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Old 05-02-2017, 06:27 AM   #31 (permalink)
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Quote:
Originally Posted by California98Civic View Post
I confess, I have always found BSFC maps labelled like this one a little confusing. The vertical axis is labelled "engine torque" but we are discussing it as if it is "load percentage." The below image from Autospeed article ECONORAM linked in post #28 above has a map labelled "engine load" on the vertical axis. Torque and load % are not the same thing, though. And on Autospeed graph it seems like 45% to 65% load would yield the best FE.

That graph is still showing engine torque up the vertical axis since it goes to 145 even though it is labeled as load. We have no way of knowing what the corresponding throttle angle is.

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Old 05-02-2017, 08:44 AM   #32 (permalink)
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Quote:
Originally Posted by sendler View Post
That graph is still showing engine torque up the vertical axis since it goes to 145 even though it is labeled as load. We have no way of knowing what the corresponding throttle angle is.
I don't know that we can trust a visual so poorly labeled. It clearly says load. If it is correctly labelled, then we don't know how to read it yet. Load percent and throttle angle are different, too. I see chaos in these images.
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Old 05-02-2017, 09:07 AM   #33 (permalink)
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This is how I read it:

The vertical axis is BMEP, or brake effective mean pressure - basically torque. An engine with a flat torque curve would be a straight line, but torque in this engine peaks at around 3500RPM and drops off above that (because the engine starts to run out of air, head doesn't flow well), so you have a curved graph.

I'm going to pick 2000RPM as an exampe: Peak BMEP there is ~140 (not sure of units, but it doesn't matter). Peak efficiency is just above 100 (75% of 140), with a highly efficient range of ~80-120 (65-85%). So, ideally you'd be shooting for about 75% load, give or take 10.

Due to how throttle plates work, the throttle opening for 75% load will be much larger at 4000RPM than at 2000RPM, since the engine needs a lot more air. There's no easy way to convert throttle opening to load - for this, you either need a vacuum gauge or an OBD II reader. Luckily, a $5 ELM327 bluetooth dongle + $3 Torque Pro app for Android can show load values:

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Old 05-02-2017, 10:27 AM   #34 (permalink)
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I did not relize that the curve accross the color-coded fuel consumption zones was also data (a torque curve). Great write-up. The graph would be even clearer if there were a couple load curves overlaid on it and the BMEP numbers were labelled simply torque. And this means that in the previous graph you described, for your engine, in post #8 above, that the thick and angukar black line crossing the fuel consumption zones near the top is also your torque "curve," correct? Makes much better sense to me. I hope the OP fully gets it too for his "noob" question about P&G. Thanks!

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