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Old 10-16-2013, 05:04 PM   #1 (permalink)
ever_green
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Join Date: May 2011
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Blueberry - '17 Mazda Mazda3 GS
90 day: 32.56 mpg (US)

EVO - '08 Mitsubishi Evolution MR
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best BSFC vs. Vacuum (engine load) using software

Finally after months of research, phone calls, emails and other time wasting activities I got the information I needed to accurately simulate my engine's function using Engine analyzer pro. I also did hours of logging with my car using a tactrix adapter. I logged injector pulse widths, total ignition timing, AFR and other important data. After feeding the data to the software I came up with a very accurate look graph for full throttle acceleration:



You can see from above chart that BSFC sweet spot is around 2500rpm at full throttle open loop acceleration. However I was more interested in partial throttle acceleration, so to find out I tested multiple different throttle settings to make this chart:

BSFC vs Vacuum at different throttle maps:

The lines at the top are BSFC in lb/hp/h. The lines at the bottom are inHg of vacuum x0.01.

Best (Cyan+Red line) BSFC with 2.7inHg of Vacuum at 2000rpm. Roughly 54 BHP of power is produced at that level.

As you can see, at lower loads engine speed sweetspot has fallen to lower RPM. Also notice the vast difference in BSFC in open loop full throttle vs just 1in-hg of vacuum (closed loop). it's clear that open loop enrichment must be avoided at all costs. 2.7inHg of vacuum gave best results at 2000rpm with BSFC of 0.435 lb/hp/h. 2.7inHg is roughly 1.3psi which translates to 13.4 MAP on your scan-gauge or about 90% LOD. Higher or Less vacuum than this did not yield better results. Also this test is assuming that there is no fuel enrichment at vacuum.

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Last edited by ever_green; 10-16-2013 at 05:09 PM..
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