Not sure what you are showing in that picture, but if you are refering to the peanut shaped dish in the top of the piston, that isn't a valve relief, its the exit of the prechamber in the head.
I'll go and take some pics of the dimentions of the head, valves, and pistons so you can see what I'm talking about.
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1986 F250HD Ex cab Fresh built up 6.9L diesel Lariat AC leather seats power everything w/full cluster, sterling rear 3.08LS gears, E4OD trans, ram intake ATS 088 turbo
1986 F150 Ex cab Lariat rollercam 5.0L on LPG AOD trans 3.55 gears 390 000Ks
OK, this is the 6.9 piston:
The valves in the head:
And an example of a diesel piston that does have valve reliefs: (mitsubishi 2.3 turbo)
You can see that the smaller piston had a larger prechamber dish in the piston than the 6.9. I'm not sure how they could get away with this, but it might have something to do with the bosch VE pump that was used on those engines. Who knows, but but both engines seem to be capable of smoke free operation without any emission controls (with a turbo).
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1986 F250HD Ex cab Fresh built up 6.9L diesel Lariat AC leather seats power everything w/full cluster, sterling rear 3.08LS gears, E4OD trans, ram intake ATS 088 turbo
1986 F150 Ex cab Lariat rollercam 5.0L on LPG AOD trans 3.55 gears 390 000Ks
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Lariat AC leather seats power everything w/full cluster, sterling rear 3.08LS gears, E4OD trans, ram intake ATS 088 turbo
