Following wheels and tyres, the next priorities in modifying your car to make it perform better are suspension and brakes, again before you touch the engine. You will find that with more cornering power at your disposal, your point-to-point times will be quicker anyway, as cornering speeds will begin to be limited only by visibility, by the need to retain the vital ability to stop safely within the distance you can see to be clear.
You will also find that a car with better suspension control is more comfortable to ride in as it does not roll so much in corners or give that uncomfortable wallowing sensation when driving on bumpy roads. Again, you can go too far. A car that is made too stiff in its suspension settings can be most uncomfortable. It is jiggly, you can leave the seat over big bumps and you will have less traction in bumpy corners as the car takes off over undulations. And it is skittish in the wet.
Ride and handling are thus a compromise, and VW in fact set a very high standard with the stock fuel-injected cars. The Mk1 cars are slightly under-damped and prone to rock-roll slightly in fast bumpy bends but the Mk2 car is superb straight out of the box. That is not to say that the Mk2 GTI cannot be improved. Far from it. To understand fully how the various suspension tweaks improve a car’s handling, let us look at the forces acting on a car when it is driven on the road or track.
Roll: a by-product of cornering, roll takes place along the longitudinal axis and in a softly sprung vehicle tries to lean the car excessively to the detriment of comfort and cornering ability. The more a car rolls, the greater the slip angles of the tyres and the less of the useful tread area is doing work. The primary component that will reduce this condition is the anti-roll bar, or swaybar as it is called in America.
Pitch: occurs on the transverse rotational axis and causes a car to dive under braking or squat under acceleration. In the absence of anti-dive, anti-squat geometry being designed into the suspension by angling the lower arm locating points, the springs and dampers play the major role in reducing the amount of pitch. Good progressive suspension prevents harsh oscillations.
Yaw: a force that provokes body motion around the vertical axis, yaw affects all the suspension components. In an ideal situation, a vehicle’s suspension should provide completely neutral handling, but most cars are designed to provide mild understeer which allows the front of the car to go wide in corners. This is a safe characteristic to keep the average driver from getting into trouble especially when braking or suddenly decelerating in a bend where a neutral vehicle could then move into oversteer and perhaps spin. If you stiffen just one end of the car at a time, you can induce severe yaw conditions; stiffening the rear induces oversteer while stiffening the front only creates understeer. Suspension development is very much a question of balance.
Modifications: to save customers a lot of time and trouble, aftermarket suspension manufacturers have developed kits for various cars providing just uprated springs, or dampers, or matching springs and dampers (which is better), as well as upgraded anti-roll bar kits to be used with the stock suspension or in conjunction with the spring and damper kits. The European manufacturers, like Bilstein, Koni, Sachs, Spax and others, favour the spring and damper kit approach while the Americans, with a more conversion-orientated custom-car background, tend to go the whole hog with upgraded anti-roll bar kits and better quality locating bushes as well.
Bushes locate suspension components to prevent metal-to-metal contact and provide isolation from road shock and noise. They are used in all moving components in the suspension and steering in modern cars and if a manufacturer is over-generous with these rubber bushes, the car can feel rubbery in its handling and ride. Too much lateral movement in suspension bushes does not help accurate suspension location and makes a car feel woolly in corners. Conversely, the metal or metal and nylon rose joints used in racing suspension are too hard and direct for road use and would destroy themselves in short order. Upgraded high-quality road-car bushes made of polyurethane, like the AutoTech ones, will keep the suspension components in check while maintaining adequate comfort. Polyurethane steering bushes will sharpen up the GTI’s steering, which has a slightly dead feel about the straight-ahead position.
AutoTech in California are US distributors for Hor Technologie parts. Hor are an original-equipment manufacturer who supply suspension, exhaust and other components to German car makers like BMW and VAG but who do their own range of aftermarket parts too. AutoTech are also agents for the excellent Japanese-made Tokico adjustable shock absorbers which match up well with Hor springs. The UK agents are Steiner Engineering.
Amongst the European suspension manufacturers, you will find that each of the kits you can buy has different characteristics and so will please customers looking for different kinds of performance. The Koni suspension has adjust-ability of damper settings as its strength. You can raise and lower the rear spring pans to adjust ride height and the dampers can be tailored from soft to fairly hard settings if you want to commute in the week and then do club events at the weekend. Koni now have another damper design with a semi-active electronically controlled system – the normal kit is user-adjustable from the shock towers.
