chiped apex seal question?
09-07-10, 11:08 PM
#1
My Motorsports
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chiped apex seal question?
I just had my newly rebuilt motor die on me because of a chipped apex seal. I’m trying to figure out if it’s something that I did or more from the company that built the motor for me. Little history on the motor. Motor originally died because of a bad bearing (120000.00 miles). Had it rebuilt. Did 1000 miles for the break in w/ no boost. Had the car tuned after that. Afr at 11 to 11.5. Car ran great. Running the stock twins with 13 psi, non sequential. 2000 miles later the engine goes again. Front rotor had the bad apex seal. Can any of you give me some feedback on what would cause this from your experience with blown motors? Any insight would be great appreciated!
09-08-10, 12:16 AM
#3
My Motorsports
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dont know what the brand of seals the company used. I know that they are the stock 2mm seals. I have the Power fc and the avcr. some more pics of the engine.
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09-08-10, 12:30 PM
#8
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the triangle part of the seal is the weakest, ergo when they break like that its a tuning problem, not a build problem
09-08-10, 02:41 PM
#9
I am the one who tuned it. arghx, If you don't recognize my name I'm part of chucks pfc tuning group as well. I will send you the map if you wish to see it. PM your email.
But what I can tell you all from the logs is load afr was 11.5 at low boost and worked its way to 11-10.8 at full load. Knock was in the 20s. Injector duty cycle was kind of high 93% peak.
Like he said he ran it fine for 2000 miles, part of which was a weekend of pure track time. With no problems at all. So if he ran lean then it was something mechanical that failed. And not the tune.
But what I can tell you all from the logs is load afr was 11.5 at low boost and worked its way to 11-10.8 at full load. Knock was in the 20s. Injector duty cycle was kind of high 93% peak.
Like he said he ran it fine for 2000 miles, part of which was a weekend of pure track time. With no problems at all. So if he ran lean then it was something mechanical that failed. And not the tune.
09-08-10, 02:48 PM
#10
My Motorsports
Thread Starter
Stock injecters and they were test when the motor was built. Do have a upgraded fuel pump with a resister. To keep it running on high. Fuel filter was changed a year or two ago
09-08-10, 06:32 PM
#14
I looked at the tune.
There isn't a whole lot of information to make any kind of definitive statement as to what caused the detonation which did this motor in. There were no glaring errors in the map in my opinion. I have no doubt it ran great on the dyno and during whatever other testing that was done. Unfortunately, something went wrong when the engine was pushed. Either there was a mechanical failure, more logging was needed to check the dyno tune under track conditions, or a greater safety margin could have been built in at the expense of at least some power.
Assuming there was no mechanical failure as the root cause, there are a couple things that could have been done to improve the safety margin in the tune. The most time consuming thing to do would have been to simulate track conditions with easy backroads driving first. Then take a lot of logs as air and water temperatures change. That's not always possible however. The following methods can be employed to increase the safety margin of a tune, in lieu of a gazillion hours of testing.
1. Overboost fuel cut. I think I'm in the minority on this one, but I'd rather hit fuel cut 20 times than overboost once. And I've hit it at least that many times in my efforts to get boost control dialed in with seemingly no ill effects. This engine used an external boost controller and fuel cut was disabled by setting boost to 2.00 kg/cm^2. For an overboost fuel cut around 13psi, the boost setting in the commander would be about .60-.65 kg/cm^2. That has to do with the factory MAP sensor calibration and the way the PFC calculates the boost pressure needed to trigger overboost fuel cut.
2. Retard the leading timing, keeping the trailing split the same. Even though the knock was low and there were no problems detected, retard the leading timing anyway--even when there seems no reason to. You do this "just-in-case" the engine can't tolerate conditions for which you have not tested.
3. Set split under boost to 15 across the board, over maybe 7psi or so. The map I saw for this car with a chipped apex seal most likely would have run about 12 split. It was uses a factory MAP sensor calibration which reads low and does not put the PFC in the correct load cell to calculate timing. 15 split increases the safety margin. It is a conservative strategy but it is not without precedent. From the factory the Rx-8 and the FC Turbo II use about 15 split under high load. In my experience it does cost power but more like 5 or 6 hp rather than say 20.
