BSFC Mapping

[drmiller100]

Originally Posted by jmcc

For back to back under controlled conditions maybe. Question was about generating a BSFC map and the errors in the fuel calculation in the ECU make this too inaccurate to be useable (in my opinion).

Reason for inaccuracy: fuel flow is calculated as a function of rail pressure and injection duration for a nominal injector. Injector flow particularly will vary, and needle lift vs electrical pulse will also be inconsistent.

OBD is accurate, but not precise.

What are you going to do with BSFC once you know it on a chassis or engine dyno?

Probably try to figure out most optimal engine parameters to run the engine at.

But you would need to compare that to precise measurements of the aerodynamics of the car, which would require a lot of time in a wind tunnel with a moving floor.

Another option is to drive your car down the road with a MPGUino and learn where your car gets the best MPG.

Sure it won't be PRECISE, but it will be hella accurate.

[IamIan]

An Alternative to the traditional Dyno wold be a sensor in the drive wheel or drive shaft that measures the real time torque and RPM in real world conditions.

The companies that I know of that will make such devices for you are in the $10,000 to $20,000 range ... that same amount of money would buy lots of dyno time... and such a device would be specific to that wheel and or shaft ... it could only be used on other vehicles using the same wheel or shaft.

Either way you still need accurate fuel flow rate measurements... measurements that are celebrated for the conditions properly ... things like temperature , pressure, etc.

The other thing I would add to the list not already included by others would be a calorimeter to test the energy content of the fuel being used ... Consistency in testing is important ... the energy content of that gram of fuel is a potential source of error if it is not accounted or tested for... a non-quantified 1% variation in fuel energy content would limit the entire systems accuracy to less than 1% accuracy... there are a variety of factors that can alter the energy content per gram of fuel by more than 1%.

[jdchmiel]

Some Can bus OBD2 ports will supply 20-100+ samples per second. Some cars are lucky enough that there are open source tuning solutions to monitor and/or reflash the factory image/program. Aftermarket engine management systems such as the megasquirt build a VE table automatically from the wideband sensor and other constants such as the fuel injector size and pressure, as well as variables such as the current calculated injector on time ( duty cycle). Over time just driving the car the VE table is 'auto tuned' from a target A/F ratio.

Another aspect that could help is measuring the power output of the engine without a dyno. There are mobile phone apps as well as windows apps that will do a pretty accurate chart of your power output. The fudge factors are the aero and rolling resistance corrections. Tbhe way these work are for the mobile phone, it just records the sound of the motor, and uses the frequency of the sample + a clock to figure out the rate the engine is changing. The windows one works similar, except you can use the line in port on the side of the laptop with a simple 5 component circuit to protect your laptop from voltage spikes / transients and take a direct ignition signal in as if it was an audio signal. The the computer, audio is just a data stream to deal with. StreetDyno is the program name that comes to mind off the top of my head. Avoid the apps that use an acceleraometer as the input as they are not that accurate. the output of the StreetDyno was within 5% of the numbers generated at the same time on a dynojet.

[some_other_dave]

Originally Posted by drmiller100

what you could get is instantaneous mpg.

which is meaningful.

Very much so for feedback on tuning your driving style! And that is one of the major things that the UG, the SG, and the MPGuino all provide. The absolute numbers are not all that accurate, certainly not accurate enough to come up with a BSFC map, but they are very useful for driving and A/B/A testing and so on.

Originally Posted by jdchmiel

Over time just driving the car the VE table is 'auto tuned' from a target A/F ratio.

According to friends of mine who have used that setup, it only gets you close. There is still quite a bit of hand-tuning that needs to be done, either on a dyno or out on the road.

Another aspect that could help is measuring the power output of the engine without a dyno. There are mobile phone apps as well as windows apps that will do a pretty accurate chart of your power output. The fudge factors are the aero and rolling resistance corrections.

And weight, which you would have to measure to have more than a guess. (That includes the weight of fuel, driver, etc.)


I'm not saying you can't get useful numbers, and I'm not saying that you can't generate numbers for a BSFC map. I'm just saying that the final map you get won't be worth the effort you have to go through to get them.

-soD

[E4ODnut]

Once again I agree with soD. I am a great fan of Megasquirt and of the Tuner Studio tuning software. While I'm sure that there are others who will disagree with me, I feel that the Auto Tune and even the VE Analyze features don't really work "as advertised" in all situations, but I think they can get you close. In my opinion, open loop tuning with lots of time and effort yields the best results.

[jtbo]

Originally Posted by E4ODnut

Once again I agree with soD. I am a great fan of Megasquirt and of the Tuner Studio tuning software. While I'm sure that there are others who will disagree with me, I feel that the Auto Tune and even the VE Analyze features don't really work "as advertised" in all situations, but I think they can get you close. In my opinion, open loop tuning with lots of time and effort yields the best results.

I agree too.

With Wide band O2 sensor, I believe that auto tune can get you somewhere in range and from there manual tuning will make best out from system.

However when you would like to get best out from it, spark control needs to be set too and for my understanding that must be mapped manually and change to that often needs change in ve map too, so any automatic feature will just get one somewhere in range and best result will come with manually tune them all.