I'll let you know after MikeM has a chance to respond. He knows more about this than I do.
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CX-9 Skyactiv 2.5L turbo engine
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I'll let you know after MikeM has a chance to respond. He knows more about this than I do.
Woodys2718
Member
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- 2016 CX 5 GT AWD, Tech & IActivesense
WOW... silenced and no debate, all I hear are crickets chirping...
dramatic reduction in timing, there is also a system in place that if the car has knock retard at high load it will extend that ignition retard for a long period of time even after the knock has stopped, reducing power throughout the entire RPM range. On top of that the ECU will sometimes add fuel, causing an excessively rich condition reducing power even further. Lets go a step FURTHER, Large amounts of knock is detected, combined with elevated exhaust gas temperatures, ECU limits ignition timing, retards it severely, enriches the fuel mixture to as much as 9.8 AFR and reduces throttle. How about further? high load, high temperature, high vehicle speed, excessive knock retard. Car goes "limp"...Throttle reduction, extreme AFR enrichment, extreme ignition drop (into negative numbers), and even shuts the engine off.
How about consistent knock retard over a period of time. The ECU records knock retard, makes a correction to the KCS value, the next time you are in that same RPM range and load, the ECU records again, Still some knock? further reduction of the KCS value, further limiting total ignition timing. Ignition timing is reduced, ECU records again, still knock? value lowered, lower, lower until you have hit the limit to ignition retard. This happens globally, non stop. Have you ever wondered why some days the engine just feels "tired" compared to other days? there yah go.
How about consistent knock retard over a period of time. The ECU records knock retard, makes a correction to the KCS value, the next time you are in that same RPM range and load, the ECU records again, Still some knock? further reduction of the KCS value, further limiting total ignition timing. Ignition timing is reduced, ECU records again, still knock? value lowered, lower, lower until you have hit the limit to ignition retard. This happens globally, non stop. Have you ever wondered why some days the engine just feels "tired" compared to other days? there yah go.
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It's way more than 25% for bridges and buildings. More like 100%. It works roughly like this. Steel design codes assume the steel is in the weakest 2% of the production run. Then, it assumes the loads are in the highest 2%. And to top it off, the allowable design stress is far below the real breaking stress for the steel. That's why when a building or bridge falls down, you know somebody screwed up big time!
A good structural engineer always stands behind his work - but never under it, according to my structural design professor. ;-)
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Wow, thanks for all the information. This confirms what I feared about the SkyActiv 13:1 compression engines on 87 octane. There are some serious detuning tables built into these engines. Mazda went super safe and added even more safety and then added additional safety just in case. The above proves this. The results will be a loss of HP and torque.
I felt it immediately when I used 87 octane, climbing a grade under load, the engine fell flat on its face. I downshifted and it pulled like garbage. It happened a few times, always when climbing grades, under load.
Then I stated using 91 octane and same grade under load, the engine pulled hard and I never had to downshift. Ever since I have been using 91 octane and the engine feels a lot stronger and doesn't fall flat on its face.
It's 91 octane for me. Well worth the few cents more.
Mazda did incredible stuff on Skyactiv no maker has ever succeeded in doing. They figured out a way to run 4-2-1 headers that scavenge hot gas allowing 13:1 on 87 octane gas. Problem was heating the cats to keep pollution within legal limit. They heated the cats quickly on cold start by burning gas mixture in the header and kept cats hot by folding 4-2-1 header and insulating it. They used the Miller Cycle to increase efficiency. They figured out a way to prevent carbon buildup on intake valves.
You won't pull timing if computer never senses serious knock. I hauled 2000# trailer across country on 87 octane gas and never heard knock or experienced a lazy engine. I've never experienced knock or lazy engine driving in the mountains of Colorado up to 13,000 feet. I have experienced knock in a 2000 LS1 Camaro running on 91 octane gas in the summer, so I know what it sounds like.
Usually you will never have conditions that serious knock is a factor in the CX-5. Towing west across Arizona (uphill most the way) in the summer, yeah, you might be pulling timing to prevent knock, but otherwise probably not. Mazda did a fantastic job.
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few things,
The computer can and does pull timing before the knock sensor hears it, that is the secondary (actually primary) knock sensing system these cars use. It's called an Ion Ignition system. They will pull timing during extremely low levels of knock before the sensor hears it. Exactly why we proved you want to use OEM plugs only. We showed, on the dyno, swapping spark plugs caused an immediate loss of 10 HP because it messed up the Ion System. We documented this on the Miata forum, and were first to discover it.
You don't hear knock. Everyone seems to think you can hear detonation, you can't. If you actually HEAR it, that means the detonation is pretty bad. You wont hear low levels of knock retard (a few degrees of ignition drop worth). If you hear it with your ears, it's pretty nasty detonation. 99% of the time knock occurs and you will never hear it with your ears.
"usually you will never have conditions that serious knock is a factor in the CX5"
have you ever datalogged a stock one on 87 octane? because you're wrong. As soon as the intake temps get hot it will start knocking and reduce timing. Not to mention the ECU pulls ignition for torque control. So I ask again, because you said it... have you EVER datalogged a stock vehicle and watched what really happens? Or?
