Should MBT then be tuned cell by cell then ?

Should we then be looking for a plateau in load or torque?

The ideal setting is then to leave it at just before the plateau?

Does this hold true when using meth as well?

Cell by cell @ loads you hit per rpm.

Keeping the variables such as BAT and IAT as close as possible is important because you really want to quantify gains from spark advance only and not let other factors skew the power levels.

It is pretty clear to see where power has been increased by the changes you made on a map so choosing the points (rpm cells) that have made a positive difference in power is just an exercise in picking out those values and finalizing them.

I'm pretty comfortable saying that if you hit 2.5 load @ 6500 rpm and have a finalized timing value... e.g. 18*, 2.4 load @ 6500 rpm will also comfortably run 18* of timing (possibly more assuming you are commanding the same AFR).

I find that there is a bit of leeway before you start to lose power... sometimes as much as 2*, so I would let power plateau, use the lowest value in which that happens and back off a * or 2 for a case of a shitty tank of gas etc.

Okay did some calling around:

Yes, if must be tuned cell by cell to see the proper gains made at each RPM instance. As the computer interpolates which value to use between specific RPM ranges you want to see specific results for specific changes.

We are looking for peak torque output as the computer uses load as a reference calculation and its not directly related to torque output at the wheels.

Yes the tune should be left at the settling as close to the beginning of the plateau that the computer can command. This allows the most torque to be produced as well as the largest margin of safety.

Regardless of fuel the engine should be tuned the same way. Changes in the fuel mixture will require a different timing curve.

The last piece of the puzzle is then what are he EGT temps at MBT. Once we know this you use EGT as a monitor to verify the tune on the street and the track. EGT values higher or lower than what is expected given current weather conditions should be investigated as a possible mechanical issue.


Back to the ringland issue, how long can the pistons sustain the temps produced at MBT? This is where I will follow up with data and time logs from the track. Using ATR we can determine how much time and therefore heat it will take to crack a ringland. This data should allow all of us to tune safer depending on our intended use of the car.

After that is determined we can see if additional cooling will allow us any headroom. It may get to a point that we will just have to address the ring gap in order to continue. At least I see that being true for track applications.

I have a feeling though the coolant and water temps will be lower on the dyno than at the track. This is due to the "duty cycle" of the motor since it needs to be shut off to upload a new map. Where as at the track the motor is running WOT every few seconds. To this affect I wonder what the balance will be for cooling, will an oil and tranny cooler with an upgraded rad allow for enough safe track time to run out of tires and fuel. It should also be noted that at what temps is it time to pull off the track and allow for some cooling.

So you are going to tune to MBT then take that tune to the track? I don't know how much value there is in that, I would be Suprised if you didn't blow a ringland after the first afternoon session doing that.

Zigatapatalka

That's the idea, I want to see how much heat the motor can take before I crack one.

Or rather once MBT is found how much should one dail it back to be safe.

Example: tune for MBT, dial it back ~4* run a time attack weekend. Compression test. Increase timing do another weekend compression test. Rince and repeat until I crack it.

I will donate/lend you one of mine, if not 2 of my egt gauges [might need a new probe for my old pro-sport one] to do the testing...

hammer out a procedure here with the guys and we'll go from there.

Do you have a way to monitor oil temperatures as well as coolant temp? Those are as big a part of the equation as the timing.

I agree the ring gap is small, but I don't know that if it was my $ I would pull the stock pistons, regap the rings and reinstall. If I am pulling the pistons I am going to slap some 2816 pistons in as well and call it a day.

Zigatapatalka

Yes I have oil and water temperature gauges. I'm debating on a trans temp as well.

Does anyone suggest multiple EGT gauges? (Placement ?)

I think 1 at the collector should be enough or behind cylinder 3 as that one is know to be the hottest.

Ziggo I have a forged engine already. I just figure instead of just swapping out the stock one might as well learn something first.

Paul, I don't know you well enough to say this, but I'm going to anyhow. Don't sacrifice an engine / pistons like that on your own dime and time.

Hell, you may not even notice the exact point and temp that the ringland gives way and waste a great deal of $ and time.

