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!