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Engine Specific Info and Questions => IDI Engine => Topic started by: farkman on July 18, 2004, 12:14:28 pm
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I was wondering if it would be possible to put some sort of switch(ball valve or something similar) in the small hose running between the intake manifold and the boost enrichment (I think that's what it's called) part of the injection pump. The switch valve would be in the car close to the driver and a small hose would run from the intake manifold into the car to the switch. A second hose would run from the switch to the injection pump. The driver can then switch the valve on to accelerate or turn the valve off for cruising. Since there would be no boost pressure applied to the injection pump less fuel would be injected, hopefully increasing fuel mileage. Do any of you think it would work or would the car not have enough power to maintain its speed because too little fuel is being injected. Any input is very appreciated.
Thanks.
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the LDA is load dependant. It only gives as much as the engine needs for things like passing, or going up a hill. No point in doing this mod.
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or would the car not have enough power to maintain its speed because too little fuel is being injected.
Exactly. The pump is providing only as much fuel as is needed to maintain whatever engine speed is requested by the pedal position. The boost enrichment device (LDA) only controls the upper limit of the injected quantity based on boost pressure. It is not really limiting injected quantity unless the pedal is at or near the floor. Cutting off boost pressure to it will only result in very sluggish performance when floored and little fuel savings, unless of course you normally drive with the pedal on the floor. :D
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Thanks for your input guys.
It looks like I'll have to think of something else to improve my mileage to hit that elusive 50 mpg mark :D .
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Drive slower. :D
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TDIMeister
I already do. On the highway I drive at a VERY leisurely 95km/h.
Any other suggestions? :D.
I was thinking about making a new tubular exhaust header out of 1.5" stainless steel. You think that could yield another 1-2 mpg.
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Just filled up our 84 rabbit tank today and it took 40.3 L and it
covered 573 KM. that works out to 40 MPG. not bad for a car
that gets driven like it was stolen just in the city.
by the way i didn't get this good mileage when i had less power
before my mod pump that is.
who says more power equals less gas mileage.
Giles
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longgg longg 5th gear. top speed on my diesel is somewhere around 170-180km/h so 100-120km/h is pretty leisurely. transmission code FF i believe... was the original 4speed + E that came in my 1982 1.6NA diesel.
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Lanny
I don't know what type of transmission I have but it does have a long 5th gear. At 2400rpm I'm at about 97km/h. Theoretically I should have a top speed of about 210km/h at 5250rpm but my car stuggles to accelerate past 120km/h at 3000rpm.
Does anyone know if having the cold start accelerator pulled out while cruising will improve/hurt fuel economy? I definitely have more power with it pulled out, but if it uses more fuel then obviously I'd rather push it in while cruising.
Thanks
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The cold start knob advances the injection timing, nothing more, and as long as it's not advanced too far, WILL improve mileage slightly.
I was going to say that you should get a TDI ;) . I get 50 MPG (Imperial) effortlessly, and this in a heavy elephant Passat :D
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TDIMeister
My best tank so far was 45 miles per US gallon, so about 54 miles per imperial gallon. And that was 80% highway, 20% city. But I want to get 50 miles per US gallon so I can go to Florida (Pompano beach area, about 2500km away from what I've been told) with only one fillup along the way, somewhere in North Carolina probably.
Although I would love to get a TDI, I don't have the money to buy one :lol: .
Peter
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What about some of those tires that they put on the Honda insight, to lower rolling resistance? I don't see why they woulnd't work on a VW Diesel too! They might be a bit hard though. :lol:
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fspGTD
I already have the hardest tires I could get for a reasonable price. They are 185/65R14 Michelin Destiny's. They have a wear rating of 680 and I have pumped to 42psi in the front and 40psi in the rear. I figured that a 185mm width tire would reduce the frontal area of the tire a little, which would reduce drag. I also chose a little taller aspect ratio than stock which would lower rpm's on the highway.
I'm beginning to think that there's very little I can do now to improve my mileage :x .
Peter
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Peter,
I drove my diesel Rabbit very carefully for about 80,000 miles over 6 years, and only rarely got better than 45 MPG. The one time I got 51 MPG, I was following a U-Haul truck that was governed to 50 MPH.
