Gas requirement

[LH451]

Before I get burned, I did search for threads regarding what gas to use.

So I've been using 87 for my fill ups mainly because the dealer told me don't bother with 91 cause it won't change anything with the car and every forum I've seen where the skyactiv engines are discussed said the same thing. However, there was a post I found on a Miata forum talking about the skyactiv-g engines and someone replied on saying that the dual VVT on the 2 liter and the 2.5 will allow it to adjust to 91 and make more power. Not sure if that's true with our engines but apparently the 4 liter V6 on the Toyota FJ Cruiser does that because of dual VVT (goes from 254hp to 285 and torque increases from 270-291, hence why I'm a little skeptical).

Any thoughts?

 

[Chibana]

I just asked this same question a few days ago. I can say with certainty that the 2012 Focus I just traded in for my 2014 3 did adjust timing automatically to make more power on higher octane gas (we have 93 octane here in Michigan). The Ford Source Book specifically states this. Also, I believe it was in Road & Track where I read a response to a letter in their tech section where the editor stated that most recent-year cars will automatically adjust timing for higher octane. I would really like to know if that's the case with this car. The difference between 87 and 93 octane in my 2012 Focus was quite noticeable. I'm going to be trying 93 octane in the 3 soon.

 

[Pengaroo]

Ecu is mapped for running 87 octane so no benefit from using premium fuel. Now if we could increase the compression ratio from 13:1 to 14:1 that is used overseas....

 

[LH451]

Ecu is mapped for running 87 octane so no benefit from using premium fuel. Now if we could increase the compression ratio from 13:1 to 14:1 that is used overseas....

The 2.5 runs with 13:1 worldwide, its only the 2 liter that has 14:1 outside the US.

 

[npaladin2000]

Got a source? I haven't been able to find anything saying either way, except for the non-specific generic SkyACTIV references to 14:1 compression ratios. find it a little hard to believe the 2.5L is 13:1-only. Unless of course the reason is that it's only available in 87 octane markets. Asia also doesn't mandate 91 octane, and so they use 13:1 compression same as us, the SkyActiv-G 1.5L gets only 99 HP there, versus 115 HP in Europe using 14:1 compression. There's actually 4 SkyActiv-G engines, and my understanding is they're only related in conceptual design, they don't share most of their parts, not even the blocks, and all the bores and strokes are different.

I could see the 2.5L never making it to Europe: engines above 2L get taxed more based on displacement, which would make a 2.5L undesirable versus a smaller turbodiesel.

 

[Pengaroo]

Thanks for the correction! Yeah I misread that part.

I don't have direct source, but I guess people tested it with the 2013 models and so no difference in performance so who knows.

 

[LH451]

Here's the 2.5 in the top trim of the Mazda6 in Mazda's French site http://www.mazda.fr/showroom/mazda6-berline/prix-specifications/
under "motorisation" look for "taux de compression" it says 13:1.

If there's 4 what's the fourth one since there's the 1.5, 2 liter and 2.5.

The thread I saw regarding the skyactiv engines adjusting timing when one puts 91 was on miata.net where they were speculating whether the next gen miata will run on 91 or 87. One of the responses to that thread stated that because of the dual VVT on the engines they will adjust and make more power. The person that was saying this was basing it off the fact that his own Toyota FJ Cruiser has an engine with dual VVT and adjusted based on the fuel he put. If he put 91 on it, the engine put out 285 hp/291 lb ft torque while with 87 it put out 254hp/270 lb ft torque. Not sure if we can post links to other forums here but if we can I'll link it in.

 

[npaladin2000]

The "fourth" one is actually the first one that came out, the SkyActiv 1.3L 83 HP.

There's a difference between adjusting valve timing, which you can do dynamically, and changing the engine's compression ratio on-the-fly. I figure if these things could do this, someone would have found out by now. the 2.0L has been around for 2 years now, it went into the Mazda3 in late 2011. Basing "it" off of what some other manufacturer does with some other engine is...frankly completely idiotic. That's like assuming Android has a start menu because Windows does and they're both computers and all. Yes, I know they're actually operating systems, I was making a point.

