I've made a mpg improvement with an aftermarket chip. Surprised.

tomstickland

daveyjp wrote: »

I have done absloutely nothing to my car, but mpg is up around 5 mpg in the last month - now getting high 30s round town, was mid thirties. The fact it is now 20 degrees rather than 5 is one reason, the roads I commute on are also quieter as the holiday season has started so that's another. 4mpg is too small an amount to say its due to a single factor.

I am well aware of statistical certainty and without the results from the AFR measurements I'd be happy to agree that the difference I was seeing was small enough to be inconclusive. In that case I'd have to build up a long term data set, swapping the chip in and out and then look for a trend.

However, measurement of AFR with a lambda sensor shows that this particular map leans part load sites. This confirms my suspicions and is enough evidence for me.

The point of all this being that, rather surprisingly, a performance chip is actually providing an opportunity to save money.
I know several people who have DIY mapped their engines, and there's quite an MSE aspect to it.

meant to add "in the event of a crash and you have not told them" , first thing an investigator looks at

Where did this particular gem come from?
Bearing in mind that aftermarket chips are often just reflashed OEM chips so look identical, the OEM themselves often changed specifications and people do swap ECUs over.

cepheus

tomstickland wrote: »

The new chip raised the rev limit from 6,500 to over 7,000rpm.....

Engines are engineered to met various compromises between emissions, fuel consumption and performance, it could be that the chip increased emissions at the cost of the other two. That is why most re-chipping is technically illegal unless the vehicle set up has been type approved.

tomstickland wrote: »

I did a measured run today. 280 miles at 80-85 on a motorway.....

Your definitely sound like a BMW driver, will the saving be enough to pay for the speeding fine?

tomstickland wrote: »

This is a 3-4 mpg improvement over the std chip...I'm impressed.

This could be for a variety of reasons other than the chip. Did you time the trip to make sure you were travelling at a comparable speed? Can you be sure that variations in speed were kept to a minimum? Was it over the same road surface. Meteorological conditions can affect fuel consumption particularily wind speed and direction, air temperature and therfore density has been mentioned already. Air pressure and rain are other factors

tomstickland

In my journey I was overtaken by 100s of other vehicles, most of which weren't BMWs. It's 20 years old btw.
You are very unlikely to receive a speeding ticket when travelling at 80mph indicated, due to speedos overreading. I also have slightly different tyre sizes which also cause an overread.

Yes, as I already pointed out, I am aware of the other factors and statistical certainty. Hence why it was initially a "suspicion". The AFR measurements confirmed my suspicion.

It's very broad brush - did I think that the chip had made fuel consumption worse, better or about the same? My opinion on limited data was that it didn't seem to have worsened, it was possibly about the same, it was possibly better.

Conor_3

tomstickland wrote: »

Yes, in general I'd be very wary of chips and the claims made for them, especially on modern engines.
That chap in the link said that pinking was a problem if you increased the fuelling using increased fuel pressure ("power boost valve").

Wierd. It's certainly the opposite of what I'm experiencing with carburettors. My Capri was pinking once you got above 4000 RPMs because the mixture was leaning right out due to the K&N on the rolling road. Drilled out the jets, increasing the mixture from the 0.2% it was up to 4% under WOT and it allowed me to dial in an additional 8 degrees advance as well. The pinto in mine is now running so much advance it's just off the markings on the crank pulley

cepheus

Of course a guaranteed method of saving fuel would be to drive slower

Conor_3

cepheus wrote: »

Of course a guaranteed method of saving fuel would be to drive slower

Riight...:rolleyes:

It's not that simple.

banger9365

"Of course a guaranteed method of saving fuel would be to drive slower" is laughable it uses more fuel,i agree with conor on that,put i will say it's easy to get more mpg out of a car if you now what you are doing and that the hard part ,that most poeple have to change the way they drive and take the blinkers off eg not letting the car roll to a stop because when idleing it uses fuel put not when it in gear rolling to a stop ,taking your foot of the gas when going down hill again no fuel been used in gear it all helps get the mpg up

anewman

cepheus wrote: »

Of course a guaranteed method of saving fuel would be to drive slower

Works with my car. 60mph long motorway journey gives about a 5mpg improvement over belting it at 75-80mph. I only do 70 or a little over now if time is an issue, but I guess the easy solution to that is to leave earlier to save the money on the petrol - after all petrol isn't the cheapest thing at the moment. I suspect going a little slower than 60 may decrease consumption a little more but probably not by much.

I guess these factors depend very much on factors like the gear ratios, engine type, and a variety of other things. I suspect there are cars out there that do just as well at 80 in 6th as they do 60 in 5th or 6th. And there are of course many many more factors, especially car maintenance/servicing.

Markyt

cepheus wrote: »

Of course a guaranteed method of saving fuel would be to drive slower

Please explain how this works ...

cepheus

Markyt wrote: »

Please explain how this works ...

Aerodynamic resistance increases as the square of the speed, and rolling resistance is approximately proportional. Since Power is speed x resistance it takes substantially more power to drive at a faster speed. Yes this places the engine at a different operating point which alters efficiency, but fuel consumption is reduced after all this is taken into account. Its a shame they no longer quote fuel consumption at a constant 56 and 75 mph.

Here we are referring to the deliberate reduction of speed on a Motorway from say 80 to 70 or 70 to 60 mph, not the reduction in average speed caused by congestion which results in more accelerations and braking which can increase mpg.