RBeyer

Just a PSA don't run your fuel low under boost, Port motor lost compression #5 in a blink, Hoping it just took the valve.

SABER28

curious, how you figure a low fuel level caused your problem?

Rookie

iTrader: (4)

+1

92nsx

Fixed it for you Throttle up

RBeyer

That was solely based on how the motor acted. It coughed then backfire through the exhaust. However after tearing it down today and checking fuel level tank was between 1/4 & 1/2 so was not fuel. It looks like a Merlin Head Casting Failure (See Pic) there is absolutely no damage other than the missing piece of casting, which and the burnt gasket that used to be there. Valves, plugs, pistons, and chambers all look good. It happened running near 90 under full boost. I'm open for other suggestions but what I thought may have been a lean issue doesn't appear to be! This is between 3 and 5. We even ran a stone across the deck of the block and its flat!

Drock78

iTrader: (2)

What it looks like to me is that the gasket failed a while ago and its been working on the casting since. Probably finally got big enough to cause the backfire.

Mbam

That is a typical head gasket failure.

Like Drock said it started to leak first, Then the combustion gas's work like a cutting torch. But that can happen really fast! There is virtually no cooling between the cylinders so that is a hot spot to begin with. I'm sure if you take a look at the rest of the gasket you can see that it is discolored from heat in those areas. Also if you measure the bead you will find that it is a few thou thinner in those spots. The block and head expand more there and along with the heat squeeze the gasket. A good chance it detonated.

Fatten it up
Cool it off
Take a little timing out of it

We had a fix that involved some small holes in the block and head to get a little water moving in that area. Our stuff was all closed cooled so I wasn't worried about rust plugging the holes. I am not sure how well it would work on a sea water cooled engine.

RBeyer

Yes the gasket did fail there if part of the head was the gasket would have as well. it seems confusing only that it ran perfect right up to the failure, The Block is perfect in the same area in fact is completely flat nothing else shows any sign of being lean. I agree to fatten it up, A close look at the area looks more like a break than burning melting. It has twins and this motor actually made a couple hundred more RPM than the other. In any event at least there is minimal damage and it looks like a fairly simple fix.

RBeyer

If the gasket failed hypothetically shouldn't it have been very obvious from that point that there was a problem. It's a Hawk 525 SC and it sounded perfect and actually made a bit more power than the other motor, I posted because I don't have all the answers.

SABER28

to me that looks too smooth to be a casting break. ive replaced 20 plus engines that broke a mount or boss in a automobile collision and they always are very rough on the surface. how deep is the gouge?