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-   -   How do you eco-drive a diesel ? (https://ecomodder.com/forum/showthread.php/how-do-you-eco-drive-diesel-5815.html)

groar 11-01-2008 09:11 AM

How do you eco-drive a diesel ?
 
Lately a lot of papers are talking about lower consumption and lower emissions (at least about CO2) of diesel. In eco-driving forums it seams that more and more people would like to have a diesel.

As half French people, I have diesel cars. If I have rather good percentage over EPA for the megane, I have difficulties with the scenic (see my signature). Of course the facts the scenic is heavier (2844 lbs vs 2491), has a bigger Cd (0.33 vs 0.31) and a bigger Frontal Area (25.3 sq.ft. vs 21.4) doesn't help, but Combined EPA ratings is better for the scenic (39.8 mpg(US) vs 35.1).

On both cars I added a front grill block and it helps to have the engine hot quicker :) I'm also using DFCO and/or NICE-On coasting, keeping a lower steady speed and having moderate accelerations. I have iMPG display only in the scenic. I can have 2.3 l/100 at a steady 70 km/h (100 MPG at 43 MPH), but it's difficult to achieve and any move of the right feet or change in road inclination will dramatically make the consumption greater and/or the speed lower.

I'm wondering if there is some advices more toward to diesel than gasoline. After a quick search I didn't found any advice on how to eco-drive a diesel except to shift up at 2000 rpm instead of 2500 for a gasoline, but I'm already doing it...

What are the eco-driving and eco-modding tips that are working for your diesel ?

Thanks in advance,

Denis.

vtec-e 11-01-2008 11:37 AM

Hi Denis. Good thread. As more people drive diesel cars, this is going to become a big issue. My other car is a kia cee'd sw 1.6crdi and i too find it difficult to get it's consumption down. Only on long drives does it warm up enough to become efficient. Anything up to an hours drive just doesn't work. All it seems to do is 5L/100k no matter how i drive it. But once the engine and gearbox is hot, it will do around 2.5 to 3L/100k at 80 to 100kph on the flat. Not too shabby at all! I get up to speed slowly and keep the rpm just shy of 2000. But the warm up hit is so bad that my trip average will be that magical number: 5L/100k!!
I have the rad 60% blocked up and used to have the tires at 50psi but wore more in the middle so they are at 38psi now. Feels like a pig! New tires next year might solve that.

ollie

COcyclist 11-01-2008 12:40 PM

Driving Diesels for Economy
 
Groar,

Here is a link to TDIclub.com that has pages of info about driving the VW TDI for economy. I drive an 04 TDI golf manual transmission and regularly get 50+ mpg on the highway. It is a long thread and I don't agree with all of the opinions in there but it's a good place to start.

Driving for better mpg - TDIClub Forums

I only use engine-on coasting (EON-C?? vs EOC) due to my concerns about turbo long-term durability and the fact that our diesel engines are much more efficient than gassers at idle, when warm (and we lose the use of our airbags when the key is off). My Scanguage shows instantaneous mpg figures in the 300-450 mpg range when EON-C. Also there are times, like on long grades or approaching a red light when it is more efficient to downshift than to coast. Under engine-braking conditions the computer completely shuts off the fuel supply to the engine. Scanguage figures go to 9999 mpg showing no fuel being used while coasting in gear (unless you start lugging it). The downside is that engine friction will slow the car down more than coasting in neutral so you don't go as far before you have to use the engine to get the car up to speed. Of course aerodynamic improvements will increase your coast times and help mpg at highway speed.

Hope this helps. Welcome, it's always good to see another diesel driver here.:cool:

Big Dave 11-01-2008 01:45 PM

Engine-on coasting is my favorite tactic. It even works in urban areas. Get it moving fast enough to get to the next stop and put it in neutral.

Most diesels have some sort of warm-up feature that allowsthem to warm up enough to have an effective heater. Mine came on in September and worked til May. The EBPV on a Ford has a distinctive whooshing sound, so you know its working. Mine worked way too much. So I electrically disabled it. Thay gained me 2 MPG back in the winter. Downside: It takes about 6 miles to warm up enough to make the heater effective.

