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Need help diagnosing blown headgasket

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Hi guys,

I just popped my first head gasket on this motor last night and after tearing it down this evening I am having a hard time determining what the root cause was. This is a fairly fresh motor, its a 6bolt 4g63t with only about 300 miles on it so far since the full rebuild, mechanically it is very solid, the block and head were decked flat during the rebuild.

I had done maybe 4 pulls from 0-120mph at 22psi with no water meth, and no issues other than some light detonation after the torque curve but only very minor.

Yesterday afternoon I started spraying water meth and started tuning for it, I am using the nitrous map to pull fuel and add timing while spraying. I pulled fuel to get around 11.7 afr and since all my audible knock had disappeared, I started to add timing, If I remember correctly I ended up adding 5degrees globally and about 7degrees up top after the torque. I still heard absolutely no knock and the car was running great, finally had the power I felt it should. I should say, I am using a knock listening device, and knock is very clear to hear.

After doing a 0-120mph run later that night, I blew a radiator hose from over pressure and confirmed a blown headgasket was the cause.

I do not see any signs of detonation on the pistons or the cylinder head but the fire ring on the headgasket is pushed out like it was detonating.

My question is, are my cylinder pressures just too high from the increased timing? There are many guys running e85 with this head gasket and stud combo at much higher boost and timing than me.

I assumed I would hear detonation with water/meth, I can understand not hearing with e85/e98/other ethanols. This is why I just kept adding timing, to be honest, I was going to add more since I didn't hear det and everything was going well.

I am using a 50/50 mix of VP racing M1 methanol and distilled water, and 93 octane pump gas(US).

I apologize for not posting any logs or screen shots of my timing table, I will post them when my tuning laptop is charged. I will be replacing the headgasket tomorrow and removing all the added timing and starting from there again, but I am curious what approach I should take towards adding ignition timing with the water/meth. I am determined to get a decent street tune before I hit the dyno, as there really isn't any eddy current/load holding dynos available to me locally at the moment.



Attached Files

What type of engine is it ur tuning man ? I've blown stock head gaskets like that before just due to increased cylinder pressure, might be worth replacing it with a mls gasket

It looks like it's damaged on the exhaust side, correct me if I'm wrong?

I don't mean to sound condescending but did you torque it in the correct pattern?

Were you listening for det when the rad hose popped off?

What ECU are you using?

It is a 91 4g63t, which is a 2.0l dohc 16v.

I cannot use mls as my block deck surface does not have the correct RA finish to allow a proper seal. Many many people have reported this composite gasket to be good at 30psi. If I felt I wouldn't have any issues installing an mls I would, but I'm worried I will end up with even more issues.

Yes the head was torqued correctly, final torque on the arp studs was 90ft/lb.

I was listening for det at the time the hg blew, I did not hear any detonation.

I am using an aem series 1 ( I know, ancient, but it works well)

Thanks for the help fellas, any input is appreciated. I'm going to do some reading on the aquamist forum today.

I really feel like your issue is the head gasket quality.


Get a cosworth headgasket and you can also use some permatex copper gasket spray and you should be good to go.

Throw that head gasket as far away as you can - Composite style head gaskets have no place on a performance engine and I'd be confident in saying that's your sole issue. On my drag 4G63 engines I used either an HKS stopper type gasket or Cosworth. The HKS with help from o-rings was good for 54 psi boost.

To be honest I have no idea why I didn't just use an MLS to begin with, my block and head were decked and according to the machinist they are below 50 RA and ready to use an mls.

Luckily the motor did not get very hot at all and likely didn't warp anything but I will check both surfaces to be sure.

It looks like Cosworth doesn't make a head gasket for the early 4g63, only the later evo 4g63. I will order an HKS and get it put back together.

Quite often with a boosted engine the head gasket will only show up as an issue when you're under boost and the cylinder pressure increases. Admittedly with a composite gasket they will be more likely to leak consistently once they are damaged, but with an MLS you could quite likely do 100,000 km of driving with a blown head gasket and never know it if you don't use any boost pressure.

Just one of the issues with a composite gasket is that they don't provide enough support for the sealing ring around the combustion chamber. It's easy to distort this sealing ring and allow the gasket to leak.

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