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

I was thinking of getting a honda HX/VX but I was reading and some of the MPG numbers put me off because they were much worse than the EPA rating. So, if you have a VX or HX, can you please post what kind of mileage you get with it?

I think you have a point that these cars get more credit than they deserve. The reason people with VXes don't have as large a gap (or even worse than EPA) as compared with other cars--is when the EPA does the test for that car, the shift light makes the drvier shift earlier than he is shifting when testing the mpg of any other car. The other reason is those LRR tires that the VX originally came with and still exist, probably, on only one VX. (Maybe you can find him on this forum ;)) But, I know that a lot of the VX owners on here drive their VX "spiritedly" I personally get in the 50s, but this tank I think may be in the low 60s because I have been EOCing and P&Ging like it was a crime to burn gas (I'm just below half tank at 373 miles). Driving without thinking twice about economy, the car will get between 40-44mpg (depending on your driving habits) --and then sipping it you can get in the 50s--but it takes some discipline. I think given that the original LRR tires are no longer to be found on VXes, a 2 door civic coupe of the same generation of the VX (but is non-VX/HX, ie., has no lean burn) can achieve by a talented driver only slightly worse numbers than the VX, and they are easier to come by. They have significantly better aerodynamics, and if you are P&Ging, there may be an argument for not needing lean burn as much, as lean burn really shines when driving at a constant speed.

Which raises a question I have. What is the power/fuel consumption ratio between lean burn and full enrichment mode? For example, how much horsepower do I get if I floor it in 5th gear--and how much fuel am I using... compared to how much horsepower I get while remaining in lean burn and how much fuel am I consuming. How do these two aspects compare? This could answer some questions about whether it's better to maintain lean burn on the pulse, or whether it's better to just floor it. If lean burn is a better combination of fuel consumption and power, (ie, you get more power per unit of fuel when in lean burn than when in full enrichment) then it makes sense it would be better to run at a higher RPM (thus a lower gear) to maintain lean burn than being at the lowest possible RPM and being in full enrichment mode (which is how I drive, since I don't have a lean burn monitor). Anyone follow what I'm getting at? Anyone know??? Would love to see these two ratios compared side by side. I probably should get in the habit of maintinaing lean bur at higher RPM as this is much better on the motor and transmission than always pushing the car at the lowest RPM.

I get around 45 MPG in a mix of off-highway and stop and go driving.

My VX is well maintained (minus the valve adjustment I've been puting off...) w/ about 140k miles on it and with 250k miles plus on the chassis. It's a very solid car. I've been given numerous offers over what I paid for it, and I'm not getting rid of it until the price of the insights starts to go down.

Great car. This is my 4th Honda now but I would recommend a VX or HX to just about anyone.

I'm at about 47mpg with highway and city driving. On the highway, I'm running 70-80 mph, but if I was able to drive slower, I would easliy be in the 50s. I would recommend getting a HX or a VX anyday. I had a 99 HX and it game me low to mid 40s. An HX would be easier to find nowadays with everyone taking the bubble hatches (92-95) and swapping in H22s, B18s, B20s, and bodykits. Like Dan said, an Insight is in my future. I wish I would have invested in one when they were more available and more reasonable in price. everyine who's selling them now has a premium on them. I've seen some used ones priced at almost new prices.

imz: "I was reading and some of the MPG numbers put me off because they were much worse than the EPA rating"

In another thread I showed that most VX owners seem to get about 45 mpg, which is a bit higher than EPA. See details here:

https://www.gassavers.org/showpost.ph...7&postcount=11

A VX doing "much worse than the EPA rating" probably has a bad O2 sensor, or other serious problems. Or is being driven very hard.

1993: "when the EPA does the test for that car, the shift light makes the drvier shift earlier than he is shifting when testing the mpg of any other car"

Really? Are you sure that EPA runs the test that way?

