Mention Corolla and engine conversion in the same sentence and you'll be hit with two kinds of people. Those who like the five-valve-per-cylinder 20-valve engine and those who prefer to do it with a four-valve-per-cylinder supercharged motor. These 1.6-litre Jap-import engines fit into Aussie Corolla engine bays like a hand in a well-worn glove and are proving extremely popular with the factory 86KW brigade who want an advantage over the later 100kW versions. Add an air filter and an exhaust system and there's even more power for the offering.

First, to add some confusion, there are two versions of the 20-valve 4A-GE engine: in 119 or 126kW versions, while the supercharged 4A-GZE engine produces 130kW.

So which is the better way to go, a 20-valve naturally aspirated; or a 16-valve supercharged motor? We got examples of each and compared them.

David Allanach and Vince Bombardiero both kindly donated their near-identical spec' Corolla SXs, coincidentally red, for us to use for this comparo. David has a 20-valve 4A-GE with the factory extractors, an air filter setup, an upgraded clutch and the 20-valve five-speed gearbox.

Vince has the 4A-GZE, installed by BD4's Motorsport, with an LSD fitted to the factory "normally-aspirated" gearbox. At the time of the shoot, Vince also had TRD wrapped extractors and an air filter set-up.

COST AND AVAILABILITY

We contacted one Sydney's major engine importers, SSS Automotive, for costings for both conversions. The 4A-GZE comes complete with factory computer, wiring harness, intercooler and air-flow meter for $2000. SSS recommends that for an AE82 Corolla, rein either the standard gearbox, or preferably use a 20-valve gearbox as the 4A-GZE gearbox will require body modifications to make it fit. A 20-vahre gearbox with drivetrain and struts comes complete for $600. If you are using an AE92 or an AE100 Corolla, then you can buy the complete engine and a 4A-GZE gearbox package for $2500.

As mentioned earlier, there are two different 20-vahre motors. The earlier model from the AE101 Corolla has a silver valve cover, which puts out 119KW, or the current model AE111 motor has a black valve cover and puts out 126kW.

The AE101 comes complete with all the electronics for $2300, with the gearbox package Listed above again $600.

The AE111 with engine and wiring is $3000. The extra cost is due to the freshness of the engine. At the time of writing SSS hadn't had one of these engines with more than 18,000km on it, with several under 10,000km. This engine is map sensed as opposed to an air flow meter, the internal rods and the flywheel are lighter, it has bigger throttle bodies and larger exhaust ports helping produce the extra seven kilowatts over the previous model. The AE111 also has option of a six-speed gearbox, which, complete with linkages and stick, comes as a conversion package for $4000.

SSS has a fairly regular turnover of both the supercharged and 20-valve motors, so the delay in obtaining either would be a couple of weeks at the most, if any. These prices are only a guide, but would be fairly indicative of what you can expect to pay around the country.

INSURANCE

It always helps to know the insurance consequences of any engine conversion, so we rang the NRMA to get an idea on insurance prices, and we were expecting the 4A-GZE to lose out badly on account of the supercharger. But they actually came out even. The NRMA rejected both engines, saying that it wouldn't insure either.They suggested ringing Shannons, or another specialist modified vehicle insurer such as Vigil, Dawes or Torque, who would evaluate each car and driver individually.

EASE OF IMPLANTING & MODIFICATIONS REQUIRED

According to BD4's, which has done several implants of each, the actual conversion process is fairly straight-forward. Use the original gearbox so only the driver's side engine mount may need to be modified to make either engine fit.

Prior to installation, the timing belt should be replaced and the injectors should be cleaned - for peace of mind.

However, for the 4A-GZE, the front engine mount should be Nolathaned to help prevent the engine moving. Ideally, a bonnet vent should be fitted for air-flow to the intercooler.

With both engines the clutch should be upgraded with a heavier pressure plate and, from BD4's experience, an organic clutch plate for the 20-valve and a brass button for the supercharged.

Both being 1 6-litres, generally an engineer's inspection isn't required, but it's a good idea to consult one anyway, because of each state's specific requirements.

POWER DELIVERY & CHARACTERISTICS

The 20-valve has quite a smooth, revvy power delivery, much like a VTEC, and is very user friendly. The 4A-GZE is more like a small-capacity turbo engine without the lag. It has a lot of torque and can break traction fairly easily, especially in the wet, due to its instant power response courtesy of the supercharger. This does make it a little annoying in day-to-day traffic, but it is much quicker from a standing start. Once the 4A-GZE hits around 5500rpm however, the power tapers off, whereas the 20-valve, while a little slower to wind up, will quite happily rev beyond 8000rpm.

RELIABILITY

Reliability-wise, both engines are very strong and, if properly installed and maintained, shouldn't give any major problems with the standard settings. Naturally, once boost or performance is increased, reliability will suffer, but Toyota traditionally makes strong engines.

AVAILABILITY OF & RESPONSE TO MODIFICATION PARTS

Both engines will respond well to the usual air filter and exhaust mods. A cold-air induction system will benefit the supercharged engine more, to compensate for the heating effect of the compressor.

With three incarnations of the supercharged engine, fitting a bigger air flow meter to the earlier two versions will provide a decent power gain. With only a cast manifold provided in standard trim, extractors would be a useful mod for the 4A-GZE.Camshafts are a good idea for an improved top-end, while larger pulleys also provide a boost gain. BD4's has a regular stock of modification parts for these engines.

The 20-valve came with an excellent extractor set-up as standard, with tuned length secondaries which have twin flexes in them. Otherwise the 20-valve runs pretty well standard, and, other than exhaust and filter mods, the next step for any worthwhile gain is internal engine modifications such as pistons and porting.

So what'll it be: supercharged or 20-valve? The 20-valve seems to offer a mild power upgrade, the engine looks very neat and as we've seen in the past, looks great in older cars. If performance is your desire, it's hard to go past forced induction and, although the supercharged engine is an older design, it not only has more power in standard trim, it has a lot more scope for improvement. If the decision of faith is still unclear, consult advice from a convert.

NOTE: this artical came from a Fast fours & Rotaries magazine from Australia. the october 98 issue.