Cyl-4 Blown Yet again

[sense of nature]

He would'nt be the only 1 look around for 07 sti w/ low compression I've had several machinists look @ my pistons ( which look identical to those posted) each said it was a material contamination or processing flaw FWIW

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[STi_Guy04]

Originally Posted by hotrod

Yes given how Subaru engines come apart it is a pretty good bet he has had plenty of opportunity to see if similar things are going on in other cylinders. You should always look at all the cylinders if you have something like this happen. If you see similar early signs in the other cylinders you can be pretty confident that the tune or fuel or boost controller or some other "global" issue is at fault. If all the other cylinders look fine than you have some sort of problem unique to this cylinder.

Larry

Thank you for the insight, Well I have looked at all cylinders and inspected every piston and ring land, the other 3 where fine no similar damage, I removed the rings and found no broken ringlands, or abnormal skirt wearing patters, I`am a Novice here, If you would like i can post pics of all cylinders & pistons.

I`am thinking there must be some Flaw in my Kit Such as how cylinder four is being fueled, Possibly a injector maybe the perrin fuel rails, or perhaps how its set-up.. from the looks of it i do not think it was a Mahle piston problem, it looks like a dang detonation issue, let me know what your guys think or wana see,

I do have some abnormal cam wear, sad to say there are some scratches you can feel on the cam caps, the cams them selfs, and what ever you`d like the call the spot under the cam its self, the cam journals? i`ll post some pics of those up here tomorrow

[flycaster]

Boy, this is eerily reminiscent of what happened to ejh25. In his case, it was a bad fuel rail that caused an injector to momentarily lift [unseat] while at WOT on the dyno and, whamo, it blew a single Mahle piston into bits.

If all the other slugs and plugs show zero sign of detonation, I'd start with the injector and the fuel rail.

[hotrod]

I`am thinking there must be some Flaw in my Kit Such as how cylinder four is being fueled, Possibly a injector maybe the perrin fuel rails, or perhaps how its set-up..

Simple solution for the injector question send them out to be cleaned and flow tested then you will know for sure if you have a partially clogged injector in that hole.

Larry

[STi_Guy04]

right I have plans to do so, Yeah the 3 plugs show normal color, and of course number for spark plug, is carbon and oil build up... and the thing thats gets me is, I blown number 4 cylinder 2 other times, this was when Kingpin was working on my car so that leaves alot on the table, 1st time was on the dyno, I walked around the corner, when i came back massive amounts of smoke! they then took my motor out and just droped in a single stock piston 2 months later same affect!

So this weeks plans are send out fuel injectors and maybe inspect the fuel rail, there so simple i dunno what really could go wrong.

And thanks Again

[modaddict]

Originally Posted by STi_Guy04

So this weeks plans are send out fuel injectors and maybe inspect the fuel rail, there so simple i dunno what really could go wrong.

And thanks Again

Do you have any idea if the area of the piston ringland that broke.... was it at the bottom of the cylinder bore (as the engine lays flat in the car)? If you don't remember, you may be able to look at the scratches in the cylinder wall to see....

It's interesting that an engine with fuel rails has this problem.

You might want to try and talk to your tuner to verify your tune. I wish I had individual cylinder timing compensation like the new 07 ecu.

[Remnex]

If it hasn't already been said, Mahle pistons are worthless.

[flycaster]

Originally Posted by modaddict

...It's interesting that an engine with fuel rails has this problem...

Yes it is.

[MRF582]

Originally Posted by STi_Guy04

Well I agree. It could be detonation damage, With that said.. why would the Hydra not pick up on this detonation?

Is it possible that the knock thresholds were not set properly?

I also recently replaced piston # 4 due to detonation damage.


The datalogs on the stock ECU show just various intermittent knock through out. My old 2.0L had seen MUCH more knock in the datalogs through it's life and when I swapped shortblocks, the piston ringlands were perfect. My theory for why my stock ECU wasn't reporting as much knock as existed centers around how piezoelectric sensors work and the way they are oriented.


