Too much of a good thing --15 minute gravity drop
 

I guess I'm lucky with the start of my commute, in that I drop from 7400' in elevation to 5800' in my first 9.5 miles every day. Right now on an average day I can touch the gas once if no one is around, just enough to get from a rolling stop to 30mph on one flat spot after a stop sign. If there's traffic, I usually have to use gas to get from 30-45 for a merge (mountain highway with a 45mph speed limit), but without traffic, I can roll up to merge speed fairly easily, just late in the ramp.

My question is just how much should I tempt fate with this gravity drop. It takes a good 15 minutes and that's a lot of time to waste with an idling engine. I want to start playing with EOC, but obviously with that big of a drop, I'm on and off the brakes for short pulses several times a minute with the twisty mountain roads. I saw the thread on adding a PVC vacuum reservior from 2008 and that's very tempting, but even if I extended my number of brake applications from 2 to 6 or 7, I'd have to recharge my vacuum every 1-2 minutes to maintain safe, solid brakes. Is it worth it? Are there any other alternatives, like maybe figuring out some kind of 12v vacuum pump? I just hate the idea of not taking advantage of this tremendous geographic advantage since I'm definitely paying for every drop of gas to get to the top of this mountain.

Seems like you could take advantage of DFCO, where you get the benefit of both the vacuum being generated for the brakes and zero fuel use of EOC... At least what I'm understanding is that the route is steep enough to require brake use, so taking advantage of engine braking too would (slightly) reduce the need for brake use.

Your vacuum reserve will last a lot better if you don't lift your foot off the brake any more than is necessary. Also, just get used to the non-boosted effort. Graham Hill used to set his cars up to require 180 lbs on the pedal to skid, to gain sensitivity.

i'd agree with this.

Currently i have a 2 mile section on my commute where i can p&g between 60-50mph by doing the following.
Use slope to accel car up to 60 in IDLE
Use dfco in 4th to engine brake to 50

Th slope is such that the car will often maintain above 50 for quite some time in dfco.

I also use dfco for slowing whilst driving in 'accordian' traffic
helps me keep my distance and keeps brakes avail if required in addition.

I'd probably try to find myself a 12V vacuum pump. Kicking the engine over for DFCO just to refill your vacuum seems like a hassle to me.

Have you tried your brakes without vacuum assist?

i'm using eo(n)c as i'm not a fan of the concept of engine off cruising regarding my car..especially in nose to tail 40mph+ driving

Therefore the engine is on anyway, so using dfco is easy..

If you have to brake, keep a steady brake foot. Apply once, release once. You can get lots of braking out of a single, shallow displacement of the brake pedal, which uses very little vacuum.

Does it maintain speed when you keep it in gear ?
Then that'd be an option.

Another option is to coast down, then shove it in top gear and bump-start it when speed builds up, slow down using engine braking, then start coasting again.
Probably won't work using an automatic transmission - but I just saw you have a manual transmission.


Before you go coasting without the engine running, check out how much longer the brakes will work !

Even in low-speed stop-and-go traffic on a slight downhill, my car ran out of braking power after only 2 stops, and the brake pedal is very hard without power assist - so engine off coasting is out of the question for me.

I installed a kill switch (toggle, not momentary). On long mountain descents I'll leave the car in 5th gear, flip the switch to kill the engine, and alternate between clutch in (EOC) to speed up, and clutch out for engine braking & to keep the vacuum booster charged. Less heat into the brakes that way, which is nice because my rotors warp easily :/

NachtRitter -

I agree.

endurance -

You should be able to tell when DFCO happens. As you decelerate closer to your idle RPM, the ECU/PCM will turn the injectors on again. There should be the slightest of "bumps" when this happens, unless your RSX is silky smooth.

dennyt -

Sweet setup!

CarloSW2

Thanks for all the great replies. I bought a used Scangauge on e-bay last weekend, so in a few days I should be able to really test what gets me the best mileage and how much of a difference it makes between EOC vs. EFCO with the Acura. It's a pretty even descent and while there are definitely some corners that require getting on the brakes and I always have to be on the lookout for deer, I don't have to worry about overheating the brakes if I'm smart about how I use them. I really hesitate on holding my foot on the pedal for a long time because of the duration of the descent, so I'm not sure I want to try that strategy.

I did find a brake vacuum pump on e-bay designed for electric vehicles that's $179, so that seems like a decent option. It only draws 4.6amps and for 15 minutes with a long climb for the alternator to recover after the descent, I think the battery fully recharge before getting into work. I also have my eye on some well priced deep cycle batteries for a home solar project, so perhaps that would add some insurance if necessary.