Bottom line is that you are doing about as well as you can expect with that car.
One technique that I've been using recently with my TDI is to short-shift from 1st to 2nd and 3rd, then go directly to 5th at about 35 MPH (50 KPH). And any time I'm rolling at or above 30 MPH, I am in 5th gear. That has bumped my fuel mileage up a couple of MPG.
BTW, what is your target MPG?
Stan
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Stan
My target is 50 miles per US gallon (80km per US gallon) all highway at around 95km/h. That would give me a range of about 1300 km on 62L(about 16.4 US gallons), or a VERY FULL tank of fuel :D . As for short shifting 1st, 2nd, 3rd and shifting directly to fifth, I pretty much do the exact opposite. I accelerate quite spiritedly so I can get into fifth as fast as I can. I can only shift into fifth at around 60km/h (1600rpm)though. Below that the engine is lugging. I anticipate stops and roll in gear as much as I can to avoid braking and consequently re-accelerating. Of course, I only expect to get 50 mpg if I drive only on the highway at a fairly constant speed for the whole time. My car is a 1994 Golf TD with the AAZ engine so it's not a really light car. I think I need to focus much more on aerodynamics though, especially on the front end.
Peter
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fspGTD
I already have the hardest tires I could get for a reasonable price. They are 185/65R14 Michelin Destiny's. They have a wear rating of 680 and I have pumped to 42psi in the front and 40psi in the rear. I figured that a 185mm width tire would reduce the frontal area of the tire a little, which would reduce drag. I also chose a little taller aspect ratio than stock which would lower rpm's on the highway.
I'm beginning to think that there's very little I can do now to improve my mileage :x .
Peter
Uh... 185/65/14's are a wide tire for a Rabbit. The original Rabbits came equipped with 155 width tires, and had as an option later on 5.5" wide rims with 175-width tires. The only Rabbits sold with 185-width tires were in '83 and '84 on the '83-'84 Rabbit GTI (in 185/60/14 size).
I would see if a 155 width is available in an application popular with electric vehicles (lowest possible rolling resistance, not just highest treadwear). I'd run them with lightweight aluminum wheels in a cookie-cutter like 5" width, if that is an option.
How about wheel fairings - IE: spun aluminum discs that cover the wheel openings making the smooth. Are you running the euro A-piller fairings? Lowering the car would help cut down on aero drag as well, as would installing an aim dam that extends down low, and putting covers over any unnecessary openings in the radiator support (forcing more air go around the more streamlined top and sides of the car.)
I think you could get well over 50's US mpg in an IDI diesel rabbit...
And oh by the way, saving weight wherever you can will also help with overall mpg. There are many things you can do to take weight off these cars - let me know if you are short on any idea in that department! I have no doubt an 1800lb rabbit diesel will get significantly better mileage than a 2200lb'er. Fuel economy in cross-country trips on my Rabbit racecar has gone up noticeably since I've taken off a lot of weight, and I think it's because less weight saves fuel. Every mountain pass you have to climb up for example, will take less fuel to do so, any little acceleration changes will take less fuel, etc. This is also the reason why we don't see the later-model TDI's with more efficient motors getting fuel economy any better than a Rabbit with an older IDI: the car bodies are so much heavier. Got as tall as possible ratio of ring and pinion and 5th gear also.
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Oops, just re-read your post and see you have a '94 Golf. I thought you were talking about a Rabbit, so anyway feel free to disregard a lot of the specific recommendations, but you can still probably apply the same concepts to getting better mpg.
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fspGTD
I apologize for not mentioning my car beforehand. Thanks for your tips, I will definitely do something about the openings in the front end and lowering the car, only a bit though. It's a good thing you mentioned that, I need new suspension anyways. Perhaps some Bilstein shocks and Eibach springs are in order. Tips on weight reduction would be appreciated.
Thanks
Peter
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As for short shifting 1st, 2nd, 3rd and shifting directly to fifth, I pretty much do the exact opposite. I accelerate quite spiritedly so I can get into fifth as fast as I can. I can only shift into fifth at around 60km/h (1600rpm)though. Below that the engine is lugging.
