Detonation why?
Discussion
It's very strange that you're not seeing the problem on the dyno.
Det is only really ever an issue at high loads. 2 issues, either too much air or too much spark.
You could have something causing a hot spot but that's unlikely.
HGF is quite a strange failure from det particually if not run for a very long period of time.
How has the gasket failed? Burnt fire ring? Blown between cylinders or to coolant jacket?
Maybe your ignintion advance curve is now wrong for the boost that you are running, too much boost too soon without enough retard?
Det is only really ever an issue at high loads. 2 issues, either too much air or too much spark.
You could have something causing a hot spot but that's unlikely.
HGF is quite a strange failure from det particually if not run for a very long period of time.
How has the gasket failed? Burnt fire ring? Blown between cylinders or to coolant jacket?
Maybe your ignintion advance curve is now wrong for the boost that you are running, too much boost too soon without enough retard?
ridds said:
Det is only really ever an issue at high loads. 2 issues, either too much air or too much spark.
Yes the detonation is at high loads.ridds said:
HGF is quite a strange failure from det particually if not run for a very long period of time.
I thought HGF was fairly common from detonation?ridds said:
How has the gasket failed? Burnt fire ring? Blown between cylinders or to coolant jacket?
The flame ring has burnt, its fine on the sealing faces but popped right thought the middle of the two faces, into a water passage. They were Felpro gaskets, I'm advised they are about the best available for this engine (limited choice). I also have the head faces, grooved with MIG wire biting into the gasket flame ring and ARP head studs, just to help the sealing.Regards,
Chris.
ridds said:
HGF is quite a strange failure from det particually if not run for a very long period of time.
HGF is not only an extremely common consequence of detonation it's more or less inevitable if the pistons don't melt first.The head gasket is also one of the best places to find evidence of detonation that hasn't yet resulted in a complete engine failure. The first symptom before the gasket blows completely is crushing of the inner edges of the fire ring. Instead of the nice smooth semicircular curve of the inner lip of a pristine fire ring it looks like someone has gone round the i/d with pliers and squeezed it flat for a millimetre or two radially. It's a salutory reminder of the incredible pressures that detonation creates at the edges of the combustion chamber.
If the OP looks at the remains of the gasket he's just removed perhaps he'll let us know if he sees this symptom.
Dave
Daveuk9xx said:
The head gasket is also one of the best places to find evidence of detonation that hasn't yet resulted in a complete engine failure. The first symptom before the gasket blows completely is crushing of the inner edges of the fire ring. Instead of the nice smooth semicircular curve of the inner lip of a pristine fire ring it looks like someone has gone round the i/d with pliers and squeezed it flat for a millimetre or two radially. It's a salutory reminder of the incredible pressures that detonation creates at the edges of the combustion chamber.
If the OP looks at the remains of the gasket he's just removed perhaps he'll let us know if he sees this symptom.
It is damaged as you say but only for about 8-10mm length on the flame ring. The pistons are forged, with quite a thick crown >8mm and show no signs of wear/tear/damage (fortunately at just over 1K for 6)If the OP looks at the remains of the gasket he's just removed perhaps he'll let us know if he sees this symptom.
Regards,
Chris.
That's quite normal. The damage doesn't extend all the way round the gasket, it appears in the areas where the detonation shock waves hit the chamber wall. Eventually it blows through the gasket in that area either to an adjacent cylinder or to another part of the block.
As you've seen it can happen without damage to the piston or combustion chamber, especially if the latter is iron, and is something a good engine builder will always look out for at stripdown time.
Dave
As you've seen it can happen without damage to the piston or combustion chamber, especially if the latter is iron, and is something a good engine builder will always look out for at stripdown time.
Dave
Most engines I've looked at have always shown some indication of Det on piston crowns or spark plugs.
Perhaps due to mainly working on Steel Lamiate gaskets which leavs little exposed to combustion pressures and temps.
Still we could talk about this forever, it'll be nigh on imposible to work out the failure mode without seeing some pics or the actual components.
I take it the Gasket is sized correctly for the bores, silly question but I've seen one where the HG bore was quite a bit smaller than the cylinder bore.
Perhaps due to mainly working on Steel Lamiate gaskets which leavs little exposed to combustion pressures and temps.
Still we could talk about this forever, it'll be nigh on imposible to work out the failure mode without seeing some pics or the actual components.
I take it the Gasket is sized correctly for the bores, silly question but I've seen one where the HG bore was quite a bit smaller than the cylinder bore.
I rebuilt a 944 engine which had sufferred detonation. The pistons were fine which surprised me but they were good quality forgings. The rings were broken though. The fire ring had a notch on the section approaching the water jacket and the fire ring wasn't round anymore 
The notch resembled the shape of a dykes ring (no jokes chaps)! The gasket had distorted so far sideways that it was encroaching downwards into the water works. Only the cylinder head studs stopped it moving any further.
The notch resembled the shape of a dykes ring (no jokes chaps)! The gasket had distorted so far sideways that it was encroaching downwards into the water works. Only the cylinder head studs stopped it moving any further.Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff