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Originally submitted by T:

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Shows the auxilliary fan fitted in front of the radiator. These fans are impedence protected so they don't blow the fuse if they get jammed. Click to Enlargen.

Driving Style:

Excessive Power:

A Driver's style can have a beneficial or negative affect on the fuel economy of a vehicle. Applying excessive power can result in excessive braking which not only burns up fuel needlessly but burns up brakes and tyres faster as well.

How You Drive:

Best economy in a Manual Gearbox Car comes from changing up to the next gear early and flooring it. Avoid revving out. Constantly changing lanes in peak hour traffic is likely to double fuel burn (Catalyst ABC TV). Repeatedly opening the throttle when accelerating into the adjacent lane burns up more fuel than sitting idling and waiting for the blocked lane to move.

When You Drive:

Peak hour traffic reduces the fuel economy in any car because standing idling burns up fuel without taking the car anywhere. Avoiding Peak Hour can pay dividends. The best economy occurs in top gear because the vehicle moves the furthest for each drop of fuel burned.


Avoid leaving objects in the car that will take extra power to move them. The less weight the engine has to move, the less fuel wil be burned making the car move.

Performance, Economy and Efficiency:


Improving the efficiency of a car will simultaneously improve both its economy and its performance. An example would be fitting alloy wheels. These will reduce the amount of mass the car has to accelerate and stop. The improvement in the vehicle's efficiency will mean better acceleration, top speed and a reduced fuel burn.


Improving only the economy of a vehicle will impact its performance. An example would be to fit a small and under-powered engine to the vehicle. The fuel burn will be less, but so will be the top speed and the acceleration.


Improving only the performance of a vehicle will make it accelerate faster and have a higher top speed, but it will come at the expense of economy. An example would be to fit a more powerful engine to the vehicle without changing the gearing to suit.


Poor State of Tune:

If a car has a dirty airfilter and plugs that are burned down it will take more petrol to make the vehicle perform the same work. That means the fuel economy will suffer.

Engine Efficiency:

Old Holdens were shipped with devices that made them affordable and suited to the conditions of their years of manufacture. Since the roads these cars are travelling on have changed significantly there are changes that can be made to the cars to keep them in step with the newer cars that are appearing on the roads around them. Improving the effiency of an engine means more power is available to the road wheels from the same quantity of fuel.


While the ignitions fitted to old Holdens were traditionally the equal or better than many international cars at the time, these ignitions pale in efficiency compared to later ignition units.
Tests have shown that  the more spark energy that goes into the cylinder the more power the engine will produce and the better the efficiency of the engine will become. Exhaust emissions will reduce as well.
Aero engines carry Dual Ignition systems that spark two plugs in each cylinder. Turning either magneto off causes the engine RPM to drop and there is a noticable loss in power.

High Energy Ignition:

The HEI system uses a transistor to switch the coil primary current. In distributor based Holden HEI's, the spark-plug gap is 1.5 mm.
There are further Ignition details here.

Spark Plug Indexing:

Positioning each Spark Plug so that it's Ground Electrode is favourably positioned provides more efficient combustion. That means more power from the same charge. Thanks to Rosco1 for this info.Spark Plug Indexing


"Keep a level head and plan this out"
Submitted by lovemyholden on Wed, 21/12/2005 - 23:35.
Since I was 18 (about 20 years ago) and in the position you're in now I've tried many combinations of carbie/cam/exhaust on the good old Holden six. What you end up with will depend on what you use the car for. If it's a daily driver (and I suspect it is, because you mention the fuel economy issue)then you should go more conservative. Also if it is an auto then again don't go big carb or cam because you'll turn your beloved Holden into a stumbling mess. Auto's need good torque down low to launch smartly from the line.
Either way consider the following. If you want a Holley Then the Holley 320 Economaster is a good Holley to try, rather than the 350. It has slightly smaller throttles giving faster airflow on smaller engines, which helps keep low end torque. Remember these carbs have BOTH barrels open together and can be a bit heavier on fuel. Cold starting is fair but the engine will hesitate a bit until it warms up.
The XF Weber is not a bad idea it is two barrels but is a progressive carbie meaning one barrel opens first to about 70% before linkage starts to open the second barrel. Economy is better because of higher air flow in the primary gives better atomization of fuel. Note this higher air flow can produce a noticable whistling induction sound at idle. (Not a problem with a decent enclosed air cleaner). Good cold starting characteristics too.
I wouldn't do the WW stromie unless you know it's off a 186 because this carb was also fitted to the 253 V8. If you put it on your six it will need rejetting and air bleeds changing too, if it's going to be any good. To be honest ANY carb change if it's going to be a complete success and run to it's best ability once you've got it on and running resonably take it to a specalist carb tuning place and they can dial in the correct jetting and idle mixtures.
As for exhausts 2 inch no more is needed, after that they just get noisier and boomier. Extractors if you like, but the standard manifold is ok and a bit quieter too. When it's all said and done though the single stromie was probably the best choice at the time when Holden produced your car. I've never found a better carbie for cold starting, low down torque, overall drivability, serviceability, and economy. (The VB Commmodore still ran a single stromie but it had a larger bore, grab a carb and manifold off one of those if you like).
Hope this helps mate!!


