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Discussion Starter #1
Quick question.

Did a quick search around here seeing if there is a way to reach the 14:1 compression ratio the non-US 2.0 liters have. I was simply wondering if it was either a thinner head gasket or a different set of pistons. Granted it could be something completely different, but if it was something simple it would be pretty sweet. At the same time though, I'm also thinking it could be more complex than that....like a whole different engine altogether lol.

Being a hot rodder at heart, I'm always tinkering around with ideas. For example, if I take all the bolt-ons and tunes available to us and get the 14:1 compression ratio, my only trade off is having to use premium (which I don't really mind) on the 2.0L.

Now...what if what made the non-US spec 2.0L have the 14:1 compression ratio works on the 2.5L? What kind of power would we expect then?

If I'm talking a lot of gibberish I apologize, maybe it's just too soon to ask these questions as the car is too new to assume that people have went into them and experiment.

I know most people have warranties to worry about also, but if the part that allows 14:1 compression ratio is a genuine Mazda part, shouldn't really have anything to worry about...might have to double check with my service department on this one.

Appreciate any feedback. I tried searching this but maybe I didn't search enough. To be honest I wouldn't be surprised if it was more complicated than I think especially the way engines are now.
 

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Curious as to why you consider that slight compression ratio is important enough to tear apart your motor to achieve a few ponies.
At the same time, you can tune the engine to achieve optimal air/fuel ratio, and even tune for 91/93 octane for essentially the same performance results without the huge hassle of compatibility and part availability.

Or maybe you just like tinkering with a wrench?
 

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Discussion Starter #5
Curious as to why you consider that slight compression ratio is important enough to tear apart your motor to achieve a few ponies.
At the same time, you can tune the engine to achieve optimal air/fuel ratio, and even tune for 91/93 octane for essentially the same performance results without the huge hassle of compatibility and part availability.

Or maybe you just like tinkering with a wrench?
It's more that I like tinkering. Also, yeah I can get similar increases with a tune, but saying you get everything you can out of the engine with just a tune and some bolt-ons is almost lying to yourself in my opinion. Granted, I can get 10 more from a tune, 5-8 more hp from an intake, etc...what about the 10hp from actual mechanical tuning? Sometimes, something like this can most likely help with bolt-ons across the board, maybe even increase gains from them by simply bumping up the compression a full point.

I'm just wondering if the item needed is already provided by Mazda as an OEM. If it's pistons, then it isn't worth it. I'm just curious because I've seen compression ratios go up a point by simply having a thinner cylinder gasket.

I don't know...maybe my thinking is too old school. :p

Maybe I should check back once everyone's warranty expires...
 

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With the higher octane gas available in other countries, they could handle the higher compression. Probably not for a U.S. spec engine, hence the lower compression here. Most likely, bumping up your compression would require a higher octane gas, to avoid blowing up your engine.
 

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Discussion Starter #7
Figured the 93 octane I have here in New England was good enough. Plus, there are pumps around here that offer 100 if need be lol.
 

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Figured the 93 octane I have here in New England was good enough. Plus, there are pumps around here that offer 100 if need be lol.
I think part of the confusion is the difference on octane measurement. In the US we use AKI, while the rest of the world uses RON. From wikipedia, "the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel." For example here in california we have 87, 89 and 91. That translates to 91, 93 and 95 in the rest of the world.
 

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It's more that I like tinkering. Also, yeah I can get similar increases with a tune, but saying you get everything you can out of the engine with just a tune and some bolt-ons is almost lying to yourself in my opinion. Granted, I can get 10 more from a tune, 5-8 more hp from an intake, etc...what about the 10hp from actual mechanical tuning? Sometimes, something like this can most likely help with bolt-ons across the board, maybe even increase gains from them by simply bumping up the compression a full point.

I'm just wondering if the item needed is already provided by Mazda as an OEM. If it's pistons, then it isn't worth it. I'm just curious because I've seen compression ratios go up a point by simply having a thinner cylinder gasket.

I don't know...maybe my thinking is too old school. :p
Even if it is something as simple as drop-in pistons, I still don't see the risk/reward trade off for an extra 10 bhp and 0.5 mpg improvement from a higher compression ratio. Warranty or not, I don't think you'll ever see that kind of experimentation with the Mazda 3 crowd - perhaps with the new Miata SkyActiv engine. If a Miata shop makes camshafts, that could be worthwhile swap for optimizing high rpm performance.

