Octane?

My new regimen is 91 only on hot 100+ degree days and 89 otherwise.

I'd love to see you dyno it and see if there is a difference. Near the end of a 91 tank on a hot day, dyno it, and then next fill-up, get 87, and near the end of the tank on a day with similar temps, dyno that.
They shouldn't charge you more than about $25-80 per 3 pulls. That will save you money over the life of the vehicle if they can show you that the 87 isn't "costing you" anything.

Also bro...science!

Do it for the rest of us.
 
I'd love to see you dyno it and see if there is a difference. Near the end of a 91 tank on a hot day, dyno it, and then next fill-up, get 87, and near the end of the tank on a day with similar temps, dyno that.
They shouldn't charge you more than about $25-80 per 3 pulls. That will save you money over the life of the vehicle if they can show you that the 87 isn't "costing you" anything.

Also bro...science!

Do it for the rest of us.

I switched from 87 to 89 octane (91 for 100+ degree temps) NOT for HP or TQ or MPG gains. Lets get that out of the way.

I switched as to minimize the amount of instances where detonation occurs. Detonation will always occur and there's no way to avoid it. A higher octane minimizes detonation which is especially important considering the skyactiv engine is extremely high compression. Although Mazda has gone to great lengths as to minimize knock, it cannot eliminate it. No engine can. What helps a lot is the 4-2-1 header which allows us to use 87 safely within spec. The 2016+ Miatas do not have room for said 4-2-1 headers and they require the use of 91 octane. So I'm merely helping the ECU out here. Plus the whole skyactiv pulling timing during extreme heat thing I mean you have to give credit to Mazda for keeping us safe from detonation but I want nowhere near the edge the Skyactiv detonation protection zone. I want to be well within it.


I guess my question then for everyone is:

Does the Skyactiv ecu eliminate knock 100%?

Does higher octane help minimize knock for engines in general?

What does knock (detonation) do for a car under load (especially is high heat conditions)?
 
the new miata recommends 91 octane, not requires it... it is because it has more aggressive ignition timing and cam timings (the cams are different than all the other 2.0l SkyActivs)
Your MPGs might improve slightly with high octane gas, but what's more important is less fuel dilution of your motor oil... this is a known phenomenon with the SkyActiv engine... it's been tested over and over with proven results... you use cheap regular gas in it, the oil gets quite a bit of gas in it... use high octane? hardly any
 
I switched from 87 to 89 octane (91 for 100+ degree temps) NOT for HP or TQ or MPG gains. Lets get that out of the way.

I switched as to minimize the amount of instances where detonation occurs. Detonation will always occur and there's no way to avoid it. A higher octane minimizes detonation which is especially important considering the skyactiv engine is extremely high compression. Although Mazda has gone to great lengths as to minimize knock, it cannot eliminate it. No engine can. What helps a lot is the 4-2-1 header which allows us to use 87 safely within spec. The 2016+ Miatas do not have room for said 4-2-1 headers and they require the use of 91 octane. So I'm merely helping the ECU out here. Plus the whole skyactiv pulling timing during extreme heat thing I mean you have to give credit to Mazda for keeping us safe from detonation but I want nowhere near the edge the Skyactiv detonation protection zone. I want to be well within it.


I guess my question then for everyone is:

Does the Skyactiv ecu eliminate knock 100%?

Does higher octane help minimize knock for engines in general?

What does knock (detonation) do for a car under load (especially is high heat conditions)?

Horsepower and torque will show you when detonation is causing timing to be pulled. The dyno may not tell you the knock count, but the results of it will confirm or deny your opinion about it pulling timing with the 87 and not the 91.

KR is so advanced in current automobiles, especially ones managed as complexly as the SkyActiv family, that I feel you are ALWAYS "safely inside" the envelope.

Manufacturers do not design this vehicle to run on EXACTLY 87 octane in 72*F weather.
They design it to not go highorder if someone puts in some 87 that actually measures 85-86 and drives it through the grand canyon in summer.


ECU's pull timing to reduce knock to acceptable levels. The Skyactiv is no different. The more timing it pulls, the less power is made. It pulls timing until it's happy with what multiple sensors "hear". Knock has very specific frequencies, and sensors are tuned to it. back in the day, some sensors picked up various sounds (larger cams, louder valve-events, etc.) as knock, and were exchanged for less sensitive one's (LT1 guys installing LT4 KS's). As time as gone on, it's gotten so sophisticated, that the only REAL difference is that the car is pulling a little power. You won't ever hear detonation. You won't ever feel it. You will just play the placebo game with the 2-5bhp that is actually missing.

