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Old 07-14-2008, 08:25 PM   #71 (permalink)
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I'd be happy with just higher gear ratios. I'm generally in 6th at 45 mph.

How hard is it to change the final drive ratio(s)?

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Old 07-14-2008, 08:31 PM   #72 (permalink)
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BMEP represents is Brake Mean Effective (cylinder) Pressure. Basically this pressure is the result of the amount of fuel in the cylinder times combustion efficiency. Any given load on the engine (accel and aero drag) will require a certain pressure for the RPM at that load. Lower RPM means pressures have to be higher to compensate, thus the advantage of taller gearing.
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Old 07-14-2008, 11:10 PM   #73 (permalink)
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Here is a link to an article which is very helpful in understanding BSFC charts:

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Old 07-14-2008, 11:27 PM   #74 (permalink)
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Thank you guys VERY MUCH.

I'm assuming that the Blue lined BSFC chart is also ALH TDI.
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Old 07-15-2008, 12:53 AM   #75 (permalink)
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Looks like the Insight manages to hit 200 g/(kWh) around 4000 rpm.
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Old 07-23-2008, 11:09 AM   #76 (permalink)
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Old 07-24-2008, 11:10 AM   #77 (permalink)
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I look at the chart a little differently

Originally Posted by Daox View Post
Its really not that difficult to pick an optimal gear ratio if you have a BSFC chart for your engine.

etc, etc
When I look at the chart I see that the motor is 4 times larger than it needs to be!
If we adjust the chart for a motor 23% of the original size the torque figures drop by close to 23% (give or take), but the usage (g/kwh) figures stay much the same (give or take).
We then end up with this chart.

And then the gear ratios need changing so that 6th gear is slap bang in the lowest bsfc location (it becomes what fourth gear now is) and there are two lower gears to give some acceleration (which would still be absolutely piddling!)
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Old 07-24-2008, 11:25 PM   #78 (permalink)
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Yes, but when pulling out into fast traffic, you are going to wish the engine was 4x bigger.

Turning off cylinders (or two engines under the hood) tries to do this.
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Old 08-12-2008, 04:58 AM   #79 (permalink)
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The 07 Civic (R18A) engine opens the throttle butterfly completely under low load conditions and pumps some air back out during the compression stroke (effectively making it a 1.5L instead of 1.8).

The system is so fine tuned that I can't even guess the theoretical best engine speed/load combination. In theory in low revs and heavy load it shifts to the performance cam, thus negating the "low-load" efficiency.

Has anybody seen a BSFC chart for the R18A engine? Or anybody know a Honda engineer who has the keys to the company vault?
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Old 08-12-2008, 11:47 AM   #80 (permalink)
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Unfortunately, BSFC maps are pretty rare. The ones found here are really just from people digging and finding them on the net. I have yet to find a good source for them.

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