4. Adjust the air temperature timing compensation table ("IGN vs AirT" in settings 4). By default it doesn't kick in until 70C. You could set it up so it starts pulling timing at say 50C. Thus the more optimized timing values in the maps would still be used in street driving in cool weather, but in the summer or during track use the timing would be retarded. Having the faster responding IAT sensor can be helpful for this.
5. Adjust the water temperature timing compensation table ("IGN vs WaterT" in settings 4). This was already done in the map I saw.
6. Adjust the air temperature compensation vs load table (INJ vs Air Temp and Boost). This table can add more fuel at different air temperatures according to boost. I'm not 100% sure exactly how the PFC calculates the correction from this table, but it couldn't hurt to carefully modify it from the default settings.
7. Adjust the global air temperature vs fuel compensation map (Inj vs Airtemp in settings 2). The best way to get this adjusted is to have a lot of real world testing, but that's not fully possible unless you are a hardcore DIYer who does a lot of logging. You can still add fuel to the higher temperature boxes in the map though.
There isn't a whole lot of information to make any kind of definitive statement as to what caused the detonation which did this motor in. There were no glaring errors in the map in my opinion. I have no doubt it ran great on the dyno and during whatever other testing that was done. Unfortunately, something went wrong when the engine was pushed. Either there was a mechanical failure, more logging was needed to check the dyno tune under track conditions, or a greater safety margin could have been built in at the expense of at least some power.
Assuming there was no mechanical failure as the root cause, there are a couple things that could have been done to improve the safety margin in the tune. The most time consuming thing to do would have been to simulate track conditions with easy backroads driving first. Then take a lot of logs as air and water temperatures change. That's not always possible however. The following methods can be employed to increase the safety margin of a tune, in lieu of a gazillion hours of testing.
1. Overboost fuel cut. I think I'm in the minority on this one, but I'd rather hit fuel cut 20 times than overboost once. And I've hit it at least that many times in my efforts to get boost control dialed in with seemingly no ill effects. This engine used an external boost controller and fuel cut was disabled by setting boost to 2.00 kg/cm^2. For an overboost fuel cut around 13psi, the boost setting in the commander would be about .60-.65 kg/cm^2. That has to do with the factory MAP sensor calibration and the way the PFC calculates the boost pressure needed to trigger overboost fuel cut.
2. Retard the leading timing, keeping the trailing split the same. Even though the knock was low and there were no problems detected, retard the leading timing anyway--even when there seems no reason to. You do this "just-in-case" the engine can't tolerate conditions for which you have not tested.
3. Set split under boost to 15 across the board, over maybe 7psi or so. The map I saw for this car with a chipped apex seal most likely would have run about 12 split. It was uses a factory MAP sensor calibration which reads low and does not put the PFC in the correct load cell to calculate timing. 15 split increases the safety margin. It is a conservative strategy but it is not without precedent. From the factory the Rx-8 and the FC Turbo II use about 15 split under high load. In my experience it does cost power but more like 5 or 6 hp rather than say 20.
4. Adjust the air temperature timing compensation table ("IGN vs AirT" in settings 4). By default it doesn't kick in until 70C. You could set it up so it starts pulling timing at say 50C. Thus the more optimized timing values in the maps would still be used in street driving in cool weather, but in the summer or during track use the timing would be retarded. Having the faster responding IAT sensor can be helpful for this.
5. Adjust the water temperature timing compensation table ("IGN vs WaterT" in settings 4). This was already done in the map I saw.
6. Adjust the air temperature compensation vs load table (INJ vs Air Temp and Boost). This table can add more fuel at different air temperatures according to boost. I'm not 100% sure exactly how the PFC calculates the correction from this table, but it couldn't hurt to carefully modify it from the default settings.
