FR-S/BRZ MPG

[Reflections]

Originally Posted by Dillano609

Jaw droppingly low I hope, lol

Of course, of course! :O 21k

[devinclfalcons]

I'm putting my money on 30 mpg combined.

26 city/34 hwy

[MRZ415]

I got a feeling I'll get shitty mpg at first because i'll drive for fun ...
then back to reality then I'll be riding 6th gear once on the freeway.

I get 35mpg in my DIESEL .. so I figure with my driving style
maybe 30mpg hwy in the brz.

[serialk11r]

Originally Posted by switchlanez

So the new FB20 engine in the 2012 Impreza is 2 liters and gets 27 city/36 hwy mpg with CVT and 25 city/33 hwy for the 5MT. But it outputs 150 hp on the 2,900 pound Impreza.

The FR-S/BRZ's FA20 is based on the FB20. Also 2 liters but difference is it's been tuned to 200 hp. The D-4S direct injection is supposed to increase hp and fuel efficiency but I think the engine has to run richer (consume more gas) to achieve the huge +50 hp bump and tuning is skewed more towards power than efficiency. The FR-S/BRZ is 200 lbs. so that helps.

200 lbs. lighter but +50 hp? I think it would have the same or worse efficiency numbers than the 2012 Impreza. Also, CVT makes a difference which our car won't have. And Impreza's 5MT is geared for fuel efficiency; our 6MT should be geared for some mix of performance/fuel efficiency.

Errr...the engine only runs rich near max load and idle. And direct injection reduces the amount of fuel you need because it improves combustion efficiency and reduces cylinder temperature. In addition, the long duration cams reduce pumping loss, and the direct injection makes up for the lack of charge motion due to high lift. If anything, the FA20 should be the more efficient engine at every point.

Anyways, CVT would help in the city, but would hurt on the highway because it has high frictional losses. The manual transmission doesn't have a very tall 6th gear so it won't cruise near max. efficiency, although based on my calculations it should be able to pull a respectable 40+ mpg at 60mph. The auto has very tall 6th gear so it could hit 50mpg. Also you have to remember, rolling resistance is a very small force compared to aerodynamic drag. The Impreza is much bigger dimensionally, and will have more drag.

EPA highway != highway cruise mpg. EPA highway test includes lots of slowing down, speeding up, etc. I dunno about other people, but on the highway I almost never need the brake, and I certainly do not slow down to <45mph very often.

[devinclfalcons]

Originally Posted by serialk11r

Errr...the engine only runs rich near max load and idle. And direct injection reduces the amount of fuel you need because it improves combustion efficiency and reduces cylinder temperature. In addition, the long duration cams reduce pumping loss, and the direct injection makes up for the lack of charge motion due to high lift. If anything, the FA20 should be the more efficient engine at every point.

Anyways, CVT would help in the city, but would hurt on the highway because it has high frictional losses. The manual transmission doesn't have a very tall 6th gear so it won't cruise near max. efficiency, although based on my calculations it should be able to pull a respectable 40+ mpg at 60mph. The auto has very tall 6th gear so it could hit 50mpg. Also you have to remember, rolling resistance is a very small force compared to aerodynamic drag. The Impreza is much bigger dimensionally, and will have more drag.

EPA highway != highway cruise mpg. EPA highway test includes lots of slowing down, speeding up, etc. I dunno about other people, but on the highway I almost never need the brake, and I certainly do not slow down to <45mph very often.

I didn't know that it was already known that the auto has a taller 6th gear... Wonder how much difference it will make?

I doubt either will get more than 40 mpg... High 30's at best at optimum conditions...

[serialk11r]

Originally Posted by devinclfalcons

I didn't know that it was already known that the auto has a taller 6th gear... Wonder how much difference it will make?

I doubt either will get more than 40 mpg... High 30's at best at optimum conditions...

It makes a huge difference actually. The Civic Si has a super short 6th gear and it can do high 30s cruising. Typically cruising gear places the engine in the 20% full BMEP range, where efficiency is horrendous. Just by changing the gear, you can typically reduce fuel consumption 30% under steady state cruise, although it reduces the extra power available.

If the Civic Si was geared a bit longer, it could do >>40mpg. Any modern, small car is capable of 45mpg on the highway or better if the highest gear is at the right ratio. Engine mechanical efficiency these days is pretty high, combustion efficiency is good, so what's left is pumping loss due to suboptimal operating conditions.

