Well, I have fallen victim to the turbo learning curve.

Zack

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Im going to say it now....I have many aspects of turbo ownership to learn and apply. Id say this is my fault 100% Now on with the show!

First, I started off with backpressure problems and horrible detonation.
I swapped in new valve springs and added a dump. Problem solved.
I messed with A/F over the months and never heard detonation.
I would listen for detonation by closing the dump and running the exhaust through the stock mufflers (which are baffled)
If it doesnt ping like that, it definitely should not ping with the dump open (since its near impossible to hear with it open)

So, after a spirited highway pull in 3rd gear Saturday, I was left with a knarly engine knock. I thought it would be a bearing but I was wrong. :ugh:
I do know the A/F was 12.0:1 (which Im learning quickly is too lean for a turbo car)
I pulled the engine and found this:






OOPS.
Everything else looks good though:




The repair process is already underway. Ill most likely replace all 8 pistons, with coated tops. I spoke with my engine guy and he's definitely seen this before. He explained to me its detonation, but not in the conventional form (meaning the lack of audible sound) He said I had too much timing for the amount of boost pressure in the cylinder at a particular moment. That is what lifts the ring lands.
Although you probably cant see clearly, there is absolutely no sign of detonation on any of the piston tops.

Is it an inconvenience? Absolutely
Do I care? Haha hell no. This isnt the first engine problem Ive had, or the first self-inflicted wound Ive caused, nor will it be the last.

I knew I was not getting the A/F in the 11's like I normally do, but it did hold a 12.0. I knew it was the ragged edge and didnt hear detonation, so I pushed it. Its difficult not being a tuner, making all kinds of changes and not being able to go to a dyno everytime something is switched around. Plus its 2 hours each way. I verified both pumps are working, but the 2nd is activated by a hobbs switch. That may have failed, I do not know yet.

I do know this: all of the fancy warning devices, controllers and blinking lights turbo guys install are for good reason....to save themselves from situations like this.
I have learned a valuable lesson in this method of atmospheric compensation I chose to install, and intend on applying all of my new found intelligence to the second go-around.

BECAUSE TURBO CAR.. :jg:
 

RICH17

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:fu: But at least you got it before anything else happened
 

Yaj Yak

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i love [MENTION=4846]Zack[/MENTION] 's gettin the fuck after it style.
 

Bad Merc

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I believe that's why the turbo guys are running alky systems to control the hidden detonation that doesnt show up or reads a miniscule amount on a scanner. Usually by the time the scanner reads it you are already to late and have caused some engine damage.
 

wolfe

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I will give you credit. I remember you posting a few years ago that you wanted your tune on the edge and didn't care about hurting it. You stuck to that, are learning from it, and moving on. Good luck with it in the future.
 

deviantlx

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12.0 isn't that hard and I have run well over that # in my boosted grand national and not caused damage like that.

remember timing and fuel are EVERYTHING to a boosted car.
 

b4black

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You'll never hear detonation in a modern engine (unless something is horribly wrong). The knock sensor hear's the knock and the ECM yanks timing so fast, you can't here anything going on. A scan tool or knock gauge is a must.
 

Turbocharged400sbc

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id honestly guess that maybe the rings were gapped a hair tight or the bore sizing wasnt right for the extra heat/thermal expansion of the top of the forging

unless high angularity was causing a thrust issue....but that usually results in a closed land it isnt entirely unlikely though id expect more scuffing on the skirt.

note the compression ring gap clocking and clean and toss into the bore and feeler out the gap just to see if you can rule at least one thing out....

shitty when shit fails
 

Zack

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All 8 pistons are out.
2 more were starting to lift, and the other 5 are all scuffed above the ring land.

Gonna make a list of what needs to be ordered on Saturday after measuring stuff.
I think I'm going to use E85 when it's fixed, since I mainly use the car locally.

And.....ill run it a lot richer. Lol
 

ProRauder

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Get a used FAST or BS3 system and switch to speed density so you can have a wide band O2 monitor at all times.
 

SleeperLS

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Is it possible for you merc guys to play with the sensitivity of the knock sensor through your tuning software?
 

IZZy

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I dont think there is knock sensors on mod motors
 

Zack

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Is it possible for you merc guys to play with the sensitivity of the knock sensor through your tuning software?
They are a joke for removing timing.
They do work well for adding timing believe it or not.
I always disable them, because they give a false sense of 'security'
 

SleeperLS

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fair enough, that makes sense. I wish you the best of luck getting that beast back on the road...badass ride you have there.
 

wildabeast

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running 12.0 AFR is ok IF the following is true:
Intake temps under 115
You have a honda (j/k)
You have an abundance of fuel flow (aka, really big fuel pump(s), and injectors are less than 80% duty cycle (ever).
Great fuel return (to prevent fuel pulsing and starvation on certain injectors)
During winter months, I'm around 12.5 AFR on 20lbs of boost (yes, you read that right)
During summer I'm closer to 12.0AFR, and when I'm racing/tracking for 20min session: 11.8
I've gotten knock i think twice ever since i've been boosted (that I can hear)
HOWEVER, reading the logs, Ive gotten a lot more and tuned it out. Now when I race, I get about 1-5pts of knock in the logs at any given track event/race, but its "ghost" knock from high rpm fuel cut shifts.
 

IZZy

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They are a joke for removing timing.
They do work well for adding timing believe it or not.
I always disable them, because they give a false sense of 'security'
Where would those be located at?
 

Zack

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Just measured the ring gaps for fun.
.022 top
.025 bottom

So that was good
 

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