The Bilstein Sportpak was the first kit on the market for the original GTI and gives a firm ride but brilliant handling. It may be too firm for those who live near less-than-smooth roads, and the gas filled dampers are not adjustable. The kit for the Mk2 is more supple and was the last of the three Europeans to appear.
While Sachs were last on the scene with the Mk1 GTI kit, they were at the head of the queue with the Mk2. Their Mk1 kit strikes a good comfort/handling balance for most people but may still be too soft for really press-on drivers. The Sachs Mk2 kit, on the other hand, is well-nigh perfect, with very little comfort lost over the standard suspension, and it also gives very progressive handling on the limit. All these kits lower the ride height by about an inch which helps stability.
It is not unusual for road testers in different countries to form slightly different opinions of a given car, especially in ride and handling terms. There are several reasons for this, not least of which is that suspension settings are in fact often tailored to the country of destination. The Americans like a softer-riding car despite the good quality of their roads and enthusiasts then complain that the car does not handle properly. Grip and tyre noise are affected by the content of the road surface and this varies from country to country. Thus, a Pirelli P6 manufactured in the UK for local use may turn out to be different from one made at Pirelli’s German factory or indeed one made in the home market of Italy. Suspension, wheel and tyre tuning must thus be done for local conditions and, on that score, companies like Automotive Performance Systems (APS) in California specify different damper settings for their Bilstein kits from those that you would find in Europe. By the same token, a German-bought set might prove a touch hard for use in the LK. Caveat emptor…
Anti-roll bars: the suspension design of the Golf and Golf-derived cars allows the inside rear wheel to pick up under hard cornering. While this is safe in practice, it is indicative of a very severe roll attitude. The solution is to increase the roll stiffness of the chassis without affecting suspension travel and thus ride comfort adversely. The AutoTech front anti-roll bar is a direct replacement for the factory original and comes with all the fitting hardware. The rear factory bar is part of the torsion beam assembly and thus upgrading it means adding an additional external bar. Such an external bar will have different pivot points from the torsion beam and, once the beam is deflected, this would cause the anti-roll bar to push or pull the end of the beam out of alignment. AutoTech’s rear bars use a clever sliding end design to allow the beam to move properly and yet be usefully acted on by the anti-roll bar.
Stressbars: when a car is cornered hard, the forces produced by the act of the tyres gripping the road transmit high loadings back through the suspension to the monocoque bodyshell. Even though the mounting points are reinforced, the shell still deflects. A hatchback car with its large rear aperture is less rigid than a saloon, a convertible potentially even worse. When the shell deflects, it affects the suspension geometry, the accuracy of which is vital for good handling and grip. The Golf Mk1 shell is much less rigid than the Mk2 and the Cabriolet even weaker despite substantial bracing to compensate for the loss of the roof. The Cabriolet also has a higher centre of gravity and so benefits even more from suspension bracing and uprating.
The weakest point of the Mk1 chassis is the lower front and the car benefits tremendously from a lower brace to stabilize the lower wishbone mountings. This has been done in more than one way by various manufacturers. The normal after-market European brace is a single bar which attaches to the front joints of both lower wishbones via the retaining bolts and then has two further bolts which attach it to the floorpan. Realising the weakness of the chassis, the factory developed a similar brace for the Scirocco 16Y and this used a wholly tubular design with four mounting points which did the same job. Techtonics market a brace for the Mk1 cars which they admit is a direct copy of this.
The most comprehensive lower strut brace is the triangulated, fully adjustable one from AutoTech which is really a subframe. This connects the front and rear mounting points of the lower wishbones for maximum bracing and is then triangulated between front and rear bars. It is fully adjustable to take in the production tolerances of individual cars.
A lower brace is more effective than an upper one on all Mk1 floorpan cars, i.e. Golf 1, Scirocco 1 and 2 and Jetta, but an upper shock tower brace is icing on the cake. The improvement in turn-in and cornering stability is instantly felt with the lower brace and steering becomes more positive. In the long term, the continuous loadings on the suspension strut towers weaken a car’s structure. The upper stressbar helps to prevent this fatigue and staves off squeaks and rattles in higher-mileage cars. The Mk2 has a rigid front subframe from the factory- and only needs a top stressbar.
