Not sure of the term, but is my thinking right...?

[aronhk_md]

In the basic thread I saw here with terms listed I did not see what I tend to do.......a method I know has increased my mileage. Its not DWL where you pick a speed and maintain it, but rather the opposite.

As an example I'll use highway cruising. For uphills with my little 1996 toyota tercel automatic I'll slow down.....choosing a gas pedal position higher than for flatlands. So if I was cruising at 65 on flat I may slowly ease on the pedal and reduce to 60 mph on an incline. If its very steep I may slow as far as 55 mph. On the downhills I'll often increase speed, and I may hit 70, 75, or even 80....depending on other drivers and the road.

I've found it takes very little increased pedal to get that extra speed on the downhills, but at the same time I am increasing my average cruise speed.

Doing this I have managed to increase my highway mileage from approximately 35 mpg to 38 mpg. Delaware is fairly flat though, and our hills are not very big. Is there a term for this? I know I must not be the first to try it.

I have also taken during the summer to cycling the A/C according to those same hills. On the uphills I'll turn it off, and I turn it back on heading downhill. Sometimes it gets a bit warm on the uphills, depending.....lol. Too warm and I'll turn it back on regardless.

I'm new here, so I apologize if I'm just repeating common practices....or doing them wrong.........lol

[theholycow]

Originally Posted by aronhk_md

Its not DWL where you pick a speed and maintain it, but rather the opposite.

DWL usually means one of the following two definitions:

1. Using an instant fuel economy display, pick a target MPG and attempt to keep exactly at that instant MPG.

2. Pick a throttle position and stick with it, similar to what you describe.

Picking and maintaining a speed, I would just call that cruise control.

Each of these strategies can be helpful. Which one works for you is best left up to experimentation; there are too many variables to predict the best choice. It sounds like you found a strategy that works well for you - your car, your route, your driving style, your traffic, etc.

In a modern fuel-injected manual transmission car I prefer quite the opposite strategy. I accelerate uphill and neutral-coast downhill. It keeps my speed steady, which helps with impatient traffic uphill and helps avoid speeding tickets downhill. It operates my engine at better efficiency due to lower pumping losses at the throttle and lower RPM (which means lower reciprocating and frictional losses). It also reduces the total quantity of revolutions, again saving reciprocation and friction losses.

In an automatic I have to be less aggressive with the throttle because the transmission will downshift.

I now drive an old carbureted car with tall gears and not a lot of power and I use a modified strategy. I use my vacuum gauge to try to stay out of enrichment, using as much throttle as I can without vacuum going too low. This results in my strategy working very much like yours; I lose speed while climbing, and I try to store as much inertia as possible while descending. My fear of speeding tickets limits how much gravity assist I'll use, though. Keeping as much of a constant vacuum level as I can, it is effectively another form of DWL.

My hills are mostly under 1 mile long, light to medium grade, constantly rolling with not much flat land.

[aronhk_md]

Thanks again Holy......your 2nd strategy is like what I'm doing I just didnt see this listed in the explanation of DWL.

I am keeping the lightest pressure on the accelerator (and therefore vacuum)I can under all circumstances, except dowhills where I sacrifice a drop for some extra speed. My Tercel is very underpowered, so even on moderate uphills it slows......almost bogs in my opinion. To get it to stay at an even speed I'd need to give it considerable pedal....and therefore fuel (The hills around here arent enough to coast down, btw.).

2 possible reasons here aside from it just having a low hp engine....

1. I am running 185/65/14's on it instead of the original 155/85/13's (handling was HORRIBLE with those tires and the speedo read 3-4 mph over actual at 60-65) and now the speedo reads exactly.......handling is 100% better as she'll carve turns now in almost a sporty way, but the slightly taller tire did slow acceleration while improving my highway mileage on level ground. It has made uphills more of a challenge though.

2. Even before the tire/wheel change I always thought she was not very responsive to vacuum changes, and doesnt downshift out of overdrive without a moderate lugging on the drivetrain. In addition, I believe she shifts into overdrive a bit too soon....which gives doglike performance and in the end costs more fuel because it is NOT in what little powerband I have.

