Anyone seen a gen3 piston failure like this?

[cbrtrx]

Spent most of today tuning the new motor. It seems to take 3-4 deg more timing on true pump gas before finding the knock limits. At 1.9 load was touching 20 deg and at 2.1 load maybe 17. Honestly I was hoping to be able to add 5-6 but it just wouldn’t take it.

Yeah I'd only expect about a 3* increase. On the dyno it would be interesting to see the amount of additional timing vs dimishined gains.

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[SheepDog]

Spent most of today tuning the new motor. It seems to take 3-4 deg more timing on true pump gas before finding the knock limits. At 1.9 load was touching 20 deg and at 2.1 load maybe 17. Honestly I was hoping to be able to add 5-6 but it just wouldn’t take it.

Still though, for 93 octane, that is really good. Maybe pulley down a little?

 

[engineermike]

Still though, for 93 octane, that is really good. Maybe pulley down a little?

That’s the goal, wanting to wind up in the 20 psi range. We ran into a bit of a snag in the individual cylinder BLK timing offsets and how the cylinder numbering works. Some parameters are a function of cylinder number, some are firing sequence number, and some are firing sequence minus 1.

 

[Blueflash]

Curious about how the motor was broke in, and what's the proper way to set cylinder pressure limits tune-wise?

 

[Excelerater]

looks like a typical piece of shit cast piston that was beat the heck up .

I miss OEM forged Pistons

 

[GrabberBargeCaptain]

Tis but a flesh wound.

 

[engineermike]

Curious about how the motor was broke in, and what's the proper way to set cylinder pressure limits tune-wise?

The original one or the low compression replacement?

 

[Blueflash]

The low compression replacement..

The original one or the low compression replacement?

 

[engineermike]

The low compression replacement..

Just took it easy for a couple hundred miles then changed the oil.

On finding cylinder pressure limits, I looked at about a dozen cylinder pressure limit timing maps for different coyote variants and found that the Raptor R version looks like it’s well-developed by Ford with approximately the absolute values where we wanted them to be, so we copied it over.

On finding knock limits, I put it in per cyl mode and set the SDLF to keep it in per cyl all the time. I set the knock advance limit to 2 deg then start adding 1 deg at a time to the mapped point borderline until I pick up repeatable knock (any step change reduction in knock advance) on >1 individual cylinders. Where I got hung up is that sometimes one cylinder could knock up to 2 deg before another, so you can build that into the commanded spark, but the cylinder number I don’t think is consistent between the tuning and logging parameters.

 

[engineermike]

I spot checked a few ring gaps on the old motor and they were .015 top ring and .030 2nd ring. Coyote spec is .008-.012 top and .020-032 2nd.

 

[Robottrainer]

I spot checked a few ring gaps on the old motor and they were .015 top ring and .030 2nd ring. Coyote spec is .008-.012 top and .020-032 2nd.

I haven't built an engine in awhile. I thought the 2nd ring was usually a smaller gap than the first. Is this a piston material thing? And of course more gap if we are talking FI or nitrous.

 

[engineermike]

I haven't built an engine in awhile. I thought the 2nd ring was usually a smaller gap than the first. Is this a piston material thing? And of course more gap if we are talking FI or nitrous.

Ford doesn’t subscribe to that train of thought. The oem ring gap specs are mind boggling if you have the old mind-set. I was there as well. Some of the ford top ring specs are as tight as .008, even on ecoboost. I’ve heard other oems are doing the same because it helps the top ring stay seated against the bore due to pressure differential.

 

[Robottrainer]

Ford doesn’t subscribe to that train of thought. The oem ring gap specs are mind boggling if you have the old mind-set. I was there as well. Some of the ford top ring specs are as tight as .008, even on ecoboost. I’ve heard other oems are doing the same because it helps the top ring stay seated against the bore due to pressure differential.

Are the aftermarket piston and ring suppliers using the same mindset? I believe they also use a low ring tension.

 

[SheepDog]

I spot checked a few ring gaps on the old motor and they were .015 top ring and .030 2nd ring. Coyote spec is .008-.012 top and .020-032 2nd.

What were the gaps on the new pistons?

 

[Oakley]

............ you boosted a NA motor with hyper-eutectic pistons.

no this is not a common failure mode, even in SC applications, however, it is FAR more common once you start forcing pressurized air into those cylinders because A. the part failure odds go up and B. the tune now becomes very important.

you boosted a motor and it let go. no mystery here.

Yeah, someone probably did something wrong (and it wasn't ford) but that doesn't matter anymore.

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