Burned piston diagnosis help

This is a pic of the piston I burned at Bonneville. Dual O2 sensors were showing 12.7 until past the 5 mile at WOT, Then indications went very erratic (I saw between 12.5 and 13.1 flash) as speed increased to a max of 231 and rpm stalled at 6400 at mile 5 due to inlet turbulence through the cowl scoop I think. Also due to 2 1/2" tire growth at that spped, altering final drive ratio. This made the fuel air distrubution spread worse and #7 went critical first. #6 wasn't far behind.
I noticed the heat and damage seems concentrated around the gas port holes. Is a gas ported piston more critical for detonation/lean condition? The detonation is furthest from the spark plug.

Biggest issue was I should've lifted at the end of mile 5 but stayed in it after rpm began dropping at 5 3/8 mile or so. Expensive mistake that precluded me from making more runs at Speed Week.
I found on teardown at least one of the middle upper water jacket slots were covered with a sealant film, which coinsided with the hottest part of pistons #7 and #6. Clearly my fault on jetting and not lifting, just trying to diagnose and fix the root cause.
I dropped my intake and heads off at Wilson Manifolds for them to work their magic. I will addrsss the inlet turbulence with strakes and a K&N filter.
Thanks

Right side

Which intake manifold?
With the standard firing order #5 robs #7 on the intake signal due to firing 90 degrees later than #5,I've had to stagger jet 440 motors with single plane intakes to help prevent #7 from peppering the plug

Lifsgrt,

A slew of things to look at. The other cylinders look like they have good ring seal. Would like to know more about the pistons, ring setup, spark plugs used (heat range), timing, ignition system and fuel system/type of fuel. Carb(s), EFI, added water injection? Would like to see that piston and spark plug when they come out. Looks like maybe too much timing and detonation from bad ring seal/oil in that hole for starters.

Im no expert but I'll give my opinion any way... I would think that with 100+ pulses of super hot gasses going back and forth in the gas port holes it would tend to heat up that area of the piston more than if there were no holes there, this would be fine for a drag motor where it runs WOT for 8 seconds (or so) but something running WOT for miles on end at a very ihgh output level it may just be too much especially if your tune is not perfect. The area around the hole is already a weak part of piston (ring lands) and the sustained high heat is just not a good combo.

It’s my understanding if the majority of the holes are good for color, condition, etc. then the basic combination is good. That means the hard part selection is good.

Too much timing, wrong plug type, etc. will only “find” the lean cylinders.

Looks like the distribution is off.

The top of the piston looks like detonation was occurring. Detonation on my boosted stuff has always started away from the plug towards the exhaust side. The thinnest part of the piston is at the top ring land to intake valve notch. I am in the process of gas porting my own pistons. We've been warned to stay away from the intake notch. from the info I've read lateral gas port is preferred on boosted applications. Looks like a lot of gas port holes as well. Everyone I've talked to says 10-13 holes. We just burned a piston in my sons turbo car at the intake notch. Though it was not gas ported.
Doug

If I was running wide open throttle for that long of a time I would want to know EGT on all cylinders all the time.

Glad i'm not the only one who noticed this! Keith Black pistons had a problem with this(piece of the piston broke off above the first ring). There is info on installing them in there literature and if it's not fallowed it states this can happen. Can't say this is your issue because we don't have the info.

Yes if your class allows any type of datalogging EGTs would be pretty valuable.

The inlet turbulence you mentioned also probably played hell on fuel distribution. Could have been rich in some lean in others which might "average" out around your target air fuel on the gauge.

I don't know how you would do it with a carb but with EFI you can add fuel over time to help keep things cool. So say after X amount of time wide open it starts to richen up the mixture to keep things cool.

Look more broke then melted to me.

I agree looks ore broken than melted from here. Detonation likely the cause if so. What kind of timing are you running in that B1 at WOT? What fuel? O2's areas good as their calibration and sample rate. I see a LOT if folks with them set for the wrong calibrations. Rarely changing them from the factory setting of 14.7-1 which likely is not close to Stoich for their fuel

Keith Black pistons did not have a problem with broken ring lands. Just builders that refused to follow directions.

Doesn't really matter IMO

If on a gasoline scale then 14.7 is 1.0 lambda of course. So, if he was running 12.7 that's about .86 lambda.

Would read the same whether it's actually on gasoline, or alcohol

B1 intake, 1mm,1mm (Napier),3mm rings. Single QF1250 carb, AR3910 Plugs. I had pistons coated on the heads and skirts. When engine came off the dyno I installed it and checked the timing. It was at 41° with two different MSD boxes, crank triggered. I was told engine made best power at 37°, so I set it at 36° with an MSD HVC Pro and specific coil. I do not understand how the crank triggered ignition can do that unless the ignition system it was connected to on the dyno could change the fixed timing.
It is a 4-7 swap cam. Aeromotive tank with internal pump, solid at 6psi.
Plugs looked good, although I think I had a heads up from the plugs in some "peppering" , extremely fine black specks (not aluminum) which I now am convinced was some thermal coating leaving the pistons on a couple holes.
The oil contamination occurred when the piston/rings failed and pressurized the crankcase above what the 6-stage Dailey Eng oil pump could evacuate. Do not have the piston out of the bore yet.

