[30ONA]

Probably a bit of a loose question. So to clear it up, if you were to do a rebuild on one of these engines, full tear down, what else could/would you do to improve fuel efficiency from combined 10L/100ks to 8L/100ks, (20% reduction in fuel. At this point all hypothetical but I am interested in suggestions that are practical and possible. If you know what the cost of any fuel efficiency improvement would be that would be interesting too.

Tighter build tolerances?
Different cam?
More compression?
Really small turbo?
Extra sensors?
All of the above?

[Gwagensteve]

Taller axle gears.
Lower car
Narrower tyres
convert to part time 4WD
Remove weight

Reduce inlet and exhaust restriction
Use a more thermally efficient fuel (98 octane with no ethanol) with advanced timing
Retard cam shaft timing


I'm not sure if you are familiar with the term "Brake specific fuel consumption" but it's the basis for the way we assess efficiency.

All engines burning fossil fuel derived petrol consume near enough 0.5lb of fuel per hour per horsepower.
There are some small variations between very efficient engines and very inefficient engines, naturally, but really, the only way to make significant changes to how much fuel an engine consumes is to limit the power you're requesting (drive more efficiently) or limit the power the car requires (reduce weight, aerodynamic drag and rolling resistance)

If you're looking for proof, a 576hp HSV GTS consumes the same amount of fuel at 100km/h as a 67hp Sierra. That's because both cars require about the same amount of power to push down the road. (approximately 40hp) For the sierra. Thats 3500rpm and about 2/3 throttle worth for the sierra, for the HSV it's circa 1750rpm and barely any throttle at all. The HSV is twice the weight of the Sierra, but it's much more aerodynamic.

So, what I'm really saying is that with a modern, alloy head/block, knock sensed, computer controlled engine, you're not going to get 20% out of the fuel economy. The most obvious way is to limit overall power developed ( so literally, a throttle stop) Otherwise, you need to reduce rolling and aerodynamic resistance.

Reducing cruise revs might be an option, unless you're lugging the engine, at which point economy will suffer.

[30ONA]

So in essence fuel efficiency has nothing to do with engine efficiency, it is a function of the cars combination of parts and makeup. I get that.

Getting more theoretical, take the engine out of the car. Surely if you took a selection of 2 liter engines from different manufactures and bench tested them running at say 40hp, they would use different amounts of fuel. This would be the engine efficiency. What variance would you see, assuming all working as new.

[watermouse]

Probably much less than 10% difference. In EFI engines particularly emissions control is one of the biggest factors limiting efficiency, with it being difficult to run lean while limiting NOx out the tailpipe.

I went down the same path with the same engine in my GV. The biggest difference made got it to 9.1L/100km by doing this:

Gwagensteve wrote:

Use a more thermally efficient fuel (98 octane with no ethanol) with advanced timing

[Gwagensteve]

30ONA wrote:

So in essence fuel efficiency has nothing to do with engine efficiency, it is a function of the cars combination of parts and makeup. I get that.

Getting more theoretical, take the engine out of the car. Surely if you took a selection of 2 liter engines from different manufactures and bench tested them running at say 40hp, they would use different amounts of fuel. This would be the engine efficiency. What variance would you see, assuming all working as new.

By a very tiny amount associated with combustion chamber design and materials. Like .45 to .55 lb/hour/hp from least to most efficient - and that's a broad range including very old, cast iron motors with low compression to modern designs.

The obvious exception is the effect of direct injection. At a steady state 40HP, direct injection engines can run very lean (like 15:1 or leaner - so lean a regular engine wouldn't even run*) but the control software and tuning is enormously complex. Additionally, under these circumstances, exhaust temperature (and NOX) goes sky high, so NOX scrubbing and complex exhaust systems are required. And even then, if the computer doesn't sense fuel is up to scratch, (or any other of the 4895648575647 things it's measuring a jallionty times a second), it won't lean the engine out. It is feasible to swap in a direct injection 2.0 motor and enjoy the benefits of low emissions? No, because the systems that run the car are now so complex and interconnected they're well out of the reach of us, financially, to configure. And in any case, as soon as that direct injection motor needs to make power, it's back to the same 12.7:1 stoichiometric ratio as every other motor and the amount of time the car spends in direct injection (sometimes referred to as "stratified" mode) can be very small. In fact, the early direct injection VW's into Australia never ran in "stratified" mode because our fuel wasn't up to scratch.