As the rear torsion beam twists, so the loadings are transmitted to the bodyshell. A simple adjustable bar can be used to join the tops of the towers and this is easily removed when you need to use the car’s full luggage earning capacity. For more serious high-speed work, a multi-link triangulated set up is available from APS (Neuspeed) which has permanent fixtures in the bodywork via aircraft type Nutserts. The crossbrace, however, can still be removed.
For owners of right-hand-drive Golf, Jetta and Scirocco cars with the Mk1 floorpan, brakes are rather a sore point. Because RHD was something of an afterthought, RHD cars retained their brake servo on the left-hand side of the bulkhead and the pedal action was transmitted via a bell crank linkage system with no less than eleven pivot points! This was somewhat less effective than the system used by Ford with their Escort or by BMW in their contemporary cars, and left VW owners with a rather dead-feeling pedal and brakes that seemed inadequate for the car’s performance. Although you could take up the slack in the linkage, it soon loosened again and you would end up adjusting it every three months or so. Various solutions to the problem were tried. GTI Engineering would tighten up the linkage and fit Mintex M171 racing pads in the early days. This offered some improvement but the linkage would loosen with time and the racing pads, while they worked well when cold, unlike the Ferodo DS11s , would glaze-up easily in slow driving, made dreadful graunching noises when used hard and inevitably wore out the standard discs more quickly. At one point, GTI Engineering even tried grafting Ford Granada discs onto the Golf and these worked quite well but could only be used if you had 14in or larger diameter wheels fitted. It was also an expensive solution.
In 1985, the Italian brake manufacturer Tarox came on the scene with a replacement ventilated disc that was also slotted for better cooling and wear characteristics. With their own matching pads, this brake set worked very well and gave good stopping power, better pedal feel and superior fade characteristics. Tarox also make a set for the Mk2 Golf and, with the already satisfactory four disc Mk2 set-up, this gives a GTI exceptional braking ability.
Grafting the rear discs from a Mk2 onto an earlier car is not a straightforward task. The hubs are different for a start. If you can find a crashed Scirocco 16V, it is easier just to swop the rear axles and, of course, the brake proportioning valves have to be changed too.
While the initial idea was to get better pedal-feel and retardation by fitting larger discs to RHD cars, if LHD cars had satisfactory anchors with the same equipment, did it not make more sense to attack the problem at source? Autocavan certainly thought so and this British VW tuner sensibly brought out a stiffer, braced brake bar that fitted to the bulkhead and reduced the linkage pivot points to just two.
BR Motorsport’s Brian Ricketts came up with a large servo conversion kit that raised brake line pressure considerably and gave a vastly better pedal feel. He also developed a bigger disc conversion. With both these modifications in place, he effectively put paid to the old joke, ‘Why is a GTI like an Exocet? Because nothing will bloomin’ well stop it!’.
This did not mean that LHD markets were entirely happy with their brakes. When they uprated their engines, the American tuners sensibly looked for better stopping. AutoTech and APS offer big disc conversions for early and late GTI-based cars. Their latest kit uses the front discs from the G60 Corrado to stop the 170bhp turbocharged, supercharged or 2.0-litre cars they sell to clients. Buying a kit like this from these firms is very cost effective because not only do you get all the parts you need, and even Aeroquip braided hoses if you specify them, but, because of the quantities they buy from original equipment manufacturers, these tuners are able to offer the kits for about two-thirds the price you would pay if you assembled all the parts yourself from your local VW dealer.
The basic VW water-cooled single-overhead-camshaft engine has proven very amenable to tuning for more power and torque. It is a simple and strong engine, coupled to a very robust gearbox that is able to take the output of forced aspiration engines, unlike some competitors’ products which are more obviously built down to a price. The fact that the basic design started off as a 1.5-litre carburettor-equipped engine and has now ended up being taken to over 2 litres (albeit based on an evolution block) speaks volumes for the Tightness of the basic design. From a l,471cc 70bhp engine, over 200bhp has been extracted in road-going, naturally aspirated form and nearly 300bhp with nitrous oxide injection. Road-going forced aspiration engines give anything from 160bhp to 250bhp, with massive torque.
