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Old 05-09-2008, 01:31 AM   #1
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Manual conversion - will it change fuel economy???

I have a 1989 Bluebird Automatic. Here in NZ it is like the US - mostly automatics.

I wonder what a manual would do for my fuel economy? If you look at my gaslog you will see it is slowly creeping up (the rad block has helped).

My car's current gearbox is an auto, and a particularly failure-prone model (often fails at 100,000 miles... my car has done 110,000 miles...). I have been doing engine-off coasting for about 10-12% of my daily commute, or about 2.4 miles per day with the engine off, at an average speed of 40mph. The manual says to tow it at no more than 30mph, for 30 miles, if you tow it with the wheels on the ground... So I have been severely abusing the poor transmission but it is still going strong with no complaints.

Anyway, the experiment I propose, is to take a known Nissan Bluebird (my car), with an extreme hypermiler behind the wheel, and then run the following test:

(1) Auto gearbox with extreme hypermiling (e.g. my current figures)
(2) Manual gearbox with extreme hypermiling (after conversion).

What do you think? A good idea or not? Has anyone on here ever done a before and after for this conversion?

Anyway. Stage 1 is commencing this weekend. I am doing a 600-mile round trip on Sunday to collect a near-complete conversion kit (will have everything except for the clutch pedal + master cylinder... They will be easy enough to source seperately). I will have everything else (gearbox, clutch, flywheel, mountings, screws, all driveshafts, gearstick, gearstick surrond, linkage, speedometer drive). This is costing my NZ$80 for all the parts, which is probably about $60 US. A good price I think And is about the price of 85% of a tank of fuel...

Stage 1.5 is when the US company finally gets my cycle battery ready And I can then take my car off the road and do the swap while commuting on the e-bike.
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Old 05-09-2008, 04:50 AM   #2
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I don't know that anyone can ive you exact figures here. BUT I can tell you that you should DEFINITELY see an improvement with a manual transmission. SImply put, manual transmissions convert less of the power delivered by the engine into waste heat when compared to automatics. So you should see an increase. How much? Impossible to say.
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Old 05-09-2008, 05:07 AM   #3
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Check out my gaslog - I saw an increase in FE with the transmission swap from auto to manual. I did install a transmission with better ratios for FE, which helped, but just the fact that it is manual gives you more control over the way you drive.
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Old 05-09-2008, 02:01 PM   #4
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Quote:
Originally Posted by DaX View Post
Check out my gaslog - I saw an increase in FE with the transmission swap from auto to manual. I did install a transmission with better ratios for FE, which helped, but just the fact that it is manual gives you more control over the way you drive.
I see the exact same thing that happened on my (Bluey I) gaslog - you get
much better mileage but then it slightly tailed off. This happened to me after I get the wideband O2 sensor on my last car. Still a definite improvement though compared to the auto - although you can see the effects of winter coming in (I guess you are just coming out of winter now, if the seasons have 'shifted forward' like they have in the UK (and in NZ)?

I'm hoping for 50+mpg; on my Bluey I gaslog, the first jump was fuel mixture feedback, the second was engine heater, and the third ongoing improvement was SuperMID. I stupidly left my O2 sensor on my old Bluebird... And I can't get it off as it is on the other side of the planet. I will have to see if I can give instructions to a family member to take it off
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Old 05-09-2008, 05:28 PM   #5
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on an '89, definitely. newer cars use lower gears on autos and better designed boxes to close the gap (at least according to the EPA numbers)

my 90 cressida got better mileage after conversion (or at least very similar mileage with FAR more abuse) despite the auto having a lower OD gear ratio
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Old 05-10-2008, 06:37 AM   #6
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Besides torque converter losses and different gear ratios, there's another factor to consider: With a MT you can have a lot more control of what gear you're in. That means you can run 80% throttle at low RPMs and not have it downshift, which reduces engine pumping losses.

As long as you're willing to experiment with different shift points and patterns, the MT swap should allow you to gain FE.
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Old 05-10-2008, 06:53 AM   #7
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It will definitely improve your gas mileage for two and possibly three reasons.
1. Weight is reduced.
2. Drive line power loss is reduced.
3. If your automatic transmission does not have a locking torque converter your losing additional gas mileage on the highway.

When I went for maximizing my gas mileage in my Volvo 740 wagon the transmission and rear gearing swap was the first thing on the list.

You can expect between 1.5 and 3.0 mpg increase in gas mileage.
Or 2.9 to 5.8 kpg increase
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Old 05-12-2008, 05:31 AM   #8
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Yep, we're coming out of winter here, so FE is on the rise. Maybe you'll reach 50mpg with the tranny swap.
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Old 05-16-2008, 08:44 AM   #9
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My take on it is better off staying home, that's just so not worth it.
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Old 05-16-2008, 04:57 PM   #10
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Well I think that is probably more a matter of perspective than not. If the auto he has in their is 10% past the average number of miles, then it's going to have to come out, hook or crook. If he can put in a manual for $100 in parts, that is substantially cheaper than having the auto rebuilt and he will get better mileage, in addition.

You will probably only pick up maybe 10-15% in mileage, my guess. I don't think you will get anywhere near 50.
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