My goal is actually to piss off a coworker with a Jetta TDI and get better mileage than him, so eventually, I'll be willing to go to extremes if that's what it takes. A mid-life ego is a dangerous thing to mess with. He may have youth and the better mileage car, but I have the resources to convert the car to run on unicorn farts if that's what it takes to win. :D Cheat to win!

:thumbup: That's the spirit!

After looking at another thread on the subject of coasting, it sounds like DFCO only works when the car is at operating temperature. The descent is from my driveway, first thing in the morning, so I'd guess with an operating temperature of 50F when I start and barely getting up to operating temperature 5 miles into the descent, I wouldn't reap the benefits. Does that sound correct? I'm still planning on putting the Scangauge to work testing out different techniques.

I did have one bad commute on this tank, but I'm definitely noticing that simply coasting in neutral whereever I can is really making a difference. A month ago I had a Yakima bike rack on top and was content with 29mpg. Now I'm craving 34 on this tank and dreaming of 45+ with mods and more nut behind the wheel adjustment. I think I have a new addiction. Thanks for the crack guys. ;-)

where do you get your unicorn farts?

I have been considering removing my vacuum assist all together. The thing that bugs me most about EOC and loosing vacuum assist is when braking is the sudden drop in effort and lots of extra braking when I bump start.

On my car DFCO works right away.

Mine too... though it's at a higher rpm that it kicks in when the engine is cold... 1200rpm instead of 900rpm or something like that.

Of course, one way around that is to use a block heater... probably would help out all 'round (warm engine gets better FE than a cold one).

An engine kill switch that cuts power to the fuel injectors does the same thing as DFCO, but can be used at any time, at any RPM. I use one on my Altima to slow the car at lights. Normally the injectors turn back on around 1500 RPMs, now I can DFCO below that. This maintains brake pressure, and adds a little juice to the battery. The latter is essential at night since my commute home is mostly downhill and the engine is off far more than it is on.

Get a block heater.

regards
Mech

An excellent suggestion and one that I plan on following through with. I've had them in the past when I lived in cooler climates and really appreaciated them. We moved into this new house just a couple months ago and we're still getting everything out of the garage. Hopefully the unpacking will be done before the snow flies so I'll have a convenient place to plug in and won't have a windshield to defrost in the morning.

A block heater will also make a big difference in your engines operating temp on that long downhill ride. If you can get the engine to operating temp the mileage should climb dramatically, especially if you can not get it up to operating temp otherwise.

Even idling the fuel consumption would reduced by probably close to 70%.

DFCO will probably kick in much sooner.

This is based on the assumption that you are not able to get the engine up to operating temp before you get to the bottom of that considerable grade.

regards
Mech

Mech,
It's definitely high on my list for a number of reasons. Since I live at 7400', winters can be pretty harsh and waking up to sub-zero (F) temps is not all that uncommon. Even if I didn't elect to hypermile, the engine on the Acura going downhill in cold air takes at least five minutes to reach sufficient temperature to put out enough heat to start defogging/defrosting the windshield. I can't safely drive without a 5-10 minute warm up unless I can park in a garage and have a block heater that can kick on an hour or two before I get up. The mileage benefits are definitely a bonus.

Unfortunately, winter also means the Hakkapallita snow tires have to come out or it'll be a one way trip down some day in November and I won't be able to get back up the hill until sometime in March.;) My snows and winter fuel usually cost me 2-3 mpg, but hopefully my new techniques and mods that I'm learning here will still mean I get respectable mileage (34+, I hope). It's a 62 mile a day round trip (10% city streets, 60% highway (about a quarter of which is subject to stop and go traffic, especially in the winter), 30% mountain roads), but the gravity drop is kind of the ultimate pulse and glide. I do 15 minutes of continuous glide on the way to work and 15 minutes of continuous pulse on the way home.:D

This will be our first winter up at the new place, but I've lived in Colorado for 30+ years. The GF (from Texas) is convinced we'll be fighting over our one lone 4x4 truck on the snow days, but even after a four year stint living and working in Summit County, Colorado (ski country), I remain unconvinced that four wheel drive is necessary 360+/- days a year. I have a job where I can choose to work from home four out of five weeks a month, so unless there's a cosmic convergence of a mega-snowstorm on the one week a month I have to be at work and the GF just happens to need to go to work that same day (she only works 3 days a week), I think we'll be just fine.:rolleyes:

I wonder if there's an appropriate non-power brake master cylinder that could be swapped in. I know on several of my cars there is.

Same thing with my truck. Diesels have always had DFCO, regardless of temperature.

Tactically I would consider letting the engine idle when you can and using DFCO when necessary.

Trying to balance keeping the engine at operating temperature (just barely) with idling and DFCO (which will cool it off and make it run more rich).

Engine off will just make it drop below operating temp which will bring on enrichment. In essence an additional cold start.

