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Originally Posted by 1slowna
(Post 497594)
That piston pic i think it was savs piston wasnt destroyed by detonation im 90+% sure that was caused by either an extreme lean condition or an extended lean condition, Possibly doing a long pull at a slightly lean state. do you have a wb? what were your air fuels?
Jason, the HG looked perfect as far as I remember. I have no idea whether there was a hotspot in the head, since it was pretty chewed up afterwards. There is a discussion I'm involved in on the Supra boards about per-cylinder widebands for turbo cars. Apparently FJO makes a sensor good for 950*C. I may look into that. |
Big +1 on just about everything in this thread. It should be a sticky. Bottom line, built motors are not detonation proof.
Also a big +1 on the point that a higher specific power output (more boost) greatly reduces the safety margin all else being equal. Plus the decrease in margin is probably not linear, but something like exponential. Think of it this way. Higher cylinder pressures not only make it more detonation prone, but make the detonation event more damaging once it starts. Again, all else being equal. The thread below is a previous attempt to start a detailed discussion on water injection failsafe schemes. It includes discussion on pressure switches and flow meters. I am pointing to this rather than rewriting it all over again here. https://www.miataturbo.net/forum/t38494/ On the burned piston near the intake valve... Mine did the same thing, Supertech 9.5:1 forged. GT2871, WI, 17-19 psi. It happened on the #1 cyl. The rest of the pistons looked fantastic. Short answer, highly probable IMO that bad WI distribution between cylinders leading to a low WI charge to the #1 cyl was the cause. I am going to port WI. Detailed discussion about it here: https://www.miataturbo.net/forum/t38232/ I talked to an engine R&D friend of mine that has seen this before. Even though it is on the intake side, if you look at how thin the crown is at the edge of the piston due to the larger valve pocket, you can see how it is more prone to running hotter than the exhaust side. Heat cannot conduct out as quickly. Detonation starts there, it gets hotter, which leads to more detonation, which leads to this... http://lh3.ggpht.com/_jh2HiMm4nKQ/Sr...0/P9160195.JPG More pictures of that piston here http://picasaweb.google.com/zx.tex.m...Okg7adiYvhnwE# |
Originally Posted by faeflora
(Post 497588)
The motor these pistons were in was built, operated, and tuned by a moron. I don't think you can get useful data out of that other than "don't waste money on a built motor if you're a moron".
That's why I didn't build my own motor and will have someone else doing the tuning- failsafe just in case I'm a moron and I don't know it. :drool: You know, I wonder how OEMs go about tuning for high boost. If I look at high performance factory turbo motors, OEMs seem to tune wayyyyy away from the bleeding edge of performance. They don't run as much boost, don't use WI as a power adder with meth or timing etc. That's why the turbo performance aftermarket exists- since OEMs leave a lot on the table. I assume that OEMs do not want their customers busting rods and shattering pistons and that's why they play it safe. My guess is that OEMs run pretty far away from MBT and have extremely conservative closed loop trim maps. Do we honestly expect that our built motors will last 100K+ miles with so much more incurred risk? If we fuck up and put 87 octane into our motors, probably half the built motors here will sustain significant damage. If I put 87 octane into a factory turbo engine it would probably run like shit but I'm guessing it wouldn't detonate and break. I used to think hustler was a pussy for tuning on 91, running minimal boost (for his motor), and backing off timing but when you look at the thousands of $ of outlay for that built engine, those decisions seem very sensible. I think you can get 100k miles on a built engine with hundreds of track hours. Gary/TDR has done it for 5+ years on his shop car on the original built motor with 9.0:1 static compression. If the tune is on point, the pistons rings and rods are strong, then there is no reason you can't. When you're under the max-duty on the engine, the only wear lies in the rings and bearings and that's a question of the friction life of the metals.
Originally Posted by 1slowna
(Post 497594)
That piston pic i think it was savs piston wasnt destroyed by detonation im 90+% sure that was caused by either an extreme lean condition or an extended lean condition, Possibly doing a long pull at a slightly lean state. do you have a wb? what were your air fuels? i would be surprised if you were seeing below 12.5. You should give your injector o-rings and fuel filter a look. if you dont come up with anything from there what did that to the wiesco pistons in my dsm was the o-ring thing that goes from the pump to the line in the tank cracked and it was bypassing fuel back into the tank.
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Originally Posted by faeflora
(Post 497588)
You know, I wonder how OEMs go about tuning for high boost. If I look at high performance factory turbo motors, OEMs seem to tune wayyyyy away from the bleeding edge of performance. They don't run as much boost, don't use WI as a power adder with meth or timing etc. That's why the turbo performance aftermarket exists- since OEMs leave a lot on the table. I assume that OEMs do not want their customers busting rods and shattering pistons and that's why they play it safe. My guess is that OEMs run pretty far away from MBT and have extremely conservative closed loop trim maps...
Despite this, damage due to knock is very very rare on Evos. Even on tuned ones, unless the tuner is a complete knob. Certainly nothing like the meltdowns we're seeing with Miata motors at similar or less power. Evos have pretty badass knock detection, and their timing interpolates between two maps for low and high octane, so you'd have to go out of your way to get prolonged det that actually causes damage. Historically OEMs run so rich to keep the EGTs down so the catalyst can live for 100k miles. Of course, the low EGTs mean they can save $$ on exhaust valves/guide material etc... (nowadays, though, the trend on OEM turbo cars is to run stoich at full boost to save fuel). |
Originally Posted by JKav
(Post 497633)
You'd be surprised. Stock Evos run heaps of boost, and while they run rich (~10:1 afr), the spark table is jacked from the factory for US spec fuel. A bone stock Evo will log knocksum on 91 octane.