In order to believe this I'd have to see 89 and 93 octane dynos from a reputable source, certifying that the engine is dead-stock, without any modifications. The guy with the FJ Cruiser, I can almost guarantee he didn't get 30 horsepower just from going up a couple of grades of gas. Heck, Mazda's only getting 5 more HP going from 13:1 to 14:1 and from 89 octane to 91. He's claiming 30, dead stock? I smell undisclosed mods.

 

[LH451]

Oh yeah I forgot about that little thing

That's where I smell something fishy cause there's no dyno maps/graphs or a reputable source like a toyota spec sheet. The hyundai genesis coupe with its turbo 4 only gets 5% more hp and torque when swtiching to 91 and like 3 hp with the V6 and both ratings are listed on spec sheets. Even then the 2.5 has more than enough power and its probably a little underrated too.

 

[npaladin2000]

Yeah, butt-dyno says more like 190-200 HP. I'd like to get it onto an actual dyno.

 

[LH451]

Yeah, butt-dyno says more like 190-200 HP. I'd like to get it onto an actual dyno.

I'd definitely like to see that too. There was someone who dyno'd a 2014 Mazda6 and got like 160-165 on the wheels with the auto. I'd have to find that sometime.

Edit: I found the stock dyno numbers for the 2014 mazda6, 163hp to the wheels. Might be a little bit better on the 3 being much lighter so hopefully someone will take their car to a dyno soon.

 

[TerryFrench]

2014 mazda6, 163hp to the wheels. Might be a little bit better on the 3 being much lighter so hopefully someone will take their car to a dyno soon.

A dyno will not care about the weight of the car, nor its aerodynamics. it's put the car on the big rolling apparatus, floor it, wait. So you get what the engine can deliver to the wheels, regardless of anything else.
The transmission might be different in term of programming and even ratios between the 6 and the 3, but the weight will not change the dyno readings.

 

[Chibana]

I think this is the article I was referring to at Road & Track:

http://www.roadandtrack.com/go/news/new-technology/premium-fuel-futures?click=main_sr

This is the paragraph that I find most interesting:

"If the engine is tuned for regular but fueled with something of higher octane, things are a tad more complex. Most modern knock-sensed ignitions seek MBT timing and thus, at least in theory, profit from the added octane. Some, though, have preset ceilings beyond which they won't advance."

So the question is whether or not in this particular case, Mazda capped the timing advance, and if so, how high? I tweeted MazdaUSA with this question, but I doubt I'll hear anything back. Maybe I'll see if there's an email address for some tech group I can try.

The article specifically calls out Mazda SkyActiv engines, too, but doesn't answer this specific question:

"Mazda's new SkyActiv engine family is exemplary of the trend for higher efficiency and also of marketing considerations. Direct injection, artful design of piston geometry and other nuances give our Mazda3s SkyActiv powerplant an octane appetite for regular; this, despite its 13.0:1 compression ratio. The Euro version gets an even loftier 14.0:1 with commensurate enhancements of power and efficiencybut also with a premium fuel requirement unwarranted for the North American market."

 

[LennyR]

There's a difference between adjusting valve timing, which you can do dynamically, and changing the engine's compression ratio on-the-fly.

Actually, it is possible to change the effective compression ratio on-the-fly. Honda does it with VVT in the Civic engine at lower throttle settings. In order to decrease losses caused by suction against the mostly closed throttle body (aka butterfly valve, which controls airflow) during the intake stroke, Honda holds the throttle body open a bit more at low power, then keeps the intake valve open past bottom dead center to push some of the combustible gas back out the intake manifold before compression begins. This effectively lowers the engine's compression ratio during low-power operation while also making it more efficient.

 

[LH451]

I think this is the article I was referring to at Road & Track:

http://www.roadandtrack.com/go/news/new-technology/premium-fuel-futures?click=main_sr

This is the paragraph that I find most interesting:

"If the engine is tuned for regular but fueled with something of higher octane, things are a tad more complex. Most modern knock-sensed ignitions seek MBT timing and thus, at least in theory, profit from the added octane. Some, though, have preset ceilings beyond which they won't advance."

So the question is whether or not in this particular case, Mazda capped the timing advance, and if so, how high? I tweeted MazdaUSA with this question, but I doubt I'll hear anything back. Maybe I'll see if there's an email address for some tech group I can try.

