GR86 Premium MPG
 

Hi All,

This is probably a dumb question. So i have a 2018 Lexus GS 350 F Sport now. 311hp, curb weight of about 3800 lbs, and MPG is 19/27.

The new GR 86 premium is 228hp, curb weight is about 2800, and MPG is 20/27.

So how the heck can the 86 have the same(well, only 1mile more) MPG as the Lexus?

I'm gonna hazard a guess that the transmission choices of manual or 6AT make driving a pleasure, but leave a chunk of MPG on the table.
Whereas I'm gonna guess that the Lexus has a 10spd auto.

On the flip side, EPA estimates and real-world attainable MPGs are often worlds apart, but my experience with the 1G BRZ was that (even driven somewhat aggressively, or at the very least without a mind to hypermile) the BRZ/86 figures should be pretty easy to achieve (if not beat).

Not sure I'd make the same claim for the Lexus (can't speak from experience though).

Gearing, number of gears, and power curve can all make a difference. The current gen WRX STI has similar power to the Lexus and weighs 400 lbs less, yet gets 16/22.

The top gear on the Lexus is .59:1, which allows for better highway MPG. The manual BRZ is .77:1. Conversely, an auto BRZ has a 6th ratio of .58:1 and gets 30 highway MPG.

The lexus has a 6 speed auto if its AWD, 8 speed otherwise. I dont think this car is geared towards performance, more geared towards comfort.

the GR86 20/27 would be for the manual, as its geared aggressively for performance, and in 6th gear on the highway it spins at like 3000rpm wheres in the lexus im assuming in 8th gear on highway it spins at like 1500-2000rpm

the GR86 AT is 21/31 and it hink thats geared a bit more towards fuel economy.

you rev the crap out of the engines to get more power and the general public doesnt seem to realize that if you rev the engine out all the time your gas mileage will tank. The V6 has more power so it doesnt take as much effort to move a heavier car.

And a boxer motor tends to not be as fuel efficient as your typical inline 4 as well, (like say a Corolla's 2,0L with 168hp, which does something like 31/40)
Even subaru's most fuel efficient boxer motor is its most weakest motor (2.5L 155hp) and does something like 28/36

Thank you all! these all make sense! I was looking at the Gen 1 86 and it has better MPG. I totally understand the new 86 has increased HP, etc, so that makes sense MPG decreased. Planning to trade in the Lexus for a "performance" car with better MPG, that doesn't cost too much.

The 2.0L FB20 would be Subaru's most economy oriented engine at least for North America. The trouble is Subaru can't show off how fuel efficient it can be because every normal Subaru save the BRZ is AWD, so in essence the FB20 is somewhat handicapped. I genuinely don't think the boxer layout makes much of a difference as to how fuel efficient it is.

How much the automaker can invest in serious development is on the other hand what puts some engines well above others. The Toyota 2.0L Dynamic Force engine is actually astonishing in how much power it can put out while actually being eco focused. Its clear Toyota spent a lot of R&D to make this engine this substantial. Compare the FB20 in as close to equal terms with the rest of the 1.8L to 2.0Ls of its era(it launched in 2012) and it actually is pretty competitive even with the AWD penalty and if you wish to penalize the FB20 further its still efficient even with Subaru's ancient 5-speed.

Previously when Subaru had no Toyota partnership, they had only the EJ25 for effectively the whole lineup. I can definitely tell you that engine was not fuel efficient as it was an old design with none of the engine tech to get it anywhere its better funded competition. At that time buying a Subaru you acknowledged poor fuel economy vs. its competition so you could have the standard AWD.

I had a 2016 IS300 and the mileage was horrid. I'm normally at the top end of average when it comes to mpg, but I was always around 19-20 in the Lexus. Something about the tuning that Lexus does with the 3.5L w/premium fuel just sucks down fuel. I don't have my BRZ yet, but based off of comparison tests that I've seen, I estimate the BRZ won't be that much behind the old gen despite the EPA ratings.

Most cars nowadays are engineered to have the best possible mileage on paper. That makes for some questionable results in real world driving. With the BRZ it seems they did not care about the figures in the tests, which I really like. The real mileage from the few reports yet seem to be better than what the official figures suggest, which is quite the opposite of basically any other car.

Let me throw another variable into this equation. When the EPA tests a MT car, I believe it MUST use the shift points recommended in the owners manual. As you can see below, the 2022 manual suggest shifting from 1st-2nd at 12-14 mph and from 2nd-3rd at 18-23 mph. That corresponds to a 2,400-2,800 rpm shift point. For casual, “low-load” driving, that is not optimal for fuel economy. If you notice, the manual suggests shifting from 5th to 6th as low as 35 mph. 35 mph in 6th gear is about 1,500 rpm. The engine obviously has adequate power at that rpm.

