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#1
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Best MPG : 5-speed vs. auto?
Assuming an identical car, let's say a 4-cyl Honda or a Subaru or Toyota, which would get better MPG -- one with automatic tranny or 5-speed? I understand that 5 speeds vs. 4 gives a better selection of rpms, meaning at the same speed you can cruise with lower rpms, assuming the same rear axle ratio. Also I understand that 5-speeds don't have a torque converter that autos have which robbs some power. But in my experience, in city driving, it's hard to shift well for good MPG. Maybe I am shifting at wrong rpms, I am not sure. |
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#2
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Best MPG : 5-speed vs. auto?
SQ wrote:
> > Assuming an identical car, let's say a 4-cyl Honda or a Subaru or > Toyota, which would > get better MPG -- one with automatic tranny or 5-speed? > > I understand that 5 speeds vs. 4 gives a better selection of rpms, > meaning at the same speed you can cruise with lower rpms, assuming the > same rear axle ratio. > > Also I understand that 5-speeds don't have a torque converter that > autos have which robbs some power. > > But in my experience, in city driving, it's hard to shift well for good > MPG. Maybe I am shifting at wrong rpms, I am not sure. Automatics will always have some loss due to the torque convertor. However, they tend to be equal to sticks because most drivers are not good shifters. If you want good mileage, then shift at the lowest rpm possible without lugging and drive as slow as possible without getting shot. I don't know you mean about "5-speeds don't have a torque converter". Are you speaking of automatics, or sticks, or something bizarre like a convertor-less double clutch automatic? |
#3
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Best MPG : 5-speed vs. auto?
Well, this explains a lot. I have been driving a 5-speed and have been getting awful mpg in city. Now I am realizing I am shifting at very high rpms, around 2500. I will try to lower the rpms during shifting and see if it makes any difference. (I think one problem in my particular situation is that the type of engine I have derives it's power from high rpms, you have to rev it to get going, and I don't like it) |
#4
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Best MPG : 5-speed vs. auto?
SQ wrote:
> > Well, this explains a lot. I have been driving a 5-speed and have been > getting awful mpg in city. Now I am realizing I am shifting at very > high rpms, around 2500. I will try to lower the rpms during shifting > and see if it makes any difference. > > (I think one problem in my particular situation is that the type of > engine I have derives it's power from high rpms, you have to rev it to > get going, and I don't like it) Small overhead cam engines are like that. Especially ones with lots of valves per cylinder. They develop max hp and torque near max rpm. |
#5
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Best MPG : 5-speed vs. auto?
"SQ" > wrote in message oups.com... > > Well, this explains a lot. I have been driving a 5-speed and have been > getting awful mpg in city. Now I am realizing I am shifting at very > high rpms, around 2500. I will try to lower the rpms during shifting > and see if it makes any difference. > > (I think one problem in my particular situation is that the type of > engine I have derives it's power from high rpms, you have to rev it to > get going, and I don't like it) As he said, the automatic should have a little more loss, but in fact they get about as good mileage as manuals for most drivers. Drive as though you have a glass of water sitting on the dash. Hi revs usually waste fuel. Jump starts, race car tactics usually waste. |
#6
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Best MPG : 5-speed vs. auto?
On 8 Apr 2006 15:32:49 -0700, "SQ" > wrote:
> >Well, this explains a lot. I have been driving a 5-speed and have been >getting awful mpg in city. Now I am realizing I am shifting at very >high rpms, around 2500. I can't think of anything other than a large diesel engine where 2500 rpm could be considered "high" let alone "very high." If its a 4 cyl OHC engine its just barely entering the bottom of its power band at 2500. "Very high" rpms would be more in the range 0f 7000-8000. Many modern totally stock 4 cyl. engines can handle that with no ill effects whatsoever. > I will try to lower the rpms during shifting >and see if it makes any difference. > >(I think one problem in my particular situation is that the type of >engine I have derives it's power from high rpms, you have to rev it to >get going, and I don't like it) Then you should buy an old Lincoln or 500 cubic inch Cadillac Eldorado. Small engines all need to rev to produce power. FWIW automatic transmissions free-wheel under various conditions which helps offset their gas mileage reducing attributes. Its easy to see this if you have a tach. Don www.donsautomotive.com |
#7
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Best MPG : 5-speed vs. auto?
The subaru loses about 10% due to the 4wd ... so leave subaru out of
the identical cars. The 5-speed ... 5th is typically an overdrive and wins hands down on the highway ... or, if you don't do much highway/freeway driving, not much point. My '96 4.0L jeep Cherokee at about 3100 lbs is a 4 spd auto (overdrive) with lock up torque converter ... and consumes 10 litres/100km at a steady (cruise control helps the mileage) 100 kph hour at about 1800 rpm ... and that's about the same mileage as my subaru got ... at 3000 rpm. Driving in the city I normally don't exceed 1800 rpm in any gear and the acceleration is fine by me. There's always the guys in their little 4-cyls winding it out between traffic lights ... sure it's fun ... but they don't need to develop that full horsepower at high revs to move those little cars from one light to the next. Got to admit though ... if I still had the stick, I'd be winding it out too, and downshifting to brake. Back to your post ... imo ... with todays engineering, and adding to your equation equally skilled drivers ... mileage would be about the same. |
#8
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Best MPG : 5-speed vs. auto?
Oops ... subaru ... awd :-)
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#9
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Best MPG : 5-speed vs. auto?
I'm rare. I don't mind city or gridlock traffic with a manual tranny.
I've been driving one for over 15 years and think I've got it down pat. My current car is a Nissan SpecV with a QR25DE engine and 6-speed tranny. The car's EPA rating is 23/29 and I've gotten over 30mpg on some tankfuls. So, When I drive in a fair amount of low speed traffic, my mileage still doesn't drop below 26-27mpg ... as long as I'm not stopped for too long. Basically, I drive in stop-and-go traffic close to idle RPM. With modern engine management systems, the engine won't stall if you are careful with your transitions. In gridlock, I'll idle in 1st gear as long as there is room ahead of me. And when traffic starts to move ahead of me, I get going ... but no jackrabbit starts. It's likely it will slow down again a few hundred yards up the road, anyway. In slow traffic during snowstorms, I have idled the car in 2nd and even 3rd gear for miles. Never touched the gas or the clutch. It's all about thinking ahead and pacing yourself. I work in a downtown area without a set parking spot/lot so I have spent up to 35 minutes circling the blocks looking for parking. But because I drive sensibly, this driving doesn't seem to hurt my fuel economy at all even though it's mostly in 2nd or 3rd gear. There is a similar car to mine out there with the same engine but tuned for a bit less HP (165hp vs. 175hp) and people (often kids) driving these cars complain of fuel economy as low as 23mpg. --- Bror Jace |
#10
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Best MPG : 5-speed vs. auto?
And for what it's worth, at 1800 rpm the 4.0 litre hp/torque are
roughly 70 hp and 215 lb-ft respectively which is plenty on the highway .... even when pulling the 3500 lb boat/trailer :-) |
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