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Old 02-10-2009, 12:21 PM   #8 (permalink)
daqcivic
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Join Date: Nov 2008
Location: Portland, OR
Posts: 53

Daq Civic - '92 Honda Civic DX sedan
90 day: 42.54 mpg (US)

The Hardbody - '91 Nissan D21 (pickup)

The Hardbody - '91 Nissan D21 (pickup)
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Quote:
What I'm talking about is lower THROTTLE in the low gears and at low rpm, and higher throttle at higher rpm. At low rpm, it takes less to fill the cylinders, since the valves are open longer.
That makes perfect sense. I was a little confused from an earlier post where you listed a throttle % according to gear, not RPM; but of course, the engine doesn't care what gear it's in or even really what speed the vehicle is at, just what RPM it's at and what load is being demanded based on the throttle. So if there is enough time spend in gear I should begin initially with about 50% and increase up to about 80%. However, for my car's gearing, since RPMs at initial engagement speed in 2nd and 3rd are below the rule-of-thumb optimal BSFC range of about 1500-2200RPM, (around 800-1000 in 2nd and 1200-1400 in 3rd), it would seem best to begin in these gears with less than 50% throttle, until the RPM gets up to at least 1500.

Quote:
Your shifting scheme looks pretty good. You can go a little lower on the rpm, shifting a little sooner. If it growls/rumbles a bit, that's fine. As long as it can gain speed it's ok.
This is something I definitely need a gauge for. Going lower seems like it wastes fuel because I end up spending a couple more seconds at those lower RPMs with almost no acceleration. Then again, Lower shift points mean fewer overall cycles, so it would take some pretty precise testing to with good instrumentation to figure out where the optimal point is. On the upside, a few hundred RPMs difference in shifting points is probably going to have a minuscule effect on FE if the load is managed smartly.

Quote:
I hardly use 1st gear. On a downhill start, I don't - I go straight to 2nd. On flat/uphill starts, I only use it to get rolling, and shift to 2nd about as soon as it's fully engaged. (3mph or so?)
I hear most people saying this, and I don't necessarily disagree (as if I could provide any solid evidence to the contrary), but it does seem to contradict the BSFC logic of using the engine in its most efficient range because 2nd gear is used for several hundred RPMs before 1500. I'm going to accept the prevailing wisdom of this for now, though I hate lugging the engine.

Quote:
Overall, I find that getting the very best pulse less important than getting the best glide. You can do a 1:1 pulse to glide ratio, with a light pulse, or you can do a heavy pulse with a glide 3x as long. Both will give you similar results. . . . get the best glide you can.
This is really helpful! I had gotten good at maximizing coasting using very slow, light load acceleration, but it is quite a bit different and more difficult to time things (esp. in rush hour city traffic with hills and such) using heavy load acceleration. But if I know I can freely adapt the P&G ratio to fit the circumstances to get the most gliding I will probably do a lot better than trying to stick to a rigid pulse scheme.

It's definitely starting to sink in that I can't really refine things much and know if it's helping unless I get some instrumentation. Thanks MetroMPG for the advice on mpguino, I imagine I could find out where those few leads are by looking it up in a manual.

And thanks to all for your advice and willingness to help a clueless beginner!
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