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Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.
First off, 450hp RB25 Neo, using a 2.5mm Cometic headgasket (9.5:1 CR due to 26 internals)
- I noticed the these headgaskets have a very small hole for coolant passages and i noticed my intake side of the pistons to be totally clean of combustion and i burnt Cyl 6 intake side all the way to the coolant hole. So im wondering if im getting higher temps on the intake side and hence my burnt headgasket. Was thinking that maybe i could make another hole to pass more coolant on the intake side but i have zero knowledge there.
- Also, tipically, when a MLS headgasket burns a side and cracks the MLS layers, what are the common reasons? High temps, Detonation, ARP studs loosening? just wondering what to keep an eye out since i can only think that a small sudden acceleration lean condition helped the HG get burned.
I'd be very surprised if the coolant passages in the gasket were your issue, however in saying that I'm not a big fan of Cometic gaskets. i had zero luck with them back when I was running our drag car. I wouldn't be surprised if some of your issue is around the thickness of the gasket as 2.5mm is massive. While this can help reduce the compression, what you lose then is the squish effect of the piston proximity to the cylinder head which can help with forcing the mixture back towards the spark plug. This can make the engine more prone to knock which is what it sounds like you're suffering from.
The other problem facing the RB series engines is that they can be tricky to bleed the cooling system thoroughly and this can result in steam pockets forming in the cylinder head which results in local hotspots. In race applications the head is often modified to take additional bleed lines that go back to a header tank.I'd also suggest that if it is only #6 showing an issue then it may be a lean condition as a result of uneven air distribution which isn't uncommon with an inline 6 running a single plenum/throttle body. I'd guess the lean condition would have led to detonation.