LS1 cars heat-soak BAD. You could lose several mph on a pass if you heat-soaked the LS1 car. You still never felt it, even on the drag strip. It just shows up on the time clock.

Under WOT, up a hill, towing a trailer, yeah, you could probably trim more than 8bhp off the output. B ut really...why don't you just use a little less gas pedal, or not stress about it and let it pull the power? who cares?

I guess my thing is, there is no difference in performance or longevity that I've ever contemplated that is worth the price-per gallon of running ANYTHING other than 87 in my CX-5. I've tried ethanol-free, I've tried 93, I've never seen a bit of difference in any way.

*I use LS1 cars as a basis, as that's my main experience, is with GM's LSX series motors
 
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the new miata recommends 91 octane, not requires it... it is because it has more aggressive ignition timing and cam timings (the cams are different than all the other 2.0l SkyActivs)
Your MPGs might improve slightly with high octane gas, but what's more important is less fuel dilution of your motor oil... this is a known phenomenon with the SkyActiv engine... it's been tested over and over with proven results... you use cheap regular gas in it, the oil gets quite a bit of gas in it... use high octane? hardly any

Hmm even more incentive to move up from 87 if the fuel in oil thing is consistently true. Although people do a smell test it would be interesting to see oil analysis showing fuel levels in it.

Going back to the Miata timing thing hey good catch. The Mazda website says 87 is the minimum. It also says Recommended Fuel: Premium unleaded, 91 octane or greater. Wow that's a wide range. On the other hand folks are trying to say that the (US) skyactiv engines are designed with a very narrow scope of timing. Like its 87 and nothing else. Is it really that narrow in terms of non-Miata skyactiv engines's ability to adjust timing?

https://www.mazdausa.com/MusaWeb/musa2/pdf/specs/2016_Mazda_MX5_Features_Specs.pdf
 
Under WOT, up a hill, towing a trailer, yeah, you could probably trim more than 8bhp off the output. B ut really...why don't you just use a little less gas pedal, or not stress about it and let it pull the power? who cares?

You would be surprised to see how many Toyota Prius's try to race me up the I-8 from Arizona heading into California. Up the mountains. I need as much power from my 2.0 155hp engine while running AC. Go easy on the gas? Those Prius owners make it tough LOL!!!!

Okay jokes aside. Am I wasting a few bucks getting higher octane fuel even though I'm in the safe zone using 87? Likely so in most cases. Is there a placebo effect which makes me feel good about my Mazda which in turn improves my well being, my vertical jump, my confidence? Is it worth it for me? Heck yeah!!!

(in a corny douche guy hitting on chicks in a club voice) I like using 89 even though the manual states 87, because I like living on the edge baby.
 
You would be surprised to see how many Toyota Prius's try to race me up the I-8 from Arizona heading into California. Up the mountains. I need as much power from my 2.0 155hp engine while running AC. Go easy on the gas? Those Prius owners make it tough LOL!!!!

Okay jokes aside. Am I wasting a few bucks getting higher octane fuel even though I'm in the safe zone using 87? Likely so in most cases. Is there a placebo effect which makes me feel good about my Mazda which in turn improves my well being, my vertical jump, my confidence? Is it worth it for me? Heck yeah!!!

(in a corny douche guy hitting on chicks in a club voice) I like using 89 even though the manual states 87, because I like living on the edge baby.

Well if that's how you feel about it, then the only thing I disagree with is what I highlited in red. If you can afford it and you like it? In the words of my friend's kid " Yeah! **** it daddy, why not?"

*In all cases, I'm more than willing to bet (and so is Mazda, considering what's on the fuel door...)
 
...what's more important is less fuel dilution of your motor oil... this is a known phenomenon with the SkyActiv engine... it's been tested over and over with proven results... you use cheap regular gas in it, the oil gets quite a bit of gas in it... use high octane? hardly any

What's your source for this info? As a long-time SAE member who's been wrenching even longer, I'm struggling to see any correlation here.
 
I'd love to see you dyno it and see if there is a difference. Near the end of a 91 tank on a hot day, dyno it, and then next fill-up, get 87, and near the end of the tank on a day with similar temps, dyno that.
They shouldn't charge you more than about $25-80 per 3 pulls. That will save you money over the life of the vehicle if they can show you that the 87 isn't "costing you" anything.

Also bro...science!

Do it for the rest of us.

Here is the DYNO results in this PDF. Test resulted in 3.5 hp GAIN between the 87 and 91 octane on the Mazda Skyactiv 2.0l motor...

or a difference of 2.36%..
(birthday)

Apply the same 2.36% increase to 184 hp, and you get 188 hp... it is there for you if you want it...http://publicaffairsresources.aaa.biz/wp-content/uploads/2016/08/Premium-Fuel-REPORT-FINAL3.pdf
 
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I'll keep the extra $5/tank, thanks, lol!