COcyclist 11-01-2008 05:16 PM

Diesel Ecodriving
 
Our engines don't have to fight against the vacuum from the throttle plate a gasser has so they are more efficient, but also don't warm up as fast. I have noticed my car gets much better mpg when everything is fully warmed up. My VW diesel has 3 extra glow plugs that heat the coolant when the engine is cold. The coolant heater glow plugs turn off at approximately 180 degrees. I have left them operational for quicker warm-ups but added a plug-in coolant heater to help the engine get to temperature quicker and the glow-plugs to shut off and reduce the load on the alternator. Metrompg did a test of these engine heaters in his car. These could help diesel mileage when the engine has to cold start. I try to resist the urge to run the heater for the first few miles until the engine is warm. Grill blocking helps too.

groar 11-01-2008 06:18 PM

Thanks for the replies. I will read this doc again.

With the scenic, a 2001 dCi (turbo diesel common-rail), I'm currently at EPA +33% in the morning when I have light traffic. In the evening with medium traffic I have "only" EPA +10%. With some short trips during week-ends, I have a current tank at EPA +20%.

With the megane, a 1997 turbo diesel, my best tank is EPA +50% and I don't have any iMPG display in it...

Whatever I'm doing, I can't do better then the EPA +33% during my morning commutes with the scenic. On the highway my best is Highway-EPA +10%, but to do that I have to drive at 10-15MPH under the speed limit. At steady Highway speed limit the Highway-EPA is simply unachievable...

Now my best tank with the megane was done this summer with hotter temperatures (20-30C vs 5-10C now) and lower traffic (25 minutes vs 35-55 minutes now). Against traffic, I avoid heavy traffic and stop the engine when I'm idle more than 15 seconds.

I have a big hill to climb. Thanks to the iMPG display I'm now accelerating quickly at the beginning and keeping a steady speed of 70 km/h to have a 7 l/100 consumption. Before I was accelerating more slowly and had a consumption over 10-12 l/100 during all the hill.

With the scenic I'm using both NICE-On Coasting and Dfco . I'm first using NICE-On Coasting to lower MPG without loosing too much speed, then using Dfco to have a null consumption and loose more speed. With the megane I was using only NICE-On Coasting so I was not saving as much fuel. Both cars have same tires with a 51 PSI sidewall. While megane is inflated at 46, scenic is inflated at 51 currently. But the comfort in the scenic lowered a lot from 46 to 51 so I may go back to 46. During my few city driving, I feel the coasting lasting forever

About grill blocks on both cars, I closed the lower one except the sixth toward the turbo.

I'm just wondering if there could be diesel specific tips, noticeably on these common rail diesels. These high pressure diesel have a better consumption, but seams to be more difficult to eco-drive.

Denis.

ConnClark 11-01-2008 06:31 PM

As far as eco modding a diesel there are a few things you can do but don't expect a huge improvement.

Installing a free flowing muffler helps some by reducing back pressure. A free flowing muffler also helps reduce the amount of residual combustion gasses in the cylinders, this allows a greater quantity of excess air to fill the cylinder on the intake stroke. If you have a turbo diesel this also gives you slightly more boost which helps your engine run more efficiently and burn the fuel cleanly. It also helps the turbo to spool up quicker.

a nice article Browser Warning

A nice free flowing intake helps too. Also try and make sure the air you are drawing into the engine is cold. Some form of ram air induction helps too. My Mercedes Benz came stock with a cold ram air induction. The boys in Stuttgart did it for a reason.

another nice article Browser Warning

Note: do not use a K&N or similar filter. They do not filter as well as a paper filter. This allows dirt in the engine which can score the cylinder walls and drop your compression ratio. Low compression makes diesel run less efficiently and create more pollution.

The other thing to keep in mind is that if your injectors don't work right your engine won't burn all the fuel right. Keep your injectors clean and functioning properly. Sometimes improved injectors may become available and changing to these improved injectors will improve mileage and power while reducing both soot and NOx emissions.

That about does it for the easy modifications.

More advanced mods can be done but you have to know what your doing.

If you have a turbo engine adding an intercooler will help. It may shift your power band to a lower rpm to some degree but it improves both performance and mileage. It should also reduce NOx emissions.

Up grading to a more efficient turbo can help. This is not a straight forward procedure however and matching the performance curve to your engine can be tricky. A nice but very difficult upgrade is to go from a conventional turbo to a variable geometry turbo.

