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Old 05-19-2008, 02:04 AM   #11
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Originally Posted by mkiVX View Post
i don't shift when the shift light advises me to any more.
I think Honda already knows what I discovered in my test, and I think it's costing you money to ignore their advice.

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ever since i keep lean burn on it really shines in the FE section
I wonder if you could be more specific, as far as the exact comparison you did. I find it hard to believe that you've generally enhanced your FE by learning to ignore your SIL.
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Old 05-19-2008, 09:09 AM   #12
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I'm wondering what you mean by that, since throttle position and engine load are so directly related that they're virtually synonymous.
MAP sensor readings combined with TPS gives you your overall engine load reading.
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Old 05-19-2008, 12:37 PM   #13
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MAP sensor readings combined with TPS gives you your overall engine load reading.
Good point, now I understand what you mean. Throttle position correlates nicely with load, but the ECU has an even more precise indication of load if it also takes manifold pressure into account. Thanks for explaining.
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Old 05-19-2008, 01:45 PM   #14
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Great test, Monroe. I'd definitely encourage you to do it again and compare second round results with first, because unless you have a very good ear for how full the tank is when you're filling up (you can hear the sound rise as it approaches full) your two fill ups were not the same (they never are when I fill up anyway). But I think I tend to be in agreement with you that maintaining lean burn while employing P&G is less effective/efficient than WOT or near WOT settings. I think a good way to do P&G is not by how much throttle, but by a rate of acceleration. If you are going up a slight grade, you're gonna probably want WOT if you want to have a pulse that doesn't last forever. Going down a hill, you may want to do a more moderate pulse. In the Prius, WOT is not a good method for pulsing--but rather a light throttle that keeps the e-motor charging the battery during the pulse. Not sure how manual transmission and CVT compare for methods of P&G.

BTW, my car is going 75mph at 2500rpm, not 70mph. It's about 61mph at 2000rpm and about 45mph at 1500rpm. 3000rpm at around 90mph. For a short time my car was 75mph at about 2300rpm and about 2800rpm at 90mph, but that didn't last very long, but it was very puzzling to me.
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Old 05-19-2008, 03:33 PM   #15
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Is lean burn an abrupt transition, like an on-off switch, or a more gradual transition? Somewhat gradual would seem to make more sense. I feel the torque at about 1500 rpm with commensurate reduction in vibration, as well as the beginning of effective induction harmonics where individual power pulses merge into a much smoother acceleration. in gears other than 5th the rpm threshold is somewhat lower, more so the lower the gear.

My last tank using my procedure (which is still evolving) was 57.58 mpg. My normal route is 40 miles round trip at an average speed of about 40 mph with 56 traffic lights to deal with.

Under normal conditions I never exceed 2500 rpm. Throttle position would vary between 20-50 % depending on rpm and gear choice, trying to keep vacuum as low as possible relative to throttle application.

I try to maintain a consistent load, but never use WOT, unless safety requires WOT. Some of this driving is on 45 mph congested roads that require light timing to avoid idling.

In those cases I use mini P&G with speed ranges of only a few mph. I am at the rear end of the group of vehicles drafting and P&Ging. Wot would not work very well, and other drivers would think I was some kind of nut case with all the distinct changes in speed.

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Old 05-19-2008, 03:40 PM   #16
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Originally Posted by monroe74 View Post
I'm wondering what you mean by that, since throttle position and engine load are so directly related that they're virtually synonymous.
Not by a long shot. TPS and load are two different things. Having tuned cars on throttle based maps, aka alpha-n, and tuned cars on load based maps, in our case speed-density, I can tell you that they are two independent things as much as RPM and vehicle speed are independent though at a glance it may seem otherwise.

If you don't believe me, put your car in neutral, rev it up and watch the MAP voltage. Then do it in gear and watch the MAP voltage. Just like speed and RPM. In the first test, RPM / TPS will climb, while MAP / Speed remain constant. In the second test MAP and Speed will climb but not at the same rate as the first variable.

Not only that but load varies with barometric pressure, altitude, and boost, while TPS in all these cases is unaffected.

Honda like most manufacturers doesn't use TPS to calculate load, but rather they use it to make corrections. Rapid changes in throttle % require anticipated (preprogrammed) changes to fuel. Waiting for MAP to catch up causes a big hesitation.

TPS based maps are not very drive-able. They're used for race cars only.
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Old 05-20-2008, 03:42 AM   #17
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Originally Posted by 1993CivicVX View Post
unless you have a very good ear for how full the tank is when you're filling up (you can hear the sound rise as it approaches full) your two fill ups were not the same (they never are when I fill up anyway)
Good point. I definitely agree that we can't assume that these nozzles respond consistently. Especially because I was using two different pumps. On the other hand, I do pay attention to the sound, and I think I have a pretty good ear for it.

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I tend to be in agreement with you that maintaining lean burn while employing P&G is less effective/efficient than WOT or near WOT settings.
Yes, that's what I think. I think lean burn is great for situations where, for whatever reason, you simply can't do P&G.

I also can't say for sure that WOT is better than 70%, or 90%, but increasingly my hunch is that it is (assuming we're talking about a wideband-sensor system like the VX, where it seems that WOT doesn't trigger open loop, as far as I can tell).