That makes it easy to do a test, Peter. Do a careful refill and use my technique for a tank of fuel. See what it gets you.
Stan
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Stan
I should try that but I can't stand accelerating slowly. There's something addictive about the torque, it's like a drug :lol:. And if I do any more than a few dozen kilometers in the city, I will kiss the 50 mpg target goodbye anyways. I only expect to get 50 mpg, if I drive all highway at a constant 95km/h.
Peter
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Oh, I understand. I only do it when I'm not going to impede traffic. But you might be surprised at how much it helps in city traffic. Here in the San Francisco area it doesn't normally move all that fast anyway. ;)
If you don't like doing it in normal driving, you may have problems going slow on a long trip, too. I did a long run here in California's central valley at 55 mph (90 kph) and thought I'd die of boredom. But I did get 63 MPG! :shock:
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Stan
I don't accelerate fast if I see that I'll have to slow down again (such as a red light ahead), but other than that I try to get into fifth gear as fast as possible, as long as the speed limit is 60km/h or higher. Up here traffic is pretty good unless you get stuck in rush hour, but I try not to drive during those times.
As for driving at 95km/h being boring, all I need is some tunes on the radio and I'm set. I'm very used to driving slowly on the highway and I would hate to be one of those people that switch lanes every ten seconds just to gain a few minutes.
Peter
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If you want to lower your suspension, take a look on the FK suspension kit.
http://www.concept1.ca/FK%20SUSP.htm
Hi-Tec Suspension Kits: $628 CDN / $465 US
I install on kit like that on a A2 Jetta and she got a really nice ride with this :)
The rear is ajustable.
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TDIMeister
My best tank so far was 45 miles per US gallon, so about 54 miles per imperial gallon. And that was 80% highway, 20% city. But I want to get 50 miles per US gallon so I can go to Florida (Pompano beach area, about 2500km away from what I've been told) with only one fillup along the way, somewhere in North Carolina probably.
Although I would love to get a TDI, I don't have the money to buy one :lol: .
Peter
From my home here in NC, which I get onto I-95 at mile marker 88 and I'm 30 miles from 95 it was 778 miles to Pompano Fl. Made it in 10 and half hours. Would have done better but hit rush hour traffic just as I got to the North side of the city. I took my father-in-law down to his friends birthday party and a WWII reunion. We took his 98 Eldorado (sweet ride) and got 30 mpg out of that NorthStar 32valve V8. That really impressed me for such a large vehicle, engine and cruising speed. :D
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I have an idea, if it would work. What do you think of running space saver spare tires on all four wheels? I know they are not as tall but they are thinner. :wink:
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weight savings...
do you have AC? ditch it... the whole system has to be 50Ibs+
take out your back seats for long trips
get rid of a fullsize spare in favour of a space saver, or ditch it altogether along with the OEM jack and buy a can of that flat tire inflator from canadian tire.
also..
run ridiculously-skinny tires on the back for long trips (or all 4 corners..up to you)
drop the nose of the car and get a lower spoiler
replace wheel bearings if you havent before
are your tires/rims all perfectly straight/true? i gained 70km/h per tank consistantly when i changed out a rear tire, got rid of a little bit of shimmy too. had an alignment recently?
do you run a fuel system additive like stanadyne? that could help
i still think the best single way to improve economy is a super-tall 5th gear. you could also consider getting a long 5th and changing to a longer final drive when you are in there.
i made a point of seeing how the car performs at 50km/h in 5th gear last night after reading this thread.. even with the long gearbox 50km/h isn't a problem in 5th.. a little sluggish but i could probably cruise at the low 40s (~43km/h and above) no problems in 5th :D
the first time i took my friend out in my rabbit (he has a mkIII 8v gasser) i put it in 5th going up a steep hill at 60km/h just to show him the torque of the diesel... he didn't think it would pull up the hill, but the car actually accelerated (mind you, slowly). diesel power!
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Wingman
Those look pretty good but I have heard such good things about the Bilstein's. And I'm not looking to spend that much money ($628 + shipping) either :lol: .