To compensate for both these factors I began shifting in and out of overdrive manually with the button on the shifter. I shift up when I know it wont lug, and I shift down to prevent it from lugging.

I know my way of driving wouldnt make other motorists happy in a congested area, but luckily this is not such........mostly where I follow that low vacuum approach is on highways with multiple lanes and little traffic. If traffic is heavier I tend not to do it as much. But you have given me a good idea....installing a vacuum gauge would make it more fun on both the tercel, and the new-to-me Civic VX.

Thanks!

[theholycow]

DWL, in its various forms, is about targeting a real-time numeric display, either of load (throttle position or vacuum) or MPG. What you describe as your strategy may not have a name, as far as I know, other than "keeping the lightest pressure on the accelerator I can".

Your fuel injected 1996 Tercel may respond better to more throttle than my carbureted car - possibly as much as you can before getting open loop WOT enrichment. Maximizing vacuum (the lightest pressure on the accelerator) may not be the best policy, and even on my carbureted Buick it isn't. However, with the automatic you of course want to avoid it downshifting excessively.

I would use the most pressure on the accelerator that doesn't cause an unintended downshift, although I hear that Toyota and Honda automatics do not downshift as readily as the GM and Ford automatics I'm used to (which agrees with your description of having to manually downshift).

You may want to get a ScanGauge or UltraGauge for your Tercel, if you plan on keeping it after you get the VX into a daily-driver condition. It would be far, far more useful than a vacuum gauge. Unfortunately your options for the VX, which is pre-OBDII, are not so clear/easy/pleasant.

[aronhk_md]

When you say the most pressure on the accelerator without downshifting.....do you mean in an uphill condition? I ask because in those uphill conditions.....lets say I am trying to maintain 60 mph as an example. The engine is lugging, and my foot is in the pedal.....not deep enough to cause a downshift, but deeper than I like and she's lugging a little. I could maintain that, or........

.....if I manually pop it out of overdrive she'll immediately rev a little higher, stop lugging and begin picking up speed, even uphill. So if I really WANT to just maintain 60 mph I can now lift my foot off the pedal a bit. She maintains 60 mph more smoothly under this condition, with what I BELIEVE would be less vacuum.....and she also doesnt feel like she's working as hard.

But I'm not an expert here, only going on my basic understanding of physics and automotive mechanics.

As a side note on the VX......I have thought I might turbocharge it. Turbos are nice in that, when you arent pushing into it hard its like they arent there. No parasitic drag like a supercharger, no increased fuel consumption. Just there when you need it. With say 7-8 psi boost I would not likely be putting a lot of strain on the other components, but could easily gain 25-30 hp when needed (freeway onramps, etc). There are so many turbos out there for these D motors that picking one up cheap is a matter of waiting for someone that bought a whole kit and never used it.

Might also consider adding a DIY fuel injection kit like the megasquirt. I can then program it to match the lean burn characteristics the VX always had, but without the problems the VX encountered switching between modes.

This is more a "see what I can do" experiment than anything. My thought is with the turbo I could actually make it feel quite peppy/sporty (unlike how it came from the factory). 25 extra ponies would make that little 2100 lb car scoot, and with the fuel injection I might be able to obtain 60 mpg highway. All for potentially under $2000

$900 for the car
$1100 for bodywork, panels, clutch and paint in my shop
$2000 for turbo and fuel injection
$600 for a vintage air type A/C system (if I cant easily retrofit from a junk car or dont feel like messing with used stuff)

So $4600 hopefully for a car that at least matches what a Prius can do. Thats why this sounds so fun! Of course it has to wait until I get my Trans Am back on the road this fall.....lol

[theholycow]

Originally Posted by aronhk_md

When you say the most pressure on the accelerator without downshifting.....do you mean in an uphill condition?

