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Old 12-14-2010, 05:41 PM   #1 (permalink)
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Hi From New Zealand

Hey Ecomodders,

I'm new here but have been interested in getting good fuel economy for many years. I often drive with economy in mind and have also done a few improvements to my vehicles to help improve the fuel burn figure.

My 1994 Subaru Legacy RS (Japanese import) gets on average 20 MPG combined cycle (here in NZ we are metric, but I don't mind converting for you guys ) and thats with the occasionally boost up to full power, it is my weekend a fun car after all!
I've owned it for 7 years now, and in its originally spec it was a 2.0l twin turbo, terribly inefficient and fuel guzzling!
I have converted it to a single turbo turbo setup, which un-complicates a very complicated and inefficient induction system.
Added a free flow cat-less exhaust (we dont have emission testing here, yet).
I've also increased the ignition voltage to 16v, which actually does create more complete fuel burn and has slightly increased mileage, so far I haven't burnt out any coils so thats a bonus!
I plan to fit mpguino soon (its OBD1) to keep a better eye on fuel consumption. 20 mpg is not impressive I know, but for a 4wd car thats capable of 300hp thats quite respectable it think, and there are still improvements to be made that wont compromise performance or reliability too much.

My daily driver is a 1992 Isuzu MU, I think in the US they are called a GMC Amigo? Anyway its a small SUV with a 2.8l turbo diesel engine. It returns a reasonable 30mpg on a combined cycle. I'm happy with that for now, diesel has gone up to $1.30 a litre so I'll be looking at doing a few mods soon to stretch the economy even more. One idea I have is to fit a fuel pre-heater before the injector pump (yes mechanical diesel injection) that is heated the fuel slightly by the engine coolant flow.

I look forward to sharing ideas with you all in the near future.
Bye for now,
Leigh.

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Old 12-14-2010, 07:06 PM   #2 (permalink)
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Welcome to Ecomodder, it's cool to see another NZer on here.

What part of NZ are you from? I'm from Wellington, one of the biggest tricks here is learning to use the hills to your benefit: not going too hard on the gas on the way up and using engine braking (DFCO) on the way down.
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Old 12-14-2010, 07:59 PM   #3 (permalink)
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I'm in Hamilton, the Waikato is reasonably flat so I mostly employ 'light footedness' and driving without brakes (in the diesel).
I've ofter wondered, would fuel consumption be comparable driving economically in hilly areas to driving economically in flatter areas?
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Old 12-14-2010, 09:00 PM   #4 (permalink)
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Quote:
Originally Posted by Leighos View Post
I'm in Hamilton, the Waikato is reasonably flat so I mostly employ 'light footedness' and driving without brakes (in the diesel).
I've ofter wondered, would fuel consumption be comparable driving economically in hilly areas to driving economically in flatter areas?
Depends a lot on the hills. If the hills are so steep that you have to brake on the way down, it's often less efficient. But if the hills are enough to maintain speed in neutral or with light engine braking (just enough to get deceleration fuel cut off), you can often get better fuel economy than on the flat.

Driver skill comes into play a lot more on hills, and manual transmissions really shine in comparison to autos (especially on the way up).

Are your cars manual? If they are, what at what kinda revs do you shift up?
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Old 12-14-2010, 10:26 PM   #5 (permalink)
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Welcome to EM, Leigh!

I've been to New Zealand -- does that count? We visited for about 2 months, back in 1982. It's a wonderful place.
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Old 12-14-2010, 10:47 PM   #6 (permalink)
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Quote:
Originally Posted by tumnasgt View Post
Are your cars manual? If they are, what at what kinda revs do you shift up?
Yes both my vehicles are manual, I've actually never owned an auto!

With the Subaru, when I'm driving economically, I drive totally off boost and change up around 3000. If figure keeping the manifold pressure low but still using adequate RPM to best use the engines torque, is a good way to keep the fuel burn low.
Although my concern with turbocharged petrol engines when driving off boost, is effectively they are acting as a normally aspirated engine, but having a very inefficient compression ratio (My Subaru is 8.0:1) and a restriction in the intake (the turbo and intercooler). I guess its all about compromise though with auto engines.

