porting npi heads

98COBRA281 · Feb 14, 2008

is it worth porting npi heads i dont have the money to do a pi swap because im only 16 years old but i want some more power i was also thinking of getting the heads shaved a little to bring up my compression?

CobraRed_96_GT · Feb 14, 2008

porting NPI has been proven to be effective:

ported Non-PI and ported PI Heads

Lift in Inches – Non-PI (’96-‘98) – PI (’99-’04)

.100 – 061 – 060
.150 – 089 - 086
.200 – 112 - 116
.250 – 131 - 141
.300 – 146 - 160
.350 – 160 - 169
.400 – 173 - 176
.450 – 185 - 182
.500 – 188 - 185
.550 – 193 - 186

i'd recommend buying a spare set on the cheap. Making sure its guides and valves are tip top in the process of having it sent of to be ported. FYI tho, porting NPI heads will cost more than buying used PI heads.

98COBRA281 · Feb 14, 2008

if i did pi head what else would i need thought i already have the intake

rugster · Feb 14, 2008

i have a set of NPI heads laying around if you wanna scoop them up on the cheap side...

deftsound · Feb 14, 2008

98COBRA281 said:
if i did pi head what else would i need thought i already have the intake

cams

SaleenGT2001 · Feb 14, 2008

deftsound said:
cams

i have a set of those too. PM me

forum155pl · Feb 14, 2008

most of the PI heads will come with cams unless someone stripped em out.. you also need cam bolts, new head gaskets and head bolts.. oh yeah and a PI dipstick tube

PI head swap is pretty cheap for what it is really... if you want more power bolt in some used PI cams along with your PI intake and it will give you a noticeable gain!

Green&GoldGT · Feb 15, 2008

Ported NPIs will flow about the same as unported PI heads, and even more at very high lift, although that wouldn't do anything if you didn't have better camshafts. I wouldn't expect to see a high cfm out of a ported and polished NPI head, unless it was ported by a place like steen or fox lake. Porting and polishing your NPI heads is more expensive than just buying a set of used PI heads. The PI heads will also increase compression ratio and ported NPIs would decrease it. Go for the PI heads unless you can find a set of P&P NPI heads on ebay, since those go cheap if you can find a pair.

CobraRed_96_GT · Feb 15, 2008

Green&GoldGT said:
Ported NPIs will flow about the same as unported PI heads, and even more at very high lift, although that wouldn't do anything if you didn't have better camshafts. I wouldn't expect to see a high cfm out of a ported and polished NPI head, unless it was ported by a place like steen or fox lake. Porting and polishing your NPI heads is more expensive than just buying a set of used PI heads. The PI heads will also increase compression ratio and ported NPIs would decrease it. Go for the PI heads unless you can find a set of P&P NPI heads on ebay, since those go cheap if you can find a pair.

i disagree, if you look at the flow numbers, the ported NPI heads flow better than PORTED PI heads in certain ranges. Yes high lift would favor the PI head (with both having stock springs) - but gains NPI ported vs PI ported have shown to be around the same since the NPI heads has a lot of room to widen. I agree that PI heads are cheaper tho.

FYI: stock NPI heads flow 150/150, PI heads flow 165/150 - so it's not exactly a huge step up. That's why im glad mine flow a lil better.

And i dont see why ported NPI heads would lose compression since they dont have the low rpm emissions intake wall that's scraped out of ported PI heads. I'd prefer less compression since you could then run a proper amount of boost

98COBRA281 · Feb 15, 2008

i was actually thinking of porting them my self i have done alot of port work on 2 strokes and some on big block mopars, does any one know how much i will have to shave them to bring my compression up to around 10 or 10.5-1

Stan Weiss · Feb 15, 2008

Without knowing your head gasket thickness, piston deck height, etc. I will just give total area volumes
A 281 ci engine at
9.0:1 CR needs 71.91 cc total area
9.5:1 CR needs 67.68 cc total area
10.0:1 CR needs 63.92 cc total area
10.5:1 CR needs 60.56 cc total area

forum155pl · Feb 15, 2008

porting them wont give you any more compression.. it will just make em flow better

Green&GoldGT · Feb 15, 2008

CobraRed_96_GT said:
i disagree, if you look at the flow numbers, the ported NPI heads flow better than PORTED PI heads in certain ranges. Yes high lift would favor the PI head (with both having stock springs) - but gains NPI ported vs PI ported have shown to be around the same since the NPI heads has a lot of room to widen. I agree that PI heads are cheaper tho.

