The BSFC chart thread (post 'em if you got 'em)

[P-hack]

you can also sort of make one as you go with the right logging and processing:

AutoSpeed - FuelSmart, Part 1

[bikenfool]

Originally Posted by P-hack

you can also sort of make one as you go with the right logging and processing:

AutoSpeed - FuelSmart, Part 1

Care to elaborate? That link doesn't say anything about how to get BFSC data. I think measuring torque or hp accurately outside of a dyno would be tough.

[P-hack]

tough, a little bit, for any hope of accuracy you would have to do some coastdown tests and have you and your vehicle weighed with a consistent fuel load (and tire psi) and warmup to determine CDA and CRR. Plus you want consistent atmospheric conditions.

HP to the wheels would be a function of drag at speed and change in velocity.

Fuel consumption would be monitored by an injector (or other accurate source).

Speed is the VSS signal (or rpm if using different gears).

Map is indicitive of load.

So you log fuel rate, speed, map. Accelerate at different map values using your foot and determine the hp required (and fuel consumed)between steps as you accelerate. Build the bsfc chart row by row by keeping map consistent during each run (As practical).

Standard testing, run in both directions and average, repeat. Flat test area with no wind is best.

[some_other_dave]

So, 2 runs each direction. 10 RPM samples, 10 load samples. That's 400 data runs in "consistent conditions".

Joy to you if you try it. I hope your weather stays exactly the same for a week...

-soD

[P-hack]

If you are targeting acceleration bsfc, then you just do one run per map/load row, you decide how accurate and repeatable you want to be, just document the procedure a bit. The horizontal part should have lots of data points automatically.

After that you can do some steady state sanity tests north/south/east/west of peak acceleration bsfc. It should be a binary search if you are looking for peak (which is relatively few runs).

[Piwoslaw]

Originally Posted by some_other_dave

So, 2 runs each direction. 10 RPM samples, 10 load samples. That's 400 data runs in "consistent conditions".

Joy to you if you try it. I hope your weather stays exactly the same for a week...

-soD

At this point paying for dyno visit may be better than sacrificing so much time and fuel for results which are less accurate.

[Focus-Ak]

There are two curves for a "Taurus like engine" in Appendix A of "Technical Options for Improving the Fuel Economy of U.S. Cars and Light Trucks by 2010–2015" (http://s3.amazonaws.com/zanran_stora...2470551122.pdf). They are described on page 6 (page 22 of the pdf file):

"Technically inclined readers can see some of the efficiency benefits of our assumed engines by comparing the baseline engine map of Figure A2 with that of the improved engine shown in Figure A3. The top curve of the map represents the peak brake mean effective pressure (bmep, which determines the torque delivered by the engine). The improved design is higher across the board, and notably so at low RPM, which allows
responsive driving in more efficient engine modes. The "island" of minimum brake specific fuel consumption (bsfc, how much fuel is burned per unit of energy output) is not only lower, corresponding to higher peak efficiency, but also covers a broader portion of the map, meaning higher efficiency throughout the driving cycle."

The charts are on pages 74-75 of the pdf file.

[ever_green]

While tuning my naturally aspirated 2.5L Subaru on the dyno i spent an extra $150 and did some part throttle pulls to find BSFC sweetspot. Since dyno pulls are expensive I only did 4 runs of roughly 15, 20, 25 and 40% throttle. I cannot vouch for the dyno's BSFC estimation accuracy but it used torque at wheels, injector pulse width, rpm, mas air flow and other data. the efficient region seemed to be at a very narrow engine load and speed of 1800rpm @5"Hg vacuum. Any more vacuum (or smaller throttle opening) or engine speed resulted in the BSFC suffering in an exponential manner. even lean burn mixtures and high ignition timing could not make up for pumping losses at high vacuum.

• 40% TPS run reported ~13.9 AFR w/full manifold pressure (no vaccum)

• lower throttle positions were in locked Torque Converter mode with ~14.3-14.7 AFR

here it is in a graph form:

[P-hack]

not quite a complete picture, but very interesting all the same.

green looks like 265gm/kwh and red is ~294 @ 1800rpm

I wouldn't be suprised if there were more efficiency at a higher rpm with a little more than %25 throttle, but yah, pulls are $$$

I don't have the brain cells to turn it into a bsfc map at the moment though. Part of the issue is that tps isn't load, but is a function of rpm and load.

Do you have more detailed data in table format by any chance?

edit: I think this is the sort of reasonable first step anyway based on the graph, not exactly sure how to translate to load instead of tps, some rpm based scaling and interpolation I guess.

re-expressed as tps/rpm in gm/kwh
50
45
40	285	280	282	276	278
35
30
25	272	266	265	269	275
20	272	270	271	278	285
15	288	289	294	308	324
10
	1400	1600	1800	2000	2200

[ever_green]

Originally Posted by P-hack

not quite a complete picture, but very interesting all the same.

green looks like 265gm/kwh and red is ~294 @ 1800rpm

I wouldn't be suprised if there were more efficiency at a higher rpm with a little more than %25 throttle, but yah, pulls are $$$

I don't have the brain cells to turn it into a bsfc map at the moment though. Part of the issue is that tps isn't load, but is a function of rpm and load.

Do you have more detailed data in table format by any chance?

edit: I think this is the sort of reasonable first step anyway based on the graph, not exactly sure how to translate to load instead of tps, some rpm based scaling and interpolation I guess.

re-expressed as tps/rpm in gm/kwh
50
45
40	285	280	282	276	278
35
30
25	272	266	265	269	275
20	272	270	271	278	285
15	288	289	294	308	324
10
	1400	1600	1800	2000	2200

I will make a thread about this in general efficiency forum and post some more data:

http://ecomodder.com/forum/showthrea...tml#post472141

also i'm not good at making charts. here is data from wider engine speed operations should you wish to make a graph (attached too). Vacuum and power should help you determine load.