7. Adjust the global air temperature vs fuel compensation map (Inj vs Airtemp in settings 2). The best way to get this adjusted is to have a lot of real world testing, but that's not fully possible unless you are a hardcore DIYer who does a lot of logging. You can still add fuel to the higher temperature boxes in the map though.
09-08-10, 06:33 PM
#15
So in conclusion... it sounds like the car ran well when it was tested, but perhaps going to the track was too much too soon, especially if boost, AFR, and temps were not closely monitored. That being said, the map could have had additional safety built into it. That would have undoubtedly costed at least some power.
And this is where the dynamic between the tuner and whoever owns the car comes into play. I can tell you from personal experience that it's hard to tell someone "I'm going to have you drive away today with power still on the table, even though I had no indication of knock or a lean condition. I could have pushed it harder, and on paper there was no reason not to, but I have decided to refrain from doing so anyway." Power brings immediate and obvious results. Safety margins are an intangible thing, hard to quantify and difficult to explain. And this is why tuning can be such a gray area. So many people think of it as a "good tune" or a "bad tune." Yet in so many cases highly competent people can disagree on what constitutes safe and proper tuning.
Ok end of lecture.
And this is where the dynamic between the tuner and whoever owns the car comes into play. I can tell you from personal experience that it's hard to tell someone "I'm going to have you drive away today with power still on the table, even though I had no indication of knock or a lean condition. I could have pushed it harder, and on paper there was no reason not to, but I have decided to refrain from doing so anyway." Power brings immediate and obvious results. Safety margins are an intangible thing, hard to quantify and difficult to explain. And this is why tuning can be such a gray area. So many people think of it as a "good tune" or a "bad tune." Yet in so many cases highly competent people can disagree on what constitutes safe and proper tuning.
Ok end of lecture.
09-08-10, 07:48 PM
#17
I really think the threat of "bad gas" is overblown. I get the off-brand crap all the time and I'm making way more power. It's not that you can't get a tank of lesser quality fuel (but still with the proper octane rating), but if normal variations in fuel quality are costing you a motor you have an insufficient safety margin.
09-09-10, 01:12 AM
#18
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I really think the threat of "bad gas" is overblown. I get the off-brand crap all the time and I'm making way more power. It's not that you can't get a tank of lesser quality fuel (but still with the proper octane rating), but if normal variations in fuel quality are costing you a motor you have an insufficient safety margin.
of course in CA we have 91...
09-09-10, 01:17 AM
#19
ha, I guess I'm not going to defend Cali gas. You know that Cobb Tuning (supplies tuning hardware for Evo, Sti, R35 GTR, etc) actually releases different maps for Cali 91 versus 91 found everywhere else? My point is that with a Power FC you have no knock control, so you can't expect the computer to bail you out if something goes wrong. Thus the safety margin is especially important when you aren't constantly logging all your runs to make sure everything is ok.
09-09-10, 10:09 AM
#21
My Motorsports
Thread Starter
Im sure the gas was fine. Some one mention to me that the lead coil might have been going bad and not let the primary spark fire correctly. Going to test them at room temp and arround 220f.
09-09-10, 10:43 AM
#24
I really think the threat of "bad gas" is overblown. I get the off-brand crap all the time and I'm making way more power. It's not that you can't get a tank of lesser quality fuel (but still with the proper octane rating), but if normal variations in fuel quality are costing you a motor you have an insufficient safety margin.
I tend to agree with this, I've seen one honest account of bad fuel from a station in the past 18yrs. I've seen more FD's lose engines to not enough fuel in the tank at the track.
~S~
09-09-10, 11:19 AM
#25
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ha, I guess I'm not going to defend Cali gas. You know that Cobb Tuning (supplies tuning hardware for Evo, Sti, R35 GTR, etc) actually releases different maps for Cali 91 versus 91 found everywhere else? My point is that with a Power FC you have no knock control, so you can't expect the computer to bail you out if something goes wrong. Thus the safety margin is especially important when you aren't constantly logging all your runs to make sure everything is ok.