Track NB compression test/leakdown - eating oil
 

Hey guys was wondering what you think is going on with my track car. Some background, car is basically track only at this point (engine mods listed below) and I noticed its been eating a bit of oil. Im feeding it about a .5 quart after every 30 min session out on track. Oil pressure is good and no smoke when out on track. The current engine is a junkyard VVT 1.8 that had 80k on it and since the swap I only put about 4 track days on it (about 8 hours or so). When I got the engine I changed all the seals, timing belt/water pump and oil pump before putting it in the car to freshen it up. So I pulled the spark plugs and noticed they were wet (oil) and smelled like oil. I looked into the plug holes and seen the tops of the pistons were also wet. I pulled out my endoscope to get a better look and sure enough all 4 pistons are pretty wet (see pics). I put the plugs back in, warmed the car up then did a compression test (results below). I figured the results were a bit skewed since it was so wet so I did a leakdown test (results below). I believe my piston rings are tired as the I could hear the air coming out of the oil fill cap on all 4 cylinders. Thoughts?

Edit: Wanted to add oil temp never exceeds 230*F on track, probe in the oil pan. Water temp never exceeds 190-195*F on track, probe in the heater hose hose at the back of the head.

99 NB with 1.8 VVT Swap
MS3
Boundary Engineering oil pump
Squaretop intake manifold
Custom carbon intake
Ebay headers
Spec miata exhaust
Castrol Edge Gold Bottle 5w30

Test
Cyl 1 - 180psi - 35% leakdown (sound coming from oil fill cap)
Cyl 2 - 175psi - 48% leakdown (sound coming from oil fill cap)
Cyl 3 - 173psi - 30% leakdown (sound coming from oil fill cap)
Cyl 4 - 178psi - 28% leakdown (sound coming from oil fill cap)


cyl 1
https://cimg3.ibsrv.net/gimg/www.mia...fd74e3eda9.jpg
cyl 2
https://cimg4.ibsrv.net/gimg/www.mia...221dab1a97.jpg
cyl 3
https://cimg6.ibsrv.net/gimg/www.mia...3e5b70d618.jpg
cyl 4
https://cimg7.ibsrv.net/gimg/www.mia...54493e6b2e.jpg

Looks a lot like detonation damage on the pistons. When you pull the engine apart double check your timing belt.

The leakdown tells you what you really need to know though. The bottom end is done.

Yeah I see what your saying about the pitting on the pistons. Shame because I always run 50/50 93oct and 100oct mix at the track to ward off any potential detonation as cheap insurance. Of course this last event I just ran straight 93oct.. I thought I heard a slight tick under a high load, low speed, 2nd gear uphill section but I thought it was the valvetrain, very well could have been detonating. Ill post my tune a bit later if you wouldnt mind taking a look at it. To me, it was a little aggressive but nothing I would say omg at, then again im not the best at this tuning thing. My afr's were always in the mid 12s if that counts for anything lol so it was nice and rich "safe". I was thinking if it was possible that the VVT map was overly aggressive, I dk.. Im not upset though shit like this happens, especially in a racing environment, were not just doing a couple gear pulls on the street then shutting it down.. Glad everything is cheap on these cars lol.

Rings are toast. Pistons look like they're in rough shape. Would definitely check your tune and timing as well. The only reason your compression test is halfway decent is because there's oil everywhere which helps seal everything up when you're cranking it.

I don't think the pistons have detonation on them that's just carbon and rough casting looks normal to me besides the oil on them

https://cimg7.ibsrv.net/gimg/www.mia...6ee3637457.jpg
https://cimg9.ibsrv.net/gimg/www.mia...17504c75cd.jpg

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The only area where you'll see casting marks is on the valve reliefs. It's clearly rough on the machined surfaces

I agree that the pistons look like they have seen some detonation. I was looking at the pistons on my original BP4W motor that I smoked mishifting 3>2 instead of 3>4 and they have the smooth machined top besides the valve relief area. Attached is my tune if you guys wouldnt mind taking a look at it. Thanks

The later higher compression pistons are very different from the early low compression ones. There are casting marks all over the later ones.

ahh I didn’t know that, interesting 🤔

https://cimg7.ibsrv.net/gimg/www.mia...4a652b4c02.jpg
Early BP


https://cimg3.ibsrv.net/gimg/www.mia...ba0f025a91.jpg
BP4W


https://cimg5.ibsrv.net/gimg/www.mia...54ebbeae54.jpg
BP6D

Sorry for the crappy pictures but you get the idea. None of these saw any detonation.

Thanks for the pics, yes looking at those they seem ok in that case. I was using the "compare tune" feature in tunerstudio comparing my tune against the MS basemap and it really isnt that aggressive at all. Actually compared to the basemap im running 1* less total timing in the high load cells (90-100kpa) and upto 3* less timing in the 80-90kpa areas. Besides rescaling to eliminate the boost areas since im NA, its a pretty "easy" tune. Im going to check my timing on the cams tomorrow. As a side note I did set the base timing per the MS instructions when I first installed the ecu.

Cam timing was good so that’s eliminated. Assuming there’s no detonation happening and me running a 50/50 mix of 93 and 100oct would you guys continue to track it and finish out the season? Reviewing my lap data the loss of power past the rings is costing me about 1-1.5 seconds per lap all else being equal. Oil pressure and all temps were fine with the motor in its current condition it just felt “lazy”. My fear is I don’t want to completely ruin the motor. If it will survive, just be down on power I’m fine with that. Either way it’s getting rebuilt at the end of the season wether I cut the season short now or finish it out.

I just tore my engine out and took it down to the bearings in 2 hours. Do yourself a favor, remove the engine, tear it down, order your parts, throw some pistons, ball hone, rings, and bearings at it, and enjoy the rest of your season.

Seconded. I've dingle berry honed my block 3 times now and it's still doing it's thing with rental car like usage.

When you say pistons, do you mean new ones in oem size?
I did all the above and since my pistons were damaged I just got a second pair used.

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You can get used non-damaged ones, or you can bore a block out for oversized pistons. A ball hone can be done at home, a bore requires a machine shop. Pour ATF over the ball hone, put it in your drill, and go at a medium constant speed up and down 3-4 times. You're just looking to scuff it up so the new rings can seat.

3-4 times? Wut
I used a 3(4?) Armed one I found unused at my work. But used engine oil and ran it for about 15 seconds up and down at rather slow pace.
The cylinders were glossy and they became more flat afterwards.

Yeah, that's 6-8 strokes, that's all I need ;)

Bumping my old thread in case this helps someone in the future. Engine is coming out this weekend and will be adding pics as it gets rebuilt. Ill be doing an inspection as I break it down to get hard answers on the problem. I ended up finishing out the season with that engine and it held up fine, smoking but fine lol.
https://cimg0.ibsrv.net/gimg/www.mia...d8d121c363.jpg

A little shock porn :burncash:

https://cimg2.ibsrv.net/gimg/www.mia...5b7e8b158c.jpg