If anything, the VW engine starts off with one basic disadvantage; it does not have a crossflow head design on its eight-valve version. A crossflow head, where the intake and exhaust tracts are on opposite sides, is logical for optimum gas flow, but the eight-valve engine lacks this refinement. For all that, it gives no ground to its obvious competitors, and in smoothness, power and torque delivery, it was the class standard for many years. The increased efficiency of the Oettinger and VW factory 16-valve crossflow heads reaped immediate rewards in power and torque and it is this newer version of the same basic engine that will take the GTI-based cars into the 1990s.
Brian Ricketts of BR Motorsport was the former Engineering Director of GTI Engineering, and the first British engineer to do serious modi-fication work on the GTI back in 1977. According to Brian, the 1.6-litre engine was over-engineered for the task it had to perform. Not having done such a car before, VW erred on the side of strength. Brian remembers building a 182bhp car,
back in 1979, that revved to 8,500rpm. The internals had no special toughening or crank hardening. All that was done was a blueprint and balance. This car was a Group 2 European Saloon Car Championship runner. There are no particular major problems with the engine, says Brian, apart from the fact that, as they get older, some heads tend to crack between the valve seats. Sometimes blocks crack at the ends between the oil drain holes and head studs, but we are talking of massive mileages, between 80,000 and 100,000 miles. Of all the engines, the 110bhp 1.6 is potentially the most reliable because it is the simplest of the lot with the least moving parts.
The early 1.8-litre engines had head gasket problems but this was cured by changing the head bolt torque-down sequence. Valve guides on these engines could also give way at around 30,000 miles or less. The material was sub-sequently changed, and longer guides used to prevent the valves ‘walking about’ on the seats. Usually though, problems with GTI engines arc not failings of the engine but of ancillaries, especially those with electronic control systems. The 16-valve car is a favourite here as it can suffer from idle-stabilization circuit problems. Some-times these are erratic and hard to trace. In 1984 cars, the wiring for the idle-stabilization circuit was too short and, with engine movement under acceleration and braking, it tended to chafe where it went through the bulkhead.
The 1.6-litre GTI engine is identified by the EG code stamped on the block. The Mkl 1.8-litre engine is a DX, the Mk2 an EV and the Digifant injection cars are denoted by the PB mark. The 16-valve is the KR series.
When you open up the 1.6 and 1.8-litre engines, the chief difference you will notice is in the combustion chamber design. The 1.6 has a flat head with the combustion chambers wholly in the piston tops. This design is akin to the racing VW engines and is preferred by tuners. The 1.8-litre engine’s combustion chambers are shared by the head and the piston tops. The early Mk2 1.8-litre engines and then the 1984-onward DX engines in the Scirocco used air-shrouded injectors to clean up the idle mixture for smoother running, cleaner emissions and better fuel economy. These air-shrouded injectors gave better atomization and had idle air coming down the air rail when the throttle was closed. The air travelled through a bypass into the head which shut off as soon as the throttle was opened.
Another change around this time was the move from a direct oil-to-air oil cooler to a water-to-air one. The water-to-air oil cooler aids the initial heating of the engine oil with resultant shorter engine w arm up. This also meant that the engine could come off its cold-start cycle faster with a resultant reduction in emissions and fuel consumption.
In late 1985, eight-valve cars went over to hydraulic tappets which were in fact the same as those used on the Mercedes-Benz 190E 2.3-16 and later the Cosworth Sierra. With the valve spring platform sunk further into the head, these engines had shorter valves. In service, they work very well with an extremely low failure rate.
On the induction side of things, the change from DX to EV 1.8-litre engines was marked by a re-arrangement of the air-flow meter box to the other side of the engine. A larger air-filter (same size as the Ford Capri 2.8 injection) was used and the compound throttle body was changed from a 38/45mm unit to the Audi-type 38/52mm unit. The longer inlet tract gave it better torque characteristics to pull the now larger car, rather than going for greater horsepower.
When the 16-valve engine first came out, there were complaints that cars did not meet their performance claims. Early cars had 44mm diameter intake runners and the factor}” enlarged these to 50mm which improved matters somewhat. US-spec cars with their emission-controlled engines and 123bhp come with this smaller diameter manifold, so a quick power boost can be achieved by using the 50mm Euro manifold. It is not cheap however, and on the Corrado, the 44mm manifold is used again.
