SR20det boost creep problem

[David Pereira]

Hello everybody,

I came here to ask for help, although I think it's not a software or linkecu issue in particular, but maybe someone can help me, probably a mechanical problem.
I already did some SR20det with plug-in linkecu and other ecu's and with some different setups of turbos etc. and I never had major problems to solve, but right now I have an SR20det with monson ecu , the engine is forged and with a GTX2867 turbo and horsham exhaust manifold.

I have a problem that after more or less 5000rpms the boost grows a lot, even with DC 0% and at this moment I have a wastegate with a 7psi spring and I already relieved it until the wastegate port at rest is already open . I've already done tests with the wastegate disconnected and with the wastegate port wide open, in any case the turbo pressure increases and after 5000-5500 rpm it goes from 1.4 bar at the end of the rpms, I've even tested it without the downpipe seeing the wastegate port open mechanically disconnected without obstruction.
After all this I started to suspect that the ignition was too retard, I went back to confirm the ignition timing with the light and it seems ok, the ignition has already grown a lot on my map and yes the pressure does not go up so much.

The reality is that after many tests I ended up burning the head gasket, I opened the engine and the gasket burned in the second cylinder on the exhaust side but all the cylinders and pistons had small marks of starting to melt on the exhaust side. I thought maybe I had abused the ignition a bit, although I didn't hear anything significant in the knockblock and when I was tuning I was always taking the spark plugs out to analyze and try to prevent damage to the engine.
At this moment I've already reassembled the engine, but I'm afraid, because I still haven't been able to figure out where I'm going wrong.
I've heard about detonation due to too-delayed ignition, but I've never seen such a fact, could it be that I have such a large ignition drift that it can cause me such a delay in ignition?
Anyone here who has been through a similar situation or has any ideas that can give me some advice?

Thank you in advance

Sorry for the long text.

SR20det GTX2867R when head gasket burned.pclr

[Stevieturbo]

Often a little porting of the wastegate orifice makes a huge difference. Nothing major, just smooth the flow into it. And do not damage the seat the flapper sits against.

 

[Adamw]

It sounds more like pre-ignition to me.  With pre-ignition you will usually see evidence of extreme heat type damage, usually starting with sharp edges/corners of exposed aluminium parts melting/rounding off, spark plug ground strap melted, burnt fire ring on the gasket etc.  Sometimes if bad enough for long enough a sagging piston crown or heavy scuff marks on the piston skirts, damaged exhaust valves or a groove "torched" through the head. 

Damage from detonation on the other hand will usually exhibit erosion (pitted surface or a sandblasted like texture) around the edge of the piston crown, and if bad enough there will be mechanical damage caused by the shock wave, such as missing or cracked spark plug insulators, broken ring lands etc. 

Note since pre-ignition generates extreme heat and higher cylinder pressure it will often cause detonation as a secondary consequence also.  So it is not too uncommon to still see some detonation damage in cases where pre-ignition is the root cause, usually the heat-related damage will be the most prevalent however.  

So, what causes pre-ignition?  Generally something in the combustion chamber either very hot or "glowing" near the self-ignition temperature of the fuel, spark plug heat range too high, retarded ignition causing the exhaust valves to glow, too little exhaust valve clearance, a sharp or thin feature on the piston, lean air fuel mixture, undersize fire-ring diameter, lack of coolant flow in cyl head.

My initial thought since it sounds like you have pre-ignition and boost creep was "it must be retarded", but your main ignition table looks somewhere in the ballpark for an SR20 - assuming pump gas.  Have you confirmed the TDC mark on the front pulley?  The pulleys can come loose and slip around on SR20's, so I would def check that if you haven't already.  The ECU statistics show the coolant temp has reached 124°C at some stage also.