FR-S/BRZ MPG

[carbonBLUE]

Originally Posted by tranzformer

Most of the time going up mountain passes you have to pass slow moving semis and other drivers that are in the right lane. Might as well downshift and finish the pass properly. Probably more efficient instead of leaving it in 6th and bogging the engine down.

my celica hovers around 3k rpms on the highway and i rarely leave 6th to pass anyone, i use about 10% more throttle to pass someone, you probably wont need to downshift to pass anyone, but it will be more fun if you do..

theres a hill by my house thats a 15% grade on the freeway and i dont need to leave 6th to climb it either, i cruise at 70 and my pedal doesnt really move when i go up that hill...

lighter cars dont struggle as much up hills even though they are torque less wonders...

[Allch Chcar]

Originally Posted by Quentin

My definition is interstates running through the Appalachian mountains. My 6MT GTI reved around 3k at 70mph and had plenty of immediate power if I just punched it without a downshift. It was very pleasant to drive on the interstate because it constantly felt on boil. It felt engaging like it was ready to leap into action like a sporty car should feel.

Shifting to make minor speed changes on the interstate is for the birds, IMO. This is a sports car, not an economy car. Going 70mph everywhere instead of 80mph will save you more money in gas than a taller final drive will.

While I doubt you will "need" to gear shift for minor acceleration, you'll want to shift into the power band for "acceptable" acceleration.

This engine has barely more torque than some compact cars, the advantage is this "sportscar" has it all in better gearing and more power from 4k-7k RPM. This is an involved car, not a lazy DD.

Originally Posted by serialk11r

This is a sports car, the whole point of having close ratios is so you have more choices for the optimal gear, and you have to put work into shifting to make that happen. Tell me why you need lots of passing power in 6th gear when your 5th gear can do it much better? Fuel efficiency doesn't matter in a sports car? Tell me, would you rather be cruising at 50mpg, engine very quiet, or 32mpg, engine roaring? Fuel efficiency is a byproduct of proper, intelligent design.

And no, a short gear going 70 vs long gear going 80 is a massive difference in load. A long gear going 80 could be putting the engine at 90% peak efficiency while the short gear could be putting the engine at as low as 50% peak efficiency on some cars, while the actual power requirement difference between 70 and 80 is something like 40%.

You really need to say which "efficiency" you are talking about. Internal combustion engine typically max out around 32-37% peak efficiency. Before drive train and belt losses.

Originally Posted by serialk11r

Sorry that was perhaps a slight exaggeration. You don't really need a BSFC map though, it's very reasonable to expect that the low load efficiency is going to be similar to say a 2ZR-FXE, which has similar cam timing, although direct injection changes things a bit.

A Prius can cruise at over 95% efficiency, while a Honda S2000 cruises at around 60% efficiency. That's the kind of spread you see even among small engines. That's the difference between good gearing and bad gearing really.

The AT will require about 52Nm from the engine at 60mph, while the manual requires about 40Nm. The 2ZR is 1.8L instead of 2L so we can multiply these by 0.9, which will give the approximate corresponding load on the 2ZR.

The AT will be able to run the engine at around 270g/kWh efficiency. The MT runs the engine at around 300g/kWh efficiency. Peak efficiency is slightly better than 230g/kWh.
Sorry for all the edits by the way.
EDIT: I'll add in the numbers at 75mph for reference, in a moment.

Okay 75mph, AT needs about 77Nm from the engine, the MT needs about 60Nm. AT is running at 240g/kWh, MT is running at a bit over 260g/kWh. And at 80 (do 80mph speed limits even exist? I haven't seen one before...highest I've seen is 75, so that's technically the fastest you should drive :P) MT is a little over 250g/kWh, while AT is at 230g/kWh. So consistent ~10% difference or so.

Also note that at 80 your engine is running pretty efficiently, although the power requirement is much higher. With a longer rear diff or slightly longer 6th gear we can close the gap pretty much all the way, especially since an AT packs hydraulic pump losses, which eat up part of the advantage.

Moral of the story is, if you care about mpg, in the city, go manual. Lots of highway miles, AT will have probably somewhere between 5-10% better fuel economy on average. EPA test is done at lower speeds, at higher speeds the gap will close up a bit. The reason being, a modern engine has a huge range in which it is within 10% or so of peak efficiency from 100% load down to the high 30s, and across several thousand rpm. Efficiency drops off rapidly in the area where the EPA test happens, cruising at low speed, and the MT will get to the low efficiency zone faster.

