VW A1 Cabriolet Tuner

Engines

All A1 Cabriolet had 4 cylinders, 8 valves and a single overhead cam controlling intake and exhaust valves. The 1.8L JH engine introduced in 1984 was the same used in the GTI including modified fuel injection, a special cylinder head and oversized valves. However it was teamed with the standard exhaust manifold like other VW instead of the duel down pipe version found in the GTI that provided less restriction. Hydraulic valve lifters (cam followers) were introduced in 1988 that don’t require regular adjustment to maintain proper valve clearance because they are pumped up by engine oil pressure. In fact you can often tell when your oil level is low because of the increase in valve chatter noise. On board diagnostics (ODB1) was introduced in 1990 with Digifant.

Engine modifications to increase performance include upgrading to a more aggressive cam to add torque and horsepower. Cams control the duration and the amount by which the fuel and exhaust valves open. These have dramatic affects on low and top end performance, the usable power band, idle quality, and more. Mild cams add more bottom-end torque and maintain good idle, while aggressive cams provide less bottom-end torque but more top-end performance. Depending on what you choose you may have to replace valves and springs. Engines with solid valve lifters should get the famous "G-Grind," while hydraulic owners should go for a cam made for hydraulic profiles. For best low-end torque (read usable), go with a Schrick 268° or Neuspeed 256° for 8v JH engines. Upgrading to a lightened and balanced flywheel also makes a difference.

There are turbo and super chargers available for VW convertibles but they are incredibly expensive and require more "plumbing." Some people bore cylinders to the next higher capacity, swap out different blocks (ex: ABA vs. JH) or even swap entire engines (to a 16v G60). This can produce major power advances however can often be difficult and expensive. Although there is a lot of commonality designed into VW products, there are several differences in engine compartment dimensional allowances, weight and stress considerations, electrical, transmission and exhaust layouts, fuel systems, brakes, and other controls. Be prepared.

Fuel-Injection

Continuous Injection System (CIS) is a fully mechanical fuel injection system that controls the air/fuel mixture consisting of an air flow sensor, a mechanical fuel distribution control plunger and fuel injectors. Digifant uses a combination of electronic controls and sensors (like all cars built today) and was introduced to meet tougher emissions mandates. The Digifant system is described as an engine management system because fuel injection, ignition, idle speed and emissions are controlled by a single integrated system. In general, CIS is easier to troubleshoot and repair, also replacement parts are less expensive. When Digifant was first introduced it was problematic, however it became reliable after a couple years.

Beginning in 1985 the VW Cabriolet got two fuel pumps. The main fuel pump is located underneath the car on the passenger side in front of the gas tank. The second "transfer" pump is inside the gas tank. Access to the transfer pump is under the passenger side rear seat. For most owners the best thing to do for performance is to keep the fuel injectors clean, both fuel pumps working and buy good gasoline.

Intake Manifold & Exhaust

One of the best upgrades you can do for a VW Cabriolet is to switch from the standard single manifold to a dual manifold. These came on the original VW Golfs found in Europe, but except for GTIs and some of the earlier Cabriolet, were switched on most North American VW cars because of cost cutting. They produce about 5 to 8 hp more but need to be mated to a dual down pipe and maximized exhaust system to get the best results (Techtonics Tuning).

1989 VW Cabriolet and before with CIS injection have a smaller throttle body than the '90-93 VW Cabriolet with Digifant injection. Many people with older CIS injection use the throttle body off a '84-'91 Audi 5000/100 because it is much larger and an easy bolt on. If you can, get the manifold extruded, honed and matched to the exhaust ports on the head. It will add even more power.

A common upgrade is to replace the standard VW air filer with a K&N filer. Some even cut a few more air holes in the side of their air filter box. However this is a bad idea because it lets in hot air from the engine compartment that is less dense so lowers horse power.

The VW Cabriolet has a special exhaust bend to make it fit around the spare tire and gas tank. It should also be limited to 2" instead of 2.25" because of the engine size displacement. Stick with aluminized construction because it dissipates heat better than stainless steel.

Manual Transaxles

Wheels, Suspension & Bracing

Starting in 1985, 14" alloys were matched to exterior paint color on special editions. VW typically delivers cars in North America with "soft" suspension because that's what most Americans like. Volkswagens, however, are known for excellent driving characteristics; they are European after all! The main thing to do is to replace the standard shocks and struts with a higher quality set (BOGE or Bilstein). Replacing the springs with a stiffer and lower set (H&R or Eibach), and increasing the front and rear sway bars' thickness while lowering weight (Neuspeed) should also be done. Replace all bushings with polyurethane. Although the VW Cabriolet has a number of extra bracings provided by Karmann that "compensate" for the loss of strength from the top being cut off, a very common upgrade is to add a lower strut tie-bar (Neuspeed) to brace the front suspension and provide a more solid feel.

After a while wheels will be damaged by accidents, road debris, sun and rust. There are hundreds of places that specialize in refinishing wheels. It runs around $75 per wheel and takes two or three days. It runs about $25 more a wheel if you just leave the car there and they take them off and remount them for you.

Top Replacement

Eventually the three layer convertible top will ware out. From my experience most tops last between five to six years. White is "difficult" to keep clean. Although there are canvas tops, Cabriolets come with vinyl tops and I think look the best with the original. Cabriolets even have a special vinyl texture called "Cabriolet or Pebble Grain." There are only two major suppliers of top materials in the US; differences mostly revolve around vinyl verse cloth backing options. The "horsehair" middle blanket both insulates the temperate and protects against sound better, while "foam" insulation is less expensive. Factory VW Cabriolet use horsehair. The back window and most gaskets can be reused, however, the two shock absorbers, springs and tension wire should all be replaced. Replacing a convertible top is a VERY involved affair. In my opinion, it should only be performed by someone who does it on a regular basis.

Audio

One of the biggest design flaws is the limited space for rear speakers in a VW Cabriolet. They are only 3.5" so limit direct replacement options to around 4". A common solution is to add a separate bass box in the trunk or rear seat.