What kind of mileage do you guys get with your VX?

[monroe74]

sigi: "I checked & the speedo should be off by 1.56%, so I adjust that amount."

OK, thanks for explaining.

I decided to look up your tire (Potenza RE92, 165/65R14) at tirerack. Your diameter is 22.5". The stock tire (165/70-13) is 22.2" (I used the Sumi HTR T4 specs). The tire that lots of folks seem to be using (175/70-13) is 22.7". So your tire is closer to stock than a 175/70-13! That surprised me. So that would explain why your speedo error is pretty small, and why 1st gear feels right (instead of feeling tall).

I was also very interested to notice how light your tire is: 13 lbs. Compared to 14 lbs. for the 165/70-13, and 15 lbs for the 175/70-13. So your tire seems to be lighter than stock! On the other hand, your wheel probably weighs a bit more. I think the VX wheel is about 8 lbs.

Another comparison: the Potenza has a max inflation pressure of 44. The Sumis indicate 51.

Anyway, it seems that you made a wise choice.

[monroe74]

gary: "I confirm my odometer accuracy by using the mile markers on the interstate highway"

I do the same. I found that I have an error of about 2.3% (175/70-13).

[monroe74]

1993: "I assumed that the VX without the SIL in its description had a lower EPA score because it was being shifted at a 'normal' or higher RPM when test driven, than the VX with SIL in its description"

I think you're making a mistake. Yes, certain listings (like on the EPA site) mention the SIL. But this is just a convenient way to visually distinguish the CA model from the Federal model. Assuming you don't raise the hood, the presence or absence of the SIL is the only way to tell.

In other words, the car with the SIL is Federal, which means it has the wideband sensor, and the Federal ECU, which means it has lean-burn. And I think at some point someone who designed those listings decided to say "SIL" instead of "Federal."

In their infinite wisdom, Honda decided to delete the SIL from the CA car. I don't know why. I think the SIL would help a typical driver save gas, whether or not the car happens to have lean burn. The SIL basically is just something that reminds you to shift early, which is always a good idea, lean burn or not.

I have a feeling the EPA protocol doesn't pay any attention to the SIL. I think the Federal VX got a high EPA rating not because it has a SIL, but because it has lean burn.

"larger non LRR tires"

I don't think the larger (i.e., 175/70-13) tires many folks are using are not particularly "non LRR." They're just not quite the right size.

"I also plan to get proper sized LRR tires for my car if mine ever need replacing"

I also plan to switch to the proper size eventually.

"I'd be able to keep my RPMs below 1500 with the DX transmission no matter what gear, except for 5th"

I don't really follow what you're saying about the gear ratios. When I want to (and assuming fairly level ground), I can easily keep my revs below 1500, in gears 1-4. When I'm trying to maximize FE, I'm in top gear by about 25 mph.

So I wonder if there's something unusual with your tire size, or the way your engine is running.

"this is how I've been approaching hills--highest possible gear while flooring it or near flooring it"

Same here.

"I guess I could get a SuperMid"

I think I'm getting a lot of the same information with a DMM, which is letting me monitor AFR and the injector duty cycle (although not at the same time).

[1993CivicVX]

monroe said:

"So I wonder if there's something unusual with your tire size, or the way your engine is running."

I have the same tire size as you. You don't lug the transmission at 25mph in 5th gear!? I'm astonished. Gary, with his fresh VX, says he pulls from 5th at 35mph. If I pull in 5th at any speed lower than 35mph, the car is not so happy. 25mph is not tenable at all. I can coast in gear at 25mph no problem, but I won't be touching the gas pedal at that speed in 5th.

Let me try to clarify what I mean in regards to gearing. 1st and 2nd gear are tall. So any driving at speeds of 20mph or less is tricky for me. I can't accelerate in 3rd gear at speeds less than 21mph. Since 1st and 2nd gear are so tall and far apart, it's hard to shift smoothly in these gears for one--and at 18mph in 2nd gear, I'm at 1700rpm. So at low speeds I either have to do a lot of pulse and gliding to limit the amount of time I'm at that annoying RPM that's too low to shift to the next gear but too high to net me decent FE. I could record a video of my tachometer while I'm driving in town so you can get an idea of what I'm talking about. It's hard to explain. Basically, if I had close gears, I'd always be able to find the right gear for the speed I'm going and be able to accelerate without having to go up to 1800RPMs before shifting.

[R.I.D.E.]

My driveway is a fairly steep grade uphill, probably 10 feet in 75 feet. Today I pulled up that driveway at 900 rpm in first gear (cold engine). I am also on a 55 mph road without traffic lights .3 mile from my front door, which helps with engine warmup, just over a mile in warm temps, maybe 2 minutes from engine start.

I dont wait after the initial startup, virtually instantly in gear and going. I had a 37 Ford with original engine and 6 volt system, At a cranking speed of 100 rpm the engine was prducing almost 50 psi of oil pressure in 2 seconds of cranking without the engine running (5 or 6 complete revolutions of the engine). Most oil filters today have a "chack valve which prevents the oil from draining out of the filter, and oil pressure is up to specs in less than 1 second from initial cranking.

