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Old 03-18-2015, 02:29 PM   #1 (permalink)
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BSFC from dyno

I spent a good chunk of money this week dyno tuning my Nat Asp 2.5L Subaru. Most of the funds were spent in part throttle tuning. I wanted to find the best BSFC at part and full throttle to improve my acceleration efficiency on the street. I already posted a graph in BSFC sticky but I don't think that's very helpful. I'm not good with graphs so I will just post the RAW data which the computer recorded in ascii files here. Aside from using an inductive dyno to calculate power at all wheels, the dyno used sensors on the vehicle to calculate other information such as BSFC. These sensors included injector pulse width reported by ECU, AFR at tailpipe, mass air intake and etc. The ASCII data files were huge and I used them to come up with the following information file (also attached):



I basically sorted data based on throttle position and found set of RPM's with its respective BSFC, vacuum and power for that engine speed and throttle. The best BSFC for each RPM is highlighted in bold as to simulate best method of acceleration for efficiency.

The information gathered from this dyno indicate that at higher engine speeds (+2.3k RPM) wide open throttle is required to achieve best BSFC despite fuel enrichment (λ0.92). Absolute best BSFC was observed at 1800 RPM with 3-4"Hg of vacuum. Vacuum at higher RPMs tremendously degrades BSFC. Leaner mixtures and advanced ignition timing does not make up for vacuum pumping losses but it does improve BSFC. In other words vacuum plays a bigger role than fuel mixture, timing and engine speed to a certain extent for BSFC. If these dyno numbers are to be trusted, high vacuum and engine speeds do not go hand in hand for best BSFC (nothing new here). This further supports longer gear ratios for lower RPM operations at highway speed. Eliminate or minimize vacuum and you are certainly operating at best BSFC so long as fuel mixture is not too rich and timing is not too retarded.

Notes:
  • I could not dyno past certain engine speeds at lower TPS due to lack of power
  • All runs were done in top gear (overddrive)
  • WOT and 40% run were in unlocked torque converter mode
  • Depending on vacuum the air fuel mixture ranged from λ1.0 to λ0.92
  • Ignition Timing varied with load and RPM

Attached Files
File Type: xls fullrangedyno.xls (31.5 KB, 36 views)

Last edited by ever_green; 03-18-2015 at 03:30 PM..
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Old 03-18-2015, 04:43 PM   #2 (permalink)
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Sorry I keep asking, any chance you have the original data in log file format?
i.e. just a log of tps/rpm/power/vac/bsfc/anything else?

that would be much easier to process in a script to sort it into a bfc-style chart.
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Old 03-18-2015, 05:33 PM   #3 (permalink)
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Interesting stuff

I noticed on the new Mazda2 (just launched) it has an electronic throttle body, it fairly obviously changes the throttle position at various RPM's when under full load at low rpm. I guess to maximise BFSC. So a mappable throttle body might be an easy way of achieving the ideal eco results.
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Old 03-18-2015, 05:42 PM   #4 (permalink)
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Quote:
Originally Posted by P-hack View Post
Sorry I keep asking, any chance you have the original data in log file format?
i.e. just a log of tps/rpm/power/vac/bsfc/anything else?

that would be much easier to process in a script to sort it into a bfc-style chart.
the log files are massive. um im not sure how to send it over. they record about 20 different parameters per line and about 10 of those lines per second.

Quote:
Originally Posted by cptsideways View Post
Interesting stuff

I noticed on the new Mazda2 (just launched) it has an electronic throttle body, it fairly obviously changes the throttle position at various RPM's when under full load at low rpm. I guess to maximise BFSC. So a mappable throttle body might be an easy way of achieving the ideal eco results.
yes but this is the measurement of throttle and not accelerator pedal angle and yes this car is equipped with drive-by-wire.
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Old 03-18-2015, 06:38 PM   #5 (permalink)
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lotsa ways.

if you zip them up, and they are under 100k then you can attach 'em. if under 1meg you can cheat and rename it to .xls and attach it (and make sure we know the original extension).

if they are seperate files, the upload limit is only per file, so maybe zipping them up individually or pretending they are .xls files will do (or both).

But yah, all the data you got would make the clearest picture.
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Old 03-18-2015, 09:08 PM   #6 (permalink)
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