Jacks has written a brilliant page on LPG .

Electric Fans:

As mentioned under "Cooling" at the Main Page, electric fans have their advantages. Mechanical fans turn all the time. They load the engine all the time and load the engine the most when no fan is needed at all, like when the car is cruising at 100kph. Since it takes energy to turn mechanical fans, they cause the engine to heat up which means the fan needs to turn more to compensate for its own load and unnecessary fuel gets burnt.
The position of a fan is important too. See
Fan Positioning
A rigid bladed mechanical fan turns the slowest when it is needed the most and the fastest when it isn't needed at all. Fitting electric fans to an old Holden will produce an improvement in engine efficiency since the cooling fan only turns on when it is needed. The engine will be quieter, rev up more easily and burn less fuel. Electric fans can be set up to pass the ideal amount of air over the radiator when it is most needed.

Fan Braking:

Connecting the Electric Cooling Fans to the Brake Light Switch can show efficiency gains.
Click here.

Compressor Braking:

Wiring the Air Conditioning Compressor so that it comes on with the brakes will provide an efficiency gain too. The wiring should activate the Compressor whenever the brakes are applied and the air Conditioner is in the "on" position.

Thermostatic Fans:

These are mechanical fans which are driven by a thermo-sensitve hub. The hub has a high and low speed typically 1100 and 2300 RPM with the high speed being activated when the radiator temperature is highest. The fan hub exists in the airflow from the radiator and responds to the temperature  of the air blowing past it. These do provide an improvement in efficiency over rigid bladed fans but are not as efficient as electic fans.

Spark Advance:

The degree of spark advance generated by the ignition will effect the engine's efficiency. Too little advance and the engine will lose power by blowing it out the exhaust system. Too much advance and the engine will lose power by igniting the mixture too soon and causing the pistons to be blown back against the connecting rods. The ideal amount of advance for any given situation causes maximum cylinder pressure to occur at approximately 20 degrees after TDC, regardless of speed or load. Some very modern ignition systems use a technique called "ion sensing" where a small current through the plug gap is used to measure cylinder pressure vs time after the flame has gone out. This is then fed back to the computer to maintain the magical 20 deg ATDC max pressure figure.

Weber Conversion:

Changing the carburettor can improve performance and econmy.
Weber Conversion.

Vehicle Efficiency:

Improving the efficiency of a vehicle will improve both its performance and economy.

Tyre Pressure:

Tyre pressure is related to the temperature of the day.
If the air temperature goes down, the tyre pressue will go down. Low tyre pressure eats into fuel economy as well as wearing out tyres.


Any items that stick into the air-stream will generate drag and make it more difficult
for the engine to push the car through the air.
In some cases having all the windows open produces more load on the engine than the Air-Conditioner. Experiments have been done on windows vs air-con. Basically, if doing more than 80km/h use air-con.
In the US they proved that a Ute with the Tailgate up will produce less drag on the vehicle than if the Tailgate is down.
Fitting a Tonneau cover reduces drag even more.