"those LRR tires that the VX originally came with and still exist, probably, on only one VX"

It's true that most VX owners seem be running 175/70. But the effect is probably mixed. The tire makes gearing taller, which means a speedo error of more than 2%, which means that many VX mpg claims are probably understated, by that amount. The taller gearing might also make real mpg higher than what you would get with a smaller tire (aside from making observed mpg lower than real mpg).

Anyway, it looks like tirerack has Sumi 165/70 available, so it seems possible to get back to stock, if someone wants to do that. I intend to do that when my 175/70 Sumis wear out.

"They (the EG coupe) have significantly better aerodynamics [compared with the EG hatch]"

Really? Are you sure? The VX has a coefficient of drag is 0.32. That's pretty low.

Also, I think you're incorrect to suggest that all the VX has is lean burn and LRR. You're leaving out VTEC-E (which is something separate from lean burn). There's other stuff too, like gearing, and various weight reductions. A good technical listing of various VX FE ingredients is in this pdf.

"then it makes sense it would be better to run at a higher RPM (thus a lower gear) to maintain lean burn than being at the lowest possible RPM and being in full enrichment mode"

I think high gear is always going to be better. I'm using a DMM as a lean-burn monitor, and it's certainly possible to maintain lean burn in a high gear, provided you are very gentle with the throttle.

But I still have a question very similar to yours. Being gentle with the throttle is at odds with my normal P&G technique, which is designed to minimize pumping losses. I raised this question here:

https://www.gassavers.org/showpost.ph...&postcount=147

"I probably should get in the habit of maintinaing lean bur at higher RPM as this is much better on the motor and transmission than always pushing the car at the lowest RPM."

I don't think so. Wear is roughly proportional to number of revs. Your expected engine lifetime can be expressed as a rev count. Lower revs per minute means lower revs per year, which means more years before your engine runs out of revs.

You can buy HX 14" wheels, then get 14" Insight tires (Potenza's). I did this, & my mileage has gone up.
My 90 day average is 60.79, so you can improve on the EPA numbers.

"You can buy HX 14" wheels"

You're getting great results, so that seems to be working well.

But I assume you're getting a fairly substantial speedo error. Are you correcting for that in your gaslog? If not, then the mpg you're reporting is probably understated.

Also, do you find that first gear feels tall? I assume the bigger tire would create an effect like that.

My last five tanks were 61,56,50,65,62.

My car just turned 30k miles on the original tires built in 9-93.
Only parts replaced are air filter and wiper blades.
I'm retired and avoid rush hour congestion and drive roads where I know the location of every pothole.

I reversed the air intake snorkel and shortened it just enough to draw warm air from right behind the top radiator tank and upper radiator hose.

My car came with AC, used it 10 minutes in 3 k miles, no radio ( hearing is bad enough already) and a grille block over about 60% of the drivers side of the grille from the factory.

I use the cheapest regular gas I can buy.

the car was totalled in 95 kept inside in a controlled environment. I bought it in March 08 had it shipped form Ohio to VA and repaired it with 27,492 miles on the odometer. I runs and drives like a 2 year old car, but still needs paint to be finished.

If I religously use hypermileing (engine on coasting is my preferred method) and used my best route I can easily average over 60 MPG. Drafting a large truck at 65 MPH my best mileage was 65.744 MPG, 304 miles on 4.627 gallons of cheap regular.

If you rode with me I think you would agree that my situation represents close to an ideal scenario for mileage. the only better situation would be a deserted somewhat hilly country road with no traffic. Under those circumstances with engine off coasting I know I coud top 70 MPG, maybe even 80.

I easily beat my brothers new Prius on an identical route with both cars driven carefully for best mileage.

regards
gary

"In another thread I showed that most VX owners seem to get about 45 mpg, which is a bit higher than EPA. See details here:"

45mpg is not higher than EPA under any circumstance. When I say EPA, I mean old EPA, not new EPA. Old EPA IS possible, the question is how possible. On my Lexus, the OLD EPA rating was only slightly inaccurate, not enough to piss me off too much, however I do not know if this is the case with the VX or not. I want to know how difficult it is to achieve 47 city and 56 highway. Remember, old EPA, not new EPA.