I mean in all conditions. Obviously if it's in high gear and producing more speed than you want, you need to back off (or neutral coast)...but any other time, it's better to open the throttle. Sucking all that air past the closed throttle wastes energy, and that waste (along with similar intake and exhaust waste when there are other restrictions) is called pumping loss.

I ask because in those uphill conditions.....lets say I am trying to maintain 60 mph as an example. The engine is lugging, and my foot is in the pedal.....not deep enough to cause a downshift, but deeper than I like and she's lugging a little. I could maintain that, or........

Can you define "lugging"? Everybody's definition differs, sometimes widely. Because of how common it is for people to associate lugging with engine damage, I only use it to mean that the load is so heavy at low RPM that you get spark knock/detonation.

.....if I manually pop it out of overdrive she'll immediately rev a little higher, stop lugging and begin picking up speed, even uphill. So if I really WANT to just maintain 60 mph I can now lift my foot off the pedal a bit. She maintains 60 mph more smoothly under this condition,

If at wide-open throttle you're losing speed and/or not gaining speed at all then it's time to downshift regardless of any fuel economy concerns. I can't imagine why some automatics don't.

with what I BELIEVE would be less vacuum.....and she also doesnt feel like she's working as hard.

High vacuum: Foot off the gas
Low vacuum: Wide open throttle

There are more variables than that, but that's the basic pattern. If your throttle is closed more and your RPM is higher then you've got higher vacuum, not lower. The highest vacuum you'll ever see is while engine-braking with your foot off the gas in 1st or 2nd gear descending a mountain. Zero vacuum is easily achieved with wide-open throttle at low RPM.

As a side note on the VX......I have thought I might turbocharge it. Turbos are nice in that, when you arent pushing into it hard its like they arent there. No parasitic drag like a supercharger, no increased fuel consumption.

There is some pumping loss introduced - the same sort of loss people try to reduce by installing upgraded exhaust systems. It's not much. When used in combination with a more efficient engine that has sacrificed power for efficiency, the result is better efficiency and the same power compared to a larger naturally-aspirated engine. Just slapping a turbo on an existing car won't make it more efficient but will certainly make it less efficient - you wouldn't invest in it if you weren't going to use it, and when you use it you need to run very rich (as well as needing to retard your timing).

Anyway it sure would be an interesting project, as would the Megasquirt. I'm not sure how easy it would be to program the Megasquirt to work as well as the OEM computer with the somewhat unique VX. It'd be a huge learning experience for sure.

$900 for the car

You got a VX that just needs a clutch and bodywork for $900? Score.

[aronhk_md]

Hey Holy....going to number the separate notes and responses you made in my replies...

1. Not sure I get what you mean that its better to open the throttle. The amount of air passing through the throttle is directly related to how open it is. Are you saying that in an acceleration phase it is better to open the throttle all the way to reach your cruising speed than it is to slowly accelerate with careful application of throttle? In other words......you advocate using a heavy foot? I'll have to do some research on PUMPING LOSS....maybe I'm just not understanding.....

2. Spark knock/detonation is an interesting phenomenon.....but I dont use the word lugging in association with it at all, though lugging can include detonation if the car is not running/tuned correctly. I have done a lot of research on that matter, since my other car is a turbo car.......and at the HP level that car is at the least bit of detonation or preignition will destroy it FAST. Here is a link to what I consider a really good explanation of detonation & preignition for anyone reading this later........they arent the same thing. Keep in mind that detonation can be occurring even when NOT heard.

http://www.pontiaczone.com/forum/showthread.php?t=26592

What I call lugging is an engine unresponsive to further input from the gas pedal. Or a response that is VERY slow. At its worst it is loss of rpm even under full throttle. Its usually due to a load being applied when the engine is not in its powerband, though it can be a load beyond the power capability of the engine in a particular gear. The term is used in towing quite frequently.....and when the engine is lugging in a towing condition (but really applies to any LOAD condition) you are putting severe strain on the entire drivetrain. Transmissions fail under these conditions, and engines at times too. Engines overheat. You'll also use more fuel. For these reasons its usually recommended to turn off the overdrive, and downshift when "lugging" occurs.