As you can see, for a given mechanical impulse (wavefront) the piezoelectric material will deflect along it's axis. To get maximum deflection, the sensor has to be oriented normal to the wavefront curve. 100% of the energy is being used to deform the PEM axially.


In this picture, you can see that for a given mechanical impulse, some of the energy is being used to deflect the PEM axially while some is causing shear deformation. We are not getting maximum axial deformation for a given mechanical impulse. If the knock sensor was placed tangent to the wavefront, we would see zero axial deformation for any given mechanical impulse (soundwave). The ECU would never pick up any knock no matter how severe.

The Subaru FSM clearly notes that the knock sensor must be aligned 60* counterclockwise from the longitudinal axis of the car. I suspect this is because the knock thresholds in the ECU are calibrated for that specific angle. Installing the knock sensor in any other orientation would be less than ideal. This orientation is critical in a Subaru engine because of the geometry of where and how the knock sensor is positioned. In a Chevy LSx series engine, the knock sensor is installed so that even if you rotate the knock sensor, the angle its axial axis makes with respect to the wave front never changes. With the Subaru setup, you have the ability to change the axial axis of the knock sensor and is therefore very critical to set it according to the FSM.

I did not install my knock sensor according to the FSM so the PEM wasn't deflecting as much as it could've for a given soundwave amplitude. What angle was your knock sensor installed in?

I know this is a bit hard to understand but without drawing better pictures, it's quite difficult to explain over a BBS.

PS - the ringland on my piston also blew between the 11 o'clock and 1 o'clock position if viewed with the intake valves at the 12 o'clock position.

[STi_Guy04]

I understand what your talking about, as to what angle it was installed i suppose i could look, Like you I did not install my knock sensor, I plan to change it out though with a knew one.

As for the knock thresholds, I had watched the map and did many pulls watching the knock threshold map on my hydra, I was always well under the cure, or you could say far from knock.. LoL Seeing that didnt happen I`am confused, Maybe there could be an issue with my hydra?

Does anyone know by chance the best company to go through for possibly boring and honing my motor out to 100mm along with best cylinder head servicing? I see Cosworth and Cobb both sell CNC ported Heads, How do those compare to AXis Racing, Also Which would be a better choice between cosworth and cobb, I`am sure they both flow there heads at a different lift! I called Cobb and asked them what lift they flow test there heads at and he didnt know...

All said and done, I would like to come back bigger and stronger this time around, I`am interested in those New brian Cower cams and Valve train package, Does anyone know a price, there never listed on his webpage, well the cams arnt at least

[Element Tuning]

Sorry to hear about your motor. This honestly looks like a classic case of pre-ignition due to a massive lean out in only one cylinder. Typically when you burn up a piston this is the case vs. detonation which would also show severe pounding to the rod bearing and you would also see damage to the other pistons or at least signs of contamination on the spark plugs.

I would inspect that cylinder's fuel injector o-rings and the fuel rail o-rings especially but also those electrical connections you were suspicious about.

In terms of the knock detection the system is only as good as it is setup. Typically what I will do is pull the knock threshold line down right along normal noise so that even under normal noise it might even pull a little timing occasionally. Since you said "it was way below the knock threshold" tells me it wasn't set sensitive enough for your motor. This will give the best odds against catching a severe problem as it will quickly result in a CEL and the "limp" map. Typically in cases of pre-ignition due to a massive lean out, it just happens so fast it's rare you'll be able to catch it.

Make sure you take the time to find the problem so this doesn't happen with your new motor.

Thanks,
Phil
www.elementtuning.com

[STi_Guy04]

Yeah thanks alot Phil. I`ll for sure check into those things. hopefully You`ll make it down hear to Florida to tune our cars up and get everything dialed in right!

[ride5000]

Originally Posted by Element Tuning

Sorry to hear about your motor. This honestly looks like a classic case of pre-ignition due to a massive lean out in only one cylinder. Typically when you burn up a piston this is the case vs. detonation which would also show severe pounding to the rod bearing and you would also see damage to the other pistons or at least signs of contamination on the spark plugs.

I would inspect that cylinder's fuel injector o-rings and the fuel rail o-rings especially but also those electrical connections you were suspicious about.