Rat 407
What large city are you located near? I would like to get an idea of how far away you are from the South Carolina border. Wouldn't those space saver spare tires reduce my mileage. The engine would probably be turning at close 3000 rpm compared to 2400 revs with the tires I have on now. Plus I don't want to spend a few hundred dollars on something that might not even work. I can use that money towards new suspension :D .
BlackTieTD
No I don't have AC. I specifically bought this car because it didn't have AC (and it was in good condition). I don't even need it because I don't get very hot. Do back seats even weigh that much? It looks like it only weighs about 25 pounds. I haven't replaced the rear wheel bearings but I have regreased them with Amsoil S2000 grease. The rear bearings are still in good condition but I have no idea about the front ones. Can those even be greased? or are they sealed. Changing gears or final drives is not really in my plans right now due to cost and difficulty (and I don't have the right tools either :lol: ).
What rpm were you at doing 50km/h in 5th gear. Wouldn't the engine be lugging like crazy, mine would be.
Peter
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You really think I would not answer to this thread....mmmm
Ok, tires:
Inflation at the max stated on the side of the tire (44 or 35, lucky if you have a 51 psi tire).
Treadwear: 680 is not optimum.
The best treadwear in the industry is a Michelin: the HydroEdge, 760 of treadwear.
Tranny fluid: change for Redline MTL: I gained 2.8% fuel economy with it.
How tall is this "E" fifth gear?
Drive slower than 95 kph.
Windows up, no AC is better.
Coasting in gear (I don't know if true with IDI, but the TDI cuts fueling while coasting in gear).
Travelling on flat lands vs hills helps a lot.
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Do back seats even weigh that much? It looks like it only weighs about 25 pounds.
not sure how much they weigh, 25-35Ibs seems about right. its not a huge weight savings but every little bit helps... in a sub-1900Ib car (my rabbit) i'll notice a 30Ib difference... ie: i'll notice the difference when i have my toolbox in the hatch, to acceleration anyway. its probably not really worth the trouble to take the rear seats out on a mkIII though unless you leave them out.
What rpm were you at doing 50km/h in 5th gear. Wouldn't the engine be lugging like crazy, mine would be.
How tall is this "E" fifth gear?
its lugging along, but not chugging badly or anything... its pretty low but not too bad. i usually have a rule of thumb, if i'm at 60km/h or above, i go to 5th gear. 50km/h is a little low for 5th, but i never find myself in a real-life situation where i would drive 50km/h in 5th. if the speed limit is 50km/h, i'll do 55 or 60km/h and be in 5th... if the speed limit is lower, or i'm in a residential area, i'll stay in 4th or even 3rd for better response, better accelation and feel around corners, etc..
i found this chart with 020 ratios: http://www.4crawler.com/Diesel/VW_020_transmission.shtml
the gearbox in my car is an FF, made from 6/79 to 7/83 for US market cars. final drive of 3.89 and a 5th gear of 0.76. 3500rpm in 5th will get you 83mph or about 133km/h. if my math is right, thats about 1315rpm at 50km/h in 5th, pretty low! (i don't have a tach installed yet)
i've had the car up to 160km/h (calculations say 4210rpm) and it feels like it still has some more legs...
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Farkman,
I live 120 miles from the NC, SC boarder. I'm 30 miles to I-95 and at that point it is 90 miles to the border. You can stop off and say hi to Pedro at South Of The Boarder. :)
Didn't think of the RPM you would be turning with the space saver spares on. I bet it would be a little higher. But inflated at 60psi like they say on the side it would be a rough ride.
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Rammstein
I'll pump up all the tires to their 44 psi max. The Michelin Destiny's I got had the highest treadwear for a reasonable price. I paid $93, on sale, for the Destiny's compared to $140+ for the HydroEdge's.
I put in Amsoil S2000 75W90 gear oil back in April and I gained about 6% in mileage. You think I can gain another 2-4% by switching to an 80 weight gear oil. Some Canadian Tire stores sell Redline now so I'll check it out. I have no idea how tall fifth gear is. I think the transmission I have is the 02A but I'm not sure.
Driving slower than 95km/h would probably piss off the drivers behind me :lol: . But if I do get a chance to drive slower than 95, I most certainly will. Windows are always up on the highway and I don't have AC. But if it begins to get warm, I open the sunroof a little bit.
