What, if true!! 27City, 36Hwy, is nothing to laugh about! For a high output (relatively high revving) motor that says a lot! Sure, no magic 40mpg, but considering the Civic Si gets 22city, 32hwy... Winning!

Every hidden detail about this car makes it even better, hopefully the price is a jaw-dropper.

Jaw droppingly low I hope, lol

Of course, of course! :O 21k ;)

I'm putting my money on 30 mpg combined.

26 city/34 hwy

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.

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...

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...

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

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.

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

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.

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.

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

I like the way this serialk11r person thinks. :clap:

^^ lol er...thanks?
ryude how are you getting that conclusion? If say he gets 40mpg on the highway portion of his commute (let's say this is most of the 90 miles) with the manual, and 10% better with the auto, he'd be using 2.2 gallons of gas for the manual vs. 2.05 gallons for the auto. 0.15 gallons * say, 300 days, is 45 gallons of gas, which at 4 dollars a gallon is 180 dollars a year. I'm predicting better than 40mpg (at 60-70mph), and I may be overestimating gas price so let's say 160 dollars. 6 years to pay off the auto, assuming he ONLY drives on the highway. In the city, he may not necessarily lose mpg if he avoids using 1st gear past getting the car rolling. The auto box also needs to power its hydraulic pump, which would sap some amount of energy too.

I agree. It will take about 5 years but not over 10 years to make up $1000 initial cost.
If the mpg is 10% better the annual fuel spending will be 10% less.
If one spends $3000/year the difference will be $300/year and will take little over 3yrs to get $1000 back.

The automatic gets 3mpg more on highway, which means average mpg will increase by 1 maybe? 1mpg is so insignificant that it will take you a very long time to recoup the extra cost. If you're going to buy the automatic, don't buy it for the fuel economy. Buy it because that's what you really want/need.

Will the gearing be the same on the FR-S and BRZ? Because I am going to get the BRZ.

http://fueleconomy.gov/feg/Find.do?a...31315&id=31377

Auto vs manual cruze eco.

Annual Fuel Cost Auto: $1,635 Manual: $1,536

But in the real world, the difference is very minimal.

It will probably be the same but you never know...

EPA highway test favors manuals as it involves a lot of changes in speed. Real world highway driving favors locked automatics, which almost always have higher gears.
EPA city screws autos over as it should.

^ true that.

just manually shift the auto so it stays at low rpms in the city... i heel toe everywhere in my manual even at low speeds out of habit, if i go the auto route ill be upshifting and downshift manually ALL the time :D

That's what I do in my Evo X MR :party0030:

Well you don't want to accelerate at too far below 2000 rpm since the engine loses too much heat to the cooling system at low speeds, but it's okay if you do that in 2nd gear since you got out of 1st gear early. Anything is better than an unlocked torque converter.

I'm not sure how gear spacing would change the equation. If the gears are spaced out farther then the auto would theoretically lose more energy to the engine needing to slow down more to match the next gear's speed, but effect is probably very small.

is 3000 rpm at 60 mph normal or high?

Premium gas only?

yes

its high for most engines
the higher an engine can rev the smaller you can make the gears, smaller gears means more acceleration and more torque to the ground because smaller gears multiply torque at a greater value....

for example my car puts down about 130 something torque to the ground with my current mods, a 2010 mustang puts down about 200 torque to the ground but it doesnt rev as high, if you calculate the amount of torque to the ground through gear ratios im a bit behind, but since im like 800 pounds lighter i walk away cause my engine isnt pushing a boat like the mustang...

my top speed is about 155-165 depending on which way the wind is blowing... lol
his tops out at about 150 if the governor were to be taken off...
EDIT: at these speeds CoD comes into play and im slicker through the air, he has a higher amount of torque to the ground at that point but i still have the higher top speed because i dont have to fight as much air as the mustang does....


gearing in high reving engines is a must because we lack so much in torque...

Drive it like you live your life a 1/4 mile at a time.

'
i drive like i live my life smoking corner at a time :D

soon ill be taking me and my friends 67 supercharged mustang fast back to the track :D bringing 8 sets of rear tires....

lool.

coz my car a honda fit sport has 3000rpm at 60 mph, would this also
affect the car's MPG?
i wonder what honda was thinkin when they made it like this on the fit
they should have added more hp, than just increase its rpm

It depends on the size of the engine. Your Honda Fit has what, 1.5L? Honda gave it more revs so power in the top gear would be better. If it were 2.0L, to maintain approximately the same level of reserve power you would only need 2250rpm. So in fact, it is the BRZ that is revving too high, not your Fit.

