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Discussion Starter · #1 ·
Which would produce more power a ported and polished set of NPI heads or just regular PI heads with no port and polish.
 

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the ported and polished heads should give you more with a correct tune as opposed to stock non P&P heads
 

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Discussion Starter · #3 ·
but the PI heads give roughly 40hp more because of the increased compression and cams and such because I do not have PI heads so again on my 96 what would give more HP ported NPI heads or Stock PI heads
 

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I think this is the way it would go down...if I am wrong someone please correct me.

The ported and polished NPI heads would flow better than the PI heads if done right. The PI heads would give you more power because of the smaller CC that increases the compression on NPI motors. So on that note what do you plan on doing in the future if you see a power adder then I suggest the worked NPI heads. It's not mainly the heads that hurt the NPI motors it's a combo of the heads, cams, and intake but mostly the intake, and cams.
 

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I think this is the way it would go down...if I am wrong someone please correct me.

The ported and polished NPI heads would flow better than the PI heads if done right. The PI heads would give you more power because of the smaller CC that increases the compression on NPI motors. So on that note what do you plan on doing in the future if you see a power adder then I suggest the worked NPI heads. It's not mainly the heads that hurt the NPI motors it's a combo of the heads, cams, and intake but mostly the intake, and cams.
This is what I'd recommend as well. The PI heads will give you a nice bump in compression, where the NPI heads will outflow them. So PI for a N/A or Nitrous car, ported NPI if you plan on adding a power adder.

The cams and intake are what make the most power if you take the compression bump out of the equation.
 

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If you're going to spend the money on porting then spend an extra $150-$200 for a set of PI heads on Craigslist and have those ported. Add a good set of cams and the usual bolt-ons and you'll easily be putting down 300+ HP at the wheels.
 

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Ported NPI heads flow better than Ported PI heads.
 

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Sorry, I'd have to see the numbers from a flow bench on that one. Nothing i've seen between the two in ported form confirms that. Just speaking from experience though.
 

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Sorry, I'd have to see the numbers from a flow bench on that one. Nothing i've seen between the two in ported form confirms that. Just speaking from experience though.
That's been common knowledge for about 10 years, I don't know where you've been. The problem with NPI heads is actually their inability to handle larger lift cams without going into coil bind. This can be remedied by cutting the valve seats and guides down and installing offset retainers.

The only other real problem is the intake ports. You either have to use a PI intake and deal with the port mismatch, or pay big money for an SVO intake or similar.

Until the TFS heads came out, the SVO heads were the highest flowing 2V heads on the market............ And they're NPI based.
 

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Hopefully they format correctly now:


...............................Stock.....................Ported
Lift in Inches..............'96......'01..........'96.........'01
.100...........................46.......54...........61.........60
.150..........................66.6.....78...........89.........86
.200..........................84.5.....98..........111.5......116
.250........................103.5.....119.........131.3.....141
.300........................121.3.....135.........146........160
.350........................134.7.....145.........159.6.....169
.400........................147........156.........173.3.....176
.450........................159.4.....161.........185........182
.500........................170........166.........188........185
.550........................176........166.........192.5.....186
 

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Sorry, I'd have to see the numbers from a flow bench on that one. Nothing i've seen between the two in ported form confirms that. Just speaking from experience though.

If I am not mistaking you can get on modularheadshop.com and check that for yourself cause I do believe Nick tells a little about the differences in the heads, pros and cons. If you wana call Nick out on his knowledge on the heads then I would just have to say your an idiot lol.
 

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Renegade Racing was the first to discover that the NPI's actually flowed better at low and high lift than the PI's when ported quite a few years ago. That was backed up by numbers from Fox Lake, and then again by Nick from Modular Headshop.

This is hardly new or unheard of news in the 4.6 world. Johnny Langton and Renegade Racing were the pioneers of going fast with an NPI, and were the first to really try it. Him and Kris Danner were the ones who came up with the couple different ways to put a PI intake on the PI engine as well, and even epoxied a few PI intakes so they would match up with the ports on the NPI heads, since that and cams are the real problems with the NPI setup. I've seen 9rwhp just from swapping to a PI intake, and 12rwhp from putting PI cams in an NPI engine.
 

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Discussion Starter · #13 ·
Renegade Racing was the first to discover that the NPI's actually flowed better at low and high lift than the PI's when ported quite a few years ago. That was backed up by numbers from Fox Lake, and then again by Nick from Modular Headshop.

This is hardly new or unheard of news in the 4.6 world. Johnny Langton and Renegade Racing were the pioneers of going fast with an NPI, and were the first to really try it. Him and Kris Danner were the ones who came up with the couple different ways to put a PI intake on the PI engine as well, and even epoxied a few PI intakes so they would match up with the ports on the NPI heads, since that and cams are the real problems with the NPI setup. I've seen 9rwhp just from swapping to a PI intake, and 12rwhp from putting PI cams in an NPI engine.
Wow thanks for the info guys and as always especially you Bullitt I really dont have plans for either NOS or Induction as of now just wanted to get in that 300whp ballpark and have me a decent daily driver because as of right now its out of commission completely. I have a set of PI heads I picked up for 40 bucks but they have a small gouge on them and I know that the tolerance is very limited on them but the guy at the machine shop I checked thinks theyre definitely salvageable but for 400 bucks or so and Ive seen some people are running NPI heads P&P with PI intake and cams and making decent power so I was wondering what my best bet would be paying 400 bucks to P&P my NPI's my PI's or buying some complete PI's with no problems from what you said about the Hp gains from just the PI intake and PI cam I can see my options are very open as to what I can do.
 

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If you're not going power adder in the future, the compression bump from the PI heads is worth it.
 

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Discussion Starter · #15 ·
Thanks for all the help guys I finally found some PI heads and an intake worth purchasing so the car is ready to go back together
 

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If I am not mistaking you can get on modularheadshop.com and check that for yourself cause I do believe Nick tells a little about the differences in the heads, pros and cons. If you wana call Nick out on his knowledge on the heads then I would just have to say your an idiot lol.
Great info on all the numbers but as I said before. I was just speaking from experience at the track.
 

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Great info on all the numbers but as I said before. I was just speaking from experience at the track.
No biggie man trust me I have learned alot from this site along with hands on experience also we all learn at sometime. :bigthumbsup
 
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