timbo

I have put together a variety of charts tracking consumption trends over 22,000k. I am not sure they prove much, other than that the RX-8, in common with most cars, loosens up over time and thus becomes marginally more fuel efficient. :p

As to something happening with the ECU at 20K - well, draw your own conclusions.

I shall continue to collect the data and post from time to time.

Tim

First, fuel consumption calculated at each fill (bottom axis is the odometer reading)

timbo

Next, the long run average fuel consumption (ie, progressive litres used against progressive k's travelled)

timbo

Finally, the average fuel consumption calculated in 2,000K stages

timbo

Lies, damned lies … and statistics

rpm_pwr

So according to the graph, if you put another 600,000km's on the car, it will actually start making fuel?

timbo

Yep -- I reckon it'll make that little Prius look like a gas guzzler

RXE16T

I hope you're right about the fuel economy improving Timbo, because my 8 is a gas-guzzler at the moment!

Gomez

So none of you blokes have ever driven a 440ci Six Pack (3 Holleys) Dodge then....:D

Gomez

timbo

No … but I have had a 4.6L Range Rover, which was fun to drive … from petrol station to petrol station…!

jax8

I had a de Tomaso Longchamp whose greed was in the RR category.
The hairline fractures it developped in suspension and chassis after 12 months on country roads was scary.

Hymee

iTrader: (1)

Timbo,

Very well Done!!

You get Hymee's Most Informative Post Of the Week Award!

Congratulations! As a special reward, you get to increase you post count by 1 every time you reply to this, and pat yourself on the back.

Cheers,
Hymee.

takahashi

i did a try run in the freeway today (to work) and I have 10.8L/100km

I am only up to 5600km @ the odo so plenty of time to loose up the engine.

timbo

Aw shucks, thanks Hymee

Actually, I don't know that it was all that informative. Certainly not as I thought might be the case, given my sense that I had a reasonably steady-state driving pattern. Apart from an obvious long run (but small) decline in f/c (expected), it shows again that chaos theory can and will interfere in most 'real world' tests.

I'd still like to get to the bottom of all these ECU features and myths.

Woo hoo -- look at that, I posted this and my post count increased by… by… one! :p

Hymee

iTrader: (1)

So here is a chance to up your post count, yet again

Is the trend line on the first graph calc'd by Excel, or did you eyeball it?

My impression is that if there was a "magic switch" you would see the change happen more noticably at that point in time. But a trend line, depending on the smoothing, can hide a deviation like that.

Cheers,
Hymee.

timbo

Calculated by Excel. 2nd order polynomial, as I read the fn description. It would hide the switch, as you say. That's why I then calculated averages in blocks of 2,000Ks. While that showed a switch, there were also previous ones. Result: inconclusive

Hymee

iTrader: (1)

That was a good reply - worthy of the additional post count

I think it would appear to be a long term trend, rather than a binary (on/off) sort of thing.

Cheers,
Hymee.

Gomez

I got the impression from the Renesis Tech that the mixture started leaning off around 20K...IE, no switch.

Will grill him further when I pick up the car...

Gomez

Wildcard

We can't wait to hear what he has to say! There has been rumour and speculation ever since the '8 came out about the ECU being programmed to give more power after a certain number of km's. It would be great to get some hard facts.

Hymee

iTrader: (1)

I hope it isn't the same tech who said the noise at startup was the ceramic seals

Wildcard

True.... While Mazda Japan clearly know this car backwards (because they built it), Mazda Australia seem to know f*ck all. At least that's been my personal experience. I have much more faith in the collective knowledge of this forum than I do in the Mazda Aust. tech-hotline.

Hymee

iTrader: (1)

Agreed wholeheartedly!

But I bet if ya were on the 'phone to the tech-hotline and said "I was reading on the Internet Forum about such and such...." they would laugh and think you were an idiot

(Although I would hope not!)

Cheers,
Hymee.

skc

great stats Timbo. I look forward to more economical driving as the car runs in.

timbo

Better get driving tips from labrat

RichardM

I'm surprised by the figures.

I’d have thought that the RX8 would have averaged a lower consumption figure than that? Somewhere in the mid 11s.

My average fuel consumption is 12.86 L/100km with a 5.7Litre motor (and 7.31L/100km from my 323).

Is this the fuel problem that was touched on in another thread?

timbo

I guess it all has to do with the higher RPM of the rotary, and the rich fuel/air mix used, especially once the revs top 3,250. Hymee and others have more knowledge on all this and there are some fuel/air mix charts as part of dyno runs elsewhere on the forum.

But I understand the Renesis is still somewhat more economical than earlier rotaries.

In the meantime, GM has been working hard to increase the efficiency of its bent engines: the wife's Calais (pov 3.8 V6 non s/c model) manages below 10L/100K in mixed driving -- better than my previous V6 Astina!!