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I've been looking at the 2021 Hatchback. There are 4 trim levels. All 4 have the same engine, same bore/stroke, compression, boost, displacement, redline, but LX/EX trim are rated 174hp CVT only and Sport/Sport Touring are rated 180hp and 6MT/CVT choices. The former are 31/40/34mpg and the latter are 29/35/32mpg for CVT models and the 6MT is a bit better 29/37/32mpg. And the 174hp say regular fuel and the 180hp say regular fuel but premium recommended. I guess they adjust the timing or something to get the extra 6 hp. I wonder if you run regular if it drops back to 174hp.

Anyway, anyone know what the difference is to get the extra 6hp? And why such a big drop in mpg? I presume the tires are a significant factor since the gear ratios are the same on all 4 trims.

 
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It's the knock sensor and the ECU tune. The sport/sport touring trims use the knock sensor and, based on knock count, can determine if you're using 87 or 91 octane, adjusting timing accordingly
and to answer your mpg question, there's not really a massive drop in MPG. Just did an oil change (and I use trip B to monitor that), I averaged 33.9MPG with a 60/40 highway/city split over the course of 8090.5 miles. It's all about how you drive tbh. My last few fill-ups have been in the 34.5-36MPG range

 
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Thanks for the input. I figured it was something in the computer side of things. Yeah, the 31/29 isn't too big a drop but 40/35 highway mpg seems like a big drop to me. It's all window shopping and wishing at the moment. Thanks again for replying.

 
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Any time. I should note that my car is tuned to approximately 215-220whp (had this particular tune since Jan 2021, previously had a "less powerful" tune since Feb 2019) and still getting that fuel economy.

I also found I get much better fuel economy running 91 octane than I do running 87 octane (my 2018 Sport Hatchback has seen a grand total of two 87 octane tanks since I've had it, and a 3 or 4 tanks of a 100/91 octane mix). When running 87 octane, the Sport/Sport Touring trims will run just like the LX/EX 1.5T models, when running 91 octane, that's when it adjusts timing and give it that extra hp boost. My understanding, at least.

 
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Thank you for the above info. I bought my 21 Polished Metal Sport Hatch, 6MT in Tomball, Texas, drove it home 2.5 hours north and a few days later when I needed fuel saw that premium requirement and was like why. Then I figured 10 gallons at 3.00 vice 2.60, the difference is 4 bucks.....so stop being so cheap. Was curious as to why though. The owner's manual only references wheel size. Thanks again.

 
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the wheel size thing in the manual is a roundabout way to tell everyday people which engines like premium fuel over non-premium fuel. Sport/Sport Touring/Si trims came stock with 18s and actually respond when they sip on higher octane fuels. LX/EX trims came with 17's (some with 16's I think) and don't really benefit from higher octane fuel. Not in the ways of horsepower, at least. Maybe from fuel economy, but I can't be sure of that.

With the Sport Hatch, I did a road trip experiment (so I could get everything on relatively constant speed/road grade) with 87 vs 91 octane on a stock tune. 91 got better fuel economy, by far, in comparison. 87 octane, my average fuel economy meter wouldn't go above 34mpg with my cruise control sitting at 83mph. 91 octane sat well above 38mpg with the same speed set and similar road grades. I ran 91 exclusively after that experiment, but now that I have a higher PSI tune (24psi max), I run 91 at an absolute minimum, sometimes getting frisky and doing a 100/91 octane mix