hey guys,
i have a question regarding PI heads. i have a 97 4.6L f150 and have wanted to get a set of 99-up PI heads and intake manifold and swap over. several people have suggested for me to do this, and it seems to be an easy way to pick up some HP and TQ. but one of my friends said i should ask about the compression. mine stock (if i am right) is about 9.5:1, and he told me if i switched to PI heads, it would shoot up to about 11:1 or so, because of the different kind of pistons in my truck. do you know if this is true and how it would affect my truck? it is a daily driver with 92000 miles which i drag race most weekends. i also have a 100 shot NX wet kit, so that scares me a little also, not sure how the NOS and higher compression go together. will it be safe to do this? thanks

 

HI!... The 5.4 and the 4.6 TRITON truck engines use the same piston because they have the same bore (3.552). They are just dished differently to compensate for the smaller cumbustion chamber on the "P.I" heads. That's why these engines are called "MODULAR". The 4.6 and 5.4 TRITON engines both have a 9.0:1 compression ratio. You should have no problems bolting on a set of 5.4 "P.I" heads on to your 4.6, but your compression ratio will go up to around 10:1. By the way I've been told by a buddy that works at the FORD engine plant here in WINDSOR that the "2001" - "2002" 4.6's in the F-150's that jumped up from 220H.P to 231H.P now have the "P.I" heads and a "P.I" intake manifold to match.

 

Neal,
Do you have any good sources for obtaining the PI intake??
Also I plan a mild port and polish (DYI). Any tips??

 

BullittMcQueen- There is a lot of info on the Corral and Stangnet about the compression ratio increase. Your friend is partially correct about the different pistons. But instead of varying by 4.6 vs. 5.4 or F150 vs. Mustang, it is an issue of model year. The PI heads have a smaller combustion chamber volume than a non-PI head. So when Ford switched to the PI heads, they used a different piston (I think dished) to achieve the desired compression ratio. So when you bolt a PI head to a non-PI engine, you get the compression ratio increase.

The Mustang guys are reporting anywhere from 40-60 HP increase when they bolt the PI head to a ‘96-’98 engine. Part of that increase is due to the better flowing heads, the other part due to the higher compression ratio.

While there are tons of posts on this stuff on the Corral and Stangnet, this one summarizes the issues pretty well, you'll need to read down through a number of the responses to get the info you are looking for.

http://www.corral.net/forums/showthr...+with+PI+heads

 

From what I have read on corrall the PI heads on a 97-98 4.6 will result in about 10.5 to 1 compression ratio and about 40 + horsepower increase. Look for posts about a man who goes by "The Game". Seems to be an authority and sells the heads ported and polished if you want them, in a kit with all the pieces you need.

You will need premium gas with 10.5 to 1.

 

so yes, i definitly want to do the head swap, but how will the higher compression do with me shooting a 100 shot?

see i am hearing different stories now, i have mustangers telling me higher compression, JDM tells me there will be no compression increase, neal says the same? whats the real story?

its a tradeoff........i would love to see about a 50 rw gain from heads, but if its gonna make my nitrous unuseable then what to do?

 

The non PI heads have 52cc combustion chambers and the PI heads have 49cc. You do the math. According to mine the CR will go to 9.437:1.
According to my calcs when Ford changed to the PI heads on the 5.4 and did not do anything to the piston the CR should have gone up to 9.37:1. Sooooo, if the CR stayed at 9.0:1, they must have dished the pistons or moved the pin higher on the piston. Emmm, maybe they used a thicker head gasket and that is why all the PI heads leak.....

Regards

Jean Marc Chartier

 

well thanks guys, i went over to the corral and checked out some mustang advice, got in touch with shannan wheeler, owner of DTA performance, SUPER- informative guy who told what i needed to hear. he said the head swap would be safe and very effective, especailly with the juice. he said expect a compression increase from 9:1 to 10.5:1
apparently 97-98 pistons were slightly dished but not to the extent of 99-newer. he also reccommended getting ARP head studs to guard against a blown head gasket.....so i am one happy camper. now i will be really happy if i can come across some used PI heads.....preferably GT's but i'll take the truck heads too....so anybody with any info on some pass it along to me...thanks guys.

 

I read all the posts but can't really find the answer to the question.

What year did they start to put P.I. heads and intake manifolds on the 4.6L?

 

Hey BullittMcqueen You and I have the same year truck and engine and this looks like a great idea. I have often wondered about head swaps and wondered why Edelbrock and others have not made aftermarket products for our trucks. Anyway if you could let me know how things go I would be much appreciated. Feel free to e-mail me. THX Want

 

Intel486,

The F150 had then starting in 2001. I am not positive for the expedition but I think it was 2000.

JMC

 

K thanks JMC. I have a 2000 w/ the 4.6L So I don't have PI heads and intake manifold?

How expensive are they and where can I get them?

 

Happy Holidays!

This thread raises the majority of questions and concerns related to the PI head swap. ALthough, my specific situation also includes my current use of a Magnacharger supercharger. Yet, I know owners with 2001 or newer F-150 4.6s have installed MagnaCharger supercharger kits, therefore I know there are owners with Magna manifolds that do not match their stock PI heads and with the higher compressions roaming the streets right now, with no problems......

I am bringing this thread back up in hopes that some of you that participated in this thread may have made the swap to PI heads by now and or there are others that have researched this more indepth than I have.

Here are my questions and concerns:

I have a 99' F-150 4.6 with a MagnaCharger Supercharger. I have the bazooka 11-12 lb. boost proto type pulley, 90 mm maf and 42 lb injectors that I will re-install in place of the stock 5 lb boost pulley as soon as I can get a tune. But, before I go through that process, I wanted to install PI heads. Here are my concerns associated with a PI head swap:

1. Do I need F-150 2001 or 2002 4.6 PI heads,

2. Or do I need F-150 1999-2002 5.4 PI heads,

3. Or do I need Mustang 4.6 heads of a certain year,

4. Do I need aftermarket head stud bolts to reduce chance of blown head gaskets and leaks

5. Do I use a "thinner" non-PI head gasket or a "thicker" PI head gasket when I swap to PI heads

6. Do I need to have the Magnacharger manifold ports "matched" with the PI head ports (Allen Engine development said not to worry about porting the manifold to match since their kits are used with PI and Non-PI F-150 heads with no problems)

7. Will my compression increase to a "dangerous level" since I do not have the PI dished pistions

8. Does anyone know of a source that has performed a similar install that can answer all my questions

Thanks for any and all help.

 

Yea I'm going to bump this one to the top again and try keeping it there for a little while.
I have simular questions as iron horse. I have a new 4.6 Windsor short block that I am going to start building. I also bought some PI heads with about 13,000 miles on them off of a Mustang 4.6. I want to know if my intake can be matched to the intake of the PI heads. Also, are the cams different. Part of the build I am planning involves this engine pulling past 6000 rpm so I may want a cam built for top end rather then max torque. Having a 430 rear will also help pull higher rpm's.
Any experts out there???

 

anyone with a price range yet for the swap?