All these "experts" who interject with their factless opinions is really really starting to get old and annoying.
Colorado is beautiful for just that, and where we are located, so we know quite a bit about high altitude tuning. The air is less dense here, less pressure. That equals less cylinder pressure, which equals less heat, which equals no knock
Mazda absolutely did a fantastic job.
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Things have been a little tense lately, just a friendly reminder that you might be on your way to be banned with that attitude.
I don't see your account tagged as "vendor" or "merchant" so you're probably not immune to the rules.
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few things,
The computer can and does pull timing before the knock sensor hears it, that is the secondary (actually primary) knock sensing system these cars use. It's called an Ion Ignition system. They will pull timing during extremely low levels of knock before the sensor hears it. Exactly why we proved you want to use OEM plugs only. We showed, on the dyno, swapping spark plugs caused an immediate loss of 10 HP because it messed up the Ion System. We documented this on the Miata forum, and were first to discover it.
You don't hear knock. Everyone seems to think you can hear detonation, you can't. If you actually HEAR it, that means the detonation is pretty bad. You wont hear low levels of knock retard (a few degrees of ignition drop worth). If you hear it with your ears, it's pretty nasty detonation. 99% of the time knock occurs and you will never hear it with your ears.
"usually you will never have conditions that serious knock is a factor in the CX5"
have you ever datalogged a stock one on 87 octane? because you're wrong. As soon as the intake temps get hot it will start knocking and reduce timing. Not to mention the ECU pulls ignition for torque control. So I ask again, because you said it... have you EVER datalogged a stock vehicle and watched what really happens? Or?
All these "experts" who interject with their factless opinions is really really starting to get old and annoying.
Colorado is beautiful for just that, and where we are located, so we know quite a bit about high altitude tuning. The air is less dense here, less pressure. That equals less cylinder pressure, which equals less heat, which equals no knock
Mazda absolutely did a fantastic job.
So how much horsepower will you RETAIN that would otherwise be lost just tooling around on a summer day, with 91 octane?
Serious knock will kill engine power that you call "lazy engine". I've never experienced "lazy engine" in the CX-5. Mazda's base design is great at preventing knock. Other/older cars I've driven, in hot summer and/or low octane gas, you can hear knock when you hit the gas hard (heavy load). I never hear that in the CX-5. It may pull timing, but its well controlled, and not noticeable, at least to me.
I wouldn't try to gain horsepower on a hot summer day with 91 octane gas. All cars lose hp on hot summer days because high summer temperatures reduces air density, and high octane isn't going to fix that. I would be more worried about causing engine damage due to serious knock ... if it were occurring. The only time I would run 91 octane in CX-5 would be towing, in extreme summer heat.
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- RDX Aspec Adv.
I've literally never experienced that. I think you're just hearing fuel injectors pulsing. I heard that all the time on my LS1.
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The tuner made it sound like 87 would get timing yanked regardless on a hot day especially.
If you understand the way the knock controls work, it does not take serious knock. These ECUs multiply knock retard, peak the ignition retard and hold it, like I said. If you experience 1 degree of knock retard in low RPM when you floor it you lose power all the way to the rev limiter. We have proven this many times (with dyno proof) and have documented exactly what goes on.
It does not take serious knock to lose a lot of power with these cars, all it takes is a knock event. 1* of knock retard at 2000 RPM and you will see easy 5-10HP loss at 6000. This isn't opinion we have proven this.
These cars knock often, low and high load, hot and cold. Mazdas base design is great at preventing a lot of it, but majority of it is tuned out by the calibration, and extremely aggressive knock control system. Just because you can't hear it, doesn't mean it does not happen. Put a pair of head phones on and listen to the engine, you will be surprised.
You may have not seen it in the other thread but this guy has been everything but resepctful, as far as calling me a snake oil sellsman. fake, inconsistent, fudged data, you name it.
We have a dealer in Saudi Arabia where we have tested some very extreme heat with these engines. While you will still lose some (as the ECU has maps that pull timing based on temperature alone), we still saw gains of 15HP and 20 ft lbs (I have the dyno sheet if you guys want to call me a liar) with ambient temps over 40* C. One problem you will notice is when it is hot, the more you floor it the faster you will lose gas compared to a cold day. This is because the ECU enriches fuel quite dramatically to maintain EGTs and cylinder temps.
The ECU has several EGT thresholds for different stages of fuel enrichment. 1000* EGT and it will run so rich the engine will may to misfire.
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Until proven otherwise, the shoe fits. Those were big claims, and many are still not convinced. You are knowledgeable, I'll give you that. I haven't called anyone; stupid, idiot, etc ... Chill out. Folks can disagree in civil ways, and learn from each other, nor not. I'm all ears on what knowledge you offer. Perhaps someday you'll convince us all.
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So until proven otherwise I am a snake oil sellsman? Let me ask you something. Where do you think I learned all this stuff??? The owners manual?? lmao...
From many sleepless nights burning my brain looking at code. One of these nights being that......
This is the type of fun stuff I do with ECUs every day.
scroll through our pics, see some of what we do...
https://www.ovtuned.com/pages/pictures
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Interesting. So on a hot summer day, 93 octane might be worth 20whp after the engine is heat-soaked? Wow.