Duffman 11-01-2008 08:42 PM

ConnClark gives some good advice.

With respect to the muffler, if your car is a turbo diesel then remove the muffler, I did on mine, the turbo reduces a lot of noise by itself.

I run diesel conditioner in every tank. I do it for lubricity and water control but the extra cetane will boost MPG slightly.

My truck shuts off the fuel when decelerating in gear, if your car does that there may be times that in gear decel is better than clutch in coasting.

A synthetic oil like a 5w40 will do better than a 15w40 depending what your car takes, especially if you do more short trips.

A performance chip will give you a small increase as well if it is available for your car.

JQmile 11-02-2008 11:32 AM

When you drive, make sure not to be under boost at all. If the load is too high (say, accelerating up a hill) then the turbo will start to make boost, and the fueling curve will respond to the rise in boost pressure (add more fuel). This only applies on a turbodiesel of course. Oh and a timing bump will usually give a healthy increase in mpgs, 10-20% I'd say. That's why chips give you better mileage in newer computer controlled diesels, because they usually have more timing than the stockers. If you want to get nutty, you can also inject propane or cng in the intake stream.....it's a tradeoff of about 2gal of cng to 1 gal of regular fuel, but if you can get propane or cng for cheap it is well worth it.

Piwoslaw 11-02-2008 02:51 PM

Quote:

Originally Posted by groar (Post 70411)
I'm just wondering if there could be diesel specific tips, noticeably on these common rail diesels. These high pressure diesel have a better consumption, but seams to be more difficult to eco-drive.

I recently (1-2 months ago?) read about a small contraption for common-rail diesels. It ionizes the fuel with an electric shock, so the particals are much smaller when entering the cylinder and burn much more efficiently. The artical said that someone at some university built and tested it and it improved FE by 20%. It was easily retrofitted in two existing engines at a low cost. The actual shock required only a small amount of electricity, so the alternator hardly noticed it. It sounds really neat, almost too good to be true.

Piwoslaw 11-02-2008 03:16 PM

A little google'ing, and I think I've found something on this device. Here's something very scientific, I'm not sure how relevant it is:
Analytical conditions for field ionization mass spectrometry of diesel fuel
Here is the abstract to the article I read, in it there is a link to the whole article:
Electrorheology Leads to Efficient Combustion
Here is a short commentary:
Simple device uses electrical field to boost internal combustion engine efficiency
and another, this one criticizes the company which holds the patent:
Electricity + gasoline = more mpg?

roflwaffle 11-02-2008 03:57 PM

Here's a good summary. They used it on an older IDI diesel, so it may only help w/ lower injection pressures and/or with vehicles that have a well worn FI system. Stuff like this has been around for decades IIRC, and was can be used to reduce the viscosity of crude and some of it's refined byproducts. That said there are some valid apprehensions regarding this device, and if it is a scam I think that the testers were smart to use a Benz instead of something w/ a rotary pump like a VW diesel where dynamic timing (as well as efficiency) depends on fuel viscosity.

ConnClark 11-02-2008 10:22 PM

So far the claims of this device are dubious at best. This scientist is funded by a company that makes fuel magnets. His work has only recently been published but no other independent experimental verification of his claims exists. There is some independently verifiable evidence that magnetic fields can lower the viscosity of crude oil however crude oil has a large number of chemical components and metals that are refined out when it is converted to fuel.

The following report has found no statistically significant improvements in mileage of this scientist's benefactor's device. This latest announcement from this scientist may just be an attempt to keep research money coming in by changing the magnetic field claims by this company to electric field claims.

http://wwwcgi.rand.org/pubs/technica...RAND_TR313.pdf

Until there is duplicated experiments and results by an independent party I will regard this research dubious. The key factor is if diesel fuel is indeed an electrorheological fluid. So far the only name that pops up in this area of research is this scientist. This is starting to smell a lot like the acetone scam in as far as the only evidence to back up the claims come from the person making them.

Big Dave 11-02-2008 10:30 PM

I put a free-flowing exhaust (you could drop a Cokr can through it) and a free-flowing warm air intake and it didn't help a bit.

One thing you can do. Put a pyrometer on it and drive to keep EGT under 600 degrees F.