I am wondering that myself, as there seems to be possible transfer above the top ring in the cylinders to the bores. Vertical gas porting might have been a bad idea.

I agree with you on the distro issue. I dropped off my intake and heads to Wilson Manifolds last Wednesday to hopefully help the fuel distribution problem. Thanks

Thanks Doug. I wonder, I noticed when pulling the heads that the water jacket slots on at least one pair of cylinders in the center of the block was covered with sealant. I failes to note which slit was covered, but am thinking this lack of water flow could have contributed to lack of heat absorbtion and made it worse. First time I've had an engine with gas ported pistons, also first time I've paid professionals to spec custom pistons and build the engine. Not sure gas ports was the right choice for this endurance project in retrospect, but I agreed to it for the build. Learning as I go...

Interesting, I asked that question when the engine was being built. I was told no need at this NA HP level.
Also interesting, I asked Kenny Duttweiler about EGT probes just after this happened (didn't know the extent of the damage at this point) to prevent this in the future. He suggested to skip EGT probes, as there is a delay in heating the thermocouples for EGT and by the time you have a critical indication it is too late. He suggested O2 sensors in each primary and a way to monitor it real time. While expensive, I would have probably be at the break even point now if the system would have prevented me making this mistake.
Thanks for the reply!

CP custom pistons, thermal coated heads and scuff coating on skirts. Not sure the alloy or more detail.

I think in retrospect fat is where it's at...
Started at 10.1, then 11.7, then 12.7 on the dual O2 guage. Leaned one more jet size and still showed 12.7. Thought it was good (obviously!). I had 5" dual side exhaust pipes and they had a black haze, so thought it was still rich enough. Tiny black specs on a couple plugs, I now think was thermal coating vacating, still not sure. It was not aluminum.
I think if I would have lifted at the 5 mile it would have survived, but who knows. I know for this combo about 5 3/8 miles hurt it, and I stayed in it to the 6 because I made a bad choice.

I agree, but there was aluminum plasma-sprayed on the cylinder and head so did the detonation head vaporize the piston which caused it to break? I don't know.

I was running it at 36° fixed, VP C14 fuel. Innovate Motorsports dual wideband O2, new system, calibrated per instructions, but didn't change from their calibration. One sensor in each collector, wishing I would've had one in each primary.

If you notice at the upper position on the piston where the piston is broken away is right at the ring gap. Thoughts? Is this just where it happened to give up, or will alignment of the top ring gap with a vertical gas port hole cause this?

What head gaskets are you running? Maybe its the camera but it looks to me like they were starting to also fail. The sealing rings areas look to be burned and distorted.

AFR and scale does matter if using say a Racepak set up. It is WAY easier to kill an engine going FAT than it is going lean. Especailly if one id 10-1 on a stoich scale of 14-7. Way easy to stick a ring from heat of being fat than lean, microwelding of ring lands happens from being overly fat and not that uncommon especially with certain fuels. That heat can be enough to burn a piston top but have to be pretty extreme for sure, but this application woudl be extreme. Two O2's for race tuning are almost useless in all out effort cases. Its an average only if one cylinderis WAY fat it will just drop the average number. If he was 10-1 AVERAGE that hole could have very well been well in excess of that. All race fuels have an ideal stoich number, some prefer lambda but that number is not as easily found from most race fuel manufactures. You could convert that but as I say most use Stoich racepak can use either if changed to lambda

Well yes if you are trying to target alcohol air/fuel and it's on a gasoline scale that's definitely a problem.

Just saying if you're aware it's on a gasoline scale and different fuel it can be calibrated on a gas scale to achieve the same lambda. (whatever that target may be)

Yes, I noticed that too. It almost appears that the inside edge of the Cometic gasket protruded into the chamber a bit in a few spots. Yet another issue I have to address.

I ran it on this pass showing 12.7 on both banks, which I get is an avg of those 4 holes best case, so could be all over. It stayed solid at 12.7 and accelerated well until well over 220mph, then I believe the turbulence through the unfiltered cowl scoop got to a point that it disrupted flow over the carb and affected fuel distribution to a critical point. I will be addressing that as well before next year.
Further looking at the vertical ports, I am thinking lateral gas ported rings and different pistons would be better for this application, and of course being a little richer vs a little leaner.

I let a dyno operator in Caldwell, ID put 8 O2 sensors in my Cuda B1 headers when testing a B1 motor on his dyno with the cast B1 single four intake, the customer had a custom built Dam Best 1450 CFM Dominator type carb and another smaller Dam Best Dominator carb on it.
Once we started doing the testing I realized there was no way for me, us, to fix unequal mixtures to the center cylinders by jetting or not working on inside the intake manifold to influence the mixture flow by reading the O2 readings form each cylinder
You will have a PM from me today

I'm not familiar with running B-1 heads. But 36 degrees sounds like a lot of timing. My -1 Indys run at 32. I know many racers run more timing. But my Mph doesn't improve over 32 degrees. Mine is 4.500" bore flat top, 15-1.
Doug

This! Why would a modern chamber design require so much timing? Unless its lean of course.

