Easiest way to do it is to get an oil filter sandwich adapter like Greddy and attach the pressure sensor to that. If it's a large sensor (like Autometer), it'll need to be remote mounted, since the vibrations from the engine will defintely cause it to snap off if it's directly attached. You'll just need a length of stainless steel braided line and an adapter to plug two male 1/8" NPT ends together so you can mount the sensor to the car's frame. Paintball guns use the perfect size braided line, they're available in all different sizes so you can mount the sensor anywhere in the engine bay, and they're usually good to 3000psi (stock Celica shouldn't see over 100psi
).
