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MIGClub Member
14,789 Posts
Discussion Starter · #1 ·
Before you tune anything read this.

Many of these engines no longer have the power they once had. The engine internals are very robust and usually wear well with age. The main restrictions caused by age is in the fuel and air inlets. The follow relates mainly to injection cars, but many points are still valid.

To regain the engine original power, follow these steps:

Remove the plunum box when the engine is warm and spray loads of carb cleaner (or similar product such as 10k Boost) into the inlet. Leave it for a while to penetrate then start the engine. The more smoke that comes out the better, as this means loads of crap is getting out. With the engine still running spray more carb cleaner, at the same time as revving the engine. When you are satisfied that no more is being cleaned out turn the engine off. Manually clean all internal parts that are accessible being careful not to let anything fall into the inlet. At this point replace the air filter.

Now remove the idle control valve and give that a good clean with carb cleaner. When the valve is removed you will find that it is in the closed position. To open the valve, connect the two pins on the plug to the battery.

Replace the spark plugs and HT leads with good quality items such as Champion. Check the coil is giving a good amount of power, do this by having it checked at your local Bosche dealer. Check the distributor cap and rotor arm, if these look over worn replace them.

Next you will need to have the injectors professionally cleaned. This typically costs £15 per injector. The difference this makes, especially on high mileage engines is surprising.

If you have a high performance engine, try to use Super unleaded and check that the octane plug is set to 1 (or A on the C20XE engine). Try using a cleaning additive such as Redex regularly as this will limit the further build up of deposits on the injectors. It may also be a good idea to change the fuel filter, which is located behind the drivers side rear wheel next to the fuel pump.

Do an oil change making sure the old oil is flushed out and change the oil filter. Use a good semi or fully synthetic oil with about a 15W40 rating.

Now you need to reset the ECU, do this by disconnecting the battery for at least 1 hour, it is suggested that you do this whenever any changes are made to the engine. With all this done on a typical untouched 100k mile 20XE engine will gain around 15bhp+ and will greatly improve driveability and fuel consumption.

Tips and Tricks

16 valve engines like to be rev'ved, so rev them! Many people complain that they can get power out of their 16v engine, I later discover that they are changing gear at 5500rpm!

If you own a car registered before August 1993 and you have a catalytic converter, you may remove it and fit a cat replacement pipe. This should give another 5bhp.

Remove the air box that contains the filter and drill or cut larger holes on the underside and the side against the inner wing to allow a greater flow of air.

There is usually a small air box fitted behind the front bumper, remove this leaving the rubber pipe connected to the main air box. If the air dam behind the number plate is blocked off, as with the MK2 Astra GTE and Mk3 Cavalier GSi, remove this and route large bore ducting from a cold air source (such as behind the front bumper) to the inlet of the air box. Remember the colder the air the denser it is, which equals more fuel and more power.

Try to get hold of a purple octane plug as this increases performance by fooling the ECU into thinking that a different fuel type is being used. This can result in bad economy and high emissions, but take 5 seconds to change to the old plug if desired.

Fill the car with Super Unleaded fuel, preferably Texaco or BP (Shell Super does not seem to be quite as good for with regard to power) and reset the ECU. The Bosche ECU learns as it goes, so making it learn with a higher octane fuel will increase the power of your engine.

Remove the under bonnet "carpet" to allow the engine to breathe more easily.

If you own an Astra GTE or GSi, remove the black plastic bits connected to the under side of the bonnet vents. This allows hot air to escape from the engine bay quicker and pulls more cool air in through the front.

Running the engine cooler can increase power but with reduced economy. To run the engine cooler try using a coolant additive such as Redline Water Wetter or drill small holes in the thermostat (not recommended). Cool running thermostats are available from many motorsport and tuning shops. One way to get one cheap is to go to a Vauxhall Dealer and buy an Australian or South African thermostat which is fully open at about 10 degrees lower than the UK one. Running the engine cooler can also safeguard the head from going porous.
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