[mexlatino]

now i am planning to do the swap and get pi heads for my 98 mustand. so i was readin about how the compression ratio goes up? what does this mean? will the life of the motor get cut short? please i needs some answers on this.

[HMUSN]

it just means you can only run smaller amounts of boost if you plan to go supercharged or turboed. for N/A applications it is fine and it won't decrease the life of the motor.

[mexlatino]

so even if i wanted to put for example stage 2 or stage 3 heads, its all good?

[JiMi_DRiX]

Dont you also have to use 91+ octane fuel when you put the PI heads/intake on? Doesnt the compression go up to 10:1?

[G.T. Rags]

Originally Posted by JiMi_DRiX Dont you also have to use 91+ octane fuel when you put the PI heads/intake on? Doesnt the compression go up to 10:1?

yes... but a lot of guys who mod there cars use 91 no matter what.....

i know my car runs better on the stuff

[MustangMatt96GT]

my car runs better on 87 or 104, but does not like 91. It's wierd, but more octane will allow for more timing...0

[00vabchgt]

Originally Posted by mexlatino so even if i wanted to put for example stage 2 or stage 3 heads, its all good?

with aftermarket heads (ported & polished), your compression ratio will most likely go down. this is because the combustion chamber size will increase due to the porting. PI heads have a 42cc combustion chamber, which when combined with non PI pistons dish size of 11cc will result in an increase in compression ratio...

Originally Posted by JiMi_DRiX Dont you also have to use 91+ octane fuel when you put the PI heads/intake on? Doesnt the compression go up to 10:1?

i think the compression ratio increases to 9.8:1 or so...

[BlueStangGT]

Originally Posted by 00vabchgt with aftermarket heads (ported & polished), your compression ratio will most likely go down. this is because the combustion chamber size will increase due to the porting. PI heads have a 42cc combustion chamber, which when combined with non PI pistons dish size of 11cc will result in an increase in compression ratio... i think the compression ratio increases to 9.8:1 or so...

Someone would have to REALLY hog the combustion chambers out to have significant effect on the compression ratio. If we're talking about an NA build then there probably won't be much swirl dam removal. With this in mind the compression ratio on my headswap (P&P, swirl dams contoured but intact) came in around 10.5 if memory serves.

On a forced induction build, all bets are off, lol!

[MustangMatt96GT]

Originally Posted by BlueStangGT Someone would have to REALLY hog the combustion chambers out to have significant effect on the compression ratio. If we're talking about an NA build then there probably won't be much swirl dam removal. With this in mind the compression ratio on my headswap (P&P, swirl dams contoured but intact) came in around 10.5 if memory serves. On a forced induction build, all bets are off, lol!

i agree, but even forced induction needs the swirl damns IMO...

I know of porters taking the damns completely out even on N/A motors and running more timing, but i dont understand how you car run more timing with the intake schroud removed. The only way to correctly unschroud the intake valve is to go big bore like you have. even .020 over on a 4.6 helps but a 3.700 bore helps the most.

but compression comes in around 10.4:1 with NPI pistons and PI heads with stock height head gaskets.