I've never achieved higher than 44-45 in all city with my VX, but I have a decent amount of hills. Without those, which is probably how the old EPA was tested, I would expect at least to be able to get 47 with my high-mile VX.

I've also been in the 50s for highway trips as well, and this is without matching front-to-back tires, no grill block (such as the factory one), and no rear diffuser.

The old EPA is possible if the car is in perfect shape. But for how little the VX costs I still can't see many if any hybrid coming close to beating it in the long-run for cost to own.

"old EPA, not new EPA"

Fair enough. I didn't realize that's what you meant.

"I want to know how difficult it is to achieve 47 city and 56 highway"

I think the gaslogs here show that 45 mpg overall is a very typical result. I think they also show that certain people, with mostly unmodified cars, are able to get 50-60 (and sometimes better), on a fairly regular basis.

But only you know your own driving environment and driving style, so you'll have to interpret these numbers in that context.

Anyway, I think the bottom line is that you're likely to beat a VX only by buying one of the following: something with fewer than 4 wheels; something with fewer than 4 cylinders (e.g., certain Metros); a hybrid; or a diesel. And when an item on that list beats a VX, it usually does not do so by a wide margin.

45 in the city is fine, but from the mileage figures I see, 45 on the highway is not acceptable. Do people here not drive on the highway very much? I live in the bay area where I would be doing quite a bit of highway driving. Also I read that the VX has a Drag coefficient of .32 but why does the HX have .38??:confused:

"Do people here not drive on the highway very much?"

I don't know why you're saying that, because the gaslogs explicitly reference a fair amount of highway driving.

"45 on the highway is not acceptable"

I don't know why you're saying that, because the gaslogs explicitly indicate that lots of folks beat that on the highway, or even off the highway.

"I live in the bay area where I would be doing quite a bit of highway driving"

I think you'll see a big difference between cruising at 55 as compared with cruising at 80. And I imagine both of those speeds are used on the roads you're talking about, so this is where your own details have to be considered.

Also, you'll see a big difference between driving smart (using the kind of techniques discussed on this forum), or not. So this is another reason why your own details need to be considered.

And again, if you're worried that a VX won't be good enough (however you define that), I think you have to say, compared with what. Because it's hard to beat.

"why does the HX have .38"

I don't know. Maybe the coupe design is fundamentally less slick than the hatch. That's a guess.

https://www.ashspecz.com/ashspec/zem/timingmap1.jpg
I was looking on wikipedia on ignition timing, and found this picture. Now I've got another question, why are there so few instances in this timing map where it's closed loop? I was under the impression that it only goes into open loop when the engine is at high load, high RPM, choosing the timing based off of predefined tables, usually resorting to 12:1 fuel ratio in order to protect the engine or something.

I checked & the speedo should be off by 1.56%, so I adjust that amount. 1st seems about the same.

I dont worry about the speedo much, you can check that in this area when the police set up a radar display whose purpose is to slow people down.

I found that my previous two Toyotas were 3% over the true mileage, nice way to shorten the warrantee by 1000 miles in a 36k warrantee period.

I confirm my odometer accuracy by using the mile markers on the interstate highway. In 50 miles my odometer read 49.5 so I just adjust the odometer reading by .05%, 1 mile in 200.