The reason they use a smaller engine is it has lower frictional losses at the same rpm (but not power!), and is cheaper to manufacture.

it has 1.5L engine.
But does a high RPM affect your mpg?
(i hope the brz/frs has a reasonable mpg, not a gas guzzler)
thanks

So the spark ignition internal combustion engine is extremely efficient at mid range rpm, full load. Good engines have peak thermal efficiency of around 40%. This seems like a low number, until you consider that your local power plant with its constant power, highly controlled operating conditions only manages 40%. However when we are at constant speed cruising, the power requirement is TINY, and most cars use only 20% of maximum torque. At these low specific output levels, two phenomena are by far the most important; friction and pumping loss.

Higher rpm means less torque is needed for the same power, so pumping loss increases. In addition, friction increases as a proportion of output with rpm, due to the fact that bearing forces are much higher when reciprocating mass is moving faster. An additional problem with choking the engine off so much is that the effective compression ratio is much lower, and if the gearing is bad enough, the piston does negative work on the bottom portion of the power stroke (although this typically doesn't happen). Also, much of the friction in an engine is not load dependent; as mentioned before, the reciprocating mass is always creating substantial friction. When you are asking less torque of the engine, friction only decreases slightly, and becomes a much larger proportion of total output. Add in the power lost to pumping air past the throttle, and you get that half the fuel you are burning is burned just to overcome these losses.

Now running at higher rpm does have one efficiency advantage: cooling losses. At lower speed, each power stroke occurs in a longer period of time, and so the amount of heat lost to the cooling system as a proportion of power is higher. At higher rpm the absolute quantity of heat lost is higher, but this indicates that the cylinder temperature is higher, which is good, because it means more heat is doing useful work rather than warming up the cooling water. This is why efficiency can drop off at low rpm, particularly on engines with poor surface area to volume ratio cylinders (aka, less displacement per cylinder). Another aspect that varies quite a bit is combustion efficiency; Higher rpm=intake air is moving faster=fuel mixes better, but direct injection basically rewrites this rule.

However, it is almost always the case that the relatively lower friction and pumping losses overcome the inefficiencies of low rpm cooling loss. Power and torque are directly related, thus rpm and torque at the same power are inversely related. Thus if you halve the gear ratio (the torque multiplication ratio between engine and wheel), you double the torque requirement. It's not hard to see that dropping rpms from say, 2500 to 2000 would increase the torque requirement by 25%. That would be, using 25% of the engine's torque rather than 20%. This might not seem like a big difference until you consider the fact that by increasing output by 25%, and decreasing rpms by 20%, the non-load dependent part of friction has been reduced by 20% in absolute terms, but because power is up 25%, friction has effectively been cut something like 40%! In addition, the work going into pumping the air through the throttle has decreased while your total work per unit air is increased, another win-win for efficiency.

Typically, around 50-60% volumetric efficiency is thermodynamically ideal in the sense that it dumps the least amount of heat out the exhaust. However because of the effects of friction and pumping loss, as well as the fact that more compression raises the thermal efficiency, a typical gasoline engine hits maximum thermal efficiency at about 75%-80% maximum torque. Now if you have an Atkinson cycle style engine, the maximum torque is limited about 75%, and maximum thermal efficiency is at 100% torque output.

Variable valve timing makes all this much more complicated, but the basic principles still stand. That is why a BMW 3.0L engine fails to get >30mpg even though it has a very fancy valvetrain that eliminates pumping loss at part load; the extra cylinders pose a large increase in friction, among other things.

As for this engine, what we see is that it has a relatively long duration cam that is optimized for high rpm power, and it has no variable lift/duration system of any kind. What this tells us is that at lower rpm, the inevitable thing that happens is that part of the charge is pushed back out the cylinder on the compression stroke! To achieve this however, the lift needs to be relatively high to not pose pumping resistance. This makes our engine in essence a direct injected Prius at low rpm, with a little more displacement and shorter gears. As I noted, the gears are pretty typical (aka, too short for fuel economy), so fuel economy won't be Prius stellar, but it will be pretty good because the car is so small and takes relatively little power to go through the air.

MPG schmedpg, it's a damn sports/ish car.

And to directly answer your question phenoyz, the BRZ/FRS will probably get around the same mpg as your Fit at constant cruise, because it is smaller (less aero drag), direct injected, and pumping losses will be a little greater. Overall? Hard to say.

And for people who say fuel economy be damned? Well 99% of cars never hit the track, so this is pretty relevant.