Fuel Economy

~~~

There are a lot of things that affect fuel economy. Following are a few suggestions that may increase the miles you get for a gallon of gasoline (petrol). -

  • The biggest improvement in gas mileage is with driving style - your right foot has the most effect! :-) Gentle acceleration is good. The accelerator pump in the carburetor squirts about 1.4-1.6 mls of fuel each time you floor the accelerator, but if you accelerate gently the accelerator pump does not activate, and so you save that 1.4-1.6 mls each time. That doesn't sound like much, but try counting the number of times your foot goes down on the accelerator on each drive to work - you'll be surprised!
  • Anticipating the next stop light or traffic holdup and reducing power early so you don't have to brake as hard means you've used less fuel to get there. A lot of folks don't realize that heavy braking uses more fuel - not because of the brakes but because they were burning more fuel going too fast just before the brakes were used. So hard acceleration then hard braking uses a lot more fuel than anticipating the traffic and lifting off the throttle early.
  • Correct the timing. See our Timing procedure.
  • Use the proper carburetor for you configuration. For example, The stock 34PICT/3 carburetor on a 1600cc engine (or up to a 1776cc engine for that matter) will get you better economy than a pair of Kadrons, but it won't give you as much power.
  • Overhaul the carburetor. A blocked carburetor (the car will run poorly too). A thorough carburetor overhaul will correct this problem. See our 34PICT Carburetor Overhaul procedure.

    If you have the larger 34PICT/3 carburetor, you can improve fuel economy by using the smaller H30/31 carburetor (or the older 30PICT/2). This reduces hp by 2-3 (not much) but does improve fuel mileage. This carburetor is an easy fit on the 1600cc manifold - there is a 30/34 adaptor plate for it which you can get at any VW shop (and they come in the box with each new H30/31). Most folks report about 25-26 mpg US for the stock 1600cc Bug with the 34PICT/3 carburetor, but I get about 28-29 mpg US with my '68 Bug which has a 1600cc dual-port engine running the older 30PICT/2 carburetor.

    DON'T use the earlier 30PICT/1 carburetor with a 1600cc engine - the /2 version has a power jet which is missing on the /1 version, and the larger capacity (the 30 series was designed for 1300-1500cc engines) NEEDS the power jet to prevent the mixture going over-lean at higher speeds and overheating your engine.

    Jetting in the smaller carburetor needs to be altered to suit the larger 1600cc engine, but it's not hard.

  • Installation of electronic ignition will result in a nice mileage jump. Electronic ignition will give a hotter spark and the timing is more stable, so fuel burn is more even and complete. Most folks report an improvement of 8 to 15 percent in their gas mileage. And the car will run better! That's because you’ll get rid of points-bounce and shaft-jitter and incomplete combustion at higher rpms. Plus it will start better. A LOT better.

    Contrary to popular "wisdom", however, you are not going to get a huge power increase with electronic ignition. You WILL get a lower-maintenance tuning (unless you love adjusting points and timing), which gives rock-steady ignition timing under all conditions.

  • Take the necessary steps to correct poor compression, which is usually caused by worn out piston rings or burned valves. See our Compression Check procedure.

    With a good 1600cc engine, you should get about 130 psi or more for each cylinder. As the engine ages, the compression slowly drops, until one or more cylinders are under 100 psi, then the engine needs a rebuild. With poor compression the engine will still run okay, but power will be down and fuel consumption rises very fast.

  • Don't use oxygenated fuel (e.g., "gasohol"). The use of oxygenated fuel will result in higher fuel consumption because the additive results in less "fuel" in the fuel. If you use gasohol, for instance (ethanol additive) you will need a larger main jet to bring the fuel/air mixture is closer to ideal. Using gasohol with a normal 127.5 main jet makes the engine run lean and hot. 10% alcohol/ethanol blend needs a 132.5 main jet.
  • Altitude also affects fuel economy - higher altitude causes use of more fuel because the engine is less efficient at higher altitudes, even when the carburetor is adjusted for the height above sea level. For each 5000 feet in altitude the engine runs about 2 percent rich, so you need a smaller main jet, down from 127.5 to 125 for example. If you live at 5000-foot altitude and use alcohol blend fuel, you will need a main jet that is one size smaller for the altitude (127.5 to 125) but two sizes larger for 10% alcohol blend fuel. The net result is one size larger overall (130 size).
  • Another way to increase gas mileage would be to reduce the engine capacity. The stock 1200cc engines should give about 33 mpg US, the 1300cc about 31 mpg and the 1500 about 29-30 mpg. Of course the increasing weight of the later bugs has an effect but you can't do much about that unless you strip the interior or something like that.

    For information, the 1300cc and 1500cc piston/cylinders will fit straight into the 1600cc case, so that change is easy. But if you use the same heads the compression ratio will drop with the smaller cylinders, since it's squeezing a smaller cylinder volume into the same sized head space. If you don't mind the lower compression, you can use a lower octane fuel and save a little money there too. Otherwise you need to get the appropriate heads for the 1300cc or 1500cc to keep the stock compression ratio.

    Leave the larger 1600cc doghouse cooler/fan on the engine though, even though it blows about 10% more air than the 1300/1500cc cooling system. The doghouse cooler works very well and stops any problems with overheating of #3 cylinder, which occasionally resulted from the older style cooling - it's no good trying to save fuel if it ends up with a cooked #3 exhaust valve.

  • Improve the aerodynamics. A front air dam will probably improve the aerodynamics a little, but mostly at higher speeds (from about 50 mph upwards). It will also reduce the effect of the front of the car "going light" at higher speeds, for better handling. The shape of the Bug from the side is like a fat wing, which reduces the air flowing under the car and reduces the aerodynamic lift as the speed increases. Since increasing lift also increases drag (I used to fly aircraft so I know about lift and drag), reducing drag saves a little fuel.
  • Mountains use more fuel than flat country.
  • Fat tyres use more fuel than the stock skinnys.

~~~

Dave reported to Rob - I was delighted when I first learned that my '73 Super Beetle (1600cc dual-port engine) was pushing 30 miles per gallon (36 per Imperial gallon). We got 29.1 mpg on the trip to Utah.

Rob responded - That is excellent fuel economy, especially considering that the Super is a little heavier, which counts against it fuel-wise. Most folks in the U.S. report 26-27 mpg as good. My '70 Bug used to get 36 mpg (Imperial gallon) overall, and almost 40 mpg on a trip at 60 mph.

I occasionally ran my Bug dry just to see how far it would go -- 320 miles on 10.6 U.S. gallons (30.2 miles per U.S. gallon). Once I tried driving very sedately on a whole tankful and got 350 miles -- 33 miles per U.S. gallon. That was before the became a 1600cc, though the fuel economy was still very good then -- it only dropped a mile or two.

 

* * * * *

 

 

 

 
 
Design by Erin