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post #1 of 25 (permalink) Old 09-22-2004, 06:53 PM Thread Starter
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I've got a question...

On the engine issue... I know it's not completely related, but wouldn't an NPI engine re-fitted with PI heads make more power than a PI engine? Because of the higher compression and all. I've asked this question before and I didn't get a straight answer, so I reworded it and asked again. Also, searching is useless since all I get are flame wars about NPI vs. PI. I'm thinking I'm gonna get an NPI motor and put PI heads on it instead of buying a PI motor, especially if they actually do make more power.

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post #2 of 25 (permalink) Old 09-22-2004, 07:10 PM
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I can't see how they'd make MORE power, I'd say less or equal but not more.....so I'd like to know also.

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post #3 of 25 (permalink) Old 09-22-2004, 07:20 PM
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I thought(and this could be misinformation) that I read somewhere that the PI engines have deeper dished pistons. Mind you I don't know for a fact, that is just something that jumped to my mind. I could have it completely wrong.
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post #4 of 25 (permalink) Old 09-22-2004, 08:15 PM Thread Starter
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Yeah, engines that came with PI heads (PI engines) had dished pistons, the CR on a PI engine is the same as that on a NPI-headed NPI engine. At least, that's how I understand it. So, a PI-headed NPI engine should have a higher CR. If what I've heard is true, anyway... But I suppose it's a moot point, since I'm looking at forged internals and I can just get whatever dish I need. I'm still curious, though.

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post #5 of 25 (permalink) Old 09-22-2004, 08:41 PM
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PnP NPIs and the will make some hella power...even better than PIs

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post #6 of 25 (permalink) Old 09-22-2004, 09:02 PM
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Quote:
Originally posted by SloMo228
On the engine issue... I know it's not completely related, but wouldn't an NPI engine re-fitted with PI heads make more power than a PI engine? Because of the higher compression and all. I've asked this question before and I didn't get a straight answer, so I reworded it and asked again. Also, searching is useless since all I get are flame wars about NPI vs. PI.
My '96 NPI short block with PI heads, stock exhaust manifolds, high flow cats & a 2 in/1 out mid-mounted MagnaFlow muffler dynoed at 229 rwhp & 272 rwtq.
Hopefully, one of the Explorer swap fellas will chime in with dyno numbers.
Quote:
Originally posted by smokymance
PnP NPIs and the will make some hella power...even better than PIs
Please let us not start another NPI vs. PI debate. Please.

Last edited by JR Tigerstar; 09-22-2004 at 09:13 PM.
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post #7 of 25 (permalink) Old 09-22-2004, 09:05 PM
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oh i know...i now just realized that stating anything on what makes more power just gives me less power ....

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post #8 of 25 (permalink) Old 09-22-2004, 09:07 PM
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Yes PI heads on a non-PI block should make more power with equal mods. The extra point or so in compression will yield 5% or so more power across the board.
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post #9 of 25 (permalink) Old 09-22-2004, 09:41 PM Thread Starter
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Cool. That's what I suspected, it's good to hear a concurrent opinion.

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post #10 of 25 (permalink) Old 09-22-2004, 09:54 PM
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so that means... I was right?!? WOW!
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post #11 of 25 (permalink) Old 09-22-2004, 10:02 PM
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Quote:
Originally posted by 96bird
Yes PI heads on a non-PI block should make more power with equal mods. The extra point or so in compression will yield 5% or so more power across the board.
If the 5% is true, that is a plus over the Explorer engine.
The aluminum Explorer engine weighs, what, 75-100 lbs. less than the iron block.
5% more power or 75-100 lbs reduction.
Which is better?
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post #12 of 25 (permalink) Old 09-22-2004, 10:11 PM
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Just take the exploder block and put NPI pistons in it with PI heads, there you go. Hell, shave the heads while your at it!
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post #13 of 25 (permalink) Old 09-22-2004, 11:15 PM
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Shaving your heads isn't a good idea (timing chains come to mind)...you should be able to search around for the answer to that one. Personally I would grab the exploder engine and lose the weight. If you are going to stay NA and want aftermarket cams...I would get the Flat top pistons (not stock NPI though..forged instead) to put in the explorer engine though.


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post #14 of 25 (permalink) Old 09-23-2004, 11:10 AM Thread Starter
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That's what my long-term goals are. Aluminum block, fully worked heads and some nice lopey cams, flat top pistons with forged rods and crank, and a wee little shot of nitrous, like a 75 or 100.

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post #15 of 25 (permalink) Old 09-23-2004, 11:31 AM
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NPI heads will outflow PI heads any day. Now, our stock NPI heads will not out flow PI heads, but 98 mustang NPI heads will. Of course you will have to do a lot of porting work on these heads, and so will you on the PI heads.
The reason the 98 heads are better is because in our heads, in the intake side, there is a water passage in there, you cannot grind away as much metal in the heads as you can on 98 heads(NPI of course). The reason I say 98 because they have a casting number, (don't remember what it is right now), on them that identifies what they are. I think there was some in 97 that had the same casting numbers.
Take it for what its worth.
If the PI heads where better, don't you think JL would be running them, and other guys for that matter.
I think a lot of people got in there heads that the PI heads outperform the NPI heads, in which they do not.

