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.

Reply to
SQ
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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?

Reply to
« Paul »

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)

Reply to
SQ

Small overhead cam engines are like that. Especially ones with lots of valves per cylinder. They develop max hp and torque near max rpm.

Reply to
« Paul »

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.

Reply to
<HLS

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.

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

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Reply to
Don

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.

Reply to
bowgus

Oops ... subaru ... awd :-)

Reply to
bowgus

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

Reply to
Bror Jace

I agree, 2500 is not 'very high' in the greater scheme of things. The F1 engines are now running in the range of 20,000 rpm.

Our Buick V6 runs at about 1800-2000 rpm on the highway at 70 mph. And it gets about 26 mpg doing it.

If you ran in the range where they began to develop a significant portion of their horsepower potential, then mileage will decrease significantly. I posted some of those calculations a while back.

Reply to
<HLS

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 :-)

Reply to
bowgus

Not hard at all. Forget what they said in olden days about not lugging the engine. Shift early- if the car WON'T accelerate, then you shifted too soon. But if it accelerates smoothly, even though leisurely, that is fine. Even though my Neon R/T has a fairly agressive camshaft(s), I can shift below 2K, and it will be smooth with no shudder, though it is a leisurely acceleration. Also, when you see a light ahead, shift into neutral and coast. Yeah, it is illegal in many states, but those laws were written when brakes were primitive and gas was a quarter a gallon.

There was a study in the late seventies by a European mfg. I think it was VW. They ran two cars on test trac for 100K miles, or some long distance. They lugged one car, drove other without lugging them. When they tore them down to look at crank, no discernable difference. I wish I could remember the mag I read about this test in, but I cannot (it was about 1980). Anyway, it altered my driving habits.

Reply to
Don Stauffer

But you don't NEED that much hp to drive it. One can take off with fair throttle, as soon as you are moving, begin shifting. Short shift. You will not be the leader of the pack, but you can save gas.

Reply to
Don Stauffer

Also, when you see a light ahead, shift into

I just don't get idiots that come onto a world wide web boasting about doing highly illegal and deadly practices while saying 'forget what they used to say', it's cool now to go out of control and potentially kill yourself or others....

Mike

Reply to
Mike Romain

A TC locks up at a certain speed (~38 mph) in high gear. Typical city driving rarely lets you get above that speed. I think the original poster was talking about city driving (read his post= #2).

Reply to
« Paul »

Two big unknowns prevent making a flat statement:

Does the driver know how to drive a stick shift to maximize milage. Is the test in town or on the road.

Reply to
John S.

I didn't realize that when you shifted into neutral that your brakes stopped working.

I'll cite another ancedotal study I can't find right now, they did a study of accidents, out of the 200+ or so they found only 5 where the driver would have been better off accellerating in an attempt to avoid a collision. All others it made no difference or the driver would have been a lot better off braking harder.

The idea that you lose control in neutral is baloney. You still have steering and brakes, and in most collisions I've seen there was plenty of room for the drivers to swerve to avoid. They call it taking evasive action. The problem is that most drivers in the few seconds before a collision happens, freeze up and do not steer away from the impending collision, and as a result many collisions happen that wouldn't have happened at all had the driver swerved.

Particularly in city driving when the car is seldom above 35Mph, the idea that your going to be able to downshift during a deaccelleration from

35Mph to 0Mph, and be able to suddenly power out of the way of an impending collision, is poppycock. The engine is not going to be in the right gear to be able to punch it and power out of a collision.

Ted

Reply to
Ted Mittelstaedt

I don't like that. 'lugging' the engine is what happens when you shift too soon. YOu need to shift soon enough to balance the acceleration you get after the shift with overdriving in the gear you are shifting from. Don't shift ASAP. That just waste gas.

Reply to
dnoyeB

"Don Stauffer" wrote

Do you know how much fuel is wasted trying to idle? Injector pulse width goes up upon idling. With that amount of fuel you can go twice or more of the distance you coasted in neutral to a stop. This can also wear your brakes and your auto transmission prematurely. You'll do better gas-wise with the motor shut off but that only save less than 1/4 of a cup with all the effort.

Who ever made it illegal to drive in neutral also made ridiculous law such as to shift into lowest gear (not neutral) if the engine accelerates out of control (even on a level road.)

Reply to
Burt

By coasting in neutral or with clutch in means you coast further, so you can back off gas earlier. Using the brakes would mean staying on gas longer, using some fuel.

I keep aware of what other drivers are doing, so I can shift back into gear mucho fast if I need to. However, with brakes on cars these days I believe instances where acceleration is key are rare. Rather, the lateral avoidance CAN be a key. I know how to modulate braking so as to not lock brakes, and still retain steering.

I think most of these laws were put on the books before 4-wheel and hydraulic brakes.

Reply to
Don Stauffer

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