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Turbo Destroyed - What Do You Think Caused This Level of Damage?
Ouch.
I'm at a loss as to what would have done this much damage. I have some theories, but I'm curious what you guys think. GT35R turbo. The car was running fine/strong - no sign of an apex seal being processed. The only reason it was removed is to adjust the mounting position. Really no noticeable indication of turbo or engine damage. I've never noticed a change in sound (not sure I would), boost pattern, or responsiveness.
It was purchased new as a kit about 12 years ago and has about 25k miles of street use.
High EGTs is definitely on the list - but even then this seems like more than that going on here - scarring on the housing, etc. Given its usage and general babying, I find it hard to believe this much damage. Still possible though...
No redlining or backfiring, however. Other than some spirited pulls now and again, it's never been driven overly hard. Heck, not even back-to-back pulls. Usually a quick 2-3 and settle into traffic flow, etc.
Do you run EGT gauge? What boost? Ignition timing?
Really just looks like over temp. You would expect at least some clean fractures from mechanical impact.
No EGT gauge (probably having one installed), ~15psi, and I'll have to check on ignition timing.
I think you've convinced me by pointing out no clean fractures. It does fall into Occam's Razor better than the other theories.
Originally Posted by Howard Coleman
no question heat erosion... above 2000 F
Seems so - looking up some EGT-damaged turbos really does quite similar.
I had a feeling it was EGTs related but seemed like something more. Before you guys pointed to that I had never seen one so badly damaged from it. Some scorching here and erosion there but not like this. Too bad Garrett doesn't do their CHRA discounted exchange anymore - the intake side looks unused. Either way, it does make sense - was still balanced, spooled down for days after shutdown and so on which I would assume would be potentially greatly diminished if it had processed something.
We will dig into the timing and such to try to pull those EGTs down once the car is back together.
...We will dig into the timing and such to try to pull those EGTs down once the car is back together...
Retarded timing is a frequent cause of abnormally high EGT's. The mixture may still be burning if it's retarded enough. OTOH, too much advance will cause detonation, but up until that happens, it also lowers EGT's because expansion and contact with surfaces cools the exhaust gas before it gets to the exhaust system or turbos.
No EGT gauge (probably having one installed), ~15psi, and I'll have to check on ignition timing.
I think you've convinced me by pointing out no clean fractures. It does fall into Occam's Razor better than the other theories.
Seems so - looking up some EGT-damaged turbos really does quite similar.
I had a feeling it was EGTs related but seemed like something more. Before you guys pointed to that I had never seen one so badly damaged from it. Some scorching here and erosion there but not like this. Too bad Garrett doesn't do their CHRA discounted exchange anymore - the intake side looks unused. Either way, it does make sense - was still balanced, spooled down for days after shutdown and so on which I would assume would be potentially greatly diminished if it had processed something.
We will dig into the timing and such to try to pull those EGTs down once the car is back together.
Curious, any real danger of running this turbo?
How much power were/are you putting down at 15 psi on the GT35?
Have you personally logged that? I can't see how that works given knock releases more of the heat energy in the chamber AND blows out boundary layers to transfer more of that heat to rotor/housing/head/piston. Doesn't correspond to theory or what guys like Andre Simon or Ioannis from plex say, guy literally designed two generations of combustion loggers after tuning for a Toyota dealer team and running his own tuning shop.
Sure it's not misfire and ignition on the exhaust sleeve/manifold? I guess I'll be able to lock that all down with combustion pressure logger and thermocouples myself.
sorry to have been a bit short on my comment. during conversations w Rick Engman and Dr Iannetti both used the 3500 F number for detonation. whether that temp, or something close to it, travels to the turbine i don't know. i do conclude that it is a way diff number than typical combustion chamber heat. Google says inconel melts around 2500 F. i have not seen EGTs much over 2000.
As far as high EGT's go - assuming no mechanical issue (ignition system failure, crank trigger failure, etc), it's either too lean or too retarded or both. Temperature compensation tables can have a big impact on air fuel ratio and spark timing.
The other theory that I had floating around in my head was carbon buildup from too rich of a tune (save the engine, sacrifice the turbo sorta thing) since I know 400whp is a bit outside of comfort limits for pump gas and no AI. Make it rich and "conservative" if you can call it that. I kicked around the same concept of spark plug color.
Does that apply here? Should that wheel be more brown rather than dark? My thought was overly rich mixture igniting in the exhaust manifold leaving carbon build-up. Carbon deposits being ignited will rip right through most metals. I guess that still comes back to the timing though in a roundabout way.
It was around that time that I started seeing the cast iron exhaust wheel China "GT35Rs".
That would explain a lot. The boys down at the shop thought I might have not gotten a new turbo to begin with - it didn't make sense to see this damage on a car that, for all intents and purposes, was running very well. That or my car was powered by an acetylene torch.
It was a kit from rx7store so no telling.
I'll ask them to send some more pictures if/when they can but these are the only other ones - not much to add and a bit more of the same I guess.
As far as high EGT's go - assuming no mechanical issue (ignition system failure, crank trigger failure, etc), it's either too lean or too retarded or both. Temperature compensation tables can have a big impact on air fuel ratio and spark timing.
Not that I'm going to state anything that should be surprising, but:
In piston engines, assuming you don't need to run rich to protect stuff like turbos and piston tops from heat, there is an air:fuel mixture around 14:1 that is called "lean-best-power (LBP)" where HP is maxxed out. With richer mixtures the combustion temperature is lower, and so is HP. With mixtures leaner than LBP, power and combustion temperature again drop off. Further leaning of the mixture leads to miss-fires, etc.
In the rotary, protecting the tip seals and the spark-plug area of the housing (which sees combustion 3 times as often as a piston-engine cylinder-head) from excess heat is much more important. So richer mixtures and/or other chamber-cooling methods like water/alcohol injection are the norm when seeking high HP.
Lean no load freeway cruise high EGTs is no issue, nor is retarded idle timing for idle smoothness on a big port.
Basically, with no exhaust manifold pressure (low total engine flow) the EGTs just go out the tail pipe.
Its when exhaust manifold pressure increases the boundry layer on engine and turbo components is decreased and there is massive thermal transfer (like a pressure cooker).
I ran lean 15/16:1 freeway cruise with 1000C (1800F) preturbo EGT for 15 years on same turbo. No issues from excess EGTs.
Had it pop out to13:1afrs for light grades/load and 12:1afrs for bigger hills.
No closed loop!
Dont lock in closed loop for ultra lean cruise rotary. Hills will melt components.
05-10-23, 09:30 PM
