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Old 01-14-2012, 12:23 PM   #1 (permalink)
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Max. Torque at high-revs. How do you drive to increase MPG ?

Since I have no advanced instrumentation to check live MPG readings as I drive and I suspect I'm not "doing it right", decided to come here and ask some advice for those that have experience with higher-revving vehicles.

My current car achieves its max. KW power around 5750rpm according to it's manual and the torque at a quite high 4500rpm. This is significantly higher than my previous cars since it's a 4valve per cylinder engine.

What I've experienced so far is that in city driving it seems to be ok with shifting around 2500-2700rpm or so , falling to 2000-2100rpm for the next gear, by ok I mean it has enough power to move comfortably through traffic without being sluggish. But on the highway, the situation changes, especially in 4&5th gear. Whenever driving on the highway, at around 65-70 mph (the speed limit here is quite low at 100km/h on the highway) if, because of traffic I'm obligated to slow down to let's say 55-60mph (5th gear) the car feels very sluggish and most of the time I shift back to forth. This car really loves going over 3500-4000rpm and that's where I can feel the engine pulling properly although I'm thinking the MPG's drop significantly by doing that. From what I've read on some european VW forums, these engines are a bit heavy on the fuel and it's hard to obtain factory figures on the roads.

Combined with having to switch to the higher octane 98RON plus moving a bit further away from work, it looks I'm looking at doubled fuel costs on this car...

I'm hoping to eventually bring the fuel economy to about 40MPG(6l/100km) or so...

Any thoughts or advice from drivers of similar vehicles on how to best drive this to squeeze the highest MPG's out of it ?

P.S. the reason I switched from my previous car was that it was aging, the AC wasn't functional anymore (Cyprus is HOT !), some oil leaks that seemed to get worse as well as I wanted something a bit more comfortable and spacious.

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Old 01-14-2012, 01:02 PM   #2 (permalink)
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I'd go ahead and try higher revs while accelerating. If traffic is in the way, try shifting slower instead so that you neutral coast a bit between gears.

Have you increased the tire pressure and learned the coast points of you regular commute yet?
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Old 01-14-2012, 06:47 PM   #3 (permalink)
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Well, most of my commute is the same as before, no problems there, it has just been increased a tad bit. The tire pressure is .4 bars above manufacturers recommendations (2.5 bar, won't put it higher than that because there are quite a few potholes here and there and don't want to put too much stress on the suspension.

I guess I'll just have to see/find the "sweet spot" for this engine.
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Old 01-15-2012, 03:45 PM   #4 (permalink)
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My first suggestion would be that if you're travelling at 100km/h+ you're going too fast. Most cars tend to do best in the 80-90km/h range, so if you can safely go that slow, it's worthwhile.

At 100km/h it takes 6 minutes to travel 10km, at 90km/h it takes only 40 seconds longer. If you're commuting 20km, that's less than 2 minutes added to the trip, and the slow lanes tend to have less sudden changes in speed (at least in NZ anyway), further improving fuel economy.

As for gear changing, I would recommend staying below 3000rpm unless you need the power (eg merging with fast traffic or overtaking a very slow vehicle). Like your car, my Camry has very little power below 3000rpm, I try to avoid going over 3000 unless it's unavoidable, as in not doing so would result in exposing myself or others to danger, or in the case of steep hills, I wouldn't make it to the top at more than a snails pace.
Doing so has meant that passengers often comment on how smooth my driving is, and not being stressed about going fast has also made driving in traffic much less stressful.

Best of luck,
Tom
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Old 01-17-2012, 10:11 PM   #5 (permalink)
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2002 Civic Si. I shift @ 2500 rpm, and real light on the pedal. with the close ratio gears it gets best around 40 mph in 5th. When Im trying real hard, I keep it @ 60 mph and below on the highway. But sometimes its hard to do when the speed limit it 65mph, and some are doing 80 mph...
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Old 01-17-2012, 11:20 PM   #6 (permalink)
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I haven't tested this so much on flat ground, but even on inclines, if I downshift from 5th to 4th, I lose about 25-30% fuel economy. I have a real-time gauge, and on one hill I've watched this effect closely. At ~ 35-40 mph, I'll drop from ~20 mpg to ~15 mpg... same speed, same incline. For reference, the rpm shift is from ~2,000 to ~3,000 rpm.

I would say, as long as you are cruising, you should try to stay in your highest gear. Sure, if you must pass or accelerate, you'll probably want to downshift. From the behavior I've observed in my real-time fuel gauge, I always get far better mileage while cruising than I do while accelerating... regardless of which gear I'm in and regardless of whether the engine feels sluggish.
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Old 01-18-2012, 09:13 AM   #7 (permalink)
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Quote:
Originally Posted by slurp812 View Post
2002 Civic Si. I shift @ 2500 rpm, and real light on the pedal. with the close ratio gears it gets best around 40 mph in 5th. When Im trying real hard, I keep it @ 60 mph and below on the highway. But sometimes its hard to do when the speed limit it 65mph, and some are doing 80 mph...
Real light on the pedal is probably not enough. Lower the RPM (lower gear) and increase the pedal percentage. Not sure if it would work well with the high performance engine but it does have VTech so it should perform decently at lower RPM.

Another tactic, get to speed fairly quickly, the get in the highest gear as soon as possible. Try driving in top gear down at low revs and see what the engine "likes".

This way you spend the least amount of time gulping fuel for acceleration and the most time cruising at best mileage.

Also focus on coasting and timing any lights or other forced stops. Drafting 3 stripes behind a host vehicle will help also.

regards
Mech
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Old 01-31-2012, 01:23 PM   #8 (permalink)
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Yep, get the energy sapping acceleration out of the way reasonably early with moderate acceleration. I can cruise comfortably at 40mph in 5th gear with my Probe's 2.2L Mazda engine and with my '81 VW 1.7L 8V. The 8V may have something in common with your 1.6L block, but I'm not sure. Get to a comfortable cruising speed (I sometimes use 55mph on freeways because that's the "posted" limit) and be light on the throttle over hills. A very small change in accelerator position can easily put you + or - 5 mpg (evidenced by driving my dad's Passat 30V with the live MPG feed on).

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