On the exhaust side, the factory cast iron manifold on 1.6 and early 1.8-litre engines is not badly restrictive. Careful machining can produce good flow improvements and a swop to a four-branch extractor may not be as significant as with some other manufacturers’ engines. One gaff the factory made with the early 16V engines was the horrible conical exhaust downpipe that was internally split in the middle 60mm down. For the 1986 model year, they reverted to the tw in down-pipe. The conical downpipes also suffered badly from cracking.
The cylinder head of the Digifant-equipped car is unchanged apart from the holes for the injectors which are smaller. In South Africa, a 2-litre version of the 16-valve engine has gone into production to make up for the power loss experienced at the high altitude on the reef. This 2-litre block was first put in the heavier Passat in Europe, with a catalytic convenor. In this form, it produces 136bhp at 5,800rpm and 1341b/ft of torque at 4,400rpm. Because there are not the same strict emission laws in South Africa as in Europe, the factory there has been able to tune the 2-litre engine for over 150bhp: in any case they cannot use the catalyst equipped G60 engine as there is no lead-free fuel available. As far as Europe is concerned, for the time being, such an engine would be too close in power output to the G60 cars, but this does not mean we might not see the 136bhp high-torque version of the 2-litre in the Golf GTI in the future.
In pure engineering terms, the 2-litre block is an improvement. It is a development of the KR 16V block with its front machined to fit the breather box. There is 5mm more clearance inside the block with the bore centres being spaced out slightly more. The intermediate gear Internally, the chief difference between the 1.6 and 1.8-litre engines was in the combust-ion chambers. The 1.6 had a flat head with the chambers in the piston tops, while the 1.8 had chambers partly in the head and partly in the pistons. shaft is smaller and the oil pump drive is bigger to give more crankshaft clearance. The oil feed system is superior, with oil jets from the main gallery squirting oil onto the undersides of the pistons. In previous modified 1.8 engines taken out to 2 litres, the bottoms of the pistons would foul the oil jets ifyou installed the system. Now, all 2-litre conversions use the Passat block as a starting point.
Engine modifications for increased power fall into four main categories: minor tweaks; bolt-on components; internal work; and, assuming you don’t already ow n a G60, adding forced induction. Nowadays, emission-control legislation is increasingly complex and restrictive in many countries, though as yet less so in the UK than in many other places. While power tuning an engine, if well done, can keep it as ‘clean’ as the standard specification, this is not always achieved. I f you live in a country or state where the limits are tight, it is important to check that any modifications you plan to make to your car are not going to bring you into conflict with the law.
Minor tweaks: whether you own a new or used GTI , it is amazing just how much improvement you can often gain simply by having the engine tuned to the optimum manufacturers’ standard specification. The engines are very sensitive to correct fuel/air ratios, and it is almost impossible for a dealer without a rolling-road facility to set up an injected car with 100% accuracy. The static CO setting can be corrected at idle with an exhaust-gas analyser, but w hat the car does under load may be entirely different.
It is not uncommon for a car referred to a dealer with a complaint of lack of pow er to be found to have a perfect CO reading at idle. On a rolling road, however, it turns out to be running lean at the top end. This can be very bad for the engine, causing pinking or detonation; in extreme cases the mixture can be weak enough to cause a holed piston if the car were to be driven fiat out for a short period. Production tolerances in the injection system, and perhaps too the effects of wear, mean that some cars remain correctly tuned while others cannot be set rich enough under full load. The difference can mean one car giving its full 112bhp while another produces perhaps onlv 95bhp.
Bolt-on components: basically, the car needs more fuel under load and one way to achieve this is to fit a modified warm-up regulator with a vacuum take-off in the intake plenum. Under full manifold depression, this squirts extra fuel into the system to restore power. The alternative is a rising-rate fuel pressure regulator which increases fuel pressure upon demand. Both these methods work well because they supply extra fuel only under load, w hereas if you simply raise the fuel pressure or modify the air metering flap, you alter the whole fuel-delivery curve and make the engine run over-rich at low speeds.
Getting more air in will give a useful power increase. For that reason, the large throttle body is a good upgrade for Mkl cars. Also, a free-flow air filter from a reputable manufacturer like K&N or Pipercross will help the engine breathe better while keeping damaging dirt particles out. You can even drill holes in the bottom of the air box to increase flow, but if you do, make sure you change the filter more frequently. You will also have to suffer more induction noise.