Generally if I am accelerating I can feel the intake harmonics come on at 1500RPM similar to the surge you get with a turbo but not as pronounced.

Just maintaining speed down to 1000 in any gear.

Very gradual acceleration 1200 in any gear.

Best economical acceleration 1500 in any gear.

Below that I get some vibration and literally you can feel each combustion pulse.

I think when you feel the harmonic "kick in" at 1500 you are getting better efficiency for acceleration.

Everyone seems to be concerned about when the car is in lean burn. Couldn't that be determined by the solenoid activating that controls the closing of one intake valve. I would think that would be directly related to lean burn, since the swirl is an essential component of the lean burn mode.

At such low engine rpm you certainly do not have to open the throttle much to fill the cylinders, my feeling is when you dont see any real change in acceleration you have it open enough. In most cases if I realize I am in too low a gear to keep up with the rate of acceleration of all the traffic around me I just drop it into the next lower gear, but in that case its because my acceleration would not be fast enough regardless of the throttle position in the higher gear.

regards
gary

[1993CivicVX]

in 5th gear, if I'm flooring it and maintaining speed up hill and thus maintaining RPM, 1300rpm seems to me the lowest RPM before I feel like the car is being lugged and strained. BTW, does your SIL work properly? Mine comes on too early in most gears (particularly 4th to 5th) and sometimes does not come on at all.

So at what RPM do you shift from 4th to 5th gear? (or any other gears for that matter)

[R.I.D.E.]

My SIL works, although I dont pay a lot of attention to it. It seems to work on engine vacuum. If I give it more gas at low speeds the light will actually go out without shifting. On the other hand it will tell me to put it in 5th gear as low as 1000 rpm.

My best guess would be the peak efficiency of the engine is about 1400 to 2400 rpm, it wont be much less slightly lower than 1400 but I almost never floor the gas pedal.

My reasoning is this. At very low speeds you dont need to give it much more than 50% throttle to fill the cylinders with air and fuel. The throttle plate is designed to allow enough fuel-air mix at max rpm, about 4 times the total volume at 1500 rpm. Opening the throttle to anything above 70% probably brings on some enrichment which you dont want.

When you get below 1500 the combustion pulses are far enough apart where the symptom becomes vibration which is a function of the weight of the flywheel. A heavier flywheel generally robs some power although it would allow smoother operation at slightly lower speeds.

Its a compromise, and the vibration is an indication that you are going below the ideal parameter of too low, while 2500 seems to be recognized as the point where lean burn ends.

Without a scan guage or other way of measuring instant fuel mileage I have to guess and go by how it feels, but htose senses have been refined over 42 years of driving.

It may be more important especially in stop and go traffic to learn to keep fuel shutoff activated by downshifting to decelerate while keeping engine rpm above 1000. With the tall gearing it took me some getting used to because I never like to downshift to slow down. It was partially becasue I really didn't think of it in light of the fuel shutoff advantage.

In places where you know the light timing with those drivers that like to race past you and plug up the intersection while the light is red, just downshift and kill all fuel delivery instead of coasting in neutral which consumes .2-.3 gph. That becomes a significant part of total consumption at average speeds below 40 mph since your fuel consumption is less than 1 gph, in my case less than .75 gph. At 30 mph average speed the idle consumption is approaching 50% of total consumption.

regards
gary

[monroe74]

1993: "If I pull in 5th at any speed lower than 35mph, the car is not so happy."

I guess it's a question of what objective symptoms you're talking about when you say "not so happy." There are two symptoms that you're hurting the motor by not downshifting: A) detonation (pinging); and/or B) lack of smoothness (the engine is shuddering and shaking).

Are those things happening? If not, you're fine. If you apply WOT at 30 mph in 5th, on a level road, what happens? Those symptoms? Or does the motor pull smoothly? It should do the latter.

If not, there might be some basic things to check, like timing.

"Gary, with his fresh VX, says he pulls from 5th at 35mph"

I don't recall where he said that.

"that annoying RPM that's too low to shift to the next gear but too high to net me decent FE"

There's nothing wrong with bringing RPM up to 2000 or 2500, on your way to top gear, as long as you don't stay there all day. When I'm trying to maximize FE, I usually shift at around 1500, and that works fine.

"1st and 2nd gear are tall"

I notice that too, but it's only an issue when moving from a dead stop. We make the problem a bit worse (about 2%) because of our bigger tires.

"if I had close gears"

You were making a comparison to the DX transmission, but 1, 2 and 5 are the same in the two cars. In the VX, 3 and 4 are taller. But the VX also has a taller final drive ratio.

"I'd always be able to find the right gear for the speed I'm going"

Five gears is plenty, unless for some reason your motor is not producing proper torque at low rpm.

"in 5th gear, if I'm flooring it and maintaining speed up hill and thus maintaining RPM, 1300rpm seems to me the lowest RPM before I feel like the car is being lugged and strained."

