Piston Burn Pattern?

Does it mean anything? Can we learn anything from it? This one looks odd, what does it mean?

Looks like pretty tight quench to me

Cab quench is .040, theres about 3000 miles on these. The quench area being clean makes sense to me. What is confusing to me is that on either side of the plug it is clean, right up to the intake valve notch on each piston.

Might be fuel wash. Usually after 3000 miles the only parts that would be shiny is the qunch area. Any chance the carb was on the rich side, especially at idle or cruise?

Yes, its a DP and rich on the transition, where it ends up alot during crusing. Had been richer on cruise but I had leaned it out somewhat recently before taking this pic.

You can fix that with billet metering blocks or drilling and tapping the cast blocks. You can also drill and tap the main body for a transistion slot jet.

If the carb is rich enough to wash the piston tops then it might be washing the cylinder walls too.

Maybe it is burning all the fuel near the plug on each power stroke, todays(low carbon) fuels are not like anything we burned years ago At least all four of those cylinders look consistent

If you get a chance go to youtube and watch a few videos showing wet flow technology. The dark and light spots will make more sense. Dark areas are where the burn is cold (rich) light areas are where the mixture burns hot (lean) enough to burn the carbon away. Also fuel wash can affect the coloration of the piston and combustion chamber.

Any specific links ChevyTS? I searched but didnt really find anything

to me it looks like oil in the combustion chamber cleaning the carbon on the intake charge.

Take a look at this video. You will notice that the pattern on your pistons kind of mirrors what is happing inside the chamber. https://www.youtube.com/watch?v=DCo_7Be_o3Y

Neat stuff!

I thought that I'd read that the carboned up areas have fuel in them and the clean areas lack fuel. Maybe it is along the lines of what Chevy TS talks about with the wet flow, maybe the atomization isn't good or there isn't much swirl going on to move the fuel all around inside?

What heads are you using and can you see swirl patterns in the chamber? If it would be a fuel wash as Andy suggests, I would think you could see that in the chamber better than on the piston top.

http://rehermorrison.com/tech-talk-40-wet-flow-revelations-the-monsoon-inside-your-motor/#more-290

Cylinder head: Similar pattern, a little more normal looking i.e. nothing is totally clean

It looks to me like the fuel is going tangential off the long side of the port, around the cylinder and curling in towards the center of the chamber/cylinder. It might be that the fuel gets separated out on the short side radius and mostly air is entering on that side of the intake valve blocking the rich fuel flow coming around the exhaust valve side.

Is that the Edelbrock head or the Stealth head? It may need a "wing" as Darin noted they added on their Raptor BBC head. I'd call it a bump or maybe a fin on the floor at the SSR. I've seen those on several heads over the last 10-15 years. I think Jeff K. at MCH had something like that on his SS Hemi heads. I never quite caught on that it was to aid in keeping the fuel in suspension.

That's my wild @$$ guess on what's happening. I'll be interested in what the head porters and professional engine builders have to say.

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Was the valve job on those heads redone before you used them, or is that out of the box?

PS - we can learn from everything if we have the sense to really look.

Valve job was OOTB, I lapped the valves and they produced a good pattern, but I think what youre thinking may be in line with what I'm thinking so give me your thoughts because I'm wondering if the valve job isn't up to snuff and isn't leaking.

I e-mailed some friends and one well know head porter said he thought it was too rich (already discussed) and too much timing. He thought the burn was finished before it got around to the far side away from the plug. So, something else to try.

Thanks, good to know, and I would agree that it has been too rich for sure.

Where the piston is CLEAN there is ZERO fuel.

So what is causing that/how do I fix it? Current carb is an annular booser Holley, but Ive had a few carbs on it.

Or it(the fuel mixtuure) is not hot enough to stick to the head or pistons during combustion

You don't fix it. keeping fuel suspended is one of the great challenges of performance engine building. Liquid weighs more than air. Air and fuel moving at high speed... air makes the turn and fuel doesn't. This causes the fuel to enter the chamber atomized and as a liquid. The results clearly seen in your pistons. You might experiment with carb spacers if you have room.

^^^^^^^^^^^^^^^^^^YUP^^^^^^^^^

I would spend time on the flow bench with the head first and figure out why the port is charging the bore like that, and why the fuel is separating out. Despite what I read, I have never been able to get wet flow (fuel that has fallen out of suspension) back into airflow with surface preparation.

After I was happy with the port, I would put the intake on and figure out what changes with the intake.

After all that crap, you still need carb work

I can tell you for a fact that one well know NASCAR engine builder spent 98% of his time on carbs and intakes. He made a special fixture to tests carbs on the flow bench that simulates the intake manifold and it's adjustable. I can't wait to play with it.


There is way more to it than it may appear. But your pics show some issues. Fix them and you will pick up power everywhere.

Its rich... with that many miles it would have a tan color
over to the intake valve to get a full burn... its way rich
EDIT
The timing is starting too late to cause all the burn over
on the exhaust side(all the burn is over there)

Matt , why did you pull the head ?

Long story short - engine performance is not where it should be, was re-checking cam phasing and my piston stop broke off in the #1 cylinder. Cam was degreed correctly.

Thank you!

AND Thank you!

I don't know if it's the jetting, the timing, the chamber design, or what... but that's not what I'd consider a good burn pattern. My understanding -- and it's pretty limited -- is you "should" see a more complete burn across the quench area and more uniform coloration of the chamber.

These pics aren't ideal, but show the burn pattern for this head & piston combo is spread out more. This is either a .040" or .045" quench height and the heads were pulled after about 25+ pulls on an engine dyno. Jetting was still being worked out, but tended towards the lean side. Ignition timing was 37*, IIRC. Fuel was a 50/50 blend of 110 leaded and 93 E10 unleaded.

This is good too, thanks for posting more pics. My heads are off and I'll be doing some minor tweeks here and there to the 'old' engine based on what i see in my 'chamber'. I was thinking of starting a new thread but this one has plenty of good in it already. From what I've seen, just like everything else comparatively, it has burn patterns similar to a SBC. Not that I'm disappointed in the past performance but, who's ok with leaving well-enough alone?

One thing i will say is; I'll never have sharp edges in my 'chamber' lose compression or not. "Pretty" or not, flame travel must be important enough for cup teams to d.a. $5000 piston tops. So, it's good enough for me.

What I see is a lot of carbon on the exh side and that is where your fuel is collecting,Maybe on overlap,maybe small exh system.

This is an old post guys - I did fight this car for a bit but finally got it running as strong as it should. The main issues were a vapor locking mechanical fuel pump, mufflers that were too restrictive, and very oddly the air cleaner made a big difference as well mostly on the low end & throttle response. It had a drop base on it and the lid was a bit close to the choke tower/bowl vents. A contoured moroso made a big difference in throttle response believe it or not, but the torque came from the mufflers and electric fuel pump. It made 479 RWHP on our local chassis dyno.

The burn pattern, as best I can tell, still is about the same. But the heads are coming off soon, so we’ll see if its changed at all. I think its from a rich t slot / ifr and the car mostly cruises on the t slots. I definitely have to fix that for this summer with the price of gas.

Look at your exh valve from the header side when it is off and see the buildup on the valve.

chamber

Dishes