I say that if we know this is an issue, @ the very least try to combat it and if that measure fails, we have an even better idea of how sensitive the engine really is to high heat.

If the water pump stops spinning, coolant stops flowing and becomes heat soaked.
You will still gain temps shutting the car off to load a new map at the dyno.

It's going to cost the same for me to machine a block with or without a cracked ringland.

I figure if we at least have an idea of what the safe limit is people can play within it. Building a motor is a big expense and not for everyone. I would hate to see people have to sell their car because they can't afford a build or to fix it. Especially with all the work the Nator community's put into modding the cars. I also don't want people to be scared of the track either. Adjusting the tune for the track is far easier then re-ringing the motor. Mind you re-ringing can be done in a day we have done that before but I would prefer not to have others go through that.

The way I see it other than some dyno time, it won't really cost me anything.

Would it be better for me to open the gap on the stock pistons then try to break them?

I'm open to doing that too.

105k, Stock K04, 33% E85 mix. Massive oil usage due to failed PCV and Turbo seals. 189, 70, 137, 188 compression

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I REALLY think opening up the OEM gaps , even if only the top, would solve the issue. At the least a very interesting experiment. That's just me though.

http://mail.netsecurenow.com/img/bui...oemringgap.jpg

Those are for the OEM application and we are generating 2x WHP and a lot more heat. I'll let ziggo do the maths for how much more heat is generated at 2xhp.

so typical forged piston ring gaps for turbo induction street are:

top .017
2nd .019

I wish I had measured my actual OEM gaps but assuming they were within spec opening them up to say .012 and .019 respectively would do wonders in allowing for thermal expansion. Really the OEM top gap is the issue more than likely. at .017, the oem 2nd gap isn't bad if it were at max spec.

But that is really a LOT of work for an experiment. lol

Provided my rings are good would you think I can reuse the current rings just open the gap or should I get new ones ?

I don't mind going the work. If it brings us closer to BMW smackdown so be it.

Hmm this has me all worried now cause this can happen regardless of what turbo/fuel we are running. If I get another beaner, I would like to run it on crappy gas with a tune that can handle 30+ minutes of canyon/track abuse. Should I go ahead and upgrade my radiator and oil cooler?

Sent via oil leak.

Looks like every cracked piston posted thus far has been cracked on the exhaust side.....

IDK man, again thats a ton of work no matter how you slice it. I do wonder if there is more chance of chipping the ring coating during a filing session after they have been used and heat cycled 1000s of times?

beyond that, I would just keep the rings in the same bore/location and file them down.

I suppose if your end goal is to always run OEM pistons this is a worthwhile endeavor.

and genwan pistons...right?

maybe mazda's design change was two fold. Better atomization of fuel for all the reasons implied, and better piston cooling/lubrication by removing wall wetting on the exhaust side.

If @breakfasteatre; ends up having a cracked one, he's a molestialpu.

well ban his ass if he ruins our genwan failure streak!

We gave a piston ring grinder. I essentially have next to a full shop at home. If I chip the coating and it breaks oh well I guess. My end goal is to run the forged engine. In the meantime this could be a worthy test to save others some money. The work can be done with the motor still in the car.

I think an oil cooler and the fan mod would be the end solution as well. If sure most people if faced with a build or a re-gapping would choose the gapping.

That brings back Justin's point a page ago.

If adjusting the gaps seems to solve it then we can relate this to a heat issue. I think its the exhaust side because that is the hotter side of the piston. I may then try the larger gap with oil cooler and see if that makes a difference.

If not then we can try something else.

I just want to go back to the fuel between the piston rings. Genwon having more road time, we can't limit out the possibility that pu's won't start having the issue as well more often, however genwon pistons have more shearing, hence the design change. If after tracking/ heat build up it is causing detonation of fuel between the rings could explain why the pu's are not having this as often.

I had no oil usage before tracking at VIR, which is a fast hard on track. I know my turbo seals were bad, but its possible the lands were cracked then and took 5k to deteriorate to the point they were.

sorry...must have missed that...just been skimming over the thread trying to catch up.

valid point none the less...we'll see if that canadian ruins the genwan failure streak.