3. I wasnt talking about at wide open throttle. If I open the throttle all the way or even most of the way she'll downshift. But obviously with my foot in it deep she is sucking more fuel. I'm talking about manually downshifting instead, where I dont HAVE to put my foot into the pedal deeply........by downshifting alone my foot is already deep enough that after the downshift the engine isnt straining under load any longer......its in its powerband and will actually accelerate with NO further gas..........so essentially I can ease up on the throttle just due to the downshift.

4. My apologies here....lol. I meant MORE vacuum in that statement. Yes, I do follow and understand vacuum at low and high throttle conditions....brain fart! LOL

5. You are correct. There is SOME loss due to what is essentially a restriction on the exhaust. In my expreience it has been minimal, but of course that experience has been on my 462 ci, 1064 hp animal, and some others like it. Will be interesting to see if on a smaller, economy minded engine that loss is noticeable as fuel mileage............so you do have a good point there! Definitely not as much as a belt driven supercharger would though.....the loss on those is substantial.

The nice thing about using the newer add on fuel injection ECU's IS the ability to program exactly what you want it to do under given conditions. For example I can program it to run quite lean at partial throttle settings, more fuel under higher throttle settings, more fuel under the lowest vacuum conditions, and ADD more fuel when it senses boost. In addition it can pull timing under boost, so the timing can be left in initially where it is needed. I would LOVE to get a system capable of sequential injection, because I think with that theres a good chance I could push 70 mpg.......but those systems are still quite expensive at the moment.

Of course if I put a turbo on it I'm going to use it! LOL. Just like if I put in A/C I'm going to use that too! LOL But in reality most of that use will be real world conditions where you just need the power.....freeway on-ramps, passing.......etc. At those moments I couldnt give a rats.......well, you know......about fuel economy. But once I'm on the road and cruising I can concentrate on making the most of what I have.

But more than anything it'll be fun to know I have hybrid-like capability with my own signature, and significant savings. Not to mention the fact that 5 yrs sfrom now if well maintained it'll be worth what I have in it, but that other guy's Prius wont be worth what he paid.........lol.

Yeah, I think I got a good deal at $900. She doesnt look too pretty at first glance, but really the rear quarter panels are the only difficult part. Its easy to bolt on fenders, hood, etc from a donor car. I carefully checked and she's never been in an accident. It has only 134K original, and runs VERY smoothly. Seller is delivering it to me Thurs.

Some pictures still on the sellers photobucket here

http://s279.photobucket.com/albums/k...0Sell/?start=0

It has new:
distributor
spark plugs & wires
new 5 wire O2 sensor
exhaust B pipe
all fluids within 500 miles
rear brakes
clutch master cylinder
half shafts (guessing maybe ball joints too with the newer lower control arms)

Also has:
Del Sol seats
aftermarket headlights, turn signals and tail lights
carbon fiber rear wing
Tein lowering springs
aftermarket lower control arms & front camber kit

Still needs to make it right and make it right for me...
windshield (cracked)
hood (flew up, and took out the windshield...lol)
fenders (they are just not great...want it to look good)
rear quarters.....around the wheel lip of course
alignment & maybe some odds and ends front suspension wise
clutch & press. plate
paint

[theholycow]

Don't confuse opening the throttle with accelerating faster. In the automatic Tercel it certainly does mean accelerating faster, but when you control the gears you can accelerate the same (or slower) with the throttle more open. The amount of air passing through the throttle is directly related to TWO things: Throttle opening, and RPM. RPM is the demand for air, and throttle restricts the supply; it does not PROVIDE the supply. Many people mistakenly invest in upgraded intake plumbing thinking they'll get better fuel economy because of supposed restriction in the OEM system, but then they keep their throttle closed...major restriction! Well, opening the throttle is how you can ACTUALLY reduce that restriction.

When I had my 2008 VW, I accelerated with wide-open throttle every time. I did not accelerate hard; I shifted at very low RPM (in conditions that you might label "lugging" - not anything that would damage the engine, but enough to control my acceleration). Because of the low RPM the engine simply did not demand enough air to use more fuel.