ConnClark 11-02-2008 11:37 PM

Quote:

Originally Posted by JQmile (Post 70486)
When you drive, make sure not to be under boost at all. If the load is too high (say, accelerating up a hill) then the turbo will start to make boost, and the fueling curve will respond to the rise in boost pressure (add more fuel). This only applies on a turbodiesel of course.

Boost pressure does not increase fuel. It does allow the injection system to inject more fuel if you have the petal floored. A turbocharger does however get its power from the energy not recovered by the piston. You are correct in that trying to drive with a low amount of boost is an indication of the piston extracting as much power as it can. This does not mean that you should try to prevent your turbo from creating boost via modifications. Boost actually increases the efficiency of a diesel engine by promoting more complete combustion and more heat energy going into the working fluid and less heat energy being lost to the engine block.

Quote:

Originally Posted by Big Dave (Post 70574)
I put a free-flowing exhaust (you could drop a Cokr can through it) and a free-flowing warm air intake and it didn't help a bit.

One thing you can do. Put a pyrometer on it and drive to keep EGT under 600 degrees F.

Well as I stated before you shouldn't expect a lot. I also wouldn't expect a lot of improvement from anything on a big pickup truck

Also note that a warm air intake does not make a diesel more efficient. It actually lowers its fuel economy and increase NOx emissions.

tasdrouille 11-03-2008 07:57 AM

I use boost, and plenty of it. I'm always accelerating at 5 to 10 psi in my TDI. I usually shift at 1600 rpm and cruise at the lowest speed possible. If I need to go up a huge hill, I just stick it at peak torque and give it up to 95% load. That's how I did my 79.9 MPG tank.

Quote:

Originally Posted by ConnClark (Post 70597)
Also note that a warm air intake does not make a diesel more efficient. It actually lowers its fuel economy and increase NOx emissions.

I agree with the NOx statement, but I'd like to have a reference on your reduced fuel economy claim as it's not been my experience.

Quote:

Originally Posted by ConnClark (Post 70412)
A nice free flowing intake helps too. [...]
If you have a turbo engine adding an intercooler will help. It may shift your power band to a lower rpm to some degree but it improves both performance and mileage.

The intercooler definitely help pack more air in, but I don't see how it improves fuel economy by itself. In fact it's a significant restriction in the intake. In my TDI there's a 3 psi pressure drop from the IC. Could you please provide a reference?

vtec-e 11-03-2008 08:06 AM

I tried blocking up the intercooler a bit on the diesel cee'd but the fuel economy literally tanked. I drove it easy, hard, and both drank diesel like theres no tomorrow. Maybe different brands of tdi behave differently with blocked up/ removed intercoolers. I do agree though, that gentle driving will not have the turbo compressing much, therfore cooler intake air. I can't wait to get something with a 1.4tdi next year....and a scangauge!

ollie

tasdrouille 11-03-2008 09:55 AM

Ollie,

On my TDI, timing is pulled back with higher intake air temps for NOx reduction purposes. If I unplug the IAT sensor, the ECU assumes -15 F IAT (vs ~90 F) and I can see the timing being adjusted by 2 degrees as I connect and disconnect the IAT sensor. I too blocked airflow to the IC, but instructed the ECU IAT was cold, and my mileage did not go down.

Your KIA is probably a much newer car than my 99 and there might be other emissions systems affecting how it reacts to intake air temps. A couple degrees less advance should really not affect mileage all that much alone.

Duffman 11-03-2008 12:59 PM

I think more so than in a gas engine there is an optimum intake air temperature in a diesel. Cold air is more dense and therefore has more O2 which is definately good for FE but a diesel also requires heat to run so a charge that is to cold may not run well either.

ConnClark 11-03-2008 01:38 PM

1 Attachment(s)
some data on what happens when you add an intercooler with no fuel adjustment. The more air you have in the cylinder the less heat that gets transferred to the cylinder wall when the fuel burns. Also with more excess air in the cylinder you have a leaner burn and the specific heat ratio of the combustion gases increase which further improves FE.

The same effect happens to a lesser degree with a cold air intake.

If its -60 degrees out I might consider warming the intake air, however I would have far more pressing concerns to deal with keeping my fuel from gelling up.


