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Help burned and broken pistons
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Author:  ggodec [ Wed Aug 18, 2021 9:31 am ]
Post subject:  Help burned and broken pistons
Hello, I have been running a torqstorm supercharge on my rebuilt SL6 and have about 2000 miles and a dozen runs down the strip and blew it up. I have been running out of fuel on the runs and am working on the fuel delivery but the pistons came apart so that is my big problem. To rebuild and how to determine what went wrong with what I had. I am adding some pictures of the pistons for reference. Any ideas of help would be appreciated. Head, valves look OK, it feels like I can hone the walls and clean up any scum but adding teh same pistons back in seems like I would create teh same problem. Thanks!!

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Author:  ProCycle [ Wed Aug 18, 2021 10:10 am ]
Post subject:  Re: Help burned and broken pistons
It seem obvious that if you are not getting enough fuel on a run it will go way too lean. Lean mixture will cause detonation will destroy the pistons.
That's what it looks like to me.
Author:  DadTruck [ Wed Aug 18, 2021 12:18 pm ]
Post subject:  Re: Help burned and broken pistons
Yes, that is a burnt piston, in this case the piston was the victim. The piston was not at fault.
Have to agree with the above post, the most likely cause was a lean fuel mixture, but it also could have been to much ignition advance. Are those hypereutectic pistons? You can put forged pistons in, but if you don’t fix the lean or advanced ignition issue,,you will burn those to.
Are you running an AF gauge with an O2 sensor. That is really a must with about any motor running boost. A way to data log while running hard is also just about a must.
Data logging can be as simple as a go pro device capturing a view of the AF gauge during the run. But that’s very limited data. Getting the fuel mix and rpm, air in and out temps and manifold pressure would give a better picture of the engine when pressed hard.
Author:  ggodec [ Wed Aug 18, 2021 1:24 pm ]
Post subject:  Re: Help burned and broken pistons
I have a spot for an O2 sensor but didn’t have one on - having that and getting some data out of the system would really be a way to catch things earlier then seat of the pants and give me a much better path to fix the issue before it gets this bad.

Distributor was a bit sloppy, it was a new DUI but bearings seemed questionable. I will need a better distributor for any rebuild.

They were wiesco forged pistons :(
Author:  Rick Covalt [ Wed Aug 18, 2021 1:37 pm ]
Post subject:  Re: Help burned and broken pistons
What is the compression ratio on the engine?
Author:  ggodec [ Wed Aug 18, 2021 1:55 pm ]
Post subject:  Re: Help burned and broken pistons
Wasn’t 100% sure, supposed to be 9 -1 or so and then aded 2-8lb boost at 7000 feet above sea level.
Author:  slantzilla [ Wed Aug 18, 2021 5:25 pm ]
Post subject:  Re: Help burned and broken pistons
Did you open up the top ring gap for boost? That looks like the excess heat butted the rings and broke the lands.

Boost is an unforgiving mistress.
Author:  ggodec [ Wed Aug 18, 2021 7:05 pm ]
Post subject:  Re: Help burned and broken pistons
I had it built for boost… so I’m learning assumptions kill
Author:  kesteb [ Thu Aug 19, 2021 3:31 pm ]
Post subject:  Re: Help burned and broken pistons
The stock fuel pump is only good enough to feed a BBD at best. Anything else requires something better.
Author:  ggodec [ Thu Aug 19, 2021 5:53 pm ]
Post subject:  Re: Help burned and broken pistons
Yep, Holley blue, boost referenced fuel pressure gauge - 3/8th line stem to stern. Should have been plenty but it seemed to drop pressure.

Gotta decide if I hone and put new pistons in it, then O2 sensor and maybe boost release combo or at least monitor fuel pressure, boost, O2 to make sure it’s running in a safer zone I’ll be able to be 100% sure on ring placement and gap as well as volume/compression without boost.

Or buy a modern hemi with efi and go a different direction.
Author:  Joshie225 [ Thu Aug 19, 2021 10:00 pm ]
Post subject:  Re: Help burned and broken pistons
A Holley blue pump does not put out enough pressure for more than just a few psi boost. You are far better off with an in-tank EFI pump and a bypass regulator. Fix the fuel delivery system and get a wide-band 02 sensor to monitor the mixture.
Author:  ggodec [ Fri Aug 20, 2021 9:30 am ]
Post subject:  Re: Help burned and broken pistons
In tank bypass pump was on order when I blew it up :)
It’s in a box waiting to go in, I plan on fixing and 90degree or 180 degree bends in the fuel line as well and making sure the return doesn’t have any restriction. Which were also on the list.

I should have stopped running until I solved the fuel issue - self control isn’t my strong suit.

I want to thank everyone, this has been a very useful thread and validated some fears I had and helps set thing on a good path.

Thx

gg
Author:  Ken Gibbs [ Wed Sep 01, 2021 1:36 pm ]
Post subject:  Re: Help burned and broken pistons
I have experienced the same type of failure in my boosted /6 a couple of years ago. Your pics show signs of detonation. Beside the broken ring lands, I see hot spots and small dimples. Tight ring gap may have caused the broken lands but I suspect detonation is the root cause. The pistons appear to be wiseco forgings with 6cc valve notches and the head gasket looks like a .020" steel shim. That combination along with a 58cc chamber ( common stock size) will net a comp ratio closer to 10:1 which is dangerously high for a boosted /6. You should check that out before re-ordering pistons. My engine had the same pistons but with a thick copper head gasket and 62cc chambers to yield 8.9:1 compression. With 10 psi boost, everything had to be right on in the tune. The pistons failed from a lean condition that lasted less than 4 seconds as shown in the data log. I found that a plugged fuel filter reduced pressure enough to cause the lean condition. To keep mine alive, I use 94 pump gas, water/meth injection above 4psi (460ml per minute) , 17degrees ign advance at peak torque and 19 at peak hp, 11.5:1 a/f ratio, cold air intake and an intercooler. Higher compression ratios with boost requires careful attention to details. I don't want to seem like a smart ass but I can speak from my experience. Hope this helps.

Ken
Author:  Dart270 [ Wed Sep 01, 2021 1:46 pm ]
Post subject:  Re: Help burned and broken pistons
Thanks, Ken, for your real world experience and perspectives. I agree that 9:1 would be the max compression I would consider. My turbo motor is 8.6:1. I target the same 11.5:1 AFR and use water/meth injection above about 3 psi. Same timing as you too.

Best,
Lou
Author:  Ken Gibbs [ Thu Sep 02, 2021 9:29 am ]
Post subject:  Re: Help burned and broken pistons
I just read the rest of this thread and see that you are at 7000ft. altitude. Obviously the high static compression ratio will not be an issue for you, so please ignore my opinion with regards to the high comp. Hope you come up with an easy solution to the problem. Side note... thanks Lou for your comments.

Ken
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