i have searched around and havent really found an answer that i was happy with so here goes.

im looking at a used motor that a friend has for sale, the things i know are

s5 block
streetported
als apex seals 2mm
mazda corner seals
mazda side seals
used housing and irons (mileage of hosing unknown)
14000 km on motor so lets call it 10k miles

question is what is a good compression reading for this, the oil pump has been removed so premix is being used. car has not ran in aprox 5 months

with valve out of my compression tester i got a reading of 90 - 95 on the back and same on front. reason im asking is because im not familiar enough with the
seals and s5 blocks to make a good call on if the motor is worth the money or not. builder claims the motors good for round 20 psi friends never had it higher then 12 with a gerret gt 30 turbo.

are these readings normal or is this already a low reading. i also do know the break in was done 100% accurate. he was not planning on selling, the car it was written off in an accident.

 

90-95 psi is low , did you do the compression test cold or hot and did you hold the throttle wide open ?

Cold tests will give higher results than warm and having the throttle fully opened will give higher results, dont do it with it closed.

How much is he asking for the engine?

Rotary >Pistons

 

compression is dependent on the RPM which it is being tested at. 85psi at about 200 cranking RPMs is about your bare minimum for an engine that will run reliably.