Despite this, damage due to knock is very very rare on Evos. Even on tuned ones, unless the tuner is a complete knob. Certainly nothing like the meltdowns we're seeing with Miata motors at similar or less power. Evos have pretty badass knock detection, and their timing interpolates between two maps for low and high octane, so you'd have to go out of your way to get prolonged det that actually causes damage. Historically OEMs run so rich to keep the EGTs down so the catalyst can live for 100k miles. Of course, the low EGTs mean they can save $$ on exhaust valves/guide material etc... (nowadays, though, the trend on OEM turbo cars is to run stoich at full boost to save fuel). Also, how do modern turbo cars get away with stoich at full boost? |
Originally Posted by ZX-Tex
(Post 497629)
On the burned piston near the intake valve... Mine did the same thing, Supertech 9.5:1 forged. GT2871, WI, 17-19 psi. It happened on the #1 cyl.
Hustlefucker spoke about a strategy of steady state loading on the dyno followed by a strong pull or two to simulate track loading. Can we discuss if this is a reasonable strategy. I don't think enough of us are considering the effects of prolonged loading contributing to high EGT (delta of >300*f from steady or unloaded?) bringing on det on the track. What I'm saying is, if we think that one pull on the dyno, listen for det, read egt is an effective strategy for predicting det on a track car, we need to think again. |
Originally Posted by faeflora
(Post 497643)
Jkav- with standalone EMS's like Hydra/Adaptronic/Megasquirt that have closed loop knock detection, why do you think our Miatas are still seeing this type of damage? Do you think it is because of the design of the BP?
Also, how do modern turbo cars get away with stoich at full boost? |
BINGO! I'll wager the problem is what ZX-TEX describes, the thin wall on the Supertech pistons. That's exactly where everyone's Supertechs failed.
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Originally Posted by faeflora
(Post 497643)
Jkav- with standalone EMS's like Hydra/Adaptronic/Megasquirt that have closed loop knock detection, why do you think our Miatas are still seeing this type of damage?
Even a properly setup knock sensor will just detect, what should the EMS be programmed to do after the detection? Would these changes be permanent or is there nothing to prevent this from happening on the very next gear or next lap under similar conditions? |
ZX-TEX I think the PT Cruiser turbo (GT Cruiser) runs stoich in boost. I wouldn't be surprised if the BMW 335i runs stoich at least in part boost, bec they have excellent fuel economy for the weight and power.
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Most all modern factory turbo cars run stoich at part throttle boost. The 335 definitely does, and aftermarket tuners have found that taking it to 12:1 gets the car to make a shit-ton more power.
The two standalone management units I've worked had knock detection and would react to an event. The link would pull timing in the areas it detected knock, and would keep it pulled in those zones until the ignition key was cycled. MS can pull timing and/or add fuel at knock detect. I want to say it can cut boost as well, but maybe my memory is playing a game with me. No one's really using closed loop boost on MS anyway. Point is, the response is programmable. I think the EMU I had for a while would also reduce timing advance with knock. The question then becomes--how do you get an EMS system to only respond to a real knock event, and not to other noises. With a tuned bandpass filter, maybe we can get it fairly reliable. But I doubt it's anywhere close to 100%. |
Yes the BMW N54 runs stoich at full load up to about 4500 rpm and then progressively richens up.
Others: the Smart (I think Euro-only) turbo engine is stoich everywhere; the Audi turbo and EcoBoost stuff is like the N54 IIRC... there are others. EGTs at the turbine inlet in modern gasoline turbo engines are approaching 1050 deg C. Some are already there. It requires insanely temp- and creep-resistant SS steels for the manifold and turbine housing. If you're a metals geek, go have a look at DIN 1.4849 (GX40NiCrSiNb 38-18). |
Originally Posted by ZX-Tex
(Post 497649)
My guess, less than stellar knock detection. It is not easy, and an OEM system can be tuned/optimized (sensor type, placement, A/D, signal processing) for a specific engine.
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Originally Posted by Ben
(Post 497706)
The question then becomes--how do you get an EMS system to only respond to a real knock event, and not to other noises. With a tuned bandpass filter, maybe we can get it fairly reliable. But I doubt it's anywhere close to 100%.
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I burned an exhaust valve on my 2.0L last year and I don’t think it had any knock.
I just pulled the head off my GTR powered GTX. Last night. Cylinders 1 and 3 were slightly melted. It had Flyin Miata Wisecos. A chunk of piston stuck on the exhaust valve making for zero compression on cylinder 3. Don’t think the rings had fully given up yet. The GTX is gear limited to about 130mph and it gets there with more than a 3rd of the straightaway left. It went down a cylinder near redline in fifth gear. It was running completely stock GTR ECU management with the boost turned up ~18psi. No dataloging or even error codes to the stock GTR ECU. Last time it was dynoed it was running about 11:1 and full tilt. It has an EGT gauge on it with the sensor after the turbo. The gage is placed on top of the dash directly in front of the steering wheel where it is practically in your way to see out the windshield. It still seems useless unless you stare at the dam thing the whole time you’re driving. Bob |
Originally Posted by bbundy
(Post 497802)
It had Flyin Miata Wisecos.
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Is WI a must for a street car at around 300whp?
Just bought some m-tuned rods and am going to slowly start my engine build. 300 will be my goal, but my car is not tracked. How long has Paul been pushing the "machine" and does he have WI? |
Where the he'll can I rent a borescope.
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I wonder how Gary/tdr has run his mp62 at extreme rpm for so long with no problem. Is backpressure (lack of) on my side with the tubular manifold?
Bob, have you seen any similar issue since the burnt valve? I'm going to peep at the cylinders and hopefully everything is good. This thread is more reason to stay at low boost. |
Originally Posted by webby459
(Post 497805)
Thank god.
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