The turbo CVT is more fuel efficient than the non-turbo manual.
Barely. The turbo CVT requires premium fuel
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I wonder if you put premium fuel in the non-turbo manual that it would be as fast as the turbo CVT? Can someone get on that? ![Wink ;)](https://www.autos.ca/forum/Smileys/CarTalk/wink.gif)
1) Get your facts straight - the 2014 Forester XT does not REQUIRE premium; it recommends it. I.E. it will work, and will not harm the engine, if you use regular grade fuel. Just no e85 sh!t.
2) Do you understand what premium fuel is/does? The higher the octane, the more compressible it becomes. So all that premium fuel does is retards the combustion of fuel at higher pressures. Since the FB25 dopes not have a high compression ratio, putting in premium fuel will do no better for fuel economy nor performance in this particular engine. The FA20 turbo has higher compression while in boost, which would benefit from the premium fuel. If you are not consistently flooring it though, you'd almost never have pre-mature combustion. Even if you did, on those occasions, the ECM would change valve timing to delay fuel release and combat the engine knock resulting from premature combustion.
Let me give it to you in simpler terms: The XT offers great performance with lower operating costs, assuming you drive it reasonably. Any turbocharged engine will suck fuel quicker when you have the engine in boost; however, if driven properly, the turbocharger is not often engaged, and the engine will act more like a 2.0L when it comes to fuel consumption (and lack of benefit for higher-octane fuel).
I think it's time we change the name of "premium" fuel - idiots are confused as to what it is. Let's call it what it is:
87 Octane - Normal. Use this.
89 Octane - almost never worth the cost, but oil companies would like you not to know that.
91 Octane - Only beneficial for turbocharged or high-performance engines with associated high-compression ratios. *Note on 91 pump - if you car doesn't recommend it, don't use it.
94 Octane - unless you're taking your car to the track, don't bother, even if turbocharged/high compression.
**Further note: Mazda's ridiculously awesome compression ratios may benefit from higher compression fuel, but does not require it, nor recommend it...so save your $.
The EJ25's (2011 Forester XT, which I have) compression ratio is something like 8.4:1. That's what it is while NOT in boost. The boost adds a maximum of another 11.5psi-ish of pressure to the cylinders while under wide open throttle. If you want to add more boost, you have to lower the compression ratio and use lower grade fuel so the fuel will combust more readily.
I think the stock boost of the FA20 (2014 Forester XT) is 4psi but has a higher compression ratio of 9.6:1.