More air needs more fuel if you are to keep the mixture correct. If your system is borderline, as explained already, it will now definitely need modification. Assuming the correct mixture balance, a good air filter is worth an extra one or two bhp.
Restricted air flow into the engine is one limiting factor on its performance; exhaust back-pressure on the way out is another. A good extractor manifold helps gases get away quickly and is worth a few bhp. It works best if used with a complete free-flow system like those made by Super Sprint, Jetex, Leistritz, Gillet, Ansa Sebring or Hor Technologie. A good-quality system may cost more to start with but if it gives more power and lasts longer it is an investment. The basic requirement for a good manifold is that the four pipes should merge gently; the real subtlety comes in achieving this without abrupt changes in cross-sectional area. This allows the gases an easy path and creates less adverse turbulence. Internal work: porting and polishing cylinder heads and manifolds is looked upon as a black art by some. It is really a common-sense operation, but one in which the skill ofthe operator is still at a premium so that certain gifted technicians do 165 better than others. Even after optimum port and chamber design using a Superflow flow bench, I have seen the work of two different machinists produce different power outputs from visually identical heads!
It is more important to port-match manifolds to the head than to polish them. The sparkling smooth inlet manifolds you see at shows are not in practice the best thing for power production, because polished tracts tend to ‘wet out’ with fuel droplets, especially where the atomization path is fairly long. This happens more with carburettors than fuel injection. So it is best to have a slightly matt surface. Port matching is important so that mixture flow and then exhaust gas flow is as smooth and unimpeded as possible. Smooth and shaped combustion chambers that induce enough turbulence to achieve more efficient mixture burn are a great help, while reprofiling of the valves and valve seats to get mixture velocity up and spent gases out should be aimed for.
As with most engines, useful power is to be found in the heads. The 16-valve head can be cleaned up and flowed to give an improvement in inlet and exhaust flow rates of as much as 24% and 44% respectively. With reshaped valves, this work is worth nearly 20bhp. There is an engineer-ing formula that states the ideal relationship between inlet and exhaust valve sizes, and by taking the inlet valves from 32 to 34mm and the exhaust valves from 28 to 28.5mm significant increases in power and low-speed torque are achieved. Note how small in real terms the enlargements are. While valves that are too small strangle the flow in the head, you have to be very careful with valve sizes because you can reach a situation where over-large valves give you a worse result through reduction in gas flow velocity.
As far as the use of lead-free petrol is concerned, all GTI-type engines can use lead-free as they have hardened valve seats. What has kept VW from allowing owners to use lead-free on 16V cars in the UK up to now was the non-availability of high-octane (97 RON) lead-free. It was a matter of octane rather than lead content. The fuel catalyst Carbonflo, however, has been tested and proven to allow the use of normal 95 octane lead-free in 16-valve GTI engines with no loss of power or chance of damage. There is thus nothing to stop GTI drivers from being environ-mentally conscious.
It is quite common for enthusiasts to have gas flowing, porting and polishing done and then a free-flow exhaust fitted. The step beyond this, though, takes the owner into a realm where serious money has to be spent. The old adage ‘there is no substitute for cubic inches’ still holds true today, and when it comes to making effortless power, there is no other recourse but to enlarge engine capacity for torque – unless you are willing to resort to supercharging or turbocharging.
Engine response is directly linked to compres-sion ratio which is why race cars run compression ratios far beyond the 10:1 that is the normal maximum for road cars given the quality of today’s pump petrol. Note, though, that really wild cam-shaft profiles with a lot of overlap reduce the effective compression ratio whatever the simple volumetric figure may be, so that the compression figures you see for out-and-out racing engines are not always directly comparable with road-car power units. US specification cars run 8.5:1 com-pression ratios compared to 10:1 on Euro GTIs. A good upgrade with an engine capacity increase is thus high-compression pistons. There are a lot of myths around about pistons. Yes, all the racing boys used forged pistons, but they are not necessarily the best thing for road use. Because they expand more when heated, they are looser in the bores and thus make more noise when the engine is cold, wearing the bores and allowing oil to blow past. For road use, cast pistons are just fine. All GTI s have forged steel crankshafts, so they are as strong as they need to be for any road application.
