about what should the compression be on a 509 w/ a 250 blower?,

My 509's Are 185

are they blown

More info required like compression ratio and cam specs. Even then unless someone has your exact combo it will only be educated guesses. What are your compression numbers reading?

Craig

like vette said, need cam specs and combustion chamber cc and assuming your 509 is a 4.5 bore to give you an educated guess.

First thing you want is less than 10% difference between cylinders. Blower motors can be all over the place because of cranking speeds during the test. A better test is a leakdown of each cylinder-once again less than 10% is good. Also if it leaks you can get an idea of where the problem is-better than by checking compression.

insptech is on the money the general rule of thumb is all cyclinders should be within 10% of each other a cyclinder needs roughly 100ftlbs to fire newer motors are around 150 - 185 give or take after the rings seat.