Hope this makes any sense.

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post #16 of 25 (permalink) Old 09-23-2004, 11:45 AM
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Quote:
Originally posted by SloMo228
... but wouldn't an NPI engine re-fitted with PI heads make more power than a PI engine? Because of the higher compression and all. I've asked this question before and I didn't get a straight answer, so I reworded it and asked again. Also, searching is useless since all I get are flame wars about NPI vs. PI.
Quote:
Originally posted by badbird95
NPI heads will outflow PI heads any day. Now, our stock NPI heads will not out flow PI heads, but 98 mustang NPI heads will. I think a lot of people got in there heads that the PI heads outperform the NPI heads, in which they do not.
Hope this makes any sense.
Nick
Quote:
Originally posted by JR Tigerstar
Please let us not start another NPI vs. PI debate. Please.
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post #17 of 25 (permalink) Old 09-23-2004, 12:25 PM
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Quote:
Originally posted by badbird95
NPI heads will outflow PI heads any day. Now, our stock NPI heads will not out flow PI heads, but 98 mustang NPI heads will. Of course you will have to do a lot of porting work on these heads, and so will you on the PI heads.
The reason the 98 heads are better is because in our heads, in the intake side, there is a water passage in there, you cannot grind away as much metal in the heads as you can on 98 heads(NPI of course). The reason I say 98 because they have a casting number, (don't remember what it is right now), on them that identifies what they are. I think there was some in 97 that had the same casting numbers.
Take it for what its worth.
If the PI heads where better, don't you think JL would be running them, and other guys for that matter.
I think a lot of people got in there heads that the PI heads outperform the NPI heads, in which they do not.

Hope this makes any sense.

Nick
i thought 96-98 non pi heads were all the same? they're all F5 casting. the F4 casting was used from 91-95.

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post #18 of 25 (permalink) Old 09-23-2004, 12:51 PM
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Quote:
Originally posted by fdawg97lx


i thought 96-98 non pi heads were all the same? they're all F5 casting. the F4 casting was used from 91-95.

Frank
I agree!

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post #19 of 25 (permalink) Old 09-23-2004, 02:01 PM
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Yes you are correct on the F5, F4 part.
But the number you are looking for(finally found it), is at the end of the casting number.
Also, I was wrong on the 98 part, it was 96-98 with the casting number.

The numbers are:
B22A
B24A

These heads will out - flow PI's any day, properly ported mind you.

Of course, you have to have the heads off to check the #'s.

I have a set at the house that I'm currently working on for my brothers Stang.

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post #20 of 25 (permalink) Old 09-23-2004, 03:00 PM
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I have yet to see how any F5AE casting is any different from any other F5AE casting.

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post #21 of 25 (permalink) Old 09-23-2004, 07:46 PM
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Quote:
Originally posted by Silver95Bird
I have yet to see how any F5AE casting is any different from any other F5AE casting.

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post #22 of 25 (permalink) Old 09-25-2004, 07:20 PM
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OK this is what ive picked up over the yrs.

NEVER want to try to use 91-95 heads w/o at least doing springs but are still pretty worthless to PNP. All referals below NPI heads are from 96-98.

Stock NPI heads will not flow better than Stock PI heads.

PNP NPI heads will flow better than Stock PI heads.

PNP NPI head will still outflow PNP PI heads but not by too much.

Stock NPI 4.6 has a CR of 9.1:1 as the Stock PI 4.6 has CR of 9.3:1.

Stock NPI 4.6 bottom end with PI heads will raise CR to 10.1 or so:1. Thus producing near the same power as Stock PI.

Stock NPI 4.6 bottom end with PI heads, PI intake, PI cams will have raised CR and have more power over Stock PI 4.6.

Stock NPI 4.6 bottom end with PNP NPI head, PI intake, PI cams will both have raised CR but have better flow than Stock NPI 4.6 bottom end with Stock PI heads, PI intake, PI cams. Not sure of PNP PI heads would do.

Then you can also do the combo of Stock NPI 4.6 w/ Stock heads (96-98), PI cams, PI intake will still have 9.1 CR but may produce the same or more power than Stock PI 4.6.

Ok i think that about wraps it up... if anything is wrong or have added info please feel free to educate me. I like to learn more everyday so i may post correct info often.

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Last edited by ITT-BIRD; 09-25-2004 at 07:28 PM.
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post #23 of 25 (permalink) Old 09-25-2004, 08:50 PM Thread Starter
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I think I'll go with the Bullitt intake, ported NPIs, VT Stage IIs, and high-compression forged internals. Heck, why not throw a stroker kit and an overbore on there while we're at it?

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post #24 of 25 (permalink) Old 09-27-2004, 02:55 PM
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a pi engine comes with better pistons, and i think that the compression ratio is higher (if im wrong, slap me) but my guess is that there pretty close

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post #25 of 25 (permalink) Old 09-27-2004, 03:06 PM
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Pi engines do not have better pistons they are made of the same material but they do have a dish in them so no they also do not have higher compression. You would have higher compression if you compined NPI pistons with PI heads

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