I understand GPS works nice but I would think it would not include increased distance due to elevation changes.

regards
gary

monroe, it used to be that fueleconomy.gov had two EPA ratings for the two different VX models--one was SIL (shift indicator light) and the other was not. The one that wasn't had substantially worse EPA score. I don't recall if I read on the website that the test driver has to shift earlier when driving the model with the SIL, but if I didn't, then 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 don't think the <2% taller gear ratios from larger non LRR tires are off setting the fuel economy loss of not riding on the normal sized LRR tires. The higher ground clearance is enough to offset any gains from <2% taller gear ratios. So, therefore, riding on the original LRR tires gives a better EPA score. This isn't my idea--someone else had made a post about why the VX has such great EPA numbers, using these reasons (or at least the original LRR tires that came on the car as the main reason)

I also plan to get proper sized LRR tires for my car if mine ever need replacing (they're quite new at the moment)

I'm actually not sure about this, but it makes sense given the slippery shape of the coupe. I also read somewhere on these forums (I think it was TomO) that the VX hatch design causes turbulence which causes drag--which the coupe model's design doesn't have. Driving the coupe, without touching the tires, it rolls better than mine did at 45psi. At 60psi, my VX only now rolls about the same as the coupe does, although this could be due to my ball bearings that aren't rolling smoothly, but everyone I asked about that tried to assure me it wouldn't have a noticeable effect (although someone made a post about relubing their ball bearings and the car rolling better afterward, so I dunno)

You're right, I forgot about those things, and they make a small difference. Before I knew the term hypermiler, the website gassavers, or anything about tire pressure and aerodynamics, I did a 500 mile tank over about a week or so period in the 1994 Civic 2 door coupe -half or more of those miles were on the highway- driving around 60-65 (top speed of about 70) and lots of short trips and cold starts, but it was summer time-- and I averaged 52.5mpg. Now granted I filled up at a different pump in a different state, but it was an 800 foot elevation increase from where I first put fuel in and I had gone up and down many hills. Don't get me wrong, though, I was driving to save gas! And I think at the end of the tank I was doing some P&G although I didn't know it as that at the time. Anyway, 52.5mpg is about what I'd get in my VX if I left the tires alone and drove to save gas. I'd almost prefer the DX gearbox for reasons I've already stated--because at 60mph, an extra two or three hundred RPMs on the tach isn't going to offset the substantial gains I get with close 1st, 2nd, 3rd, 4th, and 5th gears.

Let me enter into a tangent on the issue of gear ratios. Unless you are going to be doing literally 60% or more of your miles on the highway, or above 55-60mph, you are going to be getting worse mpg with the tall gear ratio. In my VX I have to give it extra clutch and gas every time I start it --wasting fuel-- then I have to climb to 2000rpm in first and 2nd gears, and I often have to drop into 1st gear where in any other car I'd be able to remain in second. I could go the same speed in 2nd gear in the DX as I could in 1st in the VX. If I had the close gearbox of the DX, given my driving habits of about 40% at 60mph and the rest less than 60mph, the one or two mpg lost on the highway because of the few extra hundred RPM is not going to outweigh the losses in feul economy dinking around town--and everyone has to dink around town. I'd be able to keep my RPMs below 1500 with the DX transmission no matter what gear, except for 5th--but then I'll just have more incentive to P&G. I think a happy medium would have been if they had made 1st gear short, 2nd and 3rd gear close, and 4th and 5th gear farther apart, so I'm not shifting at 2000rpm to go into 2nd and 3rd gear, and then only 1400rpm to go into 4th and 5th gear. It should be geared with 1600rpm shift points across the board and still have the same tall 5th gear ratio.

You cannot be very gentle with the throttle going up a hill though. If you do, then you bog down at 1000rpm. So this is how I've been approaching hills--highest possible gear while flooring it or near flooring it, rather than one gear down so I'm going up the hill at 1700rpm instead of 1400rpm. Lean burn at 1700rpm or full enrichment at 1400rpm? Seems lean burn might be better. 300 more RPM is only about 16% faster--so not sure if lean burn is more or less than 16% more efficient than full enrichment (I assume it's more than 16% more efficient) Again, need to know the horsepower output while maintaining lean burn as compared to the hp output when flooring it.

but lugging or straining the transmission is worse for the car than riding it a few hundred rpm higher.


