Piston Cooling Jets
- Thread starter Ishiftem
- Start date
Wow Dan, just Wow! 
How did you determine hole diameter? Will there be any significant pressure drop with no changes to the pump?
Schools in session..........
Details,damnit,Details!!!!!!!!!!
So basically, take careful aim and drill a hole with a long drill bit for a 8-32 tap. Drill through the main web targeting the back side of the piston. Make sure things like rods, oil pump shaft and pin bosses are out of the line of fire. Use a drill/ tap combination “drap” to get the thread started. Finish with a bottoming tap but don’t tap all the way. Drill a .025 hole through a brass set screw. Install set screw and snug it against where the threads end. Cut a groove from the main oil hole to the holes you made. It’s pain but all doable in the garage. The driver side, you have to miss the oil feed for the mains. Not much room for error. Usually something like this is done for boosted or endurance engines and will allow the use of a little more aggressive tune. I have a different issue. This engine has always butted the rings. Last time around I opened them to .040 and it still did. The bores were still very nice but 10x magnification on the ring ends told the story. The usual suspects have been ruled out. I cc’d everything again and it’s 13.3:1 compression on the money. I thought it was higher but must of screwed up. 112 fuel is plenty for that compression. This tear down I can see the piston is getting hot on the dome side. Discoloration in the top ring groove and even on the bottom side all on the dome side. After some research including a Mercedes white paper and work done by Cosworth, Ilmore, and others, it appears the huge crevice volume created by the dome along with the counter bore is causing detonation in that area. So the cooling jets are a way to help keep the piston cool along with higher octane fuel. The best solution is to get rid of the counter bore and notch by sleeving a passenger block for one. Second would be a set a pistons that fit the dome tighter to the cylinder via detonation grooves above the top ring such as this Ilmore Chevy Indy car piston.
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The bad student, Petey.......He has his hand up again........How do the grooves fight against detonation....... in the same manner as cooling fins ..??
@ an alloy steel ring temperature of 575*F (500*F delta T), the ring will grow ~ .038" in circumference. That's a hot ring to butt. Not disagreeing but definitely an issue. Most alloy steels except for high speed tool steels will begin to draw down in hardness at that.
I bet it’s quadruple! If I wasn’t feeling so lazy I would measure it.
We will find out in a few years when I tear it down again!
I was actually not questioning with any of your gap determinations, but expressing the heat required to achieve closure of a gap being hugely detrimental to the material hardness of the steel ring.
My growth estimates assume the entire ring is the same temperature which is likely not case, thus localized heat was much higher.
My race days were in blown injected alcohol, and had worked through similar issues early on. We were however super conservative where heat was concerned and in the 7.0 Pro index.
Not like cooling fins. The grooves are supposed to disrupt pressure waves as they make their way down to the ring. Secondly, the piston above the ring can be made larger to minimize crevice volume. The theory is that if you are a little to large, the grooved area will wear quickly and give material a place to go before damaging scuffing occurs. I do know this, after the reading I’ve been doing, it seems a lot of power is getting blown right out the exhaust with that counter bore. Not a good design AT ALL!