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Old 09-19-2011, 08:46 PM   #1
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Default BMEP divided by MAP, and why it's important

Branching off from another thread.

And some discussion here too, with several examples:
http://forum.miata.net/vb/showthread.php?p=5375293



Here's a great way to analyze a dyno plot.

BMEP (in psi) and BMEP per MAP in psi per atmosphere of MAP

BMEP (in psi) = tq (ft-lbs) / displacement (L) * 2.47

BMEP per MAP = BMEP / MAP (in atmosheres)

BMEP per MAP = BMEP / MAP *101 (if MAP is in kPa)

The magic number is 180 psi at torque peak.
This translates to 73 ft-lbs per L per atmo of MAP.

Here's the importance of BMEP
http://www.epi-eng.com/piston_engine..._yardstick.htm

The resulting BMEP/MAP is an indication of VE and correct ignition timing.
In my curve above, the plot from 4000-7000 is VE
The reduced VE below 4000 RPM is due to the the wastegate being closed, TIP is higher to accelerate the turbo shaft.
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Old 09-22-2011, 10:39 PM   #2
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Comparing my dyno plot and my friend's with the 3071 at ~15 psi,



looking at the BMEP/MAP curve, I can see that my VVT produces a broader torque band, and better breathing in the spoolup region (2500-4000 RPM). Or perhaps the ignition timing in the 3071 setup during spoolup, can be improved.

In the 2500-4000 RPM region, because boost is rising, one can't directly compare torque outputs between 2 setups with different boost curves. BMEP/MAP allows you to do so.
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Old 03-04-2012, 03:04 AM   #3
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Interesting data from a GT2560 on a 2.0L:

http://forum.miata.net/vb/showpost.p...3&postcount=54
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Old 03-04-2012, 10:55 AM   #4
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You get a prop because this is so cool.

I'm trying to get the Virtual Dyno guy to at least add text output of calculated torque so I can drill down to this for street spark tuning. We'll see.
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Old 03-04-2012, 01:12 PM   #5
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Its funny how few people dont know about BMEP

Im constantly seeing NA dynos (usually on dynojets) where the BMEP at peak power is well over 200 psi, sometimes as high as 240
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Old 03-04-2012, 02:55 PM   #6
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BMEP for gasoline peaks at 220 psi (89 ft-lbs per L per atmo) -this is true both for F1 and NASCAR. They must have >100% VE, maybe like running 3 psi of boost.

This link shows that both F1 and NASCAR both have a BMEP of 15 bar:

http://www.epi-eng.com/piston_engine..._cup_to_f1.htm

The following link explains BMEP. A bit lost in there is that BMEP is exactly proportional to Torque divided by Displacement (the units I like to use personally is ft-lbs per L), or simply Torque per Liter for a n/a motor at sea level. For a boosted engine, BMEP/MAP is the equivalent figure of merit, or ft-lbs per L per atmo of MAP.

http://www.epi-eng.com/piston_engine..._yardstick.htm
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Old 03-27-2012, 01:08 PM   #7
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Super duper 1.6L setup, 340 hp from 1.6L, probably runs TIP<MAP at the torque peak.

72 ft-lbs per L per atmo of MAP:

http://forum.miata.net/vb/showthread.php?t=453975
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Old 03-27-2012, 05:42 PM   #8
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Quote:
Originally Posted by hornetball View Post
You get a prop because this is so cool.

I'm trying to get the Virtual Dyno guy to at least add text output of calculated torque so I can drill down to this for street spark tuning. We'll see.
This seems to be the first reasonably easy way to create some sort of street spark tuning. I've been waiting for you and the Virtual Dyno guy to get this data output problem in place before I start messing with it.
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Old 03-27-2012, 05:49 PM   #9
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Free AEMLog will do it now (extract torque).
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Old 03-31-2012, 12:09 AM   #10
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Can I use AEMLog with MS data?

I don't know what the hold up is with VD. Seems like the request was pretty simple.
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Old 03-31-2012, 01:32 AM   #11
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AEMlog can load delimited text files.
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