2007 Mustang GT #95 Compression Test

[@top-endmotors623]

Yes, the tester adapter is specific to the engine.

[@kammer_x1606]

What size are the threads for the spark plug holes? I can’t seem to get anything to thread in there.

[@top-endmotors623]

Sorry, I don't know the thread size and pitch for this motor. I used a Snapon tester and adapter if that helps.

[@lacofdfireman]

What should compression be for that motor? Does it change if it has cams?

[@top-endmotors623]

Good question! I don't know if there is a specific pressure reading number per the design of this or any engine. Pressure readings will change some with altitude and air density as well as the compression ratio of the engine. The two things I look for in any compression test is consistency in the first puff number and the last puff number I typically run 5 compression cycles for a test). Low percentage variation between all cylinders on the final puff would indicate an engine in good condition (generally around 140 psi to 165 psi based on my experience). As well as a a low percentage variation in the first puff number would indicate the the health of the valve train, in allowing air into the engine. A worn cam lobe, damage valve spring or rocker may not let as much air in resulting in a lower first puff number than other cylinders. I have put a compression gauge in one cylinder of a running engine at idle and the pressure readings where in the 60 psi range, less time for atmospheric pressure to get in with a closed throttle and other cylinders displacing the air in the intake. Cam duration and timing does effect how much air can push into the cylinders, it may not change it much on a cranking test but I'm sure it would on a running test. That's how we get more power. The science part is above my pay grade.

[@lacofdfireman]

@@top-endmotors623 tried to check the compression in an 06 S197 4.6l today and pulled all the plugs only to find the compression tester won’t hook up. Not sure if you need a special adapter or something to fit in the smaller plug hole or what? But the one I rented didn’t work. Any ideas? Are the a special kind. Thx.