There are ways to alter the mixture in a single 4 intake, but you gott be willing to do it. This is a place where a 3 or more curcuit carb can shine. We run a single 4 intake and carb on the Vette and they are all within a tenth or so from the beginning to end of a run. There are no damns or obstructions inside the plenum as that would change the volume there. We do it with a combnation of jetting, bleeds, offset boosters and a few other little things to get it that way. Takes work but it can be done to lay perfectly together.

As for he lambda thing yes I get it trust me. I am just stating if he is using a racepak or similar they are based of stoich for pump gas. If you do not change that number in the software for your particular fuels stoich reading then the results you get are not accurate. If he was reading 10-1 based on a 14.7 he could have been much much fatter or leaner(for instance C14 is 15.07-1 stoich) than he thinks he was...FWIW you can change your racepak to read in lambda but finding the lambda numbers for alot of race fuels is not as easy.

I'm not sure if we are agreeing or not

If it's on a gasoline scale where 14.7 is stoich or lambda 1.0 and it's ran on-

E85 with 9.8 stoich

Or C14 at 15.07 stoich

At -actual- stoich, the gauge will still read 14.7-1 because that's what it's programmed to read at 1.0 lambda no matter what fuel it's running.

So take any fuel and tune it to known gasoline numbers and it tunes the same as gasoline whether it is correlating with that fuels actual stoich number or not.

10-1 on a gasoline scale is .68 lambda. (14.7x.68). So on C14 that would be 15.07 x.68, or 10.24-1



Looking at it another way, what is your target lambda? If you target .87 lambda WOT on gasoline that's 12.8-1 air/fuel on a gas scale gauge.

So any fuel you run if you wanted to target .87 lambda and your wideband is on a gasoline scale, you would tune it to 12.8-1 on that gauge.

If you change the scaling of a wideband you're just changing what number it reports for the same lambda value. (so sometimes easier to just look at it in terms of lambda instead of air fuel ratio)

Like I say Lambda s fine and universal. However finding that number for many race fuels is not so easy. And the target number varies greatly from race fuel to race fuel. Just something to consider when someone says and average AFR is 10-1 it is fat, not knowing the scale being referenced it could be dangerously fat depending on the fuel used. He is not giving you a Lambda number, only an AFR which is likely based off of an inaccurate scale. Fat mixtures create alot of heat and can cause catastrophic damage. Much more so than being overly lean can and will. All Im saying. You are converting his number to Lambda not knowing what the idea lambda number is, and he is clearly not using lambda. I have not seen any reference to what fuel he is using so just speculating. I can tell you the fuel we use in the Vette if it sees anything close to what 10-1(.68 lambda) it will absolutely microweld rings and torch a piston, ask me how I know. FWIW this is with a fuel thats target is 13.31(.91ish). Tome its why scale and fuel used matter. Id be happy to se a lambda number but without knowing the fuel used it does not mean as much. Almost as little as a single O2 per bank on a maxx effort deal like this one.

I see where your difference in view is. For me target lambda is not determined by what fuel you're using but the combination/intended use.


Either way, if you know what scale the gauge is on (and we do) and what it's outputting you can back calculate for lambda value. (whether you know what lambda you want to target or not)

To expand a bit on that.

The gauge in lambda is .5 to 1.5

So, depending on what scale you have it on (gasoline in this case)

.5 to 1.5 lambda would be- 7.35 to 22.4 on a gasoline scale

4.5 to 13.5 on alcohol scale

4.9 to 14.7 on E85 scale


The gauge is just taking lambda and converting it to an AFR number based on what scale. So, he's running on gasoline scale and sees 10 to 1 air fuel that is .68 lambda. That's all you need to see to figure it out, scale (gasoline) and observed air fuel ratio on that scale.

In his case running C14, stoich is 15.07 so at .68 lambda it wa 10.24-1.

When he observed as lean as 13.1, that was .89 lambda so 13.41-1

Engine builders /dyno operator said it made best power at 37°.
I have decided the vertical gas ports were a bad idea for this endurance engine and will replace the pistons with no vertical gas ports and lateral gas ported rings. I am confident Wilson Manifolds can make the intake fuel distribution better. I will add an air filter and figure out how to minimize the turbulence in the cowl scoop. There was a lot of (low) pressure above the scoop at speed, as the scoop was rising about 2" or so, and the high pressure of the air flowing over the scoop pushed the windshield in while rolling rhe factory style gasket off the pinch weld. We fixe dthat by putting the gasket and Lexan windshield back in place and supporting it with a 1x block of wood against the roll bar, so there was some interesting wind/turbulence happening there. I think that turbulence had a lot to do with it the fuel distribution problem. We will see. Thanks for all the feedback.

I would leave the horizontal gas ports out of the valve pocket area also. Unless you can lower the ring(s).