I finally got around to doing a compression test; which I honestly should have done a year ago when I got the car, but I digress.

I got 160 on all cylinders (Except for #4 at 165) but then I realized I did the test without the throttle open
Then I got 180/180/175/165 with the throttle open, I didn't add oil because I figure they're all within Mazda's specs and the engine doesn't act unhealthy at all.

My problem here is that I don't know how to decipher why I have 20psi lower compression on #4, or if its something I should be concerned about. Am I just paranoid or do I have something to fix before proceeding with turbo things?

 

I don't compression test for this exact reason. I know I'm going to turbo the car anyway, so I just assume it's good and go on with my plans. The last thing I want to do is throw some debatable compression numbers that make me start 2nd guessing what I know I'm ultimately going to do anyway.

You could try to test #4 again and see what you get, maybe the tester leaked a little and you'll get a better number.

Otherwise I'd vote to forget about it, add the turbo, and if it breaks sometime down the road then you can fix it.

 

Forget it, boost the car, deal with it if something breaks.

 

Mine was off by that much, and a big gain on a wet test (poor rings). Boosted anyway. Have had it up to 9.5psi with no issues.

 

I have a 1.6 shortnose anyways. Turbo's going in and I'll just see how long it takes to spit some bananas out while saving for a rods only 1.8
Solid plan? Solid plan.

 

Just fuggin' send ittttttttttt

 

I boosted my 1.8 with way worse compression numbers, YOLO

 

You wont be able to reuse your manifold, and possibly downpipe when swapping to a 1.8.