Is it worth it

BeastyVas said:

Hey folks , so from my understanding the only difference between the 99-04 Pi motor and my 98motor is the heads and cams.

Click to expand...

The pistons are different. Which is one of the reasons why if you put PI heads on a non-PI bottom end the resulting combination has a higher CR.

Knowing what I know now I personally would not replace heads while the motor is still in the car. The whole Mustang motor is not all that hard to remove and the access is so much better on an engine stand.

I personally think the lower cost option is to use a whole salvage yard PI motor from a Ford PI Romeo from a 2001+ Panther (Crown Vic, Grand Marquis, Town Car). Try car-part.com for some sample prices in your area.

Non-PI (NPI) SOHC engines have an 11-cc dish along with a 51-cc combustion chamber. The PI head has a smaller 42-cc chamber and a deeper 18-cc dish. Matching a set of PI heads with NPI pistons is a recipe for a much higher compression ratio.

This is why the trickflow heads come in two sizes - even with the bigger chamber size trickflow top end kit you’ll still increase your compression ratio. Added compression ratio pros and cons should be considered when planning out your future mods for what you want from your car.