To add a slight complication to that strategy, most cars will ignore the O2 sensors and go into open loop enrichment at WOT. Therefore, in most cars you need to use less than WOT, maybe 80% or so, to keep out of open loop but get the benefit. The VW did not have that issue because its wideband O2 sensor enabled it to measure accurately under all conditions.

Take a look at an average BSFC map:

The small circle near the top is the most efficient use of that particular engine. It is at or near WOT at 2000-3000 RPM. If you have gears to use that torque at that RPM then you will achieve the best ratio of fuel used to work produced. Actual RPM is different for every engine but the pattern is pretty consistent.

"unresponsive to further input from the gas pedal" is often exactly the best place to be for efficiency.

Understand, this is not the ONLY useful technique, but it is one and has consistently produced very good results for me. Even if you're not going to use it, learning about it will help.

The default advice for people not wanting to learn about technical stuff, not wanting to study, etc is to use light throttle because it keeps them going slower, lets automatics shift at lower RPM, and was more important with carbureted cars.

You're right about detonation and pre-ignition...that was my own brain fart. In cars without computer-controlled ignition timing, depending on how the car was adjusted, low RPM heavy throttle conditions could cause spark knock. This was quite evident in my Buick after I converted it to manual transmission and the vacuum timing advance was malfunctioning.

As far as needing to Turbo the VX, I don't see a lot of complaints from VX owners about difficulty keeping up with traffic, passing, or merging onto the freeway. It won't be exciting if you're used to a 1000hp Trans Am but I suspect it delivers every bit of speed that a Tercel does. As I understand the VX has a lot more torque than other Honda engines of that time. Don't forget also that it is very lightweight.

Are you going to remove the wing?

[aronhk_md]

Thanks Holy, I think I'm seeing what you are saying about WOT efficiency now, and its something to think about....definitely.

I have seen some VX owners complain about the lack of power, and my guess is it mostly has to due with the taller gear ratios of that transmission. It likely blunts some of the torque that motor makes. It is certainly a lightweight car, but I was somewhat surprised that the 96 Tercel was only 2005 lbs, and the 92 VX is 2102 I believe? Of course that info on the tercel was a manual 5 speed....the only info I found in a quick search. So the automatic might be a bit more.

I do love driving the trans am, and it is a pump gas street car I mainly use to cruise in, with hopefully a bit of future roadracing or Hill Climbs (Pikes Peak type). But I drive the Tercel every day, so I'm somewhat used to the low power route. I had a 2006 civic Si, and it was fun for a while.....then got tired of 25 mpg

I often tow a little harbor freight trailer with my tercel....when I go buy tools or parts. At those times I wish it had a drop more oooomph. I'm careful towing, because I dont want to overheat that transmission....it wasnt designed to tow anything. So I will likely find a hitch for the VX and do the same. One reason I'd like to find the best clutch I can. Also a reason to have the turbo for a little boost onto the ramps, etc.

I'm very impressed with the current add on FI systems out there. The one I really want for the trans am is Big Stuff 3. That sequential fuel injection would be perfect for the VX too......but the price tag is around $3500 with everything, so its more than I want to spend on the little bugger for now. Maybe later they'll come down, or other companies will have products as good or better for less. Megasquirt for example. Actually their newest has it too and its less, but still pricey in comparison. I can get a used megasquirt II and everything I need for under $600. What will be interesting then is to see if I can even improve over the factory lean burn conditions. I'm betting I can with time.

Even without sequential I can for example extend lean burn a few hundred rpm up the scale...........but allow for increased fuel under a more advanced throttle position sensor location.....as in a harder acceleration. With the old lean burn setup it was like an on/off switch going into lean burn. With FI I can ease that transition.

I think its going to be fun! after that I just need to add a boattail to it....................lol

[theholycow]

I was thinking about this more and the maximum throttle strategy I use may not apply to the VX, which needs minimum throttle to stay in lean burn. It's still worth studying and learning about though...