One of the favourite early conversions takes the l,588cc engine to l,847cc by boring it to 82.5mm and using a long-stroke 86.4mm crankshaft. When you consider that a complete engine rebuild involves a certain amount of labour, doing such a conversion on a high-mileage engine is a worthwhile alternative to straightforw ard recon-ditioning. The capacity increase is worth 15bhp and, combined with head work, change of camshaft and valve work, BR Motorsport claim 140bhp at the flywheel for such an engine.
For cars that start off with the l,781cc block, an l,870cc conversion using the standard stroke of 86.4mm and 83.0mm oversize pistons gives a more oversquare and freer-rewing engine. With modified head, cam and balancing, this gives 142bhp and a lot more low-speed torque. A similar conversion on a 16-valve unit is worth 170bhp and is as powerful an engine as most people will ever need.
For ultimate power, the 2-litre Passat block is used and, with a l,984cc capacity from a bore and stroke of 82.5mm x 92.8mm, 190bhp is possible with head work, a camshaft change and other minor modifications. The largest commercially available conversion for a 1.8-litre GTI engine is the AutoTech 2.1-litre kit which has an 84.0mm bore and 92.8mm stroke for 2,057cc. In eight-valve form, this gives 150bhp and with a 16-valve head, 170bhp, when used with an AutoTech cvlinder head and exhaust. The kit uses the 2-litre Passat crankshaft, AutoTech/Mahle oversized cast pistons, new bearings and a special head gasket. For the 16-valve engine you also get a set of reduced-height oil squirters, necessary because of the size of the crankshaft. (This would not be necessary if you started with a 2-litre Passat block, but the gains from an extra 70cc are not worth the cost of a new block.) ABT Tuning in Germany do a similar engine for which they claim 180bhp. Master of the big-engine conversions in the USA is the Riverside-based company Techtonics, run by long-time VW tuner and GTI guru Darrell Vittone.
So far, the most powerful naturally aspirated road-going GTI around was done by BR Motor-sport and Weber distributor Auto Technique of Luton for Glyn Jones. The Weber Alpha engine management system was added to a BR Motor-sport 2-litre engine and this has endowed the car with 205bhp at 6,500rpm at the flywheel, 181bhp at the front wheels, and a whopping 1631b/ft of torque at 5,250rpm. The important thing is how well the Weber system has filled out the troughs in the power and torque curves compared to the already well tuned BRM 180 car. With ever-tightening emission laws, this kind of fully programmable engine management looks like becoming the tuners’ accessory of the near future.
Camshafts: most of the larger tuners are now producing tuned cars with catalytic convenors, giving increased power w ithout affecting emission levels. Valve timing is a critical factor in the power vs emissions balance. Camshafts with too much overlap let through a lot of unburnt fuel and are therefore ‘dirty’. The famous German camshaft manufacturer Schrick does a range of camshafts for catalyst-equipped cars.
A larger-capacity engine can take a cam with a longer duration. Thus while a 260-degree duration cam may be very wild for a 1.6-litre car, it is mild when used on a 2-litre version of the same engine. Experience has shown that, for normal road driving, that 260-degree cam in a 2-litre car has such a nice civilized feel, near-stock idle – and yet so much pulling power. Anything wilder produces a car with a frustrating lack of bottom-end torque.
Many people rely too much on 0-60mph and top speed figures as a guide to a car’s performance. A slightly slower car in these terms which has more torque and is faster from, say, 30-50mph and 50-70mph will be quicker and less tiring to drive in give-and-take traffic and fast country-road conditions. Remember, bhp gives you top speed but torque gives you acceleration. Your exit speed from a corner defines your speed down the straight. Therefore, a car with good handling and grip and plenty of torque will alw ays score over the screamer w hose power is all at the top end. A torquev car that does not have to work so hard will also rew ard you at the petrol pump.
Forced induction: the robust Golf engine responds well to turbocharging, and with a good installation, as done by Callaway in the US and Turbo Technics in Britain, you will find a turbo GTI just like the standard car in terms of drivability, only much more powerful. The fact that the intake and exhaust are on the same side on the eight-valve engine means that the heat reflective shielding has to be carefully done to prevent fuel vaporization taking place. Apart from that, careful routing of intercooler pipes and casting of a high-quality exhaust manifold to take the turbo are the main design problems a turbo installer will encounter. The excellent chassis of the GTI-type cars require less uprating to take the power of a turbo than some other hot hatch-backs and, on the whole, power increases to between 150bhp and 190bhp are reasonable for road use.