For reference...this is alex's thread...

http://www.mazdaspeedforums.org/foru...ighlight=faggy

This is a correct observation and it is the common place for a lot of engines to crack ringlands. Subarus crack them in the same spot and I think we share some of their failure modes. It won't be a bad time to see what they've come up with. However surfing through forums like that can be a time waster.

Anyways, digging through my piston collection and examining the ones I have several things stand out.
- There is a lot more oil reside on the exhaust side of the piston. This can indicate the piston runs hotter one the exhaust side or that there is less oil flow on that side of the piston. Either way, this will result in the piston running hotter on the exhaust side.
- There is more piston to wall loading against the exhaust side due to the power stroke applying the highest force in the cycle. More force = more friction, more heat = more stress on that are of the ringland.
- We don't have anti-detonation grooves and we have oil cooled cast pistons.
- There is a flow imbalance in the stock intake manifold which can point to which piston is likely to fail first.
- We have single knock sensor. Its placement can favor "hearing" knock from certain cylinders.
- In the OEM configuration and COBB OTS maps, the knock sensor is turned off past 5700RPM.


So there are a few things at play here that probably contribute to the ultimate failure:
- The brittle nature of the stock pistons does not help.
- These motors experience a good amount of detonation in their lives. All engines detonate. Some more than others and detonation damage can be cumulative.
- Heat not only contributes to possible ring gap issues (which I am not sure of just yet as being the culprit) but it also contributes to detonation. Engine heat can cause detonation through hot spots just as air charge heat can cause detonation.
- The exhaust side load, extra heat, and fuel being injected against that wall probably make that area a nice place for detonation to occur and chip away at the piston.

The pistons just as the rods probably have a limited cycle life under certain conditions. So what can one do?

- Get a safe tune. This has saved many rods and it can do similar things to pistons. Be weary of detonation.
- Cooling and more cooling. Air charge cooling and engine cooling are a must especially if the car is run hard.
- Recognize the limitations of your setup, engine, and conditions.

http://www.mazdaspeedforums.org/foru...1&d=1363374459

http://www.mazdaspeedforums.org/foru...1&d=1363374459

http://www.mazdaspeedforums.org/foru...1&d=1363374459

Hope you didn't take that the wrong way, just noticed that was glanced over and you both made excellent points.

Would washing the bore cause excess friction on that one side of the ring?

In combination with what Alex pointed out, more force being placed on that side of the piston, it sounds to an untrained person like me to be pretty strong evidence for some fail.

It would cause excess friction by washing the oil off of the cylinder wall. So, maybe that has something to do with the GenPu piston redesign.

Our engines are a perfect recipe for detonation and I think that may be part of the problem as well. We run a lot of boost pressure, our static compression ratio is considered high (especially in a turbocharged application), and we run pretty aggressive timing advance. Now if you wash all of the oil off of the cylinder wall with fuel, you've created a situation that offers little to no lubrication at the time it is needed most. Our stock tunes also target AFRs all the way down to 9.8:1... If we do have a problem with fuel washing the cylinder walls, that certainly isn't helping the situation.

Pull my head and pistons and check them out during the epic meat in april? lol

Yes.

I'm down.

FWIW...Dave and I never ran unsafe tunes. And we never blew. There's a bit of difference...

There's crack ringlands causing low compression and making no more power, so we build, discover and share observations...so as to mitigate issues going forward...

vs.

Improper maintenance, unsafe tuning, disregard with NCE...WOT all day everyday...fuck yeah...then zoom zoom boom, and btw, bad ringlands too...herp derp...

If you look at the piston crowns and skirts in the pics I posted, you can see a couple interesting things:

1) Detonation is apparent on BOTH sides of the pistons, under the valves. It becomes less apparent as you move towards the center of the cylinder. This just shows that detonation, alone, may not be the biggest factor.

2) The piston skirts are worn slightly on both sides, but the wear area on the exhaust side is much larger. This lends credibility to two hypotheses: a) the combustion processes are loading the piston unevenly, pushing the piston into the wall, and/or b) there is less lubricity on that side of the piston.

