Mikes3.0cabturbo

A quick background this is a S2 3.0 stock everything internal, running 10psi boost off a T04B 60-1 hifi + standalone EMS for tuning. Great performance, no knock, AFR mixtures high 11's on max boost, 24 degrees advance. About 100,000mls total the last 3,000 on boost.

About a week back HG goes after a mild drive...

Here are the pics after it came apart.

It appears that the gasket died of 'old age' & not boost/compression may have had poor coolant in its life time. The HG is badly rotted away on the water jacket near the cylinder seal on cyl 1 which is where I got the coolant/GH blow, everything else seems fine.

No evidence of detonation on the pistons or head, pistons were immaculate when I pulled the head, some slight scratching wear on the bore gudgeon sides that has marked the bore, minimal top ring ridge can just feel it, but 190+psi on compression so its cool. The head, slight deposits on the exhaust valves, inlets clean, I did quickly wipe the head with thinners prior to pic.

So going back together with 951 rods with new bearings bottom & top, new cometic 3.2mm HG, new ceramic coating to piston tops of the S2 orginal pistons, new rings, head refresh and then crank up the boost to 1 bar.

regards
mike

gt37vgt

well Mike my deepest condolences on the incident but i would blame it on the lateral movement of the bores pegging the deck or deck plate is the an swear

333pg333

Bad luck Mike, but you would have found it pretty soon anyway. What's the standard c/r psi on a 3.0ltr anyway?

special tool

That fire ring looks folded back to me.

What means of knock monitoring did you use to determine no knock at 24 degrees at 10 psi at redline?

Also - what turbine housing and turbine are you using?

BlueRiver86

Just out of curiosity what do you mean by "poor coolant"?

Mikes3.0cabturbo

Patrick your right I think it would have gone turbo or not, the stock CR is 10.9:1 on the S2.

Adam, if it is movement and I get another 100k from the next one I'll be happy.

ST, its not actually folded back more like pushed in, but certainy not burnt, I have been using a stethascope routed from the block into the car to listen for knock, it gets very noisy at higher revs but I can hear everything thats happening, so I am filtering myself the noise vs knock, I have only had knock once that was at 26 degrees advance around 5000rpm & 35 centigrade ambient temp slight though.

Dan, coolant does lose its anti corrosion capability over time or if not mixed properly, so I was guessing that the gasket corrosion could have been caused by poor coolant matainance.

rgds
mike

333pg333

Sorry Mike I meant psi when you do a compression test. You said 190+ psi which to me sounds very high but I'm used to a lower c/r that gives us 150ish psi, so I was just wondering what the S2 would read normally.

luckett

When I pulled the headgasket off of my 968 with 160K miles, it was in a similar state of deterioration.

CarbonRevo

I believe when my S2 was tested for compression, it hit in the low to mid 180's.

I have a U.S. Spec '91. Not sure if the ROW S2's possibly had higher compression, but mine is 10.9:1

Mikes3.0cabturbo

Patrick, apprently the 968 manual states a really low figure min 10bar, but it seems most folks hover around 190-200psi, I have never been able to get a S2 quoted number, just read what others have got. Seeing as 968/S2 are both similar compression I think my numbers are ok, also I had almost zero carbon build up.

Chris thanks for sharing you experience on the HG

rgds
mike

Geneqco

Thanks Mike,

That's certainly great information about the 16v head. I had a post some time ago about 16 v 8v heads. My theory was that with better chamber design you should be able to push the envelope much further with the 16v head... for the most part, the responses were pretty vague.

Thanks for sharing your real life experiences.

Mikes3.0cabturbo

Cory - mines 10.9:1 too..the compression gauges will have some tolerances so 180ish vs 190+ is pretty close.

My precise readings were 194, 193, 196, 183(blown cyl) on a new screw in gauge good quality, six compression strokes.

rgds
mike

CarbonRevo

Mine were 0, 183, 185, 181.

My number 4 has carbon build up on the tops of the valves, and my number one had a then broken valve spring. I'm sitting at 79k miles.

333pg333

Thanks Mike. Wonder what everyone gets on their 951's?

CarbonRevo

A 951 I was looking at prior to my car hit right at 151-153 across all cylinders. 95k miles, never abused, and stock.