If you have four-wheel drive, you can afford to turn the wick up higher, as Abt Tuning did with their turbocharged 220bhp 16-valve engined syncro. This is the sort of power that would not go very well in a car with just front-wheel drive. Really pushing the limits of a front-driven Corrado chassis is the Oettinger five-valve-per-cylinder engine. Shown at the 1989 Frankfurt IAA Show, the new head has three inlet and two exhaust valves on a l,760cc (81.0mm x 86.4mm) engine block. Turbocharged, this engine gives 250bhp at 6,200rpm and torque is a phenomenal 2141b/ft at 2,500rpm. It is likely that wheelspin limits the Corrado’s 0-60mph time to 6.1 171 seconds. Top speed is 162mph! With the normal four-valve head on his engine, Treser claims 240bhp and a 15Kmph top speed for his Corrado. 0-60mph is similar to the Oettinger car.
Supercharging, popular for aviation piston-engines in the last war and for cars in the 1920s and 1930s, is making a comeback. VW is the first major manufacturer to produce a supercharged car in the second half of the 20th century, but even before the debut of their G60 models, several aftermarket tuners had had a go. Nothelle tried a 150bhp car back in 1984/5, as did Brian Ricketts when he was with GTI Engineering. In Britain also, Steiner Engineering built a 160bhp super-charged car using American parts from Auto-Tech, with limited success. Supercharging scores for its instant response and superb low-end lugging power. The cars are not dramatically quick off the line, but it is in mid-range acceleration, as when overtaking, that you reap the benefits. As with turbocharging, you need to lower the compression ratio and control the whole fuelling and ignition set-up, electronically if possible, for optimum performance and knock resistance. It would be interesting indeed if the Weber Alpha system could be applied to a super-charged version of the GTI engine.
Nitrous Oxide, chemical symbol N0 2 , is 32% oxygen by weight and is compressed and”stored in a gas bottle at -178 degrees C. When it is injected into an engine, it vaporizes and takes the heat from the incoming atmospheric air. The extra oxygen present combines with extra fuel in the combustion chambers and gives a great increase in power. A ‘fogger nozzle’, which mixes the N0 2 and fuel, is placed next to the throttle body on the inlet plenum at a calculated distance to provide optimum atomization. In stage one on a 180bhp l,802cc Golf, the power increase is around 40bhp.
In stage two, four fogger nozzles are used, one next to each inlet tract. It is vital to ensure that each cylinder gets the same amount. On a test vehicle, stage two was worth an extra 70bhp. When this is in use, the ignition timing has to be retarded. N0 2 can only be used for acceleration runs both because of the limited size of the gas bottle and because it should only be used on full throttle if you are not to damage the engine. It is a cheap way to get dramatic power increases, but you must ensure the system is installed properly and that the engine is healthy enough to take the strain of the dramatic increase in output.
Carburettors: last but not least, and perhaps an unlikely end to the engine tuning section of a book on a fuel-injected car, it is worth noting how effective carburettors are on a GTI. When VW first started experimenting with the Sport Golf, they tried the lOObhp carburettor engine from the Audi 80GT and pronounced it not powerful enough. From there on, the K-Jetronic injection system was adopted. Hut for ultimate power, there is no substitute for a single choke per cylinder, which is why the Weber Alpha injection system using bespoke single throttle bodies mounted on Weber DCOE carburettor manifolds is so effective. If you are not concerned with drivability, consumption or emissions, then sticking a pair of DCOE Weber carbs on a 2-litre 16-valve GTI engine is an interesting way to find 140-150bhp with the noise to match. If the head, cams and exhaust are done too, this motor should be good for 180-190bhp with plenty of torque in the narrow band when it is on cam.
The ultimate innocent-looking Q-car was produced for a customer by London-based Steiner Engineering, who built a 16-valve carburettor-fed engine into a five-door Golf 1.3 GL bodyshell. Standard on the outside apart from wider wheels and tyres, this 150bhp monster has the full AutoTech/I lor/Tokico suspension, strut brace and anti-roll bar set-up installed as well as heavy duty brakes. BMW 325is and Porsche 944s do not know what hit them!