(From the Diesel Engine Reference Book, Second edition) Get a copy!!!

tasdrouille 11-03-2008 02:49 PM

Thanks connClark! I will indeed get a copy of this book. The sfc figures in the pic look like they're at full load though.

Ollie, I'd like to add that when I blocked the cross airflow to the IC, the IAT did not change by a significant amount. I could see a 10 degrees difference after a ~30 seconds hill climb at full boost, but nothing in regular city or highway driving.

Duffman 11-04-2008 12:37 AM

Quote:

Originally Posted by Big Dave (Post 70574)
I put a free-flowing exhaust (you could drop a Cokr can through it) and a free-flowing warm air intake and it didn't help a bit.

One thing you can do. Put a pyrometer on it and drive to keep EGT under 600 degrees F.

From what I have seen from your other posts, IMO you have moved your cruising RPM so low as to negate any benefits.

instarx 11-09-2008 02:00 PM

Quote:

Originally Posted by Duffman (Post 70684)
I think more so than in a gas engine there is an optimum intake air temperature in a diesel. Cold air is more dense and therefore has more O2 which is definately good for FE but a diesel also requires heat to run so a charge that is to cold may not run well either.

Diesel's do not need heat to run - they need compression. The compression provides the heat. In every circumstance in diesel engines, the colder the intake air the better the efficiency.

Well, re-considering - if it is very cold the diesel needs some additional heat from the glow plugs for a few seconds, but that's a special case. It never needs warm air.

instarx 11-09-2008 02:25 PM

Quote:

Originally Posted by tasdrouille (Post 70614)
The intercooler definitely help pack more air in, but I don't see how it improves fuel economy by itself. In fact it's a significant restriction in the intake. In my TDI there's a 3 psi pressure drop from the IC. Could you please provide a reference?

Ahhh, but that pressure drop you are measuring across the intercooler isn't from a restriction in the IC, it results from the cooling of the air and it is desirable. Pressure drops caused by flow restrictions are bad, but pressure drops caused by cooling are good.

When the very hot compressed air from the turbo is cooled by the IC its pressure (and volume) drops proportionally and so it contains more air molecules per volume than did the hot air (Boyle's Law). This allows even more O2 to be stuffed into your cylinders than if you didn't have the IC.

All things being equal, the IC allows you to use less boost to get the same number of air molecules into the cylinders - and that improves fuel economy (or power, whichever way you want to look at it).

ConnClark 11-09-2008 03:20 PM

Quote:

Originally Posted by instarx (Post 71633)
Ahhh, but that pressure drop you are measuring across the intercooler isn't from a restriction in the IC, it results from the cooling of the air and it is desirable. Pressure drops caused by flow restrictions are bad, but pressure drops caused by cooling are good.

When the very hot compressed air from the turbo is cooled by the IC its pressure (and volume) drops proportionally and so it contains more air molecules per volume than did the hot air (Boyle's Law). This allows even more O2 to be stuffed into your cylinders than if you didn't have the IC.

All things being equal, the IC allows you to use less boost to get the same number of air molecules into the cylinders - and that improves fuel economy (or power, whichever way you want to look at it).

Actually it isn't from cooling. You can have hot air on one side of a room and cold air on the other side and they will be at the same pressure. If it indeed there is a 3 psi drop across the intercooler he should really consider looking at an after market intercooler to reduce this loss as it a serious loss in useful energy. I also don't know where he measured the the pressure drop from. If it was right before and right after the intercooler then the drop is all too the intercooler. If it was between the outlet of the turbo and the manifold the plumbing route could be a big contributing factor. Yet another factor is the velocity of the air at the two points of measurement as this will have different static and dynamic pressure if they are different.

instarx 11-09-2008 05:40 PM

Quote:

Originally Posted by ConnClark (Post 71641)
Actually it isn't from cooling. You can have hot air on one side of a room and cold air on the other side and they will be at the same pressure. If it indeed there is a 3 psi drop across the intercooler he should really consider looking at an after market intercooler to reduce this loss as it a serious loss in useful energy. I also don't know where he measured the the pressure drop from. If it was right before and right after the intercooler then the drop is all too the intercooler. If it was between the outlet of the turbo and the manifold the plumbing route could be a big contributing factor. Yet another factor is the velocity of the air at the two points of measurement as this will have different static and dynamic pressure if they are different.

