I just don't get it, a manual revs more even on highest gear, needs more revs to launch, switch gears at high revs. but on an auto. revs are low, especially on highway compared to stick. i had a better discussion about this on my way home but now i forgot it. any ways, how?

 

Very simple, auto trannies have a torque converter, when you brake the TQ works the same way but reverse to slow down the engine while braking, thus wasting gas. Plus in a manual tranny your car goes to neutral while stop on a light or where ever. Get it. This is also why the brakes on a manual car last a lot less than an automatic car.

This is called waste power.

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So can we can we just put our car in neutral and then we can get the same gas mileage...Why don't we just use the sport shift and throw it in neutral...

 

The manual transmission is also more efficient.

 

Everything else being equal, an aggressively driven manual will not beat a conservatively driven automatic in mpg.

If both are driven exactly the same (identical throttle engagement and rpm shift points, both up and down), the loss from the torque converter in the auto would account for some less efficiency of the auto.

I think more realistically and practically, however, that a manual as a general rule can yield higher mpg's because it allows you to shift at lower revs, and to get into the taller gears more quickly (and to stay there).

Why do I get the impression that some people on this board think that the only way to drive a manual tranny is to wring it out to or near redline in every gear?

 

Ahhhh, there's nothing more satisfying than heel and toeing down the gears approaching a turn and .......hmmm..you get the idea

My brain works alot better than any auto ECU, it doesn't have to guess what I want

 

A/T equipped cars also tend to weight more than their stick counterparts as well.

 

Ok i get it at sum point, i can believe this in city as there is a lot of stop and go traffic so while manu is in neutral and auto in gear that would waste gas. BUT, wat about highway driving? There isn't much braking dun there so why does it still beat the auto? even though it is running at lower revs, same braking (no one shifts to neutral w/ stick while braking unless to a complete stop)?

 

Hum, manual tranny have less power lost, and at the same time you should also consider the final drive as well......

 

I have a question that I'm not sure about. I know that in a manual tranny I could start at the light in first gear then switch to second then put it in five thus not going through 3rd or 4th gear.

Does an automatic do that or it has to go thru every gear?

Can you save gas doing that? I guess at some point.

 

OK, as has been mentioned (albeit sporadically) in various posts in this thread, manual trannies yield better MPGs than autos because of two factors:

1. Weight
2. Efficiency

Manual trannies tend to weigh less and have fewer moving parts (no solenoids, etc) than autos.

Manual trannies also use a manually-actuated clutch rather than a Torque Converter, resulting in more power being transferred from the engine to the wheels (instead of turning into heat).

The effect of shift points and engine braking are not significant if two cars are driven the same way. Don't forget that you can perform engine braking on a manual too.

By far the biggest difference for highway driving is the amount of energy lost due to the torque converter. However, modern TQ's like ours have a lock-up feature which vastly reduces the energy lost at cruising RPMs.

BTW Bitium: engine braking does not consume any more gas than idling. Remember that your throttle is closed to idle during the maneuver. The bad thing about e-braking is the wear on your transmission since it has to bear the brunt of the braking.

 

I guess it makes sense.

 

Actually when you're off throttle and above idle in a manual NO fuel is used. So when you engine brake the engine is actually receiving zero fuel on a manual. This is why engine braking is more effective on a manual than in an auto. The direct coupling in the manual also helps. Once the revs drop to a certain point in a manual the ECU will apply idle fuel flow so that the engine doesn't stall out...except if you drive a 00-01 Maxima 5spd where Nissan was too cheap to put the proper fuel-cut controls on the ECU which caused a lot of problems for the Maxima guys...LOL :p

As for engine braking, this puts no more wear or strain on the engine or tranny than regular driving does. You accelerate hard through the gears and you put much more of a load and wear/tear on the engine and tranny than you do with a little engine braking. But the engine and tranny are also fully lubricated so there's no more wear and tear on it if you're accelerating or decelerating and engine braking.

My family and I drove a 90 Camry 5spd for 207,000 miles with daily use of engine braking in 4th, 3rd, and 2nd gear - still runs great today. Tranny and engine are both strong, and because we used engine braking regularly (because we knew there were no ill side effects) we hardly ever had to do any brake work because they were used only lightly in conjunction with engine braking. We replaced the clutch once at 100,000 miles (only 1/3rd worn) and checked it again at around 200,000 and was 1/3rd worn.

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As for the rest of it, daverman pretty much nailed it right on the head

 

Yep, that's it really. The torque converter...you have no direct coupling until about 60 mph+ and you have a significant efficiency loss over direct coupled manuals...the end. That is the biggest factor by far.

Austin519

 

Hey... wonder if it would be possible to have an automatic where you could lock up the TQ on demand with a clutch pedal...? It would work in opposite of a clutch - when it was up the TQ would act normal, but press down the pedal and the TQ locks up. Seems to me that this could make for a true sportshift. What ya think? Hell, you could reverse it so the clutch is not used in regular mode, then you press it down and switch to sportshift mode, now you have a clutch that acts like a manual - when you raise the clutch pedal the TQ starts to lock up. If you were to keep the pedal down you'd remain in auto mode.

 

Level 10 does this as part of their Performance Transmission Systems. I'm not sure which exact part of their product line will do this, but I know that they have this capability somwhere. It isn't cheap, though...hehe

www.levelten.com

 

Yeah, I guess... the only other thing that happens during e-braking is that you're shifting the loading on the tranny gears from the "driving" face to the "braking" face. This load transfer creates stresses on the parts not present during normal driving. As to the effect it has on the longevity on the parts, I don't know if it's significant.

Yeah, I've always e-braked with my manual cars with no ill effects.