2a - just my thoughts, here: this may not be a very significant factor, because we have a centrally located spark plug, and we have close to biymmetry in the combustion chamber, and almost (b/c flycuts) perfect symmetry in the piston crown (gen1). The in-cylinder fuel mixture distribution may be at play if we think this is occurring and is a significant factor. But (this is now just my constant stream of thought, please disregard if unintelligible), that side of the combustion chamber should be richer without any sort of spray guiding system.

Hypotheses*

The loading against the exhaust side is simply due to the position of the crank during the power stroke. One side of the piston will always see more loading against the wall.

Also in your pictures I see a good amount more pitting on the exhaust side.

Lol, on my phone.

Mine tried as well, but was thwarted.

Is our wrist pin not offset to mitigate this as much as possible?

I have tracked the MS3 extensively in 95F+ degree weather in FL with oil temps in the 260s and have a different tuning strategy than Fobio for the track. I use the hardest possible pump gas map and add half a tank of race gas for safety. IMO if I am gonna blow I'd rather do it having fun than playing tooning Jesus on the highway.

Stock genwin pistons for about 16-18 track days and endless pulls. About 23-24 psi peak on the HTA3076 for about 25K of the 50k mils before the drop in.

At around the 50K mile mark dropped in Genpoo pistons with eagle rods. Done about 5 track days and also a fair amount of pulls at about 26-27 psi boot. Web cams / 5th port. On the track I rev to 7200 rpm in just about every gear change.
Stock ring gap.
About a month ago I ran a tune a lil too aggressive for the track and consistently displayed KR of about 2 to 3 toward red line on every gear change for about 20 mins. Nothing happened.

The failure rate on the ring lands on these engines isn't even close to significant. Low compression is not always a result of a cracked ring land. Most people who measured low compression didn't go through the trouble to do a leak down test.

Oh and btw Kmac made over 500 hp on stock pistons. Dturboman the same. Rod went and pistons were fine. If you ask me the stock pistons are made of kryptonite.

Alright, let's start with this. Everyone seems to be avoiding the possibility of detonation here. Why? That's probably the number one cause of broken ringlands, regardless of make/model/etc.

Even if you register no KR, is it not possible for there to still be detonation occuring? We all know that cylinder 3 runs leaner than some of the other cylinders. High boost, high compression ratio and a lean fuel mixture all add up to detonation. If we are seeing detonation ONLY on cylinder #3 for a period of time, what will that look like via the knock sensor? And to add to that question, where exactly is the knock sensor located on the block?

Or what about all of this part throttle knock that almost everyone experiences? While cylinder pressure may not be high, if the pistons are brittle enough, couldn't thousands of miles of small detonation events eventually break the ringlands? They must fatigue over time the more detonation they see. Or large detonation events during WOT runs and then thousands of miles of small detonation events on the now weakened ringland.

Another thing that I've noticed is the lean AFRs that everyone seems so fond of. Most other turbocharged platforms are running closer to 11:1AFRs. Here, people tend to want to run something closer to 12:1. Maybe this is another area to look into. Yes, it does cut into fueling headroom, but with an ethanol mix, I'd say we could cut down on a lot of heat in the combustion chamber by running a richer mixture. It has been shown that our cars pretty much don't give a shit about the AFR and are going to make similar power regardless. However, the opposite has been seen by some as well... Has anyone actually been on a dyno and adjusted AFRs to see how much power was lost or gained with different AFRs? I personally taper from 11.4AFR to 11.0AFR by redline and my power/torque did not change going from 11.4 to 11.0 after 5500RPM, but the only thing I have to verify that is virtual dyno.

Another fun fact: detonation can also cause bent rods. So, maybe these problems are actually one in the same. The rods may just happen to be the weaker point 9 times out of 10. Now that we have found ways to avoid bending the rods, the next weakest link is rearing its head. I understand that some of the "issues" I've brought up here have been written off by many, but maybe that is why we are still seeing failures so often. Detonation causes massive pressure spikes in the combustion chamber, and can explain both of these failure modes.

I'm just thinking out loud here, so if any of this sounds ridiculous, please speak up.