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Old 10-08-2007, 10:57 PM   #1
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I don't like autos

Just to say, my current car is an auto, with the following specs:

2.0i multipoint, 8 valve.

4 speed (3+overdrive) gearbox, with lockup only on overdrive, only at 45mph+

And, I have found that, if I use the SuperMID to try different techniques, going slower (with engine -on and engine off coasting) is about the same as racing hard from the lights, going faster, and so on, on the same daily commute! I just can't make my MPG go any higher.

What I think is happening is this:

When cruising at low RPMs, the torque convertor slip becomes a greater percentage of total RPMs, so at low RPMs, efficiency DROPS due to the torque convertor.

At high RPMs, the engine is less efficient... but the torque convertor is 'wasting' less of the energy.

Therefore it makes no difference what RPMs you are at because the torque convertor efficiency (better when higher RPMs) and the engine efficiencies (worse when higher RPMs) cancel each other out.

Also, as you accelerate with more throttle, you get higher engine efficiency. However, when you accelerate with more throttle, the torque convertor slips more as well. Again these seem to cancel each-other out.

So overall, My range of fuel usage has been '1.450 litres' (on an uncalibrated SuperMID) for the best journey, and 1.550 litres (on the same SuperMID) for the worst journey. I have managed to get 1.650 litres with lots of traffic but that is another matter.

Any ideas on how to get past this block? I have a long drive at 45+mph coming soon so I'm hoping that will be good, but town driving in an Auto is a joke (this car is basically mechanically the same as my last Bluebird, except it is an auto). Yet it gets half the MPG!


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Old 10-09-2007, 01:53 AM   #2
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I have found the same thing with other cars, I seem to get the best mpg at 45-50 range. at that point the TQ is locked, tranny is in OD, and the motor sill is running pretty low RPMs

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Old 10-09-2007, 08:52 AM   #3
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AutoMagic SlushBox

That sounds like a miserable transmission arrangement.

I too suffer from the auto (4-speed with 3-point TC lockup in gears 2-4, and "Hill Logic Control").

You're at the mercy of the transmission control system unless you find an aftermarket control unit. If it's something you're interested in, products may be out there for full control over the auto -- including TC engagement whenever you'd like. Someone here was selling a device similar about 6-months ago, but none for your application, IIRC.

Another route would be to play with the throttle linkage tension (if so equipped). Depends on the application...

What I do is set the tension as high as possible -- that way there's plenty of fluid pressure for shifts, and the TC engages as soon as 35 mph hits (and other variables are satisfied). Downshifts aren't a problem since the car's torque is high enough -- this is generally a concern with tightening the cable.

City Driving: I accelerate to where I think the car will shift into the next gear at throttle lift: (1-2 is manual by the gear selector and forces into 2nd) -- 3rd gear disables hill-logic, and "D4" is the usual placement for cruise.

There is generally a near-immediate shift into 2nd with gear selector "2" (about 10 mph), then into selector "D3" at 30 mph, lift, it generally shifts, then into selector 4 after the shift, then around 30-35 lift again, shifts to 4th, and at 35mph the TC generally kicks in. Accelerator action is generally TPS of 20-25 until cruise, then to 14-20 to maintain speed. The goal is top gear and TC lockup as soon as possible.

It may take a while to find out what works -- it's frustrating in the meantime, but hang in there!

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Old 10-09-2007, 02:03 PM   #4
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Yikes. Doesn't sound like fun, landspeed.

If I were forced to drive an auto, I'm sure I'd be looking closely at modding the shift points or making it so I could force t.c. lockup at will.

Still, you're doing well above EPA.
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Old 10-09-2007, 02:17 PM   #5
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my auto ranger seems OK, drive a 4-5 miles and converter locks in at 45ish. driving my wifes xterrra, i was watching rpms around 50mpg it was 2200, it seemed kinda high. after driving 15-20ish miles after my ranger would lock in it finally locked in dropping to 1800rpms at the same speed. dam that took forever to warm up.
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Old 10-09-2007, 02:56 PM   #6
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is it feasible to switch out the auto for a manual?
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Old 10-13-2007, 10:03 PM   #7
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I'm getting a Bluebird Attessa Manual soon - although I might keep 'Bluey II' as well. The Attessa means it is 4WD. It comes with no engine, and I was only getting it for the air con to fit to my car. However, I'm seriously considering putting in another engine, as the shell (appears to be) very good.

If I end up not putting in another engine and using that car, I will take all I can from it to upgrade my new Bluebird... In particular, the manual gearbox (it is reconditioned, and is worth keeping just for that reason), lights, electronics, air-con, etc, etc.

If I had my own workshop, I would take the rear axle from the 4WD, and connect that directly to an electric motor, and I would get a manual gearbox for the front 2 wheels. The electric motor would be for short journeys (or, even on long journeys, I could do the first few miles or so on electric to reduce the overall MPG, also I could do regen charging down any hills I find).

Gearshredder - to go to manual, I need a new engine computer (not that expensive secondhand), I need a new gearbox, mountings, flywheel, driveshafts, gearstick + the linkage for that too. I wish I could do it, but I don't have a workshop... or a spare car

To drift slightly back on topic... I just went out for a drive on a road where I could keep the gearbox in 'lockup' mode, so I drove at 50-60mph most of the time, and got about 35.84MPG (us). This is better than I have been getting - however, it really does seem this is about the highest my car will go and it is nothing compared to the MPGs I was getting in Bluey I (see my signature!)

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Old 01-25-2008, 12:58 PM   #8
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Autos aren't that bad. Sure you can get a few more mpg's per gallon with a manual, but in your case, get a ScangaugeII and air up those tires to maximum sidewall specifications. You'll see a great improvement!!
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Old 01-26-2008, 11:59 AM   #9
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The lock up clutch in an auto is miniscule compared to the standard clutch in a manual trans.

This is the reason the lock up point is only available in the highest gear and at low throttle (read low torque) openings.

Manual overrides can be made to work but you may destroy the clutch in short order as a result.

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Old 01-26-2008, 01:03 PM   #10
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autos are less efficient because of inherent friction (moving parts), fewer gears, and Torque converter....plus they weigh twice as much on average. They're also much more sensitive to wear, temperature, and fluid condition.

I don't like them because I tend to have a more spirited driving style and nothing is worse than being on the edge of traction around a tight corner and then the trans decides to shift..... now you have to get your car out of the ditch. Trying to control a car with a torque converter is like trying to pull something into place with a stretchy rubber band instead of a static rope.

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