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Old 03-20-2008, 07:53 AM   #11 (permalink)
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If that line does show torque at WOT, that may make it incredibly useful: could you not essentially use it to extrapolate what throttle/pedal position to use to get the engine closest to the sweet spot at a given RPM?

EG. in the Saturn chart, 7/9 throttle @ 2000 RPM looks like it would put you squarely in the 250 g/kWh island.

Of course it doesn't work quite that simply, because the engine doesn't "idle" at 2000 RPM ("0/9ths"), so you'd likely have to factor in the amount of pedal required to get there with no load on the engine.


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Old 03-20-2008, 08:35 AM   #12 (permalink)
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Why the reduction in efficiency at higher loads?

Retarded timing? Or does EGR matter that much efficiency wise?

@ MetroMPG
Most gas cars have a very nonlinear accelerator travel vs. torque output response. How a bout measuring acceleration vs pedal position at lower speeds with the ScanGauge? Maybe up a hill?
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Old 03-20-2008, 08:40 AM   #13 (permalink)
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Re: efficiency reduction @ higher RPM - I'd guess that increasing internal friction also plays a role. Power required to overcome friction is an exponential relationship. Just a thought.

Good point on tps vs. torque.
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Old 03-20-2008, 09:47 AM   #14 (permalink)
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Timing changes and pushing the engine into open loop causing fuel enrichment I would think is what causes the drop off at the extremely high loads.
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Old 03-20-2008, 07:43 PM   #15 (permalink)
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Quote:
Originally Posted by tasdrouille View Post
I always thought it was simply the torque curve at WOT through the whole range. I could be mistaken though.
Yes, min BSFC should be at the same RPM as peak torque as is in this case.
I agree.
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Old 03-22-2008, 01:21 PM   #16 (permalink)
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What you need to do with the plots now is calculate the engine torque at various engine speeds in all gears, then plot the results over the BSFC plot to give the road curves Vs BSFC.
Then you have all you need to drive at theose BSFC points you choose

If you don't have any efficiencies then calculating the engine torques for road speeds may be a little difficult, but allowing 23% for drivetrain losses is a typical figure.
A more reliable method of getting the drive train losses is to stick the car on a roalling road and do a motored run in neutral to actually measure the power it takes to achieve the road speeds.
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Old 03-24-2008, 01:04 PM   #17 (permalink)
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I'd love to see one of these for the Toyota 22r - then I'd know for sure whether regearing my rearend is a good idea. Right now, it's just a feeling that the engine could be turning a lot slower and get the job done.
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Old 03-24-2008, 02:21 PM   #18 (permalink)
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I am sercing that one of the tigra, engine X14XE, but I, do not succeed to find it.
you, can help me?
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Old 03-25-2008, 03:06 PM   #19 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
If that line does show torque at WOT, that may make it incredibly useful: could you not essentially use it to extrapolate what throttle/pedal position to use to get the engine closest to the sweet spot at a given RPM?

EG. in the Saturn chart, 7/9 throttle @ 2000 RPM looks like it would put you squarely in the 250 g/kWh island.
That's what I was trying to say in the shift timing thread. 7/9 = 77% of max torque (or load). Examining a bunch BSFC maps, and measuring the extents and center of the peak efficiency island, I found the average center point to be 72% of max load. Hence the question; Can we believe the LOD output on the scangauge as a good indication of engine load?
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Old 03-25-2008, 05:25 PM   #20 (permalink)
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sorry, it is very difficult for me to understand that your has write and in the same manner, it is very difficult for me write to you that one I think...in Italian no problem, but an English I can only try

For an correctly reading of BSFC, the map it must be without the torque value, but with the % of PME max(pressure, average real).

The map is created put the engine in the braked dyno.
the BSFC it is a consguence of vary factors: engine respiation, friction and AFR.
The engine respiration it is defined by cams phases, valves diameters, intake and exhaust tubes lengs and diameters, resonace and pulsation phenomena.
When the respiration is at the optimum, the respiration friction losses it is at the minimum, obviously at open full throttle.
The engine friction loss increase with the engine revolution, and the AFR it is an other trouble factor.
When we interpolate all factor then obtain the BSFC map.

For to go the engine in the optimal fuel economy (in this case by 250 gHP/H), it is necessry the needed load.
In normal operation, in flat road, in the last gear and without acceleration, it is impossible go to optimal area of BSFC.
Only way, it is to decrease the engine torque available the same rpm and car load throoughout AFR modification.
This, does not have effect on the friction loss and on the volumetric efficient, but only on the PME
So, we can free-moving the engine load (point in the BSFC map) with the same engine torque output
I am understandable?

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