Sorry ConnClark, but you are mistaken. In a closed system as we are discussing, temperature does effect pressure, and it is easily measured because it is constant. A room is not a closed system so it is harder to measure, but in fact if you suddenly cooled one end of a hot room there would be airflow to the cold end because of the pressure differential. True, the pressure would equalize as the air mixed, but so would the temperature. If you took 10 pressure readings in the room you are in right now they would all be slightly different - and all directly related to the slightly different temperatures at each sample point.

As for magnitude, it seems reasonable to me. Three psi is only 1/10 of an atmosphere, and reducing the temperature of air from 250F to 150F can easily induce a change of 0.10 bar (particularly when it is pressurized to begin with). Trust me on this - I spent a lifetime correcting air sample measurements to STP (standard temperature and pressure) for human exposure monitoring studies. Note that I made my biggest assumption in this paragraph - that the air was cooled about 100F by the IC. If this is way off let me know and I will recalculate the pressure drop that would be expected across the IC.

Static pressure and dynamic pressure (also known as velocity pressure, VP) are independent of each other. VP is a measurement used to measure the inertia of moving air (usualy in a duct), and has no purpose when determining the pressure drop across a restriction such as, say, a filter or IC. In this situation VP values do not complicate the situation because they are simply not applicable.

I read the post that he was getting a pressure drop measured across the IC, hence he blamed restrictive airflow in the IC. If the pressure measurements were taken other places it might change things, but those were not the parameters of the problem, and the pressure drop across the IC is almost surely due to the temperature drop.

ConnClark 11-11-2008 02:42 AM

1 Attachment(s)
Quote:

Originally Posted by instarx (Post 71651)
Sorry ConnClark, but you are mistaken. In a closed system as we are discussing,

But we are talking about an open loop system. An intercooler reduces the work required by the compressor to compress a given mass of air. It does not reduce the energy recovered by the turbine. This results in an increased mass of air compressed to balance the energy of what is recovered by the turbine. By definition this is an Open loop cycle.
Quote:

temperature does effect pressure, and it is easily measured because it is constant. A room is not a closed system so it is harder to measure,
Quote:

a room or a container is a closed loop system as there is no mass entering or leaving.
but in fact if you suddenly cooled one end of a hot room there would be airflow to the cold end because of the pressure differential. True, the pressure would equalize as the air mixed, but so would the temperature. If you took 10 pressure readings in the room you are in right now they would all be slightly different - and all directly related to the slightly different temperatures at each sample point.
However they would all have the same pressure. Pressure also equalizes far faster than temperature.
Quote:

As for magnitude, it seems reasonable to me. Three psi is only 1/10 of an atmosphere,
Since mean pressure at sea level is 14.7, 3 psi is about 20.4% or about 1/5th of an atmosphere.
Quote:

and reducing the temperature of air from 250F to 150F can easily induce a change of 0.10 bar (particularly when it is pressurized to begin with). Trust me on this - I spent a lifetime correcting air sample measurements to STP (standard temperature and pressure) for human exposure monitoring studies. Note that I made my biggest assumption in this paragraph - that the air was cooled about 100F by the IC. If this is way off let me know and I will recalculate the pressure drop that would be expected across the IC.
I will save you this trouble as it sounds like you already have a life time of work to recalculate since you assumed 1 atmosphere equaled 30 psi.
Quote:


Static pressure and dynamic pressure (also known as velocity pressure, VP) are independent of each other. VP is a measurement used to measure the inertia of moving air (usualy in a duct), and has no purpose when determining the pressure drop across a restriction such as, say, a filter or IC. In this situation VP values do not complicate the situation because they are simply not applicable.
If this is so then please explain the attached picture.
Quote:

I read the post that he was getting a pressure drop measured across the IC, hence he blamed restrictive airflow in the IC. If the pressure measurements were taken other places it might change things, but those were not the parameters of the problem, and the pressure drop across the IC is almost surely due to the temperature drop.
Once again I disagree. Any drop in pressure would be due to air flow restriction compounded by differences in velocity of the air flow at he points of measurements. Try playing around with a few simple computational fluid dynamics simulations that vary in temperature in a closed system. You will find that pressure is equal or does equalize very quickly. If you wish to invest the time, OpenFoam is a good package it just is very complex and has a steep learnung curve.

tasdrouille 11-11-2008 10:29 AM

You are right that plumbing probably played a role in the pressure drop I measured. I taped into existing lines at the turbo outlet going to the boost control solenoid and the post IC line going to the ECU.

