what is the psi on the powerstroke cycle of a normal economy car?

It would be in the region of 580psi peak combustion pressure on a regular petrol engine. A diesel would be much more than this, probably1500psi.

Do some research into BMEP, Charles'/Boyle's law and peak combustion pressure.

I have often wondered that myself. If we take a car that has a compression ratio of 8. and sea level presure is 14.6 then it is 116.8 psi. That is if there were no ignition. Be interesting to follow this question to see if anybody knows.

Edit. Upon further research it seams that Ignited fuel would expand about 10 atmospheres. For an economy car that has a compression of 8. and Atmospheric presure is 14.696 psi and fuel expands 10 atmosheres your answer is 1,175.68 psi. That's is assuming full throttle. Actual number may be slightely less or slighty more as the forward momentum of air into the intake valve can increase the number or restrictions in the intake can decrease this. There are also many other variables. But, 10 atmosphers is a good estimate. If you take a diesel with a compression of 24 at full throttle it could reach 3,527.04 psi. Wow, no wonder they have to be so heavy.

You can't calculate PSI in the combustion chamber by multiplying atmospheric pressure by compression, because there are many other factors involved, including the inertia of the air itself, residual exhaust, and changing physics at different engine speeds. Actual combustion pressure range between 1000 and 2000 psi typically, it depends on the type and size of the engine, as well as factors like speed and load. Diesels can have higher pressures than a gasoline engine..

Depends on compression ratio though the bulk will be over 100 under 200psi.

about 175 psi.