Hoo. That's an interesting conclusion given that autos typically upshift early and tall gears can help as low as 20-30mph. But shouldn't this be in technical?

[serialk11r]

lol, I'll just copy it over the day someone wants to know about it.
But the early shifts helping fuel economy makes sense, because the lower the load, the bigger the difference right?

I also have a hunch that typical automatic transmissions, when put in auto mode at least, may use gas pedal input as an indicator of overall torque demand, rather than engine load demand. That would REALLY help EPA scores.

[Quentin]

Originally Posted by serialk11r

Sorry that was perhaps a slight exaggeration. You don't really need a BSFC map though, it's very reasonable to expect that the low load efficiency is going to be similar to say a 2ZR-FXE, which has similar cam timing, although direct injection changes things a bit.

I'd be surprised if this engine has the same cam timing as the 2ZR-FXE, considering that runs an Atkinson cycle instead of your typical otto cycle. Have a link? Sounds like an interesting read. I've been waiting for the FR-S to show up on the TIS so I can get all the details, but no dice yet.

[serialk11r]

The reason why I think it's okay to extrapolate is that the engine has cam phasing, but not variable lift/duration. The 2GR-FSE makes power a good 1000 rpm lower than this engine, and in Toyota released papers they indicate an intake cam duration of ~250 degrees or so. For the 1NZ-FXE there are similar diagrams that indicate a ~270 degree intake cam.

The FA20 needs more duration than the 2GR-FSE in order to have good VE at 7000rpm, so it's reasonable to expect slightly longer duration intake cams. If you look at the released dyno charts you'll see that the torque is very weak before 3000. However the specific torque is quite a bit stronger than say the 1NZ-FXE or 2ZR-FXE at low rpm. The reason being, direct injection + premium fuel allow them to use a huge intake cam advance that causes a lot of hot exhaust gas to get trapped in the cylinder. Of course there is a limit to how much you can do this before you run into problems, so the torque under 3000 is weak. If you look at the 2GR-FSE on the other hand, its torque is weak below 2000, but is pretty good after 2000. By comparison, the 2ZR-FXE has torque that increases up to about 4000rpm. So there is definitely an appreciable difference in intake cam duration, and my guess is that the FA behaves somewhat like a direct injected Prius at medium load, low rpm. The cam is probably closer to the Atkinson cycle engines than it is to the 2GR.

In addition, may I note that Toyota's D4-S system created sufficiently homogeneous fuel mixtures at low speed even with a high flow port on the 2GR, so it's possible that an even longer duration intake cam will reduce throttling loss but not affect combustion, improving fuel economy. Direct injection, crazy stuff

[carbonBLUE]

Originally Posted by serialk11r

The reason why I think it's okay to extrapolate is that the engine has cam phasing, but not variable lift/duration. The 2GR-FSE makes power a good 1000 rpm lower than this engine, and in Toyota released papers they indicate an intake cam duration of ~250 degrees or so. For the 1NZ-FXE there are similar diagrams that indicate a ~270 degree intake cam.

The FA20 needs more duration than the 2GR-FSE in order to have good VE at 7000rpm, so it's reasonable to expect slightly longer duration intake cams. If you look at the released dyno charts you'll see that the torque is very weak before 3000. However the specific torque is quite a bit stronger than say the 1NZ-FXE or 2ZR-FXE at low rpm. The reason being, direct injection + premium fuel allow them to use a huge intake cam advance that causes a lot of hot exhaust gas to get trapped in the cylinder. Of course there is a limit to how much you can do this before you run into problems, so the torque under 3000 is weak. If you look at the 2GR-FSE on the other hand, its torque is weak below 2000, but is pretty good after 2000. By comparison, the 2ZR-FXE has torque that increases up to about 4000rpm. So there is definitely an appreciable difference in intake cam duration, and my guess is that the FA behaves somewhat like a direct injected Prius at medium load, low rpm. The cam is probably closer to the Atkinson cycle engines than it is to the 2GR.

In addition, may I note that Toyota's D4-S system created sufficiently homogeneous fuel mixtures at low speed even with a high flow port on the 2GR, so it's possible that an even longer duration intake cam will reduce throttling loss but not affect combustion, improving fuel economy. Direct injection, crazy stuff

Great explination

[Allch Chcar]

Good read and I know exactly what you are talking about. For once.