its nothing new,, almost every oem has them in their RACE applications .
Every single bridged port exh engine has them.
In a bridged port cyl, the bridge itself is thin and exposed to the center of flow from the cylinder. this is an extremely hot place on both blowdown and return wave periods. the bridge grows with heat end expands INTO the bore, these small lube holes allow a very slight exposure to lubrication and thus aid in reducing the amount of scuffing and wear on the skirt.
In any bridged cyl like the old cat 600 triples , you find in very short order that the rings are flat spotted directly on the bridge contact point. Leakdown goes up fast and below peak operating rpm power levels struggle.
In the mx world prior to the 4 stroke ruining racing,, ( my pov ) every bike had them in both bridged AND triple e port configurations, HEAT was a big issue in those days,, seizing on the subports was common place this ended that weakness.
Now, I dont drill all of them ,, only the units I see issue with .
thin or ported subports or widened main port ( ex ) will make this worse . The thinner that material is both in its chordal width and its actual depth back down the tunnel the more it will expand and crack at the cylinder opening. Ever see a crack between the exh ports ?? most cyls are split at the cores in this exact location . Casting boxs need to be removable and casting a triple exh port is complex..thats where the seem ends up from top to bottom section of core box.
drilling the lube / colling holes can't hurt anything at all, will they be a benefit ?? only the end user can answer that..
high boost even for short 4 second bursts creates big reversion heat,, we need it to make power one of the 2 edges of our boosted sword..lol
long runs at more reasonable boost and flow rates makes prolonged heat,, another exposure to that damn sword again..
Gus
.005 max clearance..start coolant temp 70 degrees, end of run coolant temp 130 ish,, wiseco skirt coating still like brand new,, both sides.
