thanks for clearing that up. knew about the two, just wasn't clear on the definition.

 

ha ha

 

Sorry to hear about the owner's if this car misfortune that is very frustrating.

I see there still has not been any disclosure regrading what brand name piston this was (can you kindy tell us or is it that important to you not to disclose same)?

Best of luck on the final outcome!

 

The piston is a Katech unit out of a street attack engine. From what I understand the piston has been sent back to Katech to be evaluated. I am still trying to get some of the information requested; Rockwell tests, fuel & spark tables, etc. I am going to try and stop by the engine builder later in the week and get some more information.

 

Sorry to hear that. Did the underside of the crown have a "double bump" reflecting two valves, or a single "bump" right across?

 

I have heard discussions about stock LS7 blocks having poor cylinder structure due in part to the larger bore, leaving little parent material behind the sleeves along with cheap quality sleeves themselves. Can this contribute to these block failures rather than writing it all off to detonation. Are the blocks that you are repairing stock engines or modified stuff with cams and tunes?

 

I am such a moron for not getting pictures of the underside of the piston. If I recall the underside did not reflect the valve reliefs at all, but was rather smooth between the wrist pin bores.

 

Pistons were evaluated by engineering and no signs of detonation or overheating were found. The forging has a material on the underside to compensate for both intake and exhaust valve pockets. Crown thickness is consistent throughout the piston. It was determined that the failure was caused by the piston exceeding it's recommended replacement interval in race conditions. Our bogey for replacing pistons in an endurance road race application is 30 hours. These pistons had 40 hours. After the 24 hours of Le Mans, one of the items on the rebuild list is new pistons.

Those are 2618 pistons.

 

Jason,

I'm curious what constitutes endurance race use. I assume the parameters are full throttle at rpms cycling from torque peak to HP peak?

I'm asking because my track car has forged pistons in it, and I'd like to know when I need to pull them out for replacement. For a motor seeing some street and track use, should you just keep track of total hours on track, or should there also be an add in factor for mild street use?

TIA.

 

Thanks Jason for clearing that up. I noticed on your Ultra Attack LS7 thread, you made a point to state that your forged pistons are durability tested at WOT for 422 hours. In a real world environment I guess that equals 30 hours? Would the addition of piston squirters extend your "bogey" on piston replacement or should one expect to refresh one of your engines every 30 hours of track use?

 

Even that is debatable. It all depends on duty cycle and you would need datalogging to compare. Even the same car/same engine would have different wear characteristics with different drivers. An amateur track day enthusiast is going to wear out an engine a lot more slowly than if you put Johnny O'Connell in the driver's seat.

You pretty much need to just keep track of the track miles (or hours). A 24 hour race is like 100,000 or more street miles, so it is not as significant.

 

There are a lot of factors that can be different between the dyno and in the car on the racetrack. Just to name a few:
-Horsepower (550 in that durability test versus 622 noted here)
-Duty cycle
-Heat
-Calibration
-Fuel
-Knock monitoring

Piston squirters will definitely reduce heat and reduce that portion of the equation. However the 30 hour bogey for endurance racing pistons doesn't change. Those engines also have piston squirters. It's a risk vs. reward situation. The pistons may last much longer, but is it worth it to find out exactly how long?

 

Impressive! 30 hours clearly a very accurate number there.

Is this with 2618 or 4032 alloy?

 

Great info in this thread, thanks fellas!

 

I would like to know which alloy this limit applies to as well

 

Well, this applies to race applications where we always use 2618.