MazdaMatt 11-11-2008 11:15 AM

physics aside... I also am looking for ways to more efficiently drive my big (huge) diesel truck. It is less aerodynamic than a brick and weighs between 5000 and 8000 pounds depending on the load. Constant throttle is no good because if i'm doing 80km/h and i reach a SLIGHT slope, i will lose 15km/h and drop down to a lower gear, then that throttle position can't maintain the high revs and i slow down even more. On a downhill, constant throttle may gain me 5km/h.

Should i be gradually accelerating towards a hill? should i be easing off the throttle during the downhills so i'm using less gas? If i drop throttle on the downhill it will not coast, it will slow down quickly and downshift.

It seems my THREE-SPEED tranny shift 95% based on speed and just barely based on load. ie, accelerating up to 65, i can drop throttle and it will upshift, or i could not drop throttle and it will shift at 70. If i DO drop throttle, by the time i'm in the new gear, i'm only doing 61-62 and any amount of throttle will cause it to downshift again... I kind of hate life when i'm driving this p.o.s.

I will not be investing in bolt-ons and upgrades. Yes, i WANT the turbo 5-speed manual, but i have the 7.3L N/A 3-speed auto... there is no changing that.

I keep my tires at sidewall max of 65psi and I drive 85-90 on the highway (100km/h) and I drive 70 in the 80km/h zones. My last trip was ~23L/100km (that's NOT mpg! my car gets about 6.8L/100km)

TestDrive 11-11-2008 02:22 PM

Is make, model year relevant?
You don't mention rpm - do you have a tach?

MazdaMatt 11-11-2008 02:27 PM

F350 with a big box (not a pickup truck box, more of a moving truck box that I use to transport my track car instead of towing it on a trailer).

Typically under normal acceleration, it shifts around 3krpm and under normal on-throttle deceleration it will downshift around 2krpm (i think). It is REALLY frustrating to be sitting at 62km/h at 2900rpm (ish) and the damn thing isn't shifting. Redline is about 3200rpm.

TestDrive 11-11-2008 04:55 PM

You didn't indicate a year. But based on Ford F-Series (Wikipedia)
it's good guess that you've got a Ford C6 transmission - (Wikipedia)

I'd verify that, then discuss it with a good transmission mechanic to see if what you've got is shifting like it should. Kind of suspect it is, but I'm no expert. While you're talking it over with the mechanic, you might want to ask questions about conversion to a automatic/manual shift, valve body or a full manual shift, valve body. (As in would it be a plausible DIY project? - I don't believe the parts are all that expensive compared to the probable gains FE.)

Something came up. Gotta go now. May post more on this later.

Duffman 11-11-2008 06:48 PM

I was thinking of the full manual valvebody as well. He will have a C6.

Anything that you can do to free up the intake track will help as well, those things got some intake baffling junk you can remove. Lots of good info on the Ford truck forums.

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MazdaMatt 11-12-2008 08:03 AM

oops... last night i typed up a reply but i didn't click send. It is a 1994 with ~166,000 km (100,000 miles?)

The manual valve bodies are interesting. I hate driving auto, so that would be a nice change. They are about 300 bucks, but depending on how long i own the truck and how many trips to the race track i get to do next year (just bought a house) it may be worth it so i can short-shift it and live with slow acceleration... or drive 64km/h without it repeatedly up/down/up/down shifting.

I will check out those sites. Thanks a lot for that list of links. Also, i will have a look at the intake path. It has an exhaust you could stick a leg into.

TestDrive 11-12-2008 03:19 PM

A few more thoughts & questions.
 
Quote:

Originally Posted by MazdaMatt (Post 71936)
Typically under normal acceleration, it shifts around 3krpm and under normal on-throttle deceleration it will downshift around 2krpm (i think). It is REALLY frustrating to be sitting at 62km/h at 2900rpm (ish) and the damn thing isn't shifting. Redline is about 3200rpm.

