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Discussion Starter #1
OK I may be wingeing, but I expected from looking at other posts that my mpg would stay roughly the same after my Speedparts ECU upgrade on my 1999 9-3 LPT auto. Instead it's gone from around 29mpg to 24mpg on comparative runs (ie same regular journey, same speeds).
The fun factor has gone up in leaps and bounds but I'm disappointed at the pumps (not to mention the recent fule price rises ).
Has anyone else had the same experience ?
 

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pen.. what do you expect man ? The fueling and air intake have all increased and into the bargain as the car gets too hot it dumps fuel into the chambers to manage temperatures.. it kinda stands to reason that MPG will suffer.

And you've also probably adapted your driving style to use the performance on offer more.
 

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MPG didn't change after ECU tuning.

It's my drivingstyle that makes the car thirsty, the Hirsch chip is not to blame. If you want the extra power, the engine will need the extra fuel.

At the Nurburgring fuel consumption was 20litre/100km.
Cruising at constant speed on the highway (no fast overtaking manoeuvres), the SID display shows 8litre/100km.
 

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If driven the same way as before you should get either the same or slightly improve MPG (advantage of the engine revving lower for the same speed). But like Mark says if you actively (and why not?
) use the extra power you will see a reduction. Just as if you always drove it hard before your MPG would go down.

FWIW I get pretty much identical fuel consumption on my 9000 (ex LPT) but I only use the extra oomph for overtaking. Rest of the time it's just cruising (no not that kind of cruising ).
 

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Discussion Starter #5
I'm convinced that I'm driving the same way as before. I do the same (18 miles each way) journey to work each day - mixture of steady 40 - 50 mph and then bumper to bumper crawling along. So there's no chance of using the extra power (except at weekends ). My mpg observations are based on my daily commutes only.

My point is that I'm not getting anywhere near the same mpg after ECU upgrade under driving conditions that make it impossible to use much power.

I'm happy to accept the fact that more fun = more fuel
 

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My mpg improved slightly with my Hirsch ECU. Perhaps this is one of the differences between tuners. Hirsch has to make sure their ECU upgrades remain emmisions legal and this is maybe why their fuel economy is better than some of the others. Just a thought.

Anyways, my daily commute mpg is only 23 mpg at best. A five minute autobahn stint at speeds usually above 100 mph makes for high fuel consumption! Also, I live in a very hilly area that contributes to my bad mileage. It was usually around 22 mpg before my Hirsch ECU!

Have fun!
 

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Originally posted by SteveN:
[qb]If driven the same way as before you should get either the same or slightly improve MPG (advantage of the engine revving lower for the same speed).  [/qb][/b]
How can the engine be revving lower?
Only changing the gear ratios can alter speed:rpm ratio.
 

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Steve probably means he's using a higher gear, wich is possible because the engine now has more power in the low revs.

After the Hirsch ECU was installed, I tend to drive in lower gears during overtaking though. Makes the car even faster
, but the fuel bills even higher
 

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Originally posted by Aero
How can the engine be revving lower?      [/b]
 Originally posted by Maarten
Steve probably means he's using a higher gear, which is possible because the engine now has more power in the low revs.[/b]
Yes and I also mean that the car previously did 2,500rpm for 60mph in 5th and now it does 2,000rpm for 60 in 5th. Fact. Someone will put it better than this but more power for the same revs will equal greater speed at those revs (or less revs required to maintain a given speed).
 

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Huh? It's as simple as this - revs x gearing (consisting of primary, gearbox, and pinion gear ratios as well as rolling tyre circumference) = speed. If at any given moment there's more torque at the wheels than needed to maintain your speed, you're accelerating.
 

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When I talk about maintaining a given speed I'm simply talking about (eg) doing a steady 60.

The FACT is my car revs lower in the same gear than previously (and I don't recall changing the final drive in the 20 minutes it took to plug in the ECU and APC solenoid ) FACT. And when I say FACT what I mean is please don't anyone bother saying it can't do that because... it does
 

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If it is a fact that your car appears to have taken on a different gearing ratio, I would advise you to have it checked out. If what you say is true, then your speed indicator could now be incorrect. Not a big deal, until the police pulls you up and presents you with a speed reading you don't recognise.

Fact is that the speed and RPM indicators are dependent on gearbox ratio and tyre profile. The size and power of the engine doesn't have a say in this. neither does the ECU. As a matter of fact (going off course here..), when you change your tyre profile, you should have the new tyre info programmed into the car via the TECH-II. Otherwise there could be trouble ahead...
 

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I'm not a an expert on later Trionic but it does sound like what's happened hear is the correction factor for the speedo has become "incorrect".

Mechanically speaking, there is no way that changing the ECU can alter the actual mph for a given engine speed in any gear. However, it would appear it is possible for it to alter the displayed mph.

As Stanley says, it needs checking/adjusting with Tech II.
 

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So what you are all saying is that my speedometer is out by approx 14.5%? You are also saying my C900's speedo is out by exactly the same amount given they both read the same speeds (ie when one is following the other at a set 50mph). And you are saying my 0-60 times have improved in the 9000 not because it is faster but because it has only reach 51mph??

Well maybe all that is possible and maybe the and maybe I'll get it checked over with TechII...
 

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Sorry, but there is not other explanation, really.

Look at it this way: as you have a manual gearbox, the connection between your engine's crankshaft and your front tyres is 100% mechanical. One revolution of the crankshaft be multiplied to a fixed rate (1.xx) through the primary chain drive, and then be reduced by one of five, again fixed, ratios in your gearbox. The pinion and ring gear which connects the output of said gear to the driveshafts, has a fixed ratio too. The only thing that is remotely variable in the whole driveline, apart from clutch slip or wheelspin, is your tyre circumference which will be slightly smaller the more tread is worn off.

Disregarding the latter, there is no way a certain road speed, in a certain car in the same gear, would result in different engine rpm's no matter what engine is connected to the gearbox, nor its state of tune or the amount of power needed to reach a certain speed (as long as it can reach that speed. There's really no kind of magical thing going on underneath, just basic mechanics at work.
 
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