tbirdscwd

That would bring it right around 9.7:1

cliffyk

I am not one to argue with direct observation, perhaps Ford's published specs are based on original design docs or some other pre-production determinations.

This does however raise the issue that if (as you have empirically determined) the OEM PI heads do have 42cc chambers, the OP's compression with the Patriot heads (46cc per their specs) has been reduced even further than I indicated in my above post.

nickmckinney

Patriot has done 2 different PI chambers, their early ones are 46cc and are fully CNC profiled everywhere and the spark plug boss was made really small. Their later ones are 44cc and only have the swirl dam removed.

cliffyk

Then they need to update the information on their website. I keep forgetting this is the automotive industry--I spent most of my career working with precisely documented, precision equipment.

And here's the most ironic part--turns out they are still 2cc bigger than stock just as I said above...