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Old 03-22-2004, 07:57 AM   #1
NeoTokyo
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Default What are PI heads?

Hey guys, I was just wondering what PI heads were, why they are better then the stock heads. Are they better then the 96-98 4V heads? I did a search through the forums but didnt come up with anything. Can someone tell me some power gains from the PI heads installed on a stock Cobra. 96-98 Stock Cobra made 305hp @ 5800rpms and 300lbs.-ft tq @ 4800rpms and the 03 Cobra makes 390hp @ 6000rpms and 390lbs.-ft tq @ 3500rpms. I was just wondering what the PI heads would do im compairison to the 03 Cobra and whatnot and if they really are worth the money to get.

Seeing that I will be purchasing a 96-98 Cobra soon after I sell my V6 stang I want to know if the PI head swap is for me. My main goal after purchasing the Cobra is to purchase a Twin Turbo kit for it but then I need to know how much hp and tq the bottom end can handle before doing something like that. All I know is that the 03 Cobra handles 900hp on the stock bottom end beautifully thanks to the studies of DiabloSport.

Thanks everyone, Anything else I need to know about the 4.6 I would like to know as well, all info is very much appriciated. Thanks!


-Eric-
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Old 03-22-2004, 10:56 AM   #2
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Default RE: What are PI heads?

There was a thread I pulled this link off of. Good article on how to do the swap. What PI heads are. What they will do for you. etc.


http://www.bossracing.net/PI%20Head%20Swap%20page1.htm

Quick and dirty, they're the better flowing heads found on '99+ 4.6L 2v engines. So if you're going to by a Cobra, it's going to be a 4v engine and the PI swap will do you no good.
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Old 03-22-2004, 01:31 PM   #3
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Default RE: What are PI heads?

yeah PI are only for 2v's, and they dont flow nearly as well as a stock 4v head
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Old 03-22-2004, 07:20 PM   #4
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Default RE: What are PI heads?

AHhh ok, I suspected that because I always saw the PI head swap refered to on GT's and never a cobra. The link doesnt work so im going to look through their site, I still want to learn a bit more about them. Thats cool that the 99+ GT heads can be swapped onto the 96-98 GT to make more power. Thats just like swapping out the stock single port heads on a 94-98 Mustang V6 and using a set of 99-01 Splitport heads, of course you need to change your intake but thats it. So far the Single ports offer more flow results with porting then the double ports but that will change soon after SuperSix figure out a better way to port them and to add larger valves without problems. The double ports have alot of potential but the single ports can be modified safely to accept 1.94" intake valves and 1.55" Exhaust valves.... Thats small block V8 material there (Im most familiar with that size on stock Small block Chevy Heads.) As we know just adding larger valves isnt crap, They fully port and polish the entire head, its pretty crazy, these heads can sustain well over 800hp (boosted, nonboosted is more likely 420something which has been done N/A), its just up to someone to do that to a V6

Unfortunatly my sixer has far too many miles and so many damn things keep breaking, and its not cheap either.... $2000 dollars in repairs over the last 3 months is not what I expected when I bought this car.... That is why I am giving up the good fight on her and going to a low mileage Cobra, Im going to get one with under 50k in the best case scenereo, Nothing over 65k. Ive learned alot about the 90 degree V6 block but damnit, if only she had 100k less miles, then she would be set right at 46k miles and NOTHING would be broken and she would still be under factory warenty, lol.

Another question I have now is how large are the valves in the 4V heads found in the 96-98 Cobra? How much can they be taken out to safely? And about how much lift and rpm can the valve train take. With the 4V is there anything I should worry about with the DOHC? I AM NOT FAMILIAR AT ALL WITH DOHC so I dont want to screw something up. Are there double timing chains like some DOHC imports? I would most certainly think there would be because both cams need to be timed correctly and somehow making it just 1 timing assembly would be hard to imagine in my mind.

One last thing, You can do a PI head swap on a GT well can you do a head swap with a 03' Cobra? If so what all is needed? Are the heads on the 03' Cobra that much better flowing then the 96-98 Heads?

Thanks for your help everyone, Sorry about all the crap to weed through I just get excited about new things and I am really excited about the Cobra


-Eric-
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Old 03-22-2004, 07:30 PM   #5
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Default RE: What are PI heads?

96-98 heads have their pros and cons, just like 99-2001. whatever you get, dont waste your time or money changing heads. each head has one timing chain, that drive both cams. as far as worrying about anything, there is nothing. as far as changing cams like you said, its pretty expensive, and not worth it unless FI and lots of boost. 4v's are very capable stock. when i dynoed my car, with stock heads and cams, the hp never peaked and dropped. it kept rising untill fuel shut off. 460 rwhp isnt bad for 8psi and a stock motor
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Old 03-22-2004, 11:38 PM   #6
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Default RE: What are PI heads?

aftermarket cams are worth it if you want the sound and a lil more power. seeing as you got the idea on the head swap, i'll just add that an SSS valvetrain upgrade with a P&P job and a set of cams would be killer on a 4V motor.
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Old 03-23-2004, 12:46 AM   #7
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Default RE: What are PI heads?

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ORIGINAL: BCisme

aftermarket cams are worth it if you want the sound and a lil more power. seeing as you got the idea on the head swap, i'll just add that an SSS valvetrain upgrade with a P&P job and a set of cams would be killer on a 4V motor.
and now he has $6,000 in head work
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Old 03-23-2004, 04:56 AM   #8
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Default RE: What are PI heads?

$6000 is, um.... Too much for heads on a Streetable car.... I can see spending like $3000 but $6000 is just well..... Alot.

What are SSS heads anyways? Are they aftermarket heads? Obviosly they are still 4V heads. Are the valves larger on them or something or what?

From what 100th is saying it sounds like the stock 4V heads are pretty damn nice and probably could use a port and polish to make them flow a little more, coupled with larger valves and stronger double valve springs they could probably do alot.
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Old 03-23-2004, 01:56 PM   #9
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Default RE: What are PI heads?

4v heads are killer stock...thats why the 03 guys are doing 800hp on stock heads and cams...not to mention all the older cobra guys doing the same thing....if you stay NA, just leave the heads alone. but if you go FI, p&p would help. SSS is a company that makes their own valvetrain kit, you will pick up 40-60hp FI, but it costs 3000 grand...personally if you really feel like taking your motor apart, before you mess with the heads, change the rods and pistons! i cant stress that enough. and after you do that, i recomend doing the IMRC delete, a set of SHM regrinds, and if you go with a single blade TB, to grind away the post in the middle of the intake.
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Old 03-23-2004, 08:13 PM   #10
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Default RE: What are PI heads?

Quote:
ORIGINAL: NeoTokyo

$6000 is, um.... Too much for heads on a Streetable car.... I can see spending like $3000 but $6000 is just well..... Alot.
lol did i forget to mention that part?
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Old 03-23-2004, 08:13 PM
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