Minimise cabin heat as much as possible without risking your safety and some semblance of comfort. Recirculate the heat if you can without excess window fogging. Fresh air requires much more engine heat to get it hot enough to be effective in extreme cold.

You objective should be to balance DFCO and idle to create just enough heat to keep the engine warm enough to operate without enrichment.

A scangauge will give you the fuel consumption data to verify your fine tuning your tactic. It may even be better to use lower gears for shorter times, versus higher gears for extended periods of time, since the longer periods of no fuel consumption could get your engine temperatures to low and increase the mixture.

It is a fascinating scenario, where the eventual tactic may be somewhat unusual. Your idle fuel consumption is probably in the range of .16 to .22 GPH. Make sure the idle speed is as low as tolerable. If you can average 50 MPH with 1/7 gal per hour consumption, you are getting 350 MPG. While not as good as infinite, you will do better when the grade levels out and you have a warm engine. It's a balancing act where you burn the least fuel to try to keep the engine warm.

How long is the downhill ride as far as time?

Keep us posted as to your progress.

regards
Mech

Hey guys we have to better then this for the man. He has to beat the MPG of the Jetta TDI coworker. That much elevation change has to allow some evil mechanical/electrical gee-whiz thing get him better mpgs.
1) Can we think of some pressure vessel that doesn't weigh anything that sits in the trunk and "breaths-in" on the downhill and "breaths-out" on the uphill that generates heat and or electricity.
2) Or a way to install regen breaking on the downhill which again generates cabin heat or recharges the battery.
3) Flywheel?

Once you've gotten a realiable system (2) that generates electricity or heat on the downhill then you can add weight (Take out trash, fill a 10 gallon container with water, etc) that you take downhill with you every day but don't bring that weight back up the hill.

That is just half the ideas. The other ideas involve sabotaging the jetta to get worse miles (Nothing serious - just make him drive to lunch on those cold days so he has more cold start/short drives, etc).

It's about 13-15 minutes and about 9.5 miles. The first 3.2 miles is driveway filled, deer covered, twisty stuff, the rest is mountain highway until I get to the interstate where I have to start climbing for about 5 miles, and then have several .25-1.5 mile coasts all the way into work. The return trip only has the one 5 mile sustained descent, which is interrupted with several flats. I know if I could discipline myself, it really does provide an excellent hypermiling commute. I'm still struggling with driving slower after a lifetime of 70mph highway driving, but I understand that speed kills mpg.

I just received and installed my scangauge tonight and while I was picking it up from my P.O. Box, I started chatting with the owner of the store about hypermiling. I mentioned needing some PVC for covering my lower grill and he mentioned that he always had the material around for making business signs. One thing let to another and I walked out with a 6"x36" piece of 1/8" thick PVC that will perfectly cover my lower grill for free! Stopped by the hardware store on the way home, picked up a normally on momentary switch, some spades, an inline fuse, some steel for manufacturing brackets for the PVC, and I think I'm set for weekend projects. I'll call my Honda dealer and make an appointment for the block heater next week. I also cleaned out one side of the garage tonight enough to get the car in, so that should help a little in the meantime until I can get the heater. Of course, if I don't get another side cleaned out before the GF moves in, she'll get dibbs on it and I'll be back outside.:rolleyes:

The Jetta is already sabotaged worse than anything I could ever do; it's driven by a 20 year old.:D Nothing kills mpg faster than a college kid with a turbo.:thumbup:

Well, after a a week with the Scangauge I've learned a lot. First off, I've been simply using DFCO for braking and brake assisting on my gravity drop and letting the engine idle while coasting. When I start the car cold in the morning I'm using 1.3 gallons per hour, which eventually drops down to .27-.43 depending on what accessories I have running. I quickly added a lower grill block because I found that even when I started with a warm engine (177F), using DFCO intermitenly with engine on coasting and the cool outdoor air I could watch the temperature drop to 152F by the bottom of the hill. If I started with a cold engine, it would never make it up to 150F, no less full operating temperature. Now with the grill block and outdoor air temps near freezing, it is managing to get up to and stay in the 155-175 range.

I discovered there isn't a block heater available for the car (the only one manufactured only fit the 02 RSX and was discontinued in 04 or 05), so I'm going with a lower radiator hose heater. It'll be an easier install anyway. What about a magnetic oil pan heater, too? Redundant?

Also on the list now is a garage door opener.:rolleyes: The garage has too big of a lip at the door to push it out safely (risk getting my legs chopped off if I'm in the door and pushing), so I have to start the car, drive out, turn off the car, get out, close the door, get back in and then bump start it going down the driveway. Seriously not worth the hassle...

I paid for three days of access to the Honda Helm site to download all the wiring diagrams I need to cut off either the fuel supply or the crankshaft position signal. It'll probably be a week or two before I can get the time to do it, but it's on my list.