Higher-rpm combined with low loads implies a very small throttle opening. A small throttle opening implies a greater intake manifold vacuum. A greater intake manifold vacuum implies higher pumping losses on the intake side. Higher pumping loses hurts engine efficiency and with that, fuel economy decreases.

The auto trans on the Lexus is probably programmed to shift around 1,600 rpm for the same type of driving, always keeping pumping losses low. If a Twin driver used lower shift points (1,800 -2,000?) in casual, around town driving, a Twin can a get better city fuel economy than it's EPA rating.

Highway fuel economy is mostly about drag and rpm. At steady speed, weight is not as much of a factor. If a Twin needs 20 hp to maintain 70 mph, that Lexus may need only 23 hp. Now the question becomes how efficiently the Lexus V6 can produce 23 hp. If that V6 operates at 1,800 rpm at 70 mph, versus 3,000 rpm for the Twin, it may have a significant advantage with regard to pumping losses. At 1,800 rpm, that V6 may have the ability to produce 23 hp on the same amount of fuel that a Twin's 2.4l engine produces 20 hp at 3,000 rpm. If the Twin cranked 2,000 rpm at 70 it would easily get 2-3 mpg more on the highway.

.

Though I agree with everything you said, it's quite interesting to me that my real world results on my gen1 have been quite contrary to some of what you're saying. When trying to drive gently and using lower shift points, yes, I tend to get good mpg (something around 29-32) with the kind of driving I have to do. When I have fun with it, I find that my mpg barely drops 1 or 2 at best. When I say fun, I just mean I give it solid throttle at opportunities I get and constantly run at higher RPM (often in a lower gear than I would be normally). Running at 3500 RPM on the highway seems to introduce pretty much no loss to my average mpg's, and I do this for a solid hour.

One of my theories that may have some truth to it, is this:

At lower RPM on the highway, for example, there is less torque. So to keep it at a steady speed or go up very gradual hills or anything like that, the gas pedal needs to be depressed further, opening the throttle more and sucking up more gas.

At higher RPM on the highway, I am sitting at more prepared torque. Keeping it at a steady speed feels much easier and just a gentle push of the throttle gets the car moving, theoretically requiring less gas is my guess.

So basically what I'm trying to say in all, is that whether I drive at a lower RPM or higher RPM, there's benefits with each, and I tend to get about the same average mpg's no matter what. So I stopped caring about driving like a grandma to work and started having more fun, only to result in about 28-30 mpg on average vs the 29-32 I would get when trying my hardest to conserve every bit of gas.

Common misconception, but rate of fuel flow isn't directly proportional to where the gas pedal is. It's also dependent on rpm. In general you will consume *less* fuel at a larger throttle opening, engine operating at higher torque at lower rpm than you will with a smaller throttle opening with engine operating at lower torque *but at the same power* at higher rpm.

As mentioned above, less pumping losses with a larger throttle opening (one reason diesels get great fuel mileage is that there is no throttle, it's just wide open all the time). Also at lower rpm frictional losses are reduced.

Driving within reason, yeah, you won't see much difference. But generally shifting sooner and staying in taller gears, with more open throttle will give you slightly better fuel economy.

Right, understood. As I said, I do agree with everything mentioned, as these are in fact... facts. It's just odd to me how I get little difference for a lot more fun from my experience. In any case, it's good information as I was not very aware of it before and just had my theories. :thumbup:

It's impractical to do an accurate experiment to determine how much fuel you'd save by short-shifting. The tank to tank variability in calculated mpg is gonna be greater than the difference you're trying to measure. You would have to drive the exact same route, with the exact same speed profile, under the same conditions (wind, temperature, rain, etc.) probably a hundred times to determine the actual effect on mpg. It's just not happenin...

True, but I drive a little over an hour to and from work every day. I take the same exact route every time. Aside from additional conditions like the weather, the rest is a wash for me. Because I'm either babying the car the whole way to and from work over and over or I'm driving it without care and stepping on it whenever I want to or running in lower gears as I've said. And in both these comparisons, that I have done, I tend to get only a couple mpg's difference on average. You're correct of course, the comparison it totally unfair. But the only comparison within those results that matters to me, is I'll take the fun and enjoyment aspect of the car for the loss of a couple mpg's over driving it like a granny just to save a couple bucks. So it's more of a personal comparison for me, more so than a true statistical one.