FYI, the brochure released says auto is 4.100 final drive, 0.582 6th gear, while manual is 3.727 final drive, 0.767 6th gear. That puts 60mph at around 2350rpm for the manual, 1960-70 rpm for the auto (quite remarkable, my mom's 3.5L Honda Pilot has this cruising rpm!). The auto would probably be somewhere around 80-90% peak efficiency, while the manual would be at 70% of peak efficiency or so. The mpgs an automaker can pick up by making 5th/6th gears taller is by far the easiest mpg they can pick up, as it costs no money whatsoever.
See my posts in this thread.
http://www.ft86club.com/forums/showp...8&postcount=60

The only downside is you can't be lazy and expect great passing power in 6th. IMO 2000rpm at 60 is a good gearing, more than enough torque to go up the steepest grades, efficiency nearing 10% of peak.

[devinclfalcons]

Originally Posted by serialk11r

It makes a huge difference actually. The Civic Si has a super short 6th gear and it can do high 30s cruising. Typically cruising gear places the engine in the 20% full BMEP range, where efficiency is horrendous. Just by changing the gear, you can typically reduce fuel consumption 30% under steady state cruise, although it reduces the extra power available.

If the Civic Si was geared a bit longer, it could do >>40mpg. Any modern, small car is capable of 45mpg on the highway or better if the highest gear is at the right ratio. Engine mechanical efficiency these days is pretty high, combustion efficiency is good, so what's left is pumping loss due to suboptimal operating conditions.

FYI, the brochure released says auto is 4.100 final drive, 0.582 6th gear, while manual is 3.727 final drive, 0.767 6th gear. That puts 60mph at around 2350rpm for the manual, 1960-70 rpm for the auto (quite remarkable, my mom's 3.5L Honda Pilot has this cruising rpm!). The auto would probably be somewhere around 80-90% peak efficiency, while the manual would be at 70% of peak efficiency or so. The mpgs an automaker can pick up by making 5th/6th gears taller is by far the easiest mpg they can pick up, as it costs no money whatsoever.
See my posts in this thread.
http://www.ft86club.com/forums/showp...8&postcount=60

The only downside is you can't be lazy and expect great passing power in 6th. IMO 2000rpm at 60 is a good gearing, more than enough torque to go up the steepest grades, efficiency nearing 10% of peak.

If the auto can get 3 mpg more than the manual on the highway, I will have to go with it over the manual. I have a 90 mile round trip to work and that could be a lot of money saved in gas...

[carbonBLUE]

my car idles at 2800 at 60... i wouldnt sweat it... i still get 35mpg average highway..

[serialk11r]

Originally Posted by devinclfalcons

If the auto can get 3 mpg more than the manual on the highway, I will have to go with it over the manual. I have a 90 mile round trip to work and that could be a lot of money saved in gas...

Well the auto probably costs more too, you'd have to be driving for quite a while to save that money back. Using 2 gallons a day vs. 1.8-1.9 gallons a day is not much of a cost difference. Not to mention, city mpg is probably worse. Unless you wanted an auto in the first place.

And also beware that I am doing calculations for 60mph cruising. As you go faster the gap closes due to higher torque requirement. So at 70-80 the difference might shrink quite a lot.

Personally I'm hoping they revise the ratios and drop 6th gear rpms a little more. It's free mpg numbers that they are choosing to not pick up for whatever reason. Lotus used retardedly short 6th gear, which killed their mpgs as well.

[tripjammer]

I predict 28 mpg combined. It's suppose to require super unleaded right?

[suprachica79]

Originally Posted by devinclfalcons

If the auto can get 3 mpg more than the manual on the highway, I will have to go with it over the manual. I have a 90 mile round trip to work and that could be a lot of money saved in gas...

I got you beat! 150 mile round trip and I'm still going with manual, I think it'd end up equal or still a bit better in manual.

[ryude]

Assuming the auto is $1000 more than the manual, the auto gets 3mpg more, and the gas price never increases (unlikely). It would take 18 years to make up the extra $1000. That's not taking into account the extra maintenance that autos require over a manual.

[suprachica79]

Originally Posted by ryude

Assuming the auto is $1000 more than the manual, the auto gets 3mpg more, and the gas price never increases (unlikely). It would take 18 years to make up the extra $1000.

Thanks for doing the math, I didn't feel like it

[switchlanez]

I like the way this serialk11r person thinks.