Diff Ratio:

Many old Holdens were shipped with diff ratios that were ideal for the time. Suburban traffic was mostly 35 mph and stopping at traffic lights. In Melbourne at least, freeways were virtually non-existent till the late 1960's.
Nick-named "Manual Automatics" old Holdens were a revelation when they first
appeared because of their ability to remain in top gear for so much of the time.
This appealing flexibility in top gear was determined by the final drive ratio or differential
ratio. Because this was a big selling point, Holden stuck to the idea. The winding single carriage roads these cars were made for made them a breeze to drive.
Now that so many of these roads have been replaced with expressways the original
gearing is no longer appropriate. The original gearing leaves the car carrying too
many RPM for the road speed. Consequently the car needlessly burns up a lot of fuel
and can run out of revs. Old Holdens are remarkably modular, meaning that many parts are interchangable.
There are a number of diff ratios that can be fitted which will improve the vehicle's
efficiency. The ratios are all listed on the main page.


Clearly the exhaust system of a car can play a big part in its efficiency.
While not for everybody, I have preferred crushing down the end of the tail-pipe in my cars.
It gives good low end torque, easy takeoff from the lights and improved fuel economy around town. I also point out that I use Trimatics coupled to tall diffs.
On the open road the performance is still fine for the legal speed ranges.

Alloy Wheels:

The reduction in mass of alloy wheels means the car takes less effort to accelerate, stop
and change direction. Because the engine has less work to do it requires less fuel to do the same task resulting
in an improvement in economy.

Power Economy Switch:

If the vehicle is fitted with a Trimatic gearbox that has electric kickdown an improvement in efficiency (and therefore economy) can be achieved by fitting a Power/Economy switch.
Further Details here .


When Cars age, the underbonnet Wiring becomes hard from Heat Exposure. As a result the Wires don't carry Current as well as they did when the Car was new. That means Voltage is lost by the Wire. Poor Wiring can be just as detrimental to Economy as the need for a tuneup.  Replacing the Alternator Feed, Primary Feed and Chassis Ground Cables with Wire that is rated to take the necessary Current will make sure the Ignition and any ECU gets the proper Voltage. Thermo Fans will then spin at the proper Rate so they will turn off sooner and the Battey will receive a proper Charge. The Ignition will get the correct Voltage and that will improve the Fuel Economy and Performance.

Economy Improvements:

253 - An Efficiency Oddessy:

Submitted by krangle on Fri, 30/12/2005 - 22:15. 253 | Engine | HZ | Modifications.
I've just finished the last of the tweaks to my 253. In a pretty short period of time I've exchanged the WW Stromberg for a near new Quadrajet, built a Cold Air Intake, removed the Clutch Fan and replaced with twin 12" thermos, added Electronic Ignition and an Electric Water Pump.
Power output is now a tad over 120kW at the Rear Wheels but the really satisfying part is how the motor wants to rev and the power delivery. You can really notice that there are fewer things to "accelerate" - I suppose its like the effect of lightening the Flywheel. Not having the Clutch Fan and the Water Pump combined with how well the 4-barrel Manifold and Quaddie flows on a 253 really turns a torquy motor into a little screamer.
I'd love to know what the Fuel Economy is like if driven sensibly but everytime I take it for a spin I can't help putting the foot to the floor! As the revs build it just pulls harder and harder. It just doesn't let up until its time to change gear (about 4800 is where peak HP's at). Even if you hold a gear a bit longer and use some of the over-rev you don't feel much of a loss of acceleration.
Basically I'm pretty bloody happy and would recommend these mods to anyone whose 253 feels a little "choked".

Economy Tests Involving an HZ Kingswood Wagon 202 Trimatic and Different Diff Ratios:

These tests were conducted by T over a period of years with several of these journeys made
with each diff.
Road type:
= Combination Highway and City.
Diff type:
= Banjo unlimited slip
Wheel and tyre combination:
= Standard 14" rims, 195/75 SR14 Tyres.
3.55:1; Original Diff
3.36:1; Fuel Consumption fell by 25% (of the original 3.55 diff fuel burn)
3.08:1; Fuel Consumption fell by another 25% (of the original 3.55 diff fuel burn)
2.78:1; Fuel Consumption fell by another 12.5% (of the original 3.55 diff fuel burn)
I've altered these details from the original post. Since I can't uncover the distance
involved I've chosen to publish the percentage drop in fuel burn instead.
VN V6's, 2 Litre Camry's and Throttle Body Injected EA 3.9 Falcon's delivered fuel burn figures very close to that of the 2.78 diff's figures on the same journey.


Alternatr Feed, Primary Feed, Chassis Ground info



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