The more I think about it, those shift rpms sound reasonable for a gasser, but entirely too near high end of scale for a diesel (more torque at lower rpms). I wonder if all oem C6's have the same valve body. Any chance some previous owner changed out the transmission? eg C6 tuned for diesel came out and was replaced with new/used/rebuilt C6 intended for gasoline engine? (Not even certain that's a valid question to ask.)

Before you talk to a/the transmission mechanic, crawl under and look for vacuum hose or electric wires leading to a shift modulator on the transmission. Could be a $20-$40 part may help the delayed shift problem.
If it's a vacuum modulator, check for a leaking vacuum diaphragm. If it's electric, look for frayed/broken wires. Consult manual for how to test.

While you're under there, write down the info off the tag on the rear-end. The transmission specialist might want to know what size tires & wheels - write that down too.

What does the transmission fluid look and smell like?

Any idea when or if the transmission fluid and filter were last changed?

Hope this helps.

MazdaMatt 11-12-2008 03:29 PM

The truck was previously owned by Hostess as a city delivery truck. Then purchased by a guy that used it to haul his off-road racer (he installed the ramp door). Hostess apparently had a rock-solid maintenance schedule and the second owner runs a small trucking company. I can ONLY ASSUME that the fluids are doing fine, but who knows if that tranny is correct or the valve body is correct... he may have scooped it up chneap from an off-road racing buddy. I woudl LOVE it if i could replace a 40 dollar part and have it start upshifting at 2000rpm instead of downshifting at that!

Great suggestions.

But moving backwards a little... what about driving technique? I follow trucks and i drive f'ing slow, i try to maintain speed at the lowest possible in the highest gear... i refuse to neutral coast because i did that once and it clunked HARD on every shift for the next hour of driving.

Duffman 11-12-2008 04:31 PM

The 7.3 should have a different bellhousing than the gas jobs, Ford was/is terrible in that regard.

Duffman 11-12-2008 04:33 PM

Matt instead of accelerating slow, maybe try to get through the first two gears briskly, then slow the acceleration.

MazdaMatt 11-12-2008 04:36 PM

...Actually... i do that... i don't floor it, i just try to "lead" the gas pedal. ie, if 3/8 gas would sit at 25, then when i'm doing 25 I have the gas down to 5/8... when it shifts, i drop back down to a little more than cruise throttle... i don't spend much time in each gear... which is easy because it is in top gear at 65km/h (40mph? guess?)

Funny enough, i think the best mileage trip i ever had, i spent about 3 hours in first gear at idle... it was stop/go traffic and i played the accordian by simply sitting there iwthout touching the pedals.

instarx 11-13-2008 07:00 AM

WARNING! Fluid dynamics post!

Quote:

Originally Posted by ConnClark (Post 71855)
If this is so then please explain the attached picture.

Once again I disagree. Any drop in pressure would be due to air flow restriction compounded by differences in velocity of the air flow at he points

I just woke up and will address many of your points later (you made some good ones, but mny are still incorrect) - but first, that picture.

That, that...thing ;), does not measure what you think it does. Note that the pressure appears to be LOWER in the area with high velocity air. But this is exactly the opposite of what you claim should happen when velocity pressure adds to static pressure, so how can that be? It is because the apparatus actually demonstrates the Bernoulli effect, where high-velocity air moving across an opening creates a localized low pressure area proportional to its velocity.

Those manometers are not measuring the static pressure along the tube, but the relative strengths of the three localized low pressure areas created by the Bernoulli effect. It is not possible to even estimate the static pressures along the tube with that poorly designed apparatus (who would ever connect three manometers in series like that - you can't tell which is measuring what). That contraption is a perfect example of how somone who doesn't understand the principles (not you, the people who put it together) can design an "experiment" or demonstration that they only think illustrates their point (unless the caption to that picture is "Demonstration of Bernoulli Efect" or "World's Worst Design of a Pressure Measuring Apparatus Using Manometers"). :)

A general comment about your interpretations of the relationships between velocity and pressure: Be careful not to confuse cause and effect. Air movement (velocity) is caused by pressure differentials, but the inverse is not true - air pressure is not changed by a parcel of air simply being in motion. This is true in air systems ranging from continental-sized weather systems, to air being pulled through a duct, to the air moving around in your living room.


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