people see the light. In the end Npis are a great head if you can afford to do work, or have some SVo's. If money is an issue, you do the PI intake/cam swap. If you have a few extra bux the entire PI swap you cant beat.