Many years ago, the quoted fuel economy figures for cars were achievable. It's now increasingly difficult to match quoted figures as the car makers are tuning their cars very specifically to pass the emissions test. What you get in real life isn't in any way related.

As a "concept" some years ago, Ferrari built a "zero emissions" V12. The car had just enough battery power to get through the urban emissions test purely on battery. As soon as the test included extra-urban, the petrol motor started up. It's an extreme case, but it's an example of how the test can be "cheated" - a zero emissions V12 Ferrari! Unpossible!

Also, consider the role of transmission in these emissions/economy figures. Modern torque converter automatics now have upwards of 8 ratios and lock in every forward gear. compared to a manual, they are typically faster AND more economical, because the transmission keeps the motor in a very narrow operating range where it's most efficient. I had an X3 3.0 diesel a few years ago with an 8 speed auto. I never had any idea what gear it was in, but it was incredibly smooth and shuffled ratios all the time. DSG cars are the same (without the torque converter) - they are working with the motor to keep everything in that sweet spot. Engines rarely now have to stretch from off idle to redline and they way they are tuned reflects this. Look at the BMW 3 litre petrol - peak torque is all in by 1450 RPM, the turbos are filling the cylinders so there's no pumping loss as the engine tries to draw air in, and every parameter can be very accurately controlled.

of course, engines with more cylinders have more internal friction, so a large engine at low output will use more fuel at 40hp than a small capacity engine, which is why there's now more 3 cylinder turbo engines compared to atmo 4 cylinder engines - less rods, bearings, cylinder walls to wet, smaller oil pump etc.

* These direct injection systems are pretty interesting. They have little bowls on the top of the pistons. As the piston nears TDC on the compression stroke, a little squirt of fuel is shot into the bowl and ignited by the plug. The average A/F ratio in the cylinder is far too lean to permit combustion, but in that tiny spot it's just rich enough. As you can image though, this doesn't work across all engine speeds, temperatures etc, and is only relevant at steady engine speeds where the computer can lean the engine out. request acceleration, and the engine switches to a normal injection mode with "regular" A/F ratios, so the efficiency gain is all about a small operating window, which takes us back to the rest of the car trying to keep the engine in that operating window.

[alien]

Gwagensteve wrote:

a 576hp HSV GTS

Pretty sure Steve just advocated a commodore engine swap =)

[Gwagensteve]

I drove a current manual GTS on Saturday. As you'd imagine, its quite rapid, and makes all manner of amusing noises. What you might not expect is that it's a very, very smooth, and balanced motor, very refined, and, exhaust gurgles and pops aside, an exceptionally quiet motor. I was expecting more intake noise and supercharger whine. I guess being two valve per cylinder and pushrod, there's little valve train noise which I think we get accustomed to with modern (particularly V6 DOHC) motors.

One of the more relaxing cars I've driven. You can short shift it like a big diesel and it just wafts along. Very impressive.

Steve.

[30ONA]

Digging.

How is the SX4 (4wd) so much more efficient with the same long block? I understand the cars are vastly different but the SX4 is getting 8l/100k's worst case compared to my GV running a city value of at least 10L/100 which I'm lead to believe is pretty common. Is there better tuning and sensors?

[atari4x4]

Taller axle gears
Lower car
Narrower smoother tyres
2WD
Remove weight

[Gwagensteve]

I don’t suppose it’s 20% lighter or 20% more aerodynamic?
How about lower drivetrain loss?

[30ONA]

The SX4 crossover (AWD) which is the one I'm referring to for fuel usage, is actually 5kg heavier but 18kw more from higher compression. Also I would not expect aerodynamics to come into effect much at low speeds <60.

[rthy]

Are you just trying to make the engine more efficient or cheaper to run?
ie. up the compression and run straight/liquid lpg?

[Gwagensteve]

Well higher compression will improve BSFC from the get go, as will lower unsprung weight.

If you don’t think aerodynamics make a difference at 60km/h I’d invite you to walk forwards into a 60km/h wind and see if you notice. The SX4 is notably notably slippery. The 5kg weight difference is negligible.

What does 8l/100km “worst case” mean? I would have thought an SX4 would be much less economical than that on there urban urban cycle. Regardless, of course an SX4 will do better than a GV- even rolling resistance would make a measurable difference.

The answer to economy is the vehicle it’s in and BSFC. Even an extremely efficient motor design will use more fuel in a less aerodynamic car with higher rolling resistance.

