Engine Specific Info and Questions > IDI Engine

modifications to get better fuel economy

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chrissev:
So I know you can modify your Turbodiesel to decrease your fuel economy and get better performance, but does anyone know if you can modify your diesel to get more fuel economy, without worrying about performance enhancements?  Would an intercooler do this?  Synthetic gear oil?  Inflate your tires more?  Any other ideas?

racer_x:

--- Quote from: "chrissev" ---So I know you can modify your Turbodiesel to decrease your fuel economy and get better performance, but does anyone know if you can modify your diesel to get more fuel economy, without worrying about performance enhancements?  Would an intercooler do this?  Synthetic gear oil?  Inflate your tires more?  Any other ideas?
--- End quote ---

Some mods would give better mileage with better performance. Other mods will give better mileage with slightly less performance.

More mileage - less performance

* Reduce full load fueling somewhat

More mileage - more performance

* Advance injection timing (more power for the same fuel, or slightly less fuel for the same power if you adjust your driving habits).
* Increase tire pressures up to max on sidewall.
* Use taller, skinnier tires (might affect speedometer reading, though). If you can find a 165R13 or even 155R13 tire that will hold the load, that will do better than the 175/70R13's. First, they are skinnier, for less rolling resistance and less air resistance. Second, they go further for each revolution than the stock 175/70R13's. The speedometer error can be corrected with an internal adjustment. Also go for lighter weight tires (usually lower speed ratings are lighter in weight).
* Use light weight, small diameter wheels (5Jx13 or 5.5Jx13). Early Scirocco alloys are good for this and have decent aerodynamics, too. Be sure to get the lugs if you get those wheels, they use longer lug bolts.
* Install a light weight header, bracing and flex pipe instead of cast iron manifold.
* Use "Energy Conserving" motor oil and synthetic gear lube in the transmission. Be sure to change out all seals when switching to synthetic gear lube. This is best done when doing a clutch replacement so you can get all the seals. Check the gear lube regularly after switching to synthetic and find and fix any leaks that open up.
* Use a light weight flywheel
* Machine brake rotors down near minimum thichkness (reduce rotating weight).
* Remove Air conditioning and power steering if that's an option. (I removed power steering, but AC is required for summer driving here).
* Remove excess weight from car.

Although it might be true, I don't recommend telling the wife or girlfriend that the car would be quicker if she lost some weight, too. The mileage increase and performance increase isn't worth the grief you get for that mod.

RAMMSTEIN:

--- Quote from: "racer_x" ---
--- Quote from: "chrissev" ---
Although it might be true, I don't recommend telling the wife or girlfriend that the car would be quicker if she lost some weight, too. The mileage increase and performance increase isn't worth the grief you get for that mod.
--- End quote ---


The last mod might get you killed, be careful... :wink:
--- End quote ---

Cheesetoast:
also, the less electrical stuff you're running in the car, the better.  rear defrost uses a lot as well as a/c.

VWRacer:
Racer_X touched on most of the biggies, but I'll add a few.

First, slow down. It is axiomatic that the slower you go (within reason) the less fuel you burn. Driving the speed limit in the slow lane instead of plus 20% in the fast lane makes a big difference. My TDI gets about 50 mpg (US) at 75 mph, but jumps to 60+ if I slow down to 55.

I would back out the max fueling screw until the car barely accelerates. Diesels don't burn extra fuel like gassers do, but if the power is there, we are often tempted to use it. Remember, any Rabbit/Jetta/Golf only needs about 12 hp to cruise at 55 mph. The more power you use on top of that the more fuel you consume.

If you are really fanatical, try the injector mod and advance the timing to about 1.1 mm. The injector mod shaves some material off the back end of the pintal, allowing the fuel to be injected more quickly. By doing this and advancing the injection timing you can raise the thermodynamic efficiency of the engine. Giles can do this mod for you.

Finally, for the truly devoted, turbocharge a 1.5 D in a Mk 1 Rabbit/Jetta. These are the lightest and least powerful deisels VW ever imported to North America. An "Ecodiesel 1.5" may be the most fuel economical car to ever hit the continent.

Cheers! Stan

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