I also picked up a used vacuum pump on e-bay for $20 and with a PVC vacuum storage canister, I should be able to have plenty of full power braking for EOC mountain driving when DFCO isn't the best technique. It'll be a winter project I'll get to sometime.

Also, I'm considering going with LED lighting to save my battery some. Still seeking out viable headlight options, but I used to build my own bike lights for 24 hour mountain bike racing, so I suspect I'll end up creating something on my own (my last light build put out over 730 lumen, but could go for over to three hours on one relatively small lithium battery). I have plenty of high output LEDs just sitting around. I also have my metal mill if I really want to get medieval on it.:D

Overall, I just wanted to say thanks for all the input. My last tank was my best tank ever (36.5mpg) and while I've been struggling with this tank because of a couple of hideous commutes (rushhour traffic snarls), I'm still probably managing over 32mpg (can't trust the scangauge mileage yet, as I haven't calibrated it with a full tank cycle yet). I've definitely gone down the rabbit hole and I have you guys to thank.;)

Before you dive into LED headlights go here and order LED lights for all the side/tail/brake lights: Super Bright LEDs ? LED Lights, Bulbs, and Accessories Won't save nearly as much as headlight LED's but its a 10minute order online and then a 15minute change out in the garage one night. When you put the front side lights back in then tape/caulk/seal around to make them more areo.

Remember, DFCO still gives you a charging system as well as engine vacuum. You get both of those as long as the engine is spinning, whether it is using fuel or not using fuel.

Thanks for the complimentary PM, it's always a pleasure to help any fellow hypermiler to beat OPEC out of some money, especially the kind you can keep in your pocket.

You might try driving with no boost to the brakes or power steering, just to get a feel for what it is like. While the inputs will be significantly heavier than when you have the engine running they should not be that bad.

regards
Mech

Endurance,

Absolutely heat your oil pan, too. When I lived in CO, we got a weekend of -35ºF temperatures. Monday morning I cranked the engine, and it felt like my crankshaft was embedded in concrete. I had to put a lit Coleman lantern under the crankcase for 45 minutes to thin the oil enough to start the engine. 90W transmission lube can use some help in cold weather.

@ busy: That's definitely the place to start. Once I've identified what bulbs I need, I'll place an order. I'm not sure what my eventual headlight design will be, but I like projects like that. I've already created LED lights that use 10-12w but put out the equivelent of 35w of halogen light. It wouldn't take much more to produce enough to get me down the road safely. The biggest challenge is finding/creating the right reflector. All the light in the world is worthless if you can't focus it where you want it and still maintain enough spill to prevent blindspots.

@ Mech: Sound advice. I've played with the brakes and while the steering at speed is fine without power, the brakes really do take more energy to apply than I'm comfortable with.

@ Sentra: I'll plan on finding something that'll work to heat the pan. The synthetic 5w20 engine oil is pretty easy to start, plus the car is in a garage, but at $30, how can I go wrong with an oil pan heater?

a radiator hose is a good idea for a couple reasons 1 it gives you heat immediately for clearer windows. 2 good circulation of heat in the engine. (Get one with a pump as your thermostat will be closed and prevent the warmed coolant from circulating well)

Magnetic ones are annoying, buy some high temp silicone and a heat pad. clean the bottom of your oil pan and apply silicone to the pad apply pad to oil pan and go to bed.

I have too many projects at the moment, especially with a new 1920s house that I'm trying to get ready for winter (talk about ecomods, how many 90 year old homes have a 91% efficient combination natural gas boiler/tankless hot water heater?). As a result, I'm really down to evenings after work as my tinkering time, which means doing the lower radiator hose is several weeks away (next weekend is deer season for me, the following weekend we're putting in a new fence, there's new windows to install...). That's a weekend project since it demands a cold radiator to work with.

That bumped up my priority on the kill switch and oil pan heater. Why is it you say the magnetic heaters are annoying? Did you have to take yours off every time? Did it fall off? I like your suggestion of the heating pad, but what are the advantages? Why not glue or silicone on a block heater?

I haven't had my car off the ground yet, but in my grill block project I discovered the entire front of the engine is pretty sealed on the under side. I need to pull body clips just to access the radiator hose. I'm not sure what kind of access I have yet, but want to keep options open until I see what I have (in otherwords, it's going to be a two step process: access and assess, and then buy what I need. For all I know, one option or the other may be out and I'd like to have as much information going in as possible going in.

Depending on engine block material magnetic ones don't stick. If the road is rough they can and do fall off. It may or may not be a problem in your case. The silicone heating padhttp://fivestarmanufacturing.com/get...ad-heater.aspx
work well because they can conform to contours on your oil pan or other places.