New Owner of a 1981 4door VW Rabbit Diesel**47.5MPG**Baseline - Page 2 - Fuel Economy, Hypermiling, EcoModding News and Forum

Daox · 02-06-2014, 06:14 PM

A bigger exhaust would probably help on a turbo diesel. I don't think it will on an N/A diesel. On a N/A you want proper exhaust scavenging. Enlarging the exhaust will likely kill low rpm torque as it would on an N/A gasoline engine.

BTW, congrats on the car! It looks to be in great shape for its age.

Jyden · 02-06-2014, 06:49 PM

Not true on the old D rabbit - I participated in the 90'es in ecomodding just that car, and a bigger exaust with more free flow gave better mpg, both on the Dyno and in daily driving. I dont know why though - but it did....

Cobb · 02-06-2014, 08:42 PM

What ever you do retorque the head bolts. Ive seen many diesel vws need a head gasket because the owner never followed the manuals requirement to have the head retorqued every so often.

Also if you are looking for MORE POWER examine the injector pump. There are a few screws you can turn to adjust things. You can limit rpms, idle and max amount of fuel injected into the engine.

deejaaa · 02-07-2014, 12:37 AM

had one of those, 82 model but 4 speed.

added an Audiovox cruise control and it made a world of difference.

Christ · 02-07-2014, 02:11 PM

MK1 and MK2 have basically interchangeable front emd parts I think... There's an MK2 'big bumper' that works better as an air dam than the stock stamped unit. I ran my 1.6 with no rad fan and a grille block in all temps, never had a problem with it, just don't let it idle for more than maybe 20 min (if you do that sort of thing). The stock exhaust makes the engine fairly anemic, its max torque and overall curve is something like the gasser, but with less AUC (area under curve). Probably the single best thing you could do for MPG and a slight boost in power is add a non-vnt turbo and manifold from an ALH TDi, 2.5" turbo back open exhaust, and actuate the wastegate at no more than 4psi. Adjust your IP till you get a little gray smoke under load, then back it off slightly, and concentrate on staying between 1800-2400 rpm.

The idea is that while diesel engines don't 'produce vacuum', they still draw in the air charge under vacuum and this requires energy that would otherwise go into the piston and rotating assembly. The turbo will use exhaust heat to keep the piston faces from seeing as much vacuum, thus increasing efficiency. Technically no need to adjust your fueling calibration with the turbo, but if you're gonna add one, might as welll get the power boost from it, too.

Christ · 02-07-2014, 02:15 PM

And don't worry about the CAI thing. Its not helping or hurting. If you add the turbo, don't bother with an intercooler and piping, at 4 psi and such low power levels you don't need it. If you have access to free washer fluid, consider water/meth injection kit. Also, the poster that mentioned PCV meant to say CCV, and that tube that vents from the valve cover to the intake manifold... put a catch can in it, or at least use a bore brush for a .45 cal. Its basically the 'flame arrestor' that Mercedes used in their CCV system, catches the oil that will eventually soak your filter amd cause a runaway condition.

elhigh · 02-07-2014, 03:18 PM

+1 on the camera lens, holy moley.

Nice find, man. If you never go fast, those old Rabbits will just go and go. Popular Science published a 75mpg rating at 35mph. Just puttering along.

The aero on those old Rabbits is just dreadful. I reckon virtually anything you do towards aero will reap huge rewards, especially in light of the engine's very modest output. You'll be pulling the power demands way, way down further into its sweet spot.

You might want to look into whether that engine has the upgraded head bolts. I understand that's a thing with the 1st gen VW diesel, head bolts loosening up and a resultant gasket blowout. [edit] Whoops, Cobb got there before me. Well, +1 on that too.