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Old 01-08-2013, 04:40 PM   #71 (permalink)
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Wide open throttle does give the best MPG. Opening the throttle eliminates pumping losses into the engine. The world record holders all use WOT followed by drift to a stop. Followed by WOT, followed by drift. Etc.
Quote:
after you pass max torque the efficiency is going -down-.
I don't know if that's true or not, but it does make sense. Though that's not what you would see on a Specific fuel consumption curve (sp?). That curve shows a peak at 1900-2000, and then drops off (consumes more fuel). When you drive an automatic it tries to hold the engine at or just below that RPM.

In any case: Max torque to the driving wheels is 1st gear at 5000 (about 26Nm), not 2nd gear at 2500 (about 13Nm). I would run in 1st gear all the way to 50 miles an hour, and then skip to 5th gear for steady state cruise, if I wanted the absolute best fuel economy. WOT followed by drift. But of course the rev limiter makes that impossible.

LINK: Brake Specific Fuel Consumption (BSFC) Maps - EcoModder
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Old 01-08-2013, 04:51 PM   #72 (permalink)
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All I can say is I don't use wide open throttle and I get 80-90 mpg on the highway and 126+ mpg out of a tank on my work commute. Those world record vehicles are not the same as our Insight, not by any stretch of the imagination. I used about 80-85% load and shifted out of 1st at about 13 mph, out of 2nd at about 21-23 mph, out of 3rd at 28-30 mph, and out of 4th at about 35 mph on my record tank of 1,692 miles at 126.1 mpg.
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Old 01-09-2013, 10:26 AM   #73 (permalink)
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My old 2002 insight had an 89.8 life average, and I used WOT all the time. 0 to 50 at WOT, and then cruising along in 5th gear. I didn't originate the idea..... I just copied it from other insighters like John Wayland.
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Old 01-09-2013, 10:33 AM   #74 (permalink)
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I find the more aggressive I am the more p&g I end up doing and having more fun over all, same mpg.


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Old 01-09-2013, 09:57 PM   #75 (permalink)
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I also feel like it's not really worth babying the throttle. I get 55mpg whether I drive the fun or I try to be careful. In the end, the climb up to my house ALWAYS kills my daily mpg.

That said, I still baby the throttle anyway.
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Old 01-12-2013, 05:11 PM   #76 (permalink)
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Originally Posted by theaveng View Post
1st to 4000rpm, then 2nd at ~2000 to 4000, then 3rd at ~2400 to highway speed (then 5th)
If anybody cares, I have been doing this. Except when the engine is cold, then I shift early at 3000 because the oil is still thick.
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Old 01-12-2013, 05:39 PM   #77 (permalink)
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Wide open in 1st to 4000 RPM wears the front tires more than I prefer.
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Old 01-12-2013, 08:17 PM   #78 (permalink)
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WOT isn't as inefficient as you would think, but accelerating slowly is still more efficient - just not by much, and the people behind you are going to hate you.

At WOT, even the Insight takes the mixture down to 12:1 - open loop, as DL says.

With a gentle foot, you can keep it in the 14.3:1 range.
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Old 01-13-2013, 12:45 AM   #79 (permalink)
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Quote:
Originally Posted by theaveng View Post
Wide open throttle does give the best MPG. Opening the throttle eliminates pumping losses into the engine.

In that case have you tried just running the engine wide open in traffic and using low gear only? I usually cruise through 30 mph speed zones in 5th gear and 1000 rpm!

The world record holders all use WOT followed by drift to a stop. Followed by WOT, followed by drift. Etc.

They also average -very- slow speeds, don't shift to higher gears, don't run the engine all the time (infinite mpg then) etc etc! In S. Fla people sometimes get tickets for "obstructing traffic" while driving OVER the posted speed limit!

I don't know if that's true or not, but it does make sense.

".... after you pass max torque the efficiency is going -down-"

Though that's not what you would see on a Specific fuel consumption curve (sp?). That curve shows a peak at 1900-2000, and then drops off (consumes more fuel).

Isn't that exactly what I stated but with other words?

Using more fuel above the max torque point ought to be a good indication that the efficiency of the engine is going down as the rpms go up." And let's not forget that max torque runs are made at WOT and varying the load on the engine. The same as when you are accelerating at WOT.


LINK: Brake Specific Fuel Consumption (BSFC) Maps - EcoModder

The charts on that link show that more of the engines get max torque and low BSFC readings at about the same RPM vs the rpm and BSFC points being greatly different.

My CRX engine happens to have max torque at 2000 rpm. The following link shows a BSFC chart vs torque curve along with a discussion of torque vs mileage,


Maximum torque vs maximum fuel efficiency - Gas Savers - Fuel Efficiency Forum

In any case: Max torque to the driving wheels is 1st gear at 5000 (about 26Nm), not 2nd gear at 2500 (about 13Nm).

We are discussing max engine torque though. Any other part of the drive train doesn't add efficiency to the engine (everything else has losses). But of course transmissions etc can allow the engine to run slower to maintain a particular speed (i.e. not wide open).

I would run in 1st gear all the way to 50 miles an hour, and then skip to 5th gear for steady state cruise, if I wanted the absolute best fuel economy.

Yet other people recommend slow acceleration for best fuel mileage. I tend to use 1st to accelerate faster than in the other gears. Sort of a "let's get it over with" tactic. But I don't use anywhere near the max power available. (I don't like running into the back of other cars for one thing.)

WOT followed by drift. But of course the rev limiter makes that impossible.
But if this statement is true, "max rpm gives best fuel mileage" then you should leave the car in 1st gear if you want to run 45 mph for best mpg. Even if you let off on the gas you would still be running a higher rpm than shifting to any other gear at any given speed.
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Old 01-13-2013, 03:36 AM   #80 (permalink)
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My former Honda Metro 50cc scooter redlined at 9000 rpms...

Here's a shift technique that's real subtle, that I didn't catch on to until having driven the car for 10000 miles. For fuel economy:

First, overall, you want to try to max out use of the electric motor upon acceleration in order to max fuel economy.

Second, launching in first gear doesn't always command electric assist, at least, not unless you rev just so and slip the clutch just so. A bit of rev, let out the clutch, and a bit more rev as you're just about to fully let up the clutch pedal, engages assist and keeps it engaged until you shift to second.

Finally - and this is the most important, tricky juncture - moving from second to third. Moving out of second gear, letting up on the throttle, rpms will drop, the FCD will rise, and if you're not too quick to shift to third and if you don't get back on the throttle too quickly or too hard, lean burn will trigger before you shift to third.

Now, if you're light on the throttle once you have it in third gear, you can hold lean burn -- yet with just a little throttle you can also command electric assist and continue accelerating. All this can happen in the same time for a regular, normal shift; there's just some real subtle timing and throttle movement necessary to get both lean burn and assist. It can happen like clockwork though once you have it down...

These are some flat ground, easy acceleration, fuel economy, probably mostly in-city driving shift techniques...
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