With the Isuzu, apart from idling, the engine is mostly always running in boost pressure, this is where turbo diesels are very efficient. I maintain around 5psi of boost and get to 2500 RPM before I change up, this seems to be a good balance of useful torque and economy. Incidentally, I also cruise at 2500 RPM in 5th gear, it give approx 85km/hr road speed which better suits the vehicle's aerodynamics also.

What sort of tyres do you run?
The Isuzu used to have 15" 'all terrain' tyres, not that great for rolling efficiency. I managed to get a set of 18" alloys with proper road tyres, I reckon that made quite a difference to economy (and road handling).
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Old 12-14-2010, 10:51 PM   #7 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
Welcome to EM, Leigh!

I've been to New Zealand -- does that count? We visited for about 2 months, back in 1982. It's a wonderful place.
Of course it counts

Come back for a visit again sometime, its still a wonderful place.
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Old 12-14-2010, 11:30 PM   #8 (permalink)
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Quote:
Originally Posted by Leighos View Post
Yes both my vehicles are manual, I've actually never owned an auto!

With the Subaru, when I'm driving economically, I drive totally off boost and change up around 3000. If figure keeping the manifold pressure low but still using adequate RPM to best use the engines torque, is a good way to keep the fuel burn low.
Although my concern with turbocharged petrol engines when driving off boost, is effectively they are acting as a normally aspirated engine, but having a very inefficient compression ratio (My Subaru is 8.0:1) and a restriction in the intake (the turbo and intercooler). I guess its all about compromise though with auto engines.

With the Isuzu, apart from idling, the engine is mostly always running in boost pressure, this is where turbo diesels are very efficient. I maintain around 5psi of boost and get to 2500 RPM before I change up, this seems to be a good balance of useful torque and economy. Incidentally, I also cruise at 2500 RPM in 5th gear, it give approx 85km/hr road speed which better suits the vehicle's aerodynamics also.

What sort of tyres do you run?
The Isuzu used to have 15" 'all terrain' tyres, not that great for rolling efficiency. I managed to get a set of 18" alloys with proper road tyres, I reckon that made quite a difference to economy (and road handling).
If your Subaru's gearing allows it, I'd recommend changing up around 2300rpm, as engines are typically more efficient at lower RPMs.

On the highway I try to stay at around 90km/h, which is around 2500RPM in the Camry and around 1900RPM in the Sonata (if only manuals had gearing like that). 90 is good because it's the legal limit for trucks, so people get less pissed off than if I was driving 85. Sometimes I'm impatient and drive at 100 though
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Old 12-15-2010, 03:27 PM   #9 (permalink)
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Quote:
Originally Posted by tumnasgt View Post
If your Subaru's gearing allows it, I'd recommend changing up around 2300rpm, as engines are typically more efficient at lower RPMs.
I have tried shifting at lower RPMs, the problem with this car is due to its relatively low compression ratio and transmission drag (full time 4wd), if the RPM drops below 2000 after a shift, the engines needs to pull a lot less vacuum to recover, resulting in more fuel usage.
Without the use of an accurate fuel consumption gauge of some description, this is only an educated guess, but my current driving style does yield a lot more mileage than other techniques I have tried.
I'd like to build a mpguino or something similar in the near future.
Do you use anything other than odometer to monitor fuel consumption?
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Old 12-15-2010, 04:16 PM   #10 (permalink)
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Quote:
Originally Posted by Leighos View Post
I'd like to build a mpguino or something similar in the near future.
Do you use anything other than odometer to monitor fuel consumption?
I'd like to get a proper meter, but the Camry isn't OBD-II, so it'd have to be an mpguino, but we might be selling it soon so my mother doesn't want me modifying it. For the Sonata, a Scangauge is a bit pricey, and we are considering downsizing it to a civic hybrid or similar, so an mpguino isn't an option for now in case we do sell it.

The Sonata has a trip meter for fuel economy, but it's not very accurate (look in the fuel log, I have the meter vs actual in the fill up notes). It's nice though because it finally got my mother to start driving more efficiently, even with the slushbox and bigger car, she is using less fuel in the new one than she used to in the Camry.

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