FYI: stock NPI heads flow 150/150, PI heads flow 165/150 - so it's not exactly a huge step up. That's why im glad mine flow a lil better.

And i dont see why ported NPI heads would lose compression since they dont have the low rpm emissions intake wall that's scraped out of ported PI heads. I'd prefer less compression since you could then run a proper amount of boost

If he says he doesn't have that much money, he's not going to go FI. Porting and polishing removes material from the combustion chamber, therefore, increasing the size of the CC and decreasing compression ratio. So in losing CR, he would lose hp in that way, although gaining power through increased flow. So if he installs PI heads, they will flow better in comparison to the lift of the camshaft he is going to use.

PI heads were designed to flow better through the mid range of the lift, so why would he want a ported NPI that flows better cfm at the top of the lift when he's going to more than likely going to get a PI camshaft that's not even going to give that much lift.

Porting and Polishing is more than just cfm, maybe you should google that and find out. Joe Blow down the street is not going to know how to port NPIs to outflow ported PI heads, or even out power them. Just because ported NPIs might out flow ported PI heads, that doesn't mean they are going to make more power.

The flow numbers you gave above don't compare anything. Are you comparing exhaust or intake? A PI head can be ported and polished to flow up to 245 cfm intake. Tell us what your comparing

98COBRA281 · Feb 15, 2008

ya i know porting wont give you any compression but thats why i said that i wanted to have them shaved down a little

blubullett · Feb 16, 2008

If you get your heads ported and find a cheap set of pi cams you would have more power than a pi swap for sure. Plus those non pi heads would love a blower in the future. And when the port they barely remove any material from the chambers, probably 1 or 2 cc at the most, they just clean them up.

Green&GoldGT · Feb 16, 2008

Shaving modular heads causes problems. Don't shave them any more than they need to be

Skidzz · Feb 16, 2008

If you can port them yourself, then ported NPI is definitely the way to go. But like Green&GoldGT said, don't shave them down a lot. You may be tempted to buy the PI's for higher compression, but just remember that the compression will be too high for boost. You may not care now, but you will when you've done all the bolt-ons and run into a wall. If I could do mine over again, I would have just gone with ported NPI's. Then I might actually be boosting it soon.

blckstng96 · Feb 16, 2008

i saw the title of this thread my first thought was WHY? if you think about cost and such it just really doesnt seem to me like the most logical thing to do.why waste all the time and money porting them just to get where a pi is now.and if they are being ported by you,you never know how much your going to get out of them.i ported a set of pi heads myself when i was in school for high performance engines and used a flow bench on them too.i saw some decent improvements and i actually just did a clean up and smooth out,not even a real port and polish.too easy to take too much out and pretty much waste a set of heads.save your time and money,do a lil shopping around and pick up a set of pi heads and cams.

Skidzz · Feb 16, 2008

blckstng96 said:
i saw the title of this thread my first thought was WHY? if you think about cost and such it just really doesnt seem to me like the most logical thing to do.why waste all the time and money porting them just to get where a pi is now.and if they are being ported by you,you never know how much your going to get out of them.i ported a set of pi heads myself when i was in school for high performance engines and used a flow bench on them too.i saw some decent improvements and i actually just did a clean up and smooth out,not even a real port and polish.too easy to take too much out and pretty much waste a set of heads.save your time and money,do a lil shopping around and pick up a set of pi heads and cams.

The reason he would want to do ported NPI's is because while he might not be thinking about a blower now, he most likely will in the future when he has more money.

I'm a good example. If I want to get my car blown now, I'm going to have to do a bunch of engine work first to bring down my compression. I'll probably end up just dropping a built short-block in. It's a lot easier and cheaper in the long run to do ported NPI's so then you can just slap on a blower with a conservative tune and be done with it.

5spd GT · Feb 16, 2008

If one looks at just the peak numbers, the NPI wins barely.

But, one needs to look at the average flow of the numbers given. A valve is not just open at .500" lift. It is open from the time the valve comes off the seat.

Ported NPI - 143.8 Average CFM

Ported PI -146.1 Average CFM

If you have the new runner volume after the porting, you can then figure out the average cross section which is quite important as well.

Just do not get caught up in just flow numbers; especially peak flow numbers

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