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Old 06-25-2008, 07:33 PM   #1
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Gear Ratio/Peak Torque/Best FE Stategy

I'm looking for opinions on the best driving technique for my particular car. (08 Accent)

Peak Torque is @ 4500 RPM

First Gear Ratio : 3.62:1
Second Gear Ratio : 2.05:1
Third Gear Ratio : 1.37:1
Fourth Gear Rato : 1.03:1
Fifth Gear Ratio : 0.84:1
Reverse Ratio : 3.58:1
Final Drive Axle Ratio : 4.06:1
Tires : 175 70 R14

At what RPM would you shift while getting to 5th gear. Lately I've been running it through the gears and shifting at about 3,000 rpm until I get to my desired speed.

The car will run in 5th gear as slow as 35mph without bogging down the engine. 60mph is about 3,000 rpm in 5th. The DOHC/CVVT seems to live up to reports of a very broad power range.

I'm really envious of the automatic overdrive on the Accents. It's 0.69:1 instead of 0.84:1. I've got plenty of power with the manual and I wish I could change the final drive ratio to about 3.7:1 or change the overdrive. That would make a sweet highway cruiser.

Just a note about the engine:

1.6-liter DOHC in-line four cylinder engine that features four valves per cylinder with CVVT (Continuously Variable Valve Timing). The DOHC and CVVT combination helps to give the engine a very broad powerband, coupled with high fuel efficiency and low emissions. The CVVT unit is positioned on the exhaust camshaft and controls the intake valve timing by advancing and retarding the intake cam in relation to the exhaust cam. The CVVT system increases volumetric and thermodynamic efficiency, which helps the engine deliver improved performance at high rpm. By optimizing valve overlap, NOx emissions are reduced due to the resulting Exhaust Gas Recirculation (EGR) effect
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Old 06-25-2008, 07:40 PM   #2
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Well if your torque curve is flat and it's pulling low, you might try shifting at 2K.
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Old 06-26-2008, 05:22 AM   #3
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Typically (conditional clause to allow for me being dead wrong) the best fuel economy as measured in miles per gallon will be obtained by traveling as slowly as possible in the highest possible gear.
In simplest terms: 35 mph in 5th will use less fuel per mile than 35 mph in 4th, 35 mph in 5th will use less fuel per mile than 45 mph in 5th.
That does not take into account how well the energy in the fuel is turned into heat which is the scientific definition of fuel efficiency. Since your interest is in distance traveled per gallon, not in BTU produced per gallon, the conversion efficiency is a moot point.
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Old 06-26-2008, 06:28 AM   #4
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My VW has gears only slightly taller than yours. I think it has no VVT. My experimentation has proven repeatedly that there is no such thing as shifting too low on my car. It does have a wideband O2, though, so it doesn't go open loop at WOT. It also must have a flatter torque curve / more torque, as it happily enters 5th as low as 25mph and still offers usable acceleration, and even if I enter 5th at 22mph I can still get up to speed.

I'd say, just experiment. Looking at your gaslog I can see that you drive a lot of miles, so it won't take long. Fill every 200 miles while you're experimenting, so you can have quicker results. In a couple weeks time you'll know for sure what the best pattern is, unless you want to experiment with skip-shifting too.
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Old 06-26-2008, 07:35 AM   #5
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I try to keep my rpm below 2,000, sometimes 2100. You have a bigger, more powerful engine than I do. Anything above 1500 should have enough power to move things along.
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Old 06-26-2008, 10:14 PM   #6
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Thanks for providing the gear ratios and tire size. Here's a speed-in-gear chart for your car, courtesy of http://www.f-body.org/gears/

RPM- 1st 2nd 3rd 4th 5th gear
500- 2 4 6 8 10 mph
600- 3 5 8 10 12
700- 3 6 9 12 14
800- 4 7 10 13 17
900- 4 8 11 15 19
1000- 5 8 13 17 21
1100- 5 9 14 19 23
1200- 6 10 15 20 25
1300- 6 11 16 22 27
1400- 7 12 18 24 29
1500- 7 13 19 25 31
1600- 8 14 20 27 33
1700- 8 14 22 29 35
1800- 9 15 23 30 37
1900- 9 16 24 32 39
2000- 10 17 25 34 41
2100- 10 18 27 35 43
2200- 11 19 28 37 45
2300- 11 19 29 39 47
2400- 11 20 30 40 50
2500- 12 21 32 42 52
2600- 12 22 33 44 54
2700- 13 23 34 45 56

If your car can handle 35mph in 5th gear, then it should be able to go 29mph in 4th, 22mph in 3rd, 14mph in 2nd, and 8mph in first.
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Old 06-27-2008, 04:56 AM   #7
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Lower is better.

It may also be just as important to use downshifting to keep fuel shutoff engaged as long as possible.

Slowing down in gear is the same as shutting the engine off without the problems associated with actually turning the engine off and restarting.

My VX fuel shutoff works down to 860 RPM, but with the aircondition on it goes up to 1200+.

Best way to determine the point where your cars fuel shutoff stops working is to put it in 2nd rear and slow down (foot off the gas completely) until you feel the engine power begin. It should be fairly obvious.

regards
gary
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Old 06-27-2008, 06:16 AM   #8
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Yea, I've been using the fuel cut off lately too. This tank is lookin pretty good. We'll see in a day or two
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Old 06-27-2008, 08:23 AM   #9
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My 96 DX does fuel cut down to 1200 rpm.
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Old 06-27-2008, 08:52 AM   #10
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2700 rpm at 56mph in 5th, that's horrible, Marvin does better than that with a 3 speed auto, 2800 rpm gets me 65mph, 55 takes about 2600. WTF is up with 5 speed manuals these days? 5th should be an overdrive ratio.

Edit: ah, it technically is, it's the final drive that screws you.
Edit2: on the plus side you could still "drive" that thing if you lost all but 3rd and 5th
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