It's a small travesty that no VX owneres on here have a SuperMid. If they did, they'd answer some of these lean burn questions!!! Imagine if every VX owner on this site had a SuperMid. We'd all be VX masters of hypermiling. Now I really want to know what my mpg is when in lean burn and when in full enrichment mode. poop. I guess I could get a SuperMid, but then I'd have to pay someone to install it cause I'm about as mechanically inclined as a chimpanzee.

In the winter I tend to get around 42-44mpg, last summer I averaged 47mpg, my vx has 250,000 miles on it although it has 195psi compression I'm sure there are parts of the engine that have enough wear that they hurt my mileage, my vx also has all the dealer options like the passenger side view mirror, mud flaps, side molding, after market sun roof, and parts of the a/c system are still in the car although the compressor is removed.
I also live in an area that has number of stop signs and stop lights at the bottom of good hills, this became very clear while driving my comuti-car I have to ride the brakes going down all the hills and come to a complete stop at the bottom, then start going up the next hill and my battery doesn't last any wear near as long as if I stick to a straight stretch.
So I would like to get better mileage and I try but so far my best idea is to use my vx less.

imz: "why are there so few instances in this timing map where it's closed loop?"

Good question, it does seem odd.

Maybe because it's a timing map, not a fuel map. Maybe the latter would look very different, in this regard. Just a guess.

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.

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).

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).

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.

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

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)

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

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.

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):

https://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.

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

You guys should get gas logs for your cars.

gary: "in most cases I will drive through several hundred miles with the engine never reaching any rpm above 2500"

In this regard your driving style is very similar to mine.

I just did a test in the following scenario: moderate uphill grade, 27 mph, top gear, 1000 rpm, WOT. The engine pulls smoothly, with no signs of detonation, hesitation, or unusual vibration. My weight, plus cargo, was about 230 lbs.

So I generally keep my revs very low, like you.

"at WOT you wont have lean burn"

Actually, AFR goes from lean to rich at a moderate throttle setting, way before WOT (about 25%). And if you define 'lean burn' as not just lean, but very lean, then this is only seen at very moderate throttle settings (about 10%). On the other hand, it's possible to cruise at a reasonable speed (50 or more) at such a setting. But I'm not sure that's the optimal strategy.

"I read a post on this forum where a member who had a Means of determining when lean burn was engaged"

I'm currently monitoring lean burn with a simple DMM. It's easy to do.

"he could actually climb a hill (probably a slight grade) and still stay in lean burn"

Yes, provided the conditions allow for a moderate throttle setting, which they often do. But I've come to believe that moderate throttle settings are generally not optimal.

"That was a critical factor in using a lower throttle position to try to maximise lean burn on acceleration"

My experience monitoring lean burn (defined as 'very lean') tells me that lean burn is easily achievable in steady cruising, but not generally achievable in anything we would normally call 'acceleration.' I've also come to believe that steady cruising is inferior to P&G. In other words, minimizing pumping losses has a better payoff than maximizing lean burn.

I think WOT minimizes pumping losses. I'm greatly influenced by this graph:

https://www.autospeed.com.au/cms/gall...0&a=110216&i=6

It shows that WOT improves BSFC.

I think some of our assumptions about avoiding WOT have to do with concerns about open-loop mode. But I'm starting to believe that a system with a wideband sensor doesn't have open-loop mode. Or if it does, it's less extreme than what happens on other cars, with low-resolution sensors.

"it would be interesting if we had a BFSC map for a VX"

The article I cited has a map for the Insight, which has a similar engine. The graph is interesting, although in some ways it seems to contradict the other graph I like.

"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."

Why is it reasonable to assume that the vacuum at 99% throttle is just as low as the vacuum at 100%?

"please understand this is not a criticism of any kind"

I don't take it that way at all. I greatly respect your opinion, and I appreciate the opportunity to learn something.