The article specifically calls out Mazda SkyActiv engines, too, but doesn't answer this specific question:

"Mazda's new SkyActiv engine family is exemplary of the trend for higher efficiency and also of marketing considerations. Direct injection, artful design of piston geometry and other nuances give our Mazda3’s SkyActiv powerplant an octane appetite for regular; this, despite its 13.0:1 compression ratio. The Euro version gets an even loftier 14.0:1 with commensurate enhancements of power and efficiency—but also with a premium fuel requirement unwarranted for the North American market."

This was a pretty good read. Don't think I'll be putting anything but 87 on my car.

 

[npaladin2000]

Actually, it is possible to change the effective compression ratio on-the-fly. Honda does it with VVT in the Civic engine at lower throttle settings. In order to decrease losses caused by suction against the mostly closed throttle body (aka butterfly valve, which controls airflow) during the intake stroke, Honda holds the throttle body open a bit more at low power, then keeps the intake valve open past bottom dead center to push some of the combustible gas back out the intake manifold before compression begins. This effectively lowers the engine's compression ratio during low-power operation while also making it more efficient.

Mazda already does something similar with exhaust timing to implement a pseudo-Atkinson cycle on the SkyActiv engine, according to my information. Besides, I'm not sure it's so easy to dynamically INCREASE the compression ratio.

Anyway, we can speculate to our hearts content here, but ultimately someone's going to have to stick a SkyActiv 2.0L on a bench and do some testing.

 

[Chibana]

This was a pretty good read. Don't think I'll be putting anything but 87 on my car.

Based on that R&T article, I'm actually thinking mid-grade (89) might be the best bet, especially if Mazda is cutting it close with timing on 87 octane. According to the Ford performance and tuning shop, FSWerks (formerly FocusSport), the 2012 Focus pulls timing on 87 octane gas, but still ends up making 5 to 10 hp more than Ford claims assuming typical FWD drivetrain loss. Going to 89 octane would give a bit of a buffer for that, and maybe eek out another few hp without a big price hit.

I've sent email to Mazda, and tweeted to their two main Twitter accounts to see if I can find out if the car will increase timing or if it's just capped at a certain timing for 87 octane gas. Even with the miles I drive, I will gladly pay the extra money for 93 octane if it means another 5 to 10 hp. Even with the miles I put on my car, the difference in price between 87 and 93 octane only amounts to a decent dinner for one per month.

 

[LH451]

Based on that R&T article, I'm actually thinking mid-grade (89) might be the best bet, especially if Mazda is cutting it close with timing on 87 octane. According to the Ford performance and tuning shop, FSWerks (formerly FocusSport), the 2012 Focus pulls timing on 87 octane gas, but still ends up making 5 to 10 hp more than Ford claims assuming typical FWD drivetrain loss. Going to 89 octane would give a bit of a buffer for that, and maybe eek out another few hp without a pig price hit.

I've sent email to Mazda, and tweeted to their two main Twitter accounts to see if I can find out if the car will increase timing or if it's just capped at a certain timing for 87 octane gas. Even with the miles I drive, I will gladly pay the extra money for 93 octane if it means another 5 to 10 hp. Even with the miles I put on my car, the difference in price between 87 and 93 octane only amounts to a decent dinner for one per month.

Keep us posted if they response, I'd like to know what you find out

 

[Pengaroo]

After reading through this thread http://www.mazdas247.com/forum/showthread.php?123815916-Octane-Rating/ the consenses seems to be that there is no power increase at all, and that there maybe a slight boost in mileage with higher octane but its not conclusive. The thread is in regards to the cx-5 but its the same 2.0 skyactiv engine.

 

[Ki||ian]

After coming from 2000 BMW 3 series that would automatically change the timing for the fuel rating I gotta say I'm gonna stick to 87 even if there is a 10+ boost in HP. In the BMW I supposedly would lose 15-20hp going with 87 instead of 91 but I honestly couldn't tell in daily driving or it just didn't matter too much. If you're going to a track day or another event that the 10 hp boost might help then yea, sure, but the increase in fuel price was just too much to warrant it for me.

Personally, going from an Auto to Manual was a big enough "boost" in performance simply being able to better control what RPMs I'm at going in and out of turns.