You are very welcome! I figured you would enjoy all the hard scientific data too!(usa)

Here we don't have a $5 difference in CA, usually only $.20-25cents diff so with a 13 gallon fill up here it is only about $2.80-$3.25 diff in a tank of 87 vs 91
 
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I'll keep my 93 here in high temp, high density altitude San Antonio.. even before I was 93 tuned.
 
Here is the DYNO results in this PDF. Test resulted in 3.5 hp GAIN between the 87 and 91 octane on the Mazda Skyactiv 2.0l motor...

or a difference of 2.36%..
(birthday)

Apply the same 2.36% increase to 184 hp, and you get 188 hp... it is there for you if you want it...http://publicaffairsresources.aaa.biz/wp-content/uploads/2016/08/Premium-Fuel-REPORT-FINAL3.pdf
Thanks for finding this AAA Premium Fuel Research report. I guess this conclusion from the report should summarize it all:

Inquiry #1: Does an engine designed to operate on Regular gasoline produce more horsepower when operated on Premium?

4.2 Findings: Maximum Horsepower
The vehicles tested did not produce more horsepower when using Premium gasoline. While some differences were recorded when comparing Regular to Premium fuels, they are very small, and are within the expected differences in run-to-run variation for maximum horsepower testing. The data collected does not support any conclusion that Premium fuel allows a vehicle designed for Regular to produce more maximum horsepower.

My biggest question is why the "real-world" horsepower is only about 80% of the rated horsepower on paper? The 3 test-runs for maximum horsepower on Mazda3 Grand Touring 2.0L I-4 which has horsepower rating at 155 @ 6000 rpm are 126.28/126.79/126.54 hp with 87-octane regular fuel and 129.78/129.25/129.52 hp with 93-octane premium fuel. This happens on all 3 test vehicles, a Tundra 5.7L V-8、a Charger SXT 3.6L V-6、and a Mazda3 Grand Touring 2.0L I-4. Why the discrepancy is so huge? (uhm)

So mazdadude, you won't get 188 hp with your 91-octane premium in reality, you can only get 152 hp at most from your 2.5L! (boom08)
 
You are very welcome! I figured you would enjoy all the hard scientific data too!(usa)

Here we don't have a $5 difference in CA, usually only $.20-25cents diff so with a 13 gallon fill up here it is only about $2.80-$3.25 diff in a tank of 87 vs 91

Oh, I was quoting 93 octane, since that's what your link was about.
 
Non US 2.0 models get 163 HP running 91 octane. I wonder if Canada and Mexico gets the lower compression models like here in the US?

On another note as Unobtanium pointed out...87 gas may really measure 85-86 depending on the station and pump? If true a case could be made that getting 89 would provide a safe buffer in that it may measure anywhere from 87-89.
 
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Snip...
Your MPGs might improve slightly with high octane gas, but what's more important is less fuel dilution of your motor oil... this is a known phenomenon with the SkyActiv engine... it's been tested over and over with proven results... you use cheap regular gas in it, the oil gets quite a bit of gas in it... use high octane? hardly any

I'd be interested in reading more about this too. What's the cause? I'm familiar with the cause of oil dilution in diesel engines using bio-diesel but this is the first I've heard of it in gasoline engines caused by using different octanes.
 
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Non US 2.0 models get 163 HP running 91 octane. I wonder if Canada and Mexico gets the lower compression models like here in the US?

On another note as Unobtanium pointed out...87 gas may really measure 85-86 depending on the station and pump? If true a case could be made that getting 89 would provide a safe buffer in that it may measure anywhere from 87-89.

The safe buffer is already present. It's called your ECU.

This is craziness. Just buy 87 unless you are competing with someone in a dyno-test war.
 
I'd be interested in reading more about this too. What's the cause? I'm familiar with the cause of oil dilution in diesel engines using bio-diesel but this is the first I've heard of it in gasoline engines caused by using different octanes.

very simple... just like any other engine/car out there, the ECU's strategy to avoid/prevent/stop detonation under the right conditions (hot weather, high engine load), is to run the engine richer (increase injector duty cycle, reduce ignition timing)... since the SkyActiv is known to run in full closed loop ECU operation (knock sensor is utilized at all times), running high octane gas WILL allow the fuel mixture to be leaner, thus excess unburned fuel will not get "washed down" past the piston rings into the oil pan

oil analysis reports can be found on other forums that proves this
 
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