In terms of the knock detection the system is only as good as it is setup. Typically what I will do is pull the knock threshold line down right along normal noise so that even under normal noise it might even pull a little timing occasionally. Since you said "it was way below the knock threshold" tells me it wasn't set sensitive enough for your motor. This will give the best odds against catching a severe problem as it will quickly result in a CEL and the "limp" map. Typically in cases of pre-ignition due to a massive lean out, it just happens so fast it's rare you'll be able to catch it.

Make sure you take the time to find the problem so this doesn't happen with your new motor.

Thanks,
Phil
www.elementtuning.com

phil, do you have any comment on the altitude change?

does the hydra have a barometric pressure sensor? if so, what are the compensations applied to the maps based on that sensor?

[R & H Garage]

something that I'd like to throw out there that many people over look.

The factory intake manifold has very large flow discrepancies between cylinders. Cylinder 4 get 22% more flow than the other cylinders at certain flow rates and RPM.

The subaru factory ecu has a timing strategy for each cylinder. Some cylinders get upwards of 3 degrees less timing than the others.

Hydra does not have a cylinder trim for timing. It does have a trim for FUEL. If you have 0 in all four and haven't fixed this flow issue, you could be hurting yourself.

If you AFR in the downpipe is 10.9:1. That's the average AFR of all four cylinders.
Chances are very good that 1 and 3 are closer to 10.3 while cylinder 2 is 11.2 and 4 is closer to 11.5.

Since it is impossible to get individual AFR on all four cylinders due to manifold pressure, it is a good idea to do these types of flow tests or get 4 EGT probes for tuning sessions. Once you get it balanced out you can remove the excess components.

Hope this helps and sparks some good ideas.

Also, get some real pistons.

Wisecos are great for the price.
CPs are ok, but they don't use an offset wrist pin and they are NOISY.
COBB's are better for detonation resistance and great quench. They use JE Forgings and you can use factory headgaskets.
TWE are great for the same reasons as COBB's and use Wiseco forgings. But you have to use a Cometic Head Gasket.

-Dominic

[ride5000]

Originally Posted by KitoAutoSport

something that I'd like to throw out there that many people over look.

The factory intake manifold has very large flow discrepancies between cylinders. Cylinder 4 get 22% more flow than the other cylinders at certain flow rates and RPM.

The subaru factory ecu has a timing strategy for each cylinder. Some cylinders get upwards of 3 degrees less timing than the others.

true.

however, does jug #4 get MORE or LESS advance than the others?



i know the answer.

Since it is impossible to get individual AFR on all four cylinders due to manifold pressure, it is a good idea to do these types of flow tests or get 4 EGT probes for tuning sessions. Once you get it balanced out you can remove the excess components.

if your goal is to balance the 4 cylinders, you certainly CAN use a wideband in each runner, since the offset to wideband sensor output will be equally applied to each of the 4. the absolute output will not be "real" but the relative output definitely will be. obviously you're not going to get useful results from an oem header or other log type of manifold.

[modaddict]

Originally Posted by KitoAutoSport

something that I'd like to throw out there that many people over look.

The factory intake manifold has very large flow discrepancies between cylinders. Cylinder 4 get 22% more flow than the other cylinders at certain flow rates and RPM.

The subaru factory ecu has a timing strategy for each cylinder. Some cylinders get upwards of 3 degrees less timing than the others.

-Dominic

However, if it flows ~295cfm and a variance in cylinders, the heads flow ~225cfm (or something like that)....why does it matter that the intake flow's more.

Won't the "restriction" in the system be equal, if the piping to the restriction is almost the same?

So this "lean" condition would happen at partial throttle whereas you are not hitting the max cfm through the head. (an thus cyl 4 IS flowing more air?) maybe, our cyl 4 concerns are happening during part throttle, or "some" boost....but not WOT like most people tune at?

Food for thought....

