Psa
 

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.

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

+1

Fixed it for you:boat: Throttle up

http://automotiveguru.net/wp-content...81-655x284.jpg

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!https://cimg9.ibsrv.net/gimg/www.off...da49db47f8.jpg

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.

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.

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.

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.

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?

Never run my junk 7.4 lx mpi's under 1/4 tank, nor any other vehicle.

I've had the same failure on some old blow thru carbed turbo motors years ago ( till I got them dialed in). Happens quickly and cuts a perfect groove. Lean motors usually make more power until... Good luck.

I/2 an inch or more. It is not entirely smooth, it almost looks like it let looses and the heat took over. You can see casting like a break with the surface starting to smooth over like melting. It certainly could be burnt but the block is perfect including the deck and that is the only damaged. we even pulled the valves and they are perfect. Even the adjacent Intake. I get the Inconel not burning.

yes, now that i think about it why didnt the block burn up too? i could see if the heads were aluminum they would go first.

this is why i went with big (557) cube n.a. engines. big , fat , and lazy engines that make good power without trying hard. those blower motors require everything just right and you know fuel quality can be an issue.

I had the same failure in my old Merc 420 NA. Brought the head to the machine shop. They welded it up, machined it smooth, put a straight edge on the block, new gasket and it was good to go. The block doesn't get torched because the block has cooling. As stated earlier, the head has a hot spot there.

This^^ block is cooled that's not a casting issue, any casting issue would surface right away, lean issues melt thigs very fast, seconds...

It was, maybe 20 seconds.

All it takes..

If a piece had broken off you would have damage to the head and cylinder from the piece ratling around in there.
You ran lean.

yes you would think that chuck would cause damage on the way out. that is amazing to me that it cut right through like a torch. learn something everyday.

My point is that it wasn't a chunk.
It was vapor. The combustion gasses turned it into aluminum vapor.

i get aluminum with its lower melting temp. but this was a cast iron head, right? looks like iron to me.

It is a cast head!

It's a common failure when a head gasket goes on an iron head. Take it to the machine shop and have them weld it with a high nickel rod. They have probably done 100 of them.

I'd say it was making more rpms because it was running leaner than the other engine. Not sure exactly why it was leaning out, but I would look into possible causes.