What is this telling me?

[JerseyDevil]

This thread made me think of some comments Darin Morgan made regarding fuel wash:

"The first thing that came to light was the myth of fuel wash. Like most racers, I believed that clean areas on the chamber walls and piston dome indicated where fuel had fallen out of suspension and cleaned off the carbon. Wet flow testing revealed the truth: The shiny areas are where there is the least amount of fuel. This lean mixture burns quickly and completely. In fact, the most fuel fallout occurs where there is a dark, sooty burn pattern on the chamber and piston. That is where the fuel falls out of suspension, creating a vortex. In this condition, the fuel burns, but it burns too slowly and too late in the cycle to create usable cylinder pressure."

[Belgian1979]

Why is the clean spot in the chamber coïnciding with the turn cut into the bowl ?

Could it be that the high dome is blocking the flame front in some way ? Maybe it needs more timing ?

[lorax]

This thread made me think of some comments Darin Morgan made regarding fuel wash:

"The first thing that came to light was the myth of fuel wash. Like most racers, I believed that clean areas on the chamber walls and piston dome indicated where fuel had fallen out of suspension and cleaned off the carbon. Wet flow testing revealed the truth: The shiny areas are where there is the least amount of fuel. This lean mixture burns quickly and completely. In fact, the most fuel fallout occurs where there is a dark, sooty burn pattern on the chamber and piston. That is where the fuel falls out of suspension, creating a vortex. In this condition, the fuel burns, but it burns too slowly and too late in the cycle to create usable cylinder pressure."

When you are talking about the wet sooty areas verses the absolutely clean quench areas, I completely agree. But the area that looks washed in the chamber and on the piston under the intake valve that looks washed, probably is washed. Its a different look than a dead area.

[PackardV8]

Is it still possible to reassemble with the used gasket and clay the chamber? Why speculate on whether the piston is hitting the head? I'd agree I don't see any definite signs, but then the photos aren't sharp. Measure and then verify with clay.

Once that fact/figure is confirmed, give the experts here the spring pressure, look for pushrod interference and so on.

[BrazilianZ28Camaro]

What PTH and piston to wall clearance was the engine set at?

[TMSJoe]

The piston under the spark plug had a defined shape that you could feel with your finger. The carbon on the heads could be from the last few runs that may not have been full out. Not sure. Based on the block measuring 8.994" it was .006 out of the hole. That with a .036 gasket put it at .030" static. Also there was significant gasket "hang in the bore" from the wrong gasket choice. The bore has marks that tell me the piston was rocking in the bore from head contact.

How much power could have been lost from piston to head clearance @ -0.006? At least the perimeter of the bore where the gasket hangs in.

Piston to wall is about .0055...

[BrazilianZ28Camaro]

The piston under the spark plug had a defined shape that you could feel with your finger. The carbon on the heads could be from the last few runs that may not have been full out. Not sure. Based on the block measuring 8.994" it was .006 out of the hole. That with a .036 gasket put it at .030" static. Also there was significant gasket "hang in the bore" from the wrong gasket choice. The bore has marks that tell me the piston was rocking in the bore from head contact.

How much power could have been lost from piston to head clearance @ -0.006? At least the perimeter of the bore where the gasket hangs in.

Piston to wall is about .0055...

You are a lucky person having just a small damage on your engine. Really lucky.

With a 4.1XX short skirt, forged piston you can spect a lot of slack, meaning the PTH clearance should be increased. I'd set no less than .0045" on your engine.

Never, never install a head gasket overhanging the bore because its edges will glow at full load and pre-ignite the charge, destroying your engine real fast.

Maybe the pig rich condition avoided that to happen. You also have a flow loss with gasket overhang.

[Dan Timberlake]

http://mk3ukr-supra.net/Combustion%20pa ... arland.pdf

I don't know if that article had anything valid to say or not. Jim McFarland was one of my heros, and was in a position to possibly know some cool stuff, but that was a long time ago.

[lorax]

http://mk3ukr-supra.net/Combustion%20pa ... arland.pdf

I don't know if that article had anything valid to say or not. Jim McFarland was one of my heros, and was in a position to possibly know some cool stuff, but that was a long time ago.

Nice info. Seems when the separation happens, where it does burn its tends to be rich. Makes sense. If there is no fuel where the clean areas are, then it has to be somewhere else, but the amount of air in the areas remains the same.

Found this one picture and comment interesting to this thread. Curious just how much putting a generous radius on the piston dome would help with the fuel separation on the intake side.

[Dan Timberlake]

http://www.english.rfi.fr/sites/english ... ers_43.jpg

[lorax]

Based on the block measuring 8.994" it was .006 out of the hole. That with a .036 gasket put it at .030" static. Also there was significant gasket "hang in the bore" from the wrong gasket choice. The bore has marks that tell me the piston was rocking in the bore from head contact.

How much power could have been lost from piston to head clearance @ -0.006? At least the perimeter of the bore where the gasket hangs in.

Piston to wall is about .0055...

You are a lucky person having just a small damage on your engine. Really lucky.

With a 4.1XX short skirt, forged piston you can spect a lot of slack, meaning the PTH clearance should be increased. I'd set no less than .0045" on your engine.

Never, never install a head gasket overhanging the bore because its edges will glow at full load and pre-ignite the charge, destroying your engine real fast.

Maybe the pig rich condition avoided that to happen. You also have a flow loss with gasket overhang.

I hope the OP is mistakenly saying bore over hang and not chamber over hang. Its one thing to have chamber overhang when the chamber is larger the bore where the overhang occurs.
BUT, if the gasket overhangs the bore then there is no added clearance to the head created by the gasket. The gasket is at deck height.
I have to assume with the piston .006 proud, the OP was using the wrong term and its chamber overhang.

The overhang into the chamber, specially if its on the intake side, could easily modify the air entry to the cylinder that caused the fuel seperation you see on the intake side, as well as added to the richness you see in the rest of the chamber. Too much fuel in some areas, none in others.

Still, even the overhang only occurs on the chamber, and not the bore, .030 deck with a short piston at .0055 is too close for my comfort.