how? It's the first time using a leak down tester

You need to inspect your piston rings and ringlands
and while you're doing that, have the head re-surfaced properly and install an oem hg

right I will do this. I'm just puzzled why cylinders 1&2 are leaking into eachother

Probably because the hg is blown and/or the head is not machined correctly. With a MLS gasket both surfaces have to be perfect

The headgasket is brand new, I can only imagine the head wasn't skimmed correctly

hello everyone, took the engine out, checked the bores, theres no cross hatch on all four, the cylinders look all polished so im going to give them a quick hone. i removed the pistons the bearings are fine, crankshaft is fine so looked ot the pistons.
i apologise for the weird order ive uploaded these pictures
https://cimg3.ibsrv.net/gimg/www.mia...83014b4c8f.jpg
Cylinder one,
https://cimg7.ibsrv.net/gimg/www.mia...54e046e8f8.jpg
Cylinder 3, it has scratches along the sides rough shape if im being honest.
https://cimg8.ibsrv.net/gimg/www.mia...8ff20c20c9.jpg
Cylinder 2
https://cimg1.ibsrv.net/gimg/www.mia...227fb5d7b4.jpg
Cylinder 4.
I also dove alittle further and looked at the cylinder head https://cimg4.ibsrv.net/gimg/www.mia...8e07d49639.jpg
Cylinder 1 head, i can feel this line. dosen't feel flat at all
https://cimg5.ibsrv.net/gimg/www.mia...e7c0c71249.jpg
Cylinder 2>3 same
https://cimg6.ibsrv.net/gimg/www.mia...a052dadfa6.jpg
Cylinder 3>4 the next two photos are for cylinder 4, the head looks poorly skimmed.
https://cimg7.ibsrv.net/gimg/www.mia...a34564b4bd.jpg

https://cimg0.ibsrv.net/gimg/www.mia...af18abedbe.jpg
What do you guys think?

I see some strong detonation in that last pic.
The machine job doesn't look really good either.
I'd also replace those rings.

looks like #3 went. more pics of the pistons and head from top.

where In the last pic? I can't see it. Yeah I will get it skimmed again by someone else, what's wrong with the rings? I'm going to replace them anyway when I hone the block. But just curious, I'm learning as I do this

number 3 cylinder is the only has signs of det I think the others are like normal

those pits in hte head on the edge of the cyl
that's either knock/detonation or something actually went into your cylinder

I see it in the squish area in last pic. I agree with 18psi. Either it chewed something briefly, or you had some amazing shockwaves create macro-asperities on the surface.

oh I see them, I think it might have chewed something, the bore has a super fine scratch in that area, but I'm going to install a knock sensor as my ecu is a Ms2 extra if that'll help

not in post mortem

I don't think I've ever seen a knock sensor actually pick up FOD: by the time it's made contact it's already too late, and even upon immediate shutoff you've still done a ton of damage already.

FOD?

Foreign object damage, just a guess actually I ninja edited after Brain answered.

its foreign object damage.

Really? would make sense i suppose because these scratches weren't there when i replaced the headgasket. but i was positive i made sure no grit or metal got down there.
Ive tried to hone the bores and 3 have come up perfect but number 3....... i can only just feel it with my finger nail so im told it'll need boring?
I did at first this could be detonation as i put a post up earlier confused why my car had terrible fuel consumption (around 9MPG) here:
https://www.miataturbo.net/megasquir...umption-92602/
I sent my map to a well known tuner and he told me the timing is very conservative so he fiddled with the timing.
But if it looks like foreign object damage then at least i can relax because im planning to fit 9:0:1 forged pistons (dont wanna go too low for a daily driver)
https://cimg1.ibsrv.net/gimg/www.mia...32a1fcd9dc.jpg

How large are your replacement pistons?