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BTW, my car is going 75mph at 2500rpm, not 70mph. It's about 61mph at 2000rpm and about 45mph at 1500rpm. 3000rpm at around 90mph.
Oops, my mistake. Thanks for the correction. I looked up some numbers, and I think the exact figure is 29.7 mph at 1000 rpm.

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For a short time my car was 75mph at about 2300rpm and about 2800rpm at 90mph, but that didn't last very long, but it was very puzzling to me.
That is a puzzle. I don't know what to make of that.
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Old 05-20-2008, 03:42 AM   #18
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Originally Posted by suspendedhatch View Post
load varies with barometric pressure, altitude, and boost
I realize all those things are going to influence load, and would be relevant in making a precise calculation of load. But it seems to me that the throttle is still the main influence.

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TPS and load are two different things.
I keep running into various sources who treat the terms as interchangeable. (I cited a few examples here: http://www.gassavers.org/showpost.ph...6&postcount=47.) Do you have any observations about why the terms seem to be used that way? If you do, I would probably learn something by hearing them.

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put your car in neutral, rev it up and watch the MAP voltage. ... MAP / Speed remain constant.
Are you saying that revving an engine in neutral will have no effect on manifold pressure? I'm surprised to hear that.
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Old 05-20-2008, 04:28 AM   #19
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Originally Posted by R.I.D.E. View Post
Is lean burn an abrupt transition, like an on-off switch, or a more gradual transition?
It depends a little bit on how you define lean burn. You could mean anything leaner than stoich, or you could mean only extremely lean. In other words, there's lean, and there's leaner.

When I use a DMM to monitor AFR, I see readings from roughly -0.8v to +0.8v. Anything positive is lean, technically, but I think when folks say lean burn they're making reference to very lean conditions, which I suppose would correspond to a reading of, say, +0.4v or greater.

Readings like that go along with low throttle settings, and they go away with heavier throttle settings. The transition is gradual, in the sense that there's an infinite range of possibilities. And you can see the intermediate settings, if you move the throttle very, very slowly. But the transition is abrupt, in the sense that a small amount of throttle motion is enough to swing the reading quickly, from the lean zone into the rich zone. This is what you see when moving the throttle in a more normal, rather than ultra-slow, manner.

It's a little bit like letting the air out of a balloon. If you work at it, you can deflate the balloon very gradually, and stop anywhere along the way. But it's also very easy to go from fully inflated to fully deflated, very quickly, in response to a small motion.

Quote:
I feel the torque at about 1500 rpm with commensurate reduction in vibration, as well as the beginning of effective induction harmonics where individual power pulses merge into a much smoother acceleration. in gears other than 5th the rpm threshold is somewhat lower, more so the lower the gear.
Whatever it is you're feeling most likely has nothing to do with lean burn, because lean burn seems to be mostly a function of throttle position, rather than engine speed.

Quote:
Under normal conditions I never exceed 2500 rpm. Throttle position would vary between 20-50 % depending on rpm and gear choice
It's hard to precisely judge throttle angle without using some kind of measuring instrument (like a DMM reading the throttle angle sensor), but my experience using a DMM to monitor lean burn tells me that it generally doesn't exist if the throttle angle exceeds 10-20%.

As I have said elsewhere, I think the amount of time you think you're in lean burn probably exceeds the amount of time you're actually in lean burn. A DMM is a good way to get a handle on this.

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Wot would not work very well, and other drivers would think I was some kind of nut case with all the distinct changes in speed.
When used properly, which means low RPM, WOT generally produces acceleration that is exceedingly moderate. And it often produces no acceleration at all. I spend a fair amount of time cruising with WOT.

As I said somewhere else: near my house is a hill, fairly long and steep. I usually climb it WOT, in top gear. Engine is at 1200 rpm, and vehicle speed is about 35. All those parameters are constant: the slope of the grade, the throttle opening, engine speed, and vehicle speed. All those parameters stay constant, for about half a mile, until I reach the crest of the hill.

Nearby drivers don't think I'm a nut case, because they have no idea what my throttle setting is. What they see is someone traveling at a constant, moderate speed, just like them.

We normally associate heavy throttle with rapid acceleration. And we tend not to associate heavy throttle with FE. So what I'm doing (along with lots of other hypermilers who use P&G effectively) is perversely counterintuitive. But it works. And it works even though it essentially rules out lean burn. Lean burn is great for situations when, for whatever reason, P&G is not an option.

I think lean burn is perhaps the reason that there is not a large gap between VX drivers who use P&G and VX drivers who don't. This is reflected in the fact that the cars in the garage scoring much higher than EPA are typically not a VX. P&G pays off in a VX, but it pays off even more in cars that lack lean burn.
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Old 05-20-2008, 05:25 AM   #20
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Good info Monroe and much appreciated.

The grades around here are very mild, no hills that would keep me at WOT for any significant amount of time.

I thought the transition would be gradual relatively speaking as you stated as long as throttle increments are very gradual for me. If the transition was abrupt it would feel like a surge so my feeling jives with you observations.

It's not soo much that I think I am or am not in lean burn, it's more an opportunity that I like to exploit to the greatest extent.

Have you tried reversing your intake snorkel for warm air intake, picking up the warm air from the top radiator tank area?

It might be worth trying when you get some consistent mileage figures. To me it seemed to make a difference, and less air density makes it possible to increase your throttle position for the same power output with less pumping losses. It could allow slightly higher throttle positions to stay in lean burn. Not a great amount, but WAI sure helps in winter.

regards
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