1993: "gas logs"

I intend to, eventually, but I think I want to wait until I develop more data, and more consistency. Lately results are erratic, because I'm trying a bunch of different weird tweaks and tests, in the car and in my driving. I haven't had it very long. And I don't put on a lot of miles, right now, so it's taking a while to accumulate the data I want.

"27mph, 1000rpm, WOT, slight up hill"

Yeah, no, my car will not do that. I mean, it *will* do it, but it just doesn't feel at all happy. Are you telling me your car sounds/feels the same at 1000rpm, WOT, 5th gear as it does at 1300rpm, WOT, 5th gear?

I'm pretty sure the VX vs HX setups are about the same weight. Higher weight wheels, but lower weight tires. I'm running 60 PSI with no problems of wear or traction.

"Are you telling me your car sounds/feels the same at 1000rpm, WOT, 5th gear as it does at 1300rpm, WOT, 5th gear?"

Yes, essentially, except for the differences that are obvious and normal. 1300 rpm is about 35 mph. Things sound a bit different because you're going a bit faster, and you feel more power starting to become available. But other than that, it feels the same.

Going up that same grade, if I release the throttle (and stay in gear) and let the speed drop to about 20 mph (750 rpm), and then reapply WOT (or any throttle at all, for that matter), this is not good. I can feel immediately, in the lack of response, and in vibration, that the motor is not producing enough power to match the load I've placed on it. The speed will continue to drop, even though I'm requesting power.

But if I'm at about 1000 rpm, the motor is happy. And remember, this was going up a slight grade. On a level road, and if I dumped the 70 lbs of cargo I was carrying, the threshold moves down to maybe 800 rpm, or maybe even less.

"it [my car] just doesn't feel at all happy [in a similar situation]"

When you say not 'happy,' what's the symptom? And have you ever checked the timing? It could be something very simple, like that.

"I'm pretty sure the VX vs HX setups are about the same weight."

Just to be clear, if I understand correctly, you're using the HX wheel with the Insight tire. The HX tire is 185/65-14. That tire weighs 16 lbs. Your Insight tire (165/65-14) weighs 13 lbs. So your setup is perhaps more properly called an HX/Insight setup.

Anyway, I think the HX rim is 11 lbs, vs 8 for the VX rim, so you may have increased your overall weight a little. But I have a feeling your Insight tire has especially low LRR, so that probably offsets the weight difference.

"I'm running 60 PSI with no problems of wear or traction."

Interesting. My Sumis are marked 51. I've been running them at 55, but I plan to go to 60. I'm even tempted to try 65. But first I'd like to hear that someone else got away with it!

Proportionally, your experience suggests I would be OK. The max marked on your tires is 44, I think.

A few things I didn't notice until just now.

You are correct that VTEC-E (what you mentioned regarding the solenoid) and lean burn are related. However, the relationship is not exactly as you described.

VTEC-E means that at low rpm, the second intake valve opens only a small amount. This provides the swirl you mentioned. And you are correct that lean burn relies on this swirl.

On the VX, the VTEC-E threshold is 2500 rpm. Above this rpm, the solenoid activates and the second intake valve opens fully. (Besides 2500 rpm, some other conditions also have to be present; e.g., the engine has to be warm.)

So lean burn does not happen over 2500 rpm. But it's important to understand that just because we're below 2500 rpm, that doesn't mean we're in lean burn. For lean burn to take place, you need to be under 2500 rpm, and you also need to be using a relatively small throttle opening.

Correct. But the important thing to understand is that you also won't have lean burn at 75%, or 50%. I think lean burn generally goes away at any throttle position greater than 10-20%.

When you're using 75% throttle, you're definitely not in lean burn. But maybe you already know that.

Also, as far as I can tell open loop does not take place on the VX. Wideband-sensor systems generally do not need to resort to open loop. But that also might be something you already know.