If you tune for premium octane, you can just run more advanced timing on the factory 13:1 ratio and have very similar power results since the engine will be knock limited with either compression ratio. In the older lower compression ratio engines, it was possible to reach maximum brake torque timing without any knock; thus, a higher compression ratio with aftermarket pistons yielded substantial power gains.
 

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Well if you ever figure it out let us know, I would be interested.

With a nice CAI, quality exhaust, and a tune we should see some better figures. Increasing the cr may be one more thing on the list, depending on the steps involved.
 

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It would be interesting to find out how Mazda made the same skyactiv 2.0 engine run 12:1 compression in the 2012-13 models with the old 4-1 header and regular octane, 13:1 in the 3 gen US Mazda 3 with the 4-2-1 header and regular octane, and 14:1 in 3rd gen non-US Mazda 3 running higher octane gas. Its possible to achieve higher compression by using a different thickness head gasket. These compression ratio ratings may also be stated based on when the cylinder reaches top dead center upon cylinder firing or varying VVT intake/exhaust function. For the latter, if you set the intake valves to slightly overlap the open period into the compression phase of the engine (towards the end of the valve air intake cycle and beginning of compression cycle), the amount of air that gets compressed is reduced as some escapes back out through the intake valves during the start of compression, thereby reducing the amount of air available for compression. In this case, ECU tuning could tweak this type compression ratio definition. I would love to find out how they do this, as it would then be possible to up the compression of one's skyactiv engine, and tune it to safety. If you run the right high octane gas, and tune the ECU accordingly, there is no reason why a US spec skyactiv 2.0 3d gen or 2nd gen (with the right header) can't be modified to 14:1, and gain a little extra power and MPG. If Mazda setup a 14:1 ratio with higher octane gas in other world markets using the same engine internals (and they did), reliability should be maintained.
 

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I would think specified figures would be based on static compression ratio.
But, it's possible they're specifying a dynamic compression ratio on the USDM 2.0l S-G, achieved by variable valve timing events, making all of the componentry the same between domestic and foreign variants of the engine. Seems like that would make tooling easier for Mazda and more cost effective.
 

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I would think specified figures would be based on static compression ratio.
But, it's possible they're specifying a dynamic compression ratio on the USDM 2.0l S-G, achieved by variable valve timing events, making all of the componentry the same between domestic and foreign variants of the engine. Seems like that would make tooling easier for Mazda and more cost effective.
Hi
 

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I think there is more difference than just the compression ratio. The Japan spec engine is a flex fuel engine able to run on E85. Is the US engine a flex fuel engine??
link with info about flex fuel ability for JDM spec? this would be huge for E85 tuning on these cars
 

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Discussion Starter #17
Well, it would be difficult to find out what gets the 14:1 here in the states. Not worth asking the people at the shop here at work since all they would most likely see are the US spec engines. Maybe someone out there outside the US took one apart. Pretty sure a few 3rd gen Mazda 3s have been wrecked already...

I look at manufacturers like a big box of legos. I mean technically the 2.5 could have the same block with a longer stroke (at least that's what I'm guessing since it gives up a few hundred RPM at the top vs. the 2.0), and a "stroker kit" can be done.

I'm still looking into this. Might hop into google and see what's out there.
 

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After doing a little digging, I discovered that skyactiv engines actually do use dynamic (variable) rather than static (fixed) compression ratios. So it seems the differences in compression ratio between models at some engine loads can be achieved by tuning, rather than hardware (eg. head gasket). The engine switches from a conventional Otto-like cycle with equal intake, compression, explosion, and exhaust phases to a Miller/Atkinson's like cycle which reduces the the compression phase and ratio by late intake valve closing like I described earlier. So the peak quote of 13:1 or 14:1 only happens at certain higher engine loads when power is needed, but not necessarily at maximum loads. I haven't been able to find out exactly where this maximum compression ratio occurs as some sources say its higher engine loads, while others say its not maximum loads, as this would be too high compression... However, there are plenty of sources which say that at lower engine loads (cruising or idling), the engine switches to the Miller/Atkinson like cycle which lowers compression ratio, and improves efficiency. This page provides some info on the Miller, Atkinson, and Otto cycles.
AutoZine Technical School
 
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I'd bet it's a two fold thing as ford does something like this on the Zetec motors. They had a 10:1 compression ratio on the Focus ST, and 9:1 compression and 9.6 on the zx2. The way they did this was mostly through just using a different head gasket thickness.
 
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