I have a rough idea that most Auto cars convert power from the engine to the wheels hydraulically, using a torque converter (thanks to howstuffworks.com)
When a car is inbetween gearchanges is there much ‘slip’ between the engine and the wheels compared to a clutch?
Do Autos still consume more fuel than their equivalent manual transmission car? (same car, same engine size, fuel type etc)
Is there any loss of power at the highest safe revs in an auto compared to a well-executed manual gear change?
Based on the sticker, some auto’s get the same or even better milage then their manual counter parts. From what I’ve read this is due to a locking torque converter. My understanding is that then both sides of the torque converter are spinning at the same speed, they come together so there is less loss.
My question is geared (get it - ‘geared’ ha ha) specifically towards non-continuously-variable transmission (ones that change to a different gear mechanically at a certain high-rev point and use the torque converter to not stall the engine)
but I guess this thread can be expanded to other types of auto transmission.
I agree that lock-up torque converters are near the efficiency of a manual. That is more so in today’s transmissions because they have at least 1 overdrive gear in the automatic.
I’ve gotten upwards of 38 mpg with my Saturn and it’s obvious that great effort was put into the engine and transmission computers. They work very well together. It’s a 2000 and I still get a kick out of how smooth it shifts.
Funny. I have a 2006 Scion Xa, with advertised MPG of 38HWY, 32 city.
The problem is, I selected a manual shift because it was cheaper than an auto trans and had higher rated economy.
I don’t think I’m getting that economy. When I drive 80mph in 5th gear, the car revs exactly at 4000rpm, which is abnormally high IMO.
My Grand Caravan (auto trans) loafs along at 80mph at 2600rpm’s.
I investigated this and found that this is a common complaint of owners of my car with the manual tranny. When I brought it up with the salesman, I was assured that “Hey, it’s a VVTi engine, it’s designed to run at high rpm’s.”
While that may be true, running 4 grand at 80 is killing my MPG. I know, drive slower, but the speed limit in my state is 70 on interstates, and there are never any police around when I go to work at 5:30am.
I’ll have to verify this but I think I’m doing 50 mph at 2000 rpm. I’m sure I would be flying at 4,000 rpm. I know if it shifts and locks at 45 mph I’m under 2000 rpm. For a manual 5 speed that doesn’t sound right at all. I Just FYI, I’m driving an SL1 which I think is smaller than a Civic.
I’m pulling almost three grand at 55mph. The car is geared funky. Booming along at 4k in 5th gear at 80mph is not normal.
I have driven many a four-banger car with a manual tranny, and all of them kept rpm’s in the 3000-3200 range at 80mph.
<<Edit>> It doesn’t help that my version of the Scion isn’t made anymore…it’s been replaced with the slightly bigger, more powerful Scion Xd.
My engine is the forlorn 1.3 litre model previously occupied by the equally forlorn Toyota Echo. It does get good gas mileage, but I can’t help but feel that this powerplant was shoehorned into a more “hip” car like the Scion as opposed to the cancelled Echo.
As such, since my Xa was only in production for three years, I think Toyota resolved a cost-effiency issue with themselves by wrenching that 103hp engine out of surplus mode and into my car.
The vehicle is actually zippy around town, with very close gearing. I often put it into 5th gear at 40mph, where it revs right at 2000rpm’s.
That is it’s problem, it needed a sixth gear or a more fuel-efficient ratio from what it curently has.
The cranky old timers with their blinders on will always contend that a manual tranny is somehow superior. Yet, any truly high performance car or race car has paddle shifters which are basically an override of an automatic transmission.
Back in the day (the 60’s and 70’s ?), the dragsters were using the old Chrysler push button transmissions because they were faster than the manuals.
If you want to pretend to maintain your masculinity by insisting on operating a manual transmission then be my guest. Otherwise, an automatic can provide the best performance unless you are so adept at out thinking the driving conditions that you can override it in the most extreme circumstances. If you are that good, get a job on the F1 circuit, there’s a lot of money there.
This is patently false. While it’s true that you can get paddle shifters for “manual mode” in an automatic transmission, most high performance cars with them are derived from manual transmissions (sequential manuals, etc.).
No, they were using those transmissions because they were brutally simple, could deal with the torque and were cheap to replace on a frequent basis. An automatic has essentially no chance of blowing the shift, something all too easy to do with a manual transmission, particularly at the power levels a drag car runs at.
There are in fact some automatics that equal or out-perform manual transmissions, but that’s not the rule. A quick survey of Ford Canada’s website, for instance, reveals that the Focus, Fusion and Mustang all do better fuel economy with manual transmissions than automatic, this despite the fact that the Fusion is available with a 6-speed automatic. GM’s dreadful 4-speed automatic, still standard on most models of their vehicles, performs woefully compared to manual transmissions (on the rare occasion that manuals are available to compare). The Honda Accord, with one of the best automatics available today, still gets better mileage with a manual transmission. The Toyota Camry does get better mileage out of its automatic than its manual, however (29/44 manual vs. 30/46 automatic for the Canadian version).
Not necessarily. My senior design project for my undergrad was working on an IVT (infinitely variable transmission, which included both a CVT and a planetary gear setup). I don’t remember the precise numbers, but gears run at somewhere around 95% efficiency per mesh, while a CVT runs somewhere around 85%. I’m not sure about all systems, but at least in the systems we were analyzing it still needed a gear to get to the CVT. Therefore, you could have to .95^x = .85, or three extra gears (when you only need two extra) to get the same effeciency.
The fuel savings of a CVT don’t come from the transmission being more efficient, but rather in allowing the engine to operate at its optimum RPMs for a greater range of speeds.
Yah, that is high reving. I checked my car last night and at 65 I’m turning 2300 rpm. at 80 I’m turning 2800 rpm. If I got it to 4000 rpm I’d be doing 114 mph. I guess if you get good gas mileage that’s all that counts.
There’s some misinterpretation of my remarks (or maybe I wasn’t clear). I’m saying that the old push-a-clutch and throw-a-lever to be a “real” driver and get maximum performance is archaic.
Like most everything, it’s not all or nothing. There are lousy automatic transmissions that can be beat with manual transmission but the development of automatics has reached the point that pushing a clutch is like carrying a pocket watch on a chain.
You mention Ford. Probably the highest performing production car they produced (although they don’t own it anymore) is the Jaguar XKR. On this side of the Atlantic it is only available with paddle shifters. That’s the way high performance cars are built these days. Nevertheless, there are still those that need a clutch in order to be a "real"driver.
If you’re in a Jaguar XKR automatic and want to see aFord GT-40 you’ll have to look at it’s tail lights because that’s all you’re going to see of the manual-only car. Same for the Shelby GT500KR(OPTIONS).. Same with the Dodge Viper.
Jaguars are built for a more genteel clientele who want luxury with their performance. And while you can get an automatic in a Porsche 911 it’s an option. “Real” sports cars have manual transmissions because they are more efficient (more hp reaches the road). The skill required is part of the experience.
In sporting events where a lot of shifting occurs in short time frames the automatic is worth the power penalty. Events where extended raw hp is needed the manual transmission is used.
So “real” drivers still benefit from manual transmissions.