It depends on the hill, so that makes a comparison difficult. But on a level road, you should be able to do what gary said: "Very gradual acceleration 1200 in any gear." I would say even 1000, in top gear.

[monroe74]

gary: "Everyone seems to be concerned about when the car is in lean burn. Couldn't that be determined by the solenoid activating that controls the closing of one intake valve."

That transition (2nd intake valve opening fully) happens at 2500 rpm. Lean burn happens at low rpm, with low throttle settings.

"I would think that would be directly related to lean burn, since the swirl is an essential component of the lean burn mode."

That's exactly right. The two things (VTEC-E and lean burn) are related, but they are separate functions. Low rpm always means that the second intake valve is mostly closed, but it doesn't always mean that lean burn is happening. WOT at low rpm means the second valve is still mostly closed, but AFR is rich.

"I just drop it into the next lower gear ... because my acceleration would not be fast enough regardless of the throttle position in the higher gear."

That's exactly how I drive. Often when I downshift it's because WOT in a higher gear was still not enough power.

"Opening the throttle to anything above 70% probably brings on some enrichment which you dont want."

I find that AFR makes the transition from lean to rich at lower throttle, about 25%. And then the richness steadily increases, all the way to WOT.

"2500 seems to be recognized as the point where lean burn ends"

I think it's true that you won't induce lean burn over 2500 rpm. But you also won't induce it under 2500 rpm, except at very moderate throttle settings.

"I almost never floor the gas pedal"

That's interesting. The essence of my P&G routine is that I use WOT very frequently. A lot of what helped convince me is here (I know about this thanks to PaleMalasian):

http://www.autospeed.com.au/cms/A_110216/article.html

"Without a scan guage or other way of measuring instant fuel mileage I have to guess and go by how it feels"

I've been getting good info from a pretty simple DMM. It's easy to monitor AFR. And the DMM has a dwell feature that lets me monitor injector duty cycle, which is supposedly a good proxy for instantaneous fuel consumption.

[R.I.D.E.]

Monroe, I have a graph in my notebook that is basically the same and have been showing it to people for years. Check the EPA hydraulic hybrid documents for graphs for diesels at 41.9% peak efficiency and gas engines at 35% peak efficiency. That range is the key to any hypermiling as well as the key to my ivt powertrain design.

Basically what you are trying to do is make the engine produce the most power for the least fuel at low rpm. The key is the low rpm issue.

Brake specific fuel consumption is a function of throttle resitrction. Once you have reduced the manifold vacuum to its lowest point, more throttle has no effect, except to add more fuel and basically apply full load enrichment.

When you achieve no more increase in your rate of acceleration because you are in too high a gear, you have the load at 100%, which combined with the minimum throttle position producing the lowest possible vacuum is the sweet spot the graph is describing.

In order to increase your rate of acceleration you must use a lower gear, which allows the engine to produce more power because of higher revs, and gives you a stronger lever with a higher gear ratio. The minimum vacuum in manifold stays the same which verifies your throttle position is suffecient (in the graphs yo ucan actually se and area where 50% is better than 75%, but the difference between the two is minimal).

This is the most basic of the principles of my powertrain design which is to accelerate with the variation of gear ratios while the engine load and throttle position is relatively constant, with no restriction to maximum fuel and air in the cylinder on every intake charge.


I don't think its a matter of who is correct or incorrect, we are both talking about very low speeds and loads that are 100%. thats a very small portion of the graph, and we are not talking about a Jag V12.

Your position of all or nothing is correct, my difference of opinion is illustrated in the graphs when you look at the 50% throttle position settings at the loads and speeds we are working with (very low).

The most efficient will be the lowest speed with the highest BSFC. I believe my strategy is the best and my mileage figures seem to illustrate this. More throttle produces nothing because the load is 100%, therefore more throttle can only have the effect of producing unwanted enrichment (which it may or may not actually do, but I believe it does).

If I was talking about 2000 rpm and not 1500 it would require larger throttle opening above 50%, beyond 2500 probably 90%, but I generally avoid wot unless its absolutely necessary and in most cases I will drive through several hundred miles with the engine never reaching any rpm above 2500.

The last time it hit 4500 was accelerating up a significant grade to merge on the interstate with close to 1000 pounds of weight in passengers and cargo, and that was the worst mileage tank (at 50) of them all.

One thing is certain, at WOT you wont have lean burn. I read a post on this forum where a member who had a Means of determining when lean burn was engaged who stated he could actually climb a hill (probably a slight grade) and still stay in lean burn. That was a critical factor in using a lower throttle position to try to maximise lean burn on acceleration. I BFSC map for the VX would probably be different from the one in the graph in the illustration.

that being said the only proof I can provide to justify my assumption is the mileage achieved.

Without the potential for maintaining lean burn I would use 75% throttle on feedbaack fuel injection cars, to avoid open loop full load enrichment.

Again please understand this is not a criticism of any kind, I can't prove my point with a scan guage (wish I could) but it would be interesting if we had a BFSC map for a VX.

regards
gary