I started making aluminum covers for the two openings in the bottom left and right side of the bumper. I may also make a cover for the center opening which feeds the radiators. Of course, I will make some openings so some air can still flow past the radiator. I will also make some air scoops for the brakes which are smaller. At least the flex pipe that I bought on ebay finally got shipped out today, so It should be here early next week :D . Then I can finally finish the downpipe for my car.
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Where did you get the Destiny?
Aren't they a brand of Michelins only sold by Canadian Tires?
Blacktietd, Passat TDI's have the same .756 fifth gear ration with a final drive of 3.156. :mrgreen:
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doh! :evil: one-upped! :lol:
i'm happy with the gearing in my car, although i was thinking this morning on the way into work (the long way :roll: ) that i wouldn't mind the gearing a little tighter through 2nd, 3rd and 4th... but strictly for accelation performance obviously.... and i already run out of gear right about when the turbo starts kicking real good so i would need to do some more mods to get more power lower in the rpm-range if i wanted tighter gearing...
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Rammstein
You're correct, I did get the tires at Canadian Tire.
I checked my transmission and it says it's a CHD. I looked for the gear ratios but I found two different ratios. The first one says .769 fifth and a 3.94 final and the other one is .75 fifth and a 3.67 final. I think my car has the second set because I calculated it out and with that gearing my speed should be 97.9km/h@2400rpm. The other gear set says 89km/h@2400rpm. And my speedometer reads a bit over 95km/h when I'm at 2400 rpm. I've heard that VW speedo's usually read a little faster than the actual speed, but I think that difference was made up by installing tires which are 3.2% larger in circumference than stock.
Yesterday I finished the two covers for the openings at the bottom of the bumper. I also made some smaller air scoops for the brakes.
Lanny, you get your welder yet? :D
Peter
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Sure did Peter. Renovating my girlfriend's new house right now, eating up my time! (..but there are plans for a garage out back 8) )
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Nice. A word of advice, try to build the absolute BIGGEST garage you can :D . There's nothing like a lot of space, trust me :lol: .
Peter
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Problems with the city and permits... time will tell. 20'x22' is the plan right now....city wants to limit us to 10'x10' :evil:
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10' x 10'. That's a shed not a garage :lol: ! My old house had a double garage which was sweet, but my new house has only a single garage. It's a PITA having to move one thing to use something else. I hope you can beat the system.
Peter
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Don't forget to have the alignment done. The least rolling resistance the better.
Now that we have sold our old house, it was on the market for over a year, I can build my garage. I'm looking at building a 26' x 36' Hopefully it will be done by Dec. My old garage at the old house that we just sold was 24' x 30'. It was nice but the extra room would be much better.
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Rat 407
I'll get an alignment done when I get my new suspension, hopefully it'll be soon. That garage should be sweet. It's about 4.5 times bigger than mine, I'm jealous :lol: .
Lanny
If you think that you'll ever upgrade your welder or purchase some semi-serious equipment/machinery, then you should consider wiring in some 230V into the garage.
By the way, I looked for Redline MTL at a few Canadian Tire stores here in Mississauga, but they don't sell it. All they have is motor oils :x .
Peter
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Lanny
If you think that you'll ever upgrade your welder or purchase some semi-serious equipment/machinery, then you should consider wiring in some 230V into the garage.
right with you there peter. we need 230v for the compressor out in the garage. just hope the city will let it all go through.. 10'x10' is a shed.
its sort of ridiculous.. the city is revamping the downtown (which i am 100% for, our downtown has taken a 180 turn for the better in the past 5 years) but they want the block of land the house is on, so they put a freeze on building additions, as they will increase properly value. the more they can stop people from improving their land, the less they will have to pay for it if/when they swoop in and take it :?
there was a guy with a very succesful restaurant right on a corner of king street where they have just finished building our new market... he refused to sell, he didn't want to have to relocate (asian restauraunt right in the middle of the asian community). so he held out and eventually the city offered him enough $ that he accepted... its almost a year later and he can't get the city to grant him a permit to relocate since he caused them a hassle. something seems a little 'wrong' there...
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The damn government always finds ways to screw the little guy.