[R & H Garage]

Originally Posted by ride5000

true.



if your goal is to balance the 4 cylinders, you certainly CAN use a wideband in each runner, since the offset to wideband sensor output will be equally applied to each of the 4. the absolute output will not be "real" but the relative output definitely will be. obviously you're not going to get useful results from an oem header or other log type of manifold.

that would sound right, however, I dont believe wide band sensors have enough range.
For example, the factory sensor will read 11.1 when it's actually 13:1 under boost. So if you were actually 11.1 under boost.. the sensor would likely read much lower than 9:1, which is out of the range of most wide band sensors and displays.
At least that is how it seems. I'm not calling this factual. Just more food for thought.

In regards to the more or less timing scheme, if you are using the open source definitions found on enginuity, you may be incorrect. The map says TRIM and shows various points of timing. It has not been tested to verify whether it's a negative or postive trim.

As for cylinder flow rates, 225cfm per intake runner is taken at 28" of water on most flow benches. The flow rates are obviously higher at boost pressures. As flow rate increases, flow restrictions also increase.
However, modaddict, you have an excellent point and I would have to do more testing to see if there was still a large flow discrepancie at the head and not just at the manifold.
I think we could probably get that set up on our flow bench.


another hijacked thread.
sorry.

-Dominic

[STi_Guy04]

Good information, I also seem to think that this could be a part throttle issue.. when I was racing and blew it up, I was under part throttle about 1/2 the time, makes me wonder how

also, If i had an injector o-ring failure wouldnt I hear, or Smell fuel Pissing out into the atmosphere

[Tea cups]

Originally Posted by KitoAutoSport

In regards to the more or less timing scheme, if you are using the open source definitions found on enginuity, you may be incorrect. The map says TRIM and shows various points of timing. It has not been tested to verify whether it's a negative or postive trim.

The Enginuity definitions for per cylinder timing comp do not designate it as "trim". There's no ambiguity involved -> positive and negative compensation is represented and there no uncertainty on this point. What has not been confirmed in testing is which table corresponds to which cylinder, although it is strongly suspected that the tables, as defined, A-D correspond to cylinders 1-4.

[ride5000]

well, i can confirm that on an a4tc400 based rom, A = 1.

i know beyond a doubt because that is the monitored cylinder in utec logs.

[Tea cups]

Originally Posted by ride5000

well, i can confirm that on an a4tc400 based rom, A = 1.

i know beyond a doubt because that is the monitored cylinder in utec logs.

Yes, we originally figured out A=1 because 'ignition timing' via SSM is for cylinder #1 (per factory manual) and this is how it was first realized that there was always a ~ 2 degree difference (up to the disable RPM) between logged timing and base timing map + advance map for USDM 16-bit ECU (no knock).

[R & H Garage]

Originally Posted by Tea cups

The Enginuity definitions for per cylinder timing comp do not designate it as "trim". There's no ambiguity involved -> positive and negative compensation is represented and there no uncertainty on this point. What has not been confirmed in testing is which table corresponds to which cylinder, although it is strongly suspected that the tables, as defined, A-D correspond to cylinders 1-4.

I stand corrected.

Any intention of figuring out just what cylinders are B, C and D?

2 and 4 had the most flow on the bench.

[Tea cups]

Originally Posted by KitoAutoSport

I stand corrected.

Any intention of figuring out just what cylinders are B, C and D?

2 and 4 had the most flow on the bench.

I'm open for suggestions. Perhaps someone with a 4-channel EGT.

[R & H Garage]

timing light maybe. with the optical pickup vs the inductive.
set the timing at 10 degrees and look for disparity between the cylinders.

we can make our own timing marks if needed.

[Element Tuning]

Originally Posted by ride5000

phil, do you have any comment on the altitude change?

does the hydra have a barometric pressure sensor? if so, what are the compensations applied to the maps based on that sensor?

The Hydra does not come equipped with a barometric pressure sensor so as you go up in altitude it will run a richer AFR or if you are tuned at high altitude and you go down it will run leaner. You can however install a GM barometric sensor into one of the available "IOs" and if you pull the menu options down you'll see you can select this. I've never used it but I know one of the long time MR2 Hydra tuners uses it on his car in Colorado.

Thanks,
Phil
www.elementtuning.com