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Long story short, twice in the last 3 years I've had detonation destroy my #1 piston. Other have had no signs of detonation. 99 miata, supertech pistons, MS3, Flow force 640, GM D-585 coils, coolant reroute. I had injectors checked after both times and they came back good. Car was dyno tuned and spent 99% of the time track driven. Here's some pics of latest carnage. Let me know what other information you need.
MAT on track vs MAT on dyno. Octane on track vs Dyno.
Check tune closely for any tweaks to fuel or spark on different cylinders. Those things are available, and could have been mistakenly turned on.
I presume no knock sensor.
I presume that both times all damage is cyl 1. On a guess, blocked coolant passage. (I think that is what moocow was hinting at.
Well, car was tuned during middle of FL summer so it was hot.. never saw AITs ever reach any danger temps.
That was my first thought as well. Had to go back and dig up some old posts. The change didn't happen until '01, coinciding with the VVT-specific head casting.
That was my first thought as well. Had to go back and dig up some old posts. The change didn't happen until '01, coinciding with the VVT-specific head casting.
NB2 on the left, NB1 on the right:
So this is interesting. I got my HG from fab 9, looking at their website there is only one option for 94-05 for the Cometic gasket. Looking on FMs site they are separate. Unfortunately I threw my HG away 🤦♂️
Please realize that your AFR table does not mean anything except that is what your tuner should have been trying to hit. It would also be used during auto-tune, or if you run VE-Analyze in Megalog Viewer to correct your VE table. Otherwise, it is not in the fueling equation, and you have EGO turned off.
Your VE table is kind of all over the place. Apparently your tuner did not smooth it. Perhaps he tuned full boost only?
Do you have any data logs? Those will tell you what the engine is actually getting regarding your AFR.
Hmm Va Beach. There is a notorious tuner there, I've heard. EDIT: Oh, that was from your thread about the 1st time cylinder 1 was destroyed. Still, you have to figure out Cylinder 1.
Are these 8.6:1 pistons? The experienced guys likely know by looking, but not I. Spark at 200kPa seems aggressive to me, but perhaps not for 8.6.
What boost are you running on track? Data logs would be good for that as well.
The individual cylinder trims I asked about are both turned off (fuel and spark), so that is not your issue.
I probably have nothing more. In for resolution.
Last edited by DNMakinson; Jun 18, 2021 at 09:54 PM.
Reason: 2 + 2 = 4
The spark is aggressive in the 3500-5000 range. Above that its likely fine. You might be seeing knock in that area. Still though its always #1, seems like maybe #1 is seeing more air and maybe less fuel. Maybe it runs lean and the only way you can figure that out would be to run a wideband for every cylinder or egt. If its the stock fuel rail I think it feeds right into #1 so I wouldnt think it would be lean but who knows.
I know of a couple of cars here that have had the 'wrong' HG fitted, both died pretty quickly but IIRC they boiled and blew the HG, I'm not aware of any other damage as a result. If that is a guide (and it may not be), it suggests there is something else going on, perhaps in conjunction with the local overheating, that makes a difference between a blown HG and a damaged piston.
What killed my engine......twice?
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