PI vs NPI engine block

Michael sommers · Jan 3, 2021

So I bought my 2002 mustang gt a little over a year now, and recently pulled off the intake manifold to replace the gaskets because i had noticed it was leaking,I noticed it was a dorman intake, but I just assumed they had somehow managed to break the original Ford one, and well...my heart sank when I saw the tear drop shaped ports. for some reason, one of the previous owners apparently had swapped either a whole NPI engine in, or just the heads. My questions is, is there anyway I can tell if the engine block itself is PI or NPI because I’m curious if they had swapped the whole engine or not, thanks!

tsemmett · Jan 6, 2021

Look for the casting numbers on the block. That should tell you where it came from and when. 4.6 2V Casting Number List

Michael sommers · Jan 8, 2021

tsemmett said:
Look for the casting numbers on the block. That should tell you where it came from and when. 4.6 2V Casting Number List

So the 02-04 pi blocks have no dowels? Because whenever I pulled my transmission off mine had one, the other one wasn’t there( assuming it broke off).

tsemmett · Jan 8, 2021

I believe they're referring to dowels for the main bearing caps. The bell housing should already have dowels (to locate the transmission when installing), but there are a couple different main cap setups, depending on the block.

Adizzle843 · Jan 8, 2021

The castings are on the drivers side of the block. The difference in dowels is Romeo or Windsor, so an older Romeo NPI block would still have the jack screws, which you can see in the pic, along with the casting numbers.

XOTrumpet · Feb 9, 2021

I had the same thing happen with mine. Almost exactly. It was a blessing in disguise with the PI swap power boost, really.

Deleted member 38176 · Feb 9, 2021

No difference between PI or NPI blocks

Michael sommers · Feb 10, 2021

XOTrumpet said:
I had the same thing happen with mine. Almost exactly. It was a blessing in disguise with the PI swap power boost, really.

Yeah I must say I agree with you on that, it’s a completely different feeling car now, and it needed to be done because my heads were seeping oil pretty good.

Michael sommers · Feb 10, 2021

Nightfire said:
No difference between PI or NPI blocks

Oh alright, thanks I wasn’t sure if there was or wasn’t

XOTrumpet · Feb 11, 2021

Also, (because I failed to actually answer the question for the sake of commiseration) as far as the differences between the actual blocks themselves, there are none except between Windsor and Romeo castings. The pistons have a shallower saucer shape dish in the NPI blocks, and they are deeper and more angular on the PI block pistons.
Why anyone would put NPI heads on a PI block, I don't know. Considering both of our cars had NPI engines in them just tells me not everyone is familiar enough with the modular engines to know the difference when they need to swap them out. "A 4.6 is a 4.6, right?" Either that, or they were put in for a quick sale. Either way, it worked out ok for us.
Sure you knew that stuff already, but putting it in for the sake of anyone that comes across the thread searching for something.

Adizzle843 · Feb 11, 2021

Nightfire said:
No difference between PI or NPI blocks

I misspoke, what I should have said was you could have a non PI engine with the Romeo jack screws, vs the dowels for the Windsor. The point I was trying to make was the jack screws on the side won’t indicate if it’s a PI or not.

Michael sommers · Feb 12, 2021

XOTrumpet said:
Also, (because I failed to actually answer the question for the sake of commiseration) as far as the differences between the actual blocks themselves, there are none except between Windsor and Romeo castings. The pistons have a shallower saucer shape dish in the NPI blocks, and they are deeper and more angular on the PI block pistons.
Why anyone would put NPI heads on a PI block, I don't know. Considering both of our cars had NPI engines in them just tells me not everyone is familiar enough with the modular engines to know the difference when they need to swap them out. "A 4.6 is a 4.6, right?" Either that, or they were put in for a quick sale. Either way, it worked out ok for us.
Sure you knew that stuff already, but putting it in for the sake of anyone that comes across the thread searching for something.

I was thinking maybe a timing issue and they noticed quickly ( after replacing timing components maybe?) and they cranked it once before they heard it, so enough to bend valves but just leave a couple marks on the pistons? But it doesn’t matter now I guess.

manicmechanic007 · May 30, 2021

Michael sommers said:
So the 02-04 pi blocks have no dowels? Because whenever I pulled my transmission off mine had one, the other one wasn’t there( assuming it broke off).

They all had dowels from the factory. Probably got lost with a trans removal . They tend to stick to the trans and pull out of the block. Send it

Adizzle843 · May 30, 2021

When I say dowels, I should clarify. I’m talking about the main caps.

Cammed f1fitty · May 21, 2022

If you are taking the heads off anyway look at the dish in the piston. The npi pistons had a smaller dish due to the larger combustion chamber on the npi heads. The pi block will have a larger dish that runs out a little closer to the cylinder wall. I can post pics as I have several pi and non pi block store down right if it would help

Cammed f1fitty · May 31, 2022

Check out my full pi swap write up I’m doing if it helps lmk if not lmk what to do different

PI vs NPI engine block

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