Anyone seen a gen3 piston failure like this?

[AcceptableNebula]

The worst scenario is actually the exhaust stroke. The piston is flung upwards at a high velocity at high rpm with little resistance as the exhaust valves are open. It comes to a crashing halt at the top of the stroke and wants to continue by inertia through the head.

I am leaning towards this explanation being the likely reason. The tensile strength of aluminum drops significantly when extra toasty. Add in material fatigue from a tough life and a possible weak spot.

As for the 850rwhp rule of thumb, I think it matters now you get to 850. Bolting a whipple on an otherwise stock mustang at 18 psi generates a decent amount of parasitic loss. This motor is likely making upwards of 1150 hp (possibly more) in order to put down 900 rwhp, not just the 1060 crank hp and assumed 15% drivetrain loss yielding 900rwhp. The pistons and rods see the actual numbers. My twins only require 14 psi and 18 degrees of timing to achieve over 900rwhp on a Mustang dyno.

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[engineermike]

I am leaning towards this explanation being the likely reason. The tensile strength of aluminum drops significantly when extra toasty. Add in material fatigue from a tough life and a possible weak spot.

Interesting thing is that in the course of the failure aftermath, something knocked the head off of one of the #1 rod bolts (#5 is the one that failed). That means that the #1 big end stayed together at high rpm with only one rod bolt!

 

[Robottrainer]

Interesting thing is that in the course of the failure aftermath, something knocked the head off of one of the #1 rod bolts (#5 is the one that failed). That means that the #1 big end stayed together at high rpm with only one rod bolt!

Wow! The force it would take to blow the head off of a rod bolt!

 

[OldbutNew]

With high speed failures the physics gets really interesting!!
I tore down a Cup series engine that had failed. Took the intake off and found a wrist pin protruding from an intake port. LOTS to unpack there!!

 

[Robottrainer]

With high speed failures the physics gets really interesting!!
I tore down a Cup series engine that had failed. Took the intake off and found a wrist pin protruding from an intake port. LOTS to unpack there!!

Mass and angular velocity

 

[SheepDog]

Owner got the car running today with the following:

• Stock block
• Stock crank
• Gt500 rods
• Mahle 10.4/1 forged pistons
• Stock heads and cams
• Boss tensioners
• Gt500 oil pan and pump

The idea was to make it tough and also have more tolerance to and power on pump gas. We made some simple tune changes to accommodate the compression ratio. It started and drove with no issue. Once he gets through the break-in period we’ll start finding knock limits at the new compression ratio. I’m super interested to see where the knock limits are now.

Did you guys use OEM head bolts, or aftermarket studs? How about the crank and rod bearings?

 

[engineermike]

Did you guys use OEM head bolts, are aftermarket studs? How about the crank and rod bearings?

Those are all oem. I have this thing about using oem parts as much as possible. Note the gt500 rods, oil pump, pan, plus mahle is an oem piston supplier.

 

[Robottrainer]

Those are all oem. I have this thing about using oem parts as much as possible. Note the gt500 rods, oil pump, pan, plus mahle is an oem piston supplier.

Are the GT500 rods just better powder metallurgy or is there more meat at the bottom end?

 

[SheepDog]

Those are all oem. I have this thing about using oem parts as much as possible. Note the gt500 rods, oil pump, pan, plus mahle is an oem piston supplier.

well, hopefully with the lower compression, head studs wouldn't really be necessary anyway. Does the Predator use the same head bolts as the Coyote?

 

[engineermike]

Are the GT500 rods just better powder metallurgy or is there more meat at the bottom end?

Yes they were definitely beefier and the bolts are bigger with different torque specs.

 

[engineermike]

Does the Predator use the same head bolts as the Coyote?

I don’t know if the Predator uses different bolts but the gen3 bolts work in the predator block. The gen3 head bolts are so big and deep, and the torque spec is so high, I have a hard time imagining the heads would lift.

 

[Robottrainer]

Yes they were definitely beefier and the bolts are bigger with different torque specs.

Too bad they didnt just use them on everything. One part to inventory across the V8s.

 

[SheepDog]

I don’t know if the Predator uses different bolts but the gen3 bolts work in the predator block. The gen3 head bolts are so big and deep, and the torque spec is so high, I have a hard time imagining the heads would lift.

Probably wont be long before my motor exits the chat, so just trying to decide on the best route for my inevitable build as well.

 

[Robottrainer]

Probably wont be long before my motor exits the chat, so just trying to decide on the best route for my inevitable build as well.

I think an I beam rod or a good manly h beam rod would be better. The crank is probably fine. And the pistons of course. I think if I were to do one ID go 9 to 1 forged and add more boost.

An aluminator might be a good bang for the bucks.

 

[SheepDog]

I think an I beam rod or a good manly h beam rod would be better. The crank is probably fine. And the pistons of course. I think if I were to do one ID go 9 to 1 forged and add more boost.

An aluminator might be a good bang for the bucks.

I really want a Predator block, but then of course the dollars go up significantly.

https://rpgracingengines.com/product/rpg-5-2l-level-2-short-block/

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