[30ONA]

rthy wrote:

Are you just trying to make the engine more efficient or cheaper to run?
ie. up the compression and run straight/liquid lpg?

I don't understand that question. Wouldn't a more efficient engine mean more miles per gallon hence be cheaper to run.

I'm just trying to come to grips with such high fuel consumption for a light car with a small engine.

[Gwagensteve]

Nothing you can do will be cost effective if you want to try and make the car cheaper to run.

At $17 per 100km, $1k spent achieving a 10% economy increase would take 58,000km to make your money back.

Efficiency is improving BSFC. This is improving power and therefore using less throttle to achieve the same outcome. This is always false economy.

Making it cheaper to run is making the car use less fuel to cover the same distance. This is rarely engine related.

I’d be perfectly happy with a GV getting 10l/100km. That’s quite reasonable.

[rthy]

30ONA wrote:

I don't understand that question. Wouldn't a more efficient engine mean more miles per gallon hence be cheaper to run.

lpg is cheaper than 91ron petrol, sure you could loose 20-40% efficiency with lpg but at around half the cost of petrol...
or importing a diesel halfcut from japan...

Then again, as above, the return on investment might take awhile and availability of lpg in whoop whoop should be considered.

Has the engine lost compression? lots of blowby?

[ZUZUKI]

Park the GV in the garage.
Let the registration run out.
Buy an approx. 2000 Daihatsu Handi / Cuore (989cc triple, manual) for $2000.
Drive it like a grandpa & you'll get into the 5s around town - on 91RON (my dad did, for years & he was a grandpa).
If you drive the 'average' which used to be / still is (?) something like 15,000km per year.
In the GV, you would have 150 lots of 100km. If you did 10L per 100km, you used 1500L - at currently say $1.60p/l = $2400 worth of fuel.
In the Daihatsu, you would have 150 lots of 100km. If you did 6L per 100km, you used 900L - at currently say $1.60p/l = $1440.
Difference $2400 - $1440 = $960p/a. Because the rego ran out on the GV, you are only paying the same one rego per year. Two years of driving & you've just about paid for the car with the savings, after that you are winning.

Oh - you wanted to go 4WDriving, or think you are going to get laughed at in a Handi?
Sorry, back to 10l/100km. There are Jimny (you know, 1.3litre little things) owners out there who live with 10L/100km around town.
Sorry, a silly post, but I think we are all trying to tell you that higher fuel consumption from a (older, petrol) 4WD is the price you pay for driving a (older, petrol) 4WD.
Rgs, Michael

[30ONA]

I'm actually getting 13.5/100

[Gwagensteve]

And what is quoted urban fuel consumption for your model?

[30ONA]

10/100

[greenzook89]

I average 10l/100 from our J24 NGV. If I add my dirtbike or camper trailer that adds another 3-4 l/100. Car is stock standard.

I also have a 2006 Swift that averages 6l/100. I've done 60000 kms in the Swift in the same 2 year period since buying the NGV. I've worked out with that distance travelled in the Swift has saved me on average $1800 a year just on fuel. Definitely covers rego each year on another car. Our NGV hardly gets used these days (wife has a company car) so 2.5 years after purchase it only has 14xxx on the clock.

Up to you which way you go, but i found buying an econobox for the general commute was the easiest way for me to save a few bucks on fuel.

[Slug]

Just started running synthetic 5-30 has made a little better fuel consumption on the trip Ararat to Sydney seen 9.5 and very low 10s in stead of 11 to 13 High 16 was the worst with a head wind loaded swag on the roof on a Inaminka trip couldn't hold 100k without the auto going back to 3rd
Same with the fort nightly trip to Ballarat again mid to high 9 and 10.5s
Don't know what shit the dealer had put in it, knowing the 40w
Have also replaced diff (witch they didn't do at 10,000) and the transfer case, my understanding is synthetic is used there from factory
Have kept fuel records from the start till now 30,000
The vehicle will never go back to a dealer and now just service it my self
I gave up on factory warrintee years ago, total rip off the dealer gets it to 20,000 or 12 months then never goes back
Got caught ot with a triton 2010 fixed price was always $560 till I had the 70,000 and geuss what $350 for the equilivent 10,000
Mines a late 2016 gv3
And if any thing major happned to the other cars I just trade them

[Gwagensteve]

I don’t believe you. A 30% fuel economy improvement from changing oil is impossible.