9/10/06
Bolt-On Engine Modifications
9/10/06
There are several rather simple ways to get a few more ponies out of your stock 4 cylinder VW engine. What I am about to describe here involves most of the quick and dirty bolt-ons that are available for the A1 watercooled VW. Once you've done all these, and it still isn't enough, go for the 16V engine swap, porting & polishing, or turbocharging (the latter being what I elected to do).
Here is the path you should take when upgrading your A1 vehicle:
Exhaust
Depending on the model, often the easiest and cheapest way to get more power is to modify the exhaust. If you own a 1983 or 1984 GTI, take heart: the stock exhaust on your car is easily the WORST that VW ever installed from the factory! The cheapest way to get more power is to find an exhaust manifold from an '82 1.7l rabbit. It has two exhaust ports, rather than the single outlet found on the '84 manifold. As you can see the obvious differences between the two manifolds in the picture below. The manifold on the left is from a 1982 rabbit, the one on the right was formerly installed on my 1984 GTI.
Keep in mind that a diesel manifold will work, but you won't have the tap for an oxygen sensor, and there won't be a CO% test pipe.
Changing the manifold will of course require you to change the downpipe. Techtonics Tuning sells a line of exhaust systems that are a favorite of most VW fans. Pictured below is the dual downpipe for a catalytic-equipped rabbit. It does not have a bung for the oxygen sensor. This item can be ordered tapped for the OXS sensor at an additional charge. They of course can be ordered for cars without a catalytic converter.
There are also a multitude of headers that can be purchased on the aftermarket. There are two basic types, one being the 4 into 2 into 1 version (known as the "Tri-Y" header), with the other being the 4 into 1. Most tuners will tell you the former is preferred, as the torque characteristics are much better. The only problem with using headers is their rather brief life span, as the rocking motion of a transversely mounted engine tends to crack the steel pipes of the header. Supersprint headers tend to last forever ,getting you around this problem, but they are tremendously expensive. Dyno tests show that headers don't do much better than the factory twin outlet manifold and a good downpipe and exhaust.
Why did VW put such a lousy exhaust system on a car that was supposed to be their premier performance model? Because they wanted to reduce noise and engine vibration. The pivot mount for the exhaust downpipe on stock GTIs lessens engine vibration transmission into the cockpit, therefore making what was at the time an aging platform seem silky smooth. The press loved it at the time, not knowing what a choke on power the system really was.
For the address and number of Techtonics Tuning, see the tuners guide on this page.
Has your stock exhaust finally rotted out? Techtonics also makes an extensive line of cat-back systems that work well. They aren't fancy, but they work. Changing the exhaust from the catalytic converter back won't give you much of the 'ol HP's until you've changed the manifold and downpipe. Depending on how much salt they throw on the roads where you live, you have options for aluminized steel or stainless steel
Intake
The intake system on the A1 chassis cars isn't the best when compared to the system on A2 cars. If you don't own a later model A1 chassis, then take a look at your fuel distributor. It it doesn't have "69K" sticker on the top of it, you've most likely got the unit with the smaller bore. Find a wrecked GTI and get the fuel distributor from it. These are the 80mm units, and they will supply a great deal more air to the engine. Once you've seen the 80mm unit, you can see how much larger the unit is in comparison to the older distributors.
Step two is to replace the throttle body with a unit from an A2 vehicle (which requires flipping it upside down and reversing the linkage), an Audi 5000 (see Power.txt for a description), or a new unit from Neuspeed - with the Neuspeed option being the most expensive of course. This is often one of the first modifications people do to their cars, since it's relatively easy and cheap. Once you have the throttle body ready to change, you will need to port the intake manifold to match. This can be done with a dremel tool, or a ported version can be purchased from Bellevue Motorsports. Don't expect a huge difference with this modification. Even with match porting the intake manifold, expect about a three horsepower gain at high RPMs.
Many people believe there are gains to be found by "drilling" the intake airbox. Bluntly, this means drilling holes underneath the air filter, with the theory being that this will allow more air to enter the intake. I haven't done this, and I have my doubts about it's effectiveness, since this means you'll be pulling warmer air from the engine compartment into the intake, rather than the cooler air coming from the intake snorkel. Rather than drill holes, the best tactic is to replace your stock paper-element air filter with a K&N reusable filter. These can be purchased for about $27 from a multitude of aftermarket suppliers.
The next level of modification on the intake manifold is to port and polish the unit. As mentioned above, the quickest way to get the performance associated with porting and polishing is to purchase one from Bellevue Motor Sports, but if one is careful it can be accomplished in the garage. A word of warning, however - don't expect much of a gain, and if you mess up and clearance the inside too much, you'll have a lovely hole in your intake manifold which will requie aluminum welding by someone experienced in such a thing.
Camshafts
There's nothing wrong with the stock cam. It provides reasonable performance with good emissions and idle quality. That's not to say you can't improve on matters here and still stay with stock parts. The camshaft from the european GTI, otherwise known as the "G-grind" cam, is an excellent all-around cam with an improved mid-range and stock-quality idle. The best part is almost everyone reports passing emission tests with this cam installed. Once again, Techtonics supplies OEM quality g-cams at about $130. DON'T BUY A COPY! The OEM parts are made from German chill-hardened steel, and the lobes won't wear over time. The $99 version sold by Autotech comes from an American-made billet, and reports are that the lobes wear out quickly due to the softer steel. I was unable to get a good idle with the Autotech cam.
Keep in mind the g-grind cam is for solid lifter engines. If you have an A2 platform car, or have converted your solid lifter head to hydraulic, an excellent cam for every-day use is the Neuspeed 268. This cam will still idle well, and you'll still have about 14" of vacuum at about 1000 rpm according to Techtonics. Of the many cams tested by Techtonics, this one was selected as one of the best.
Why are we only talking about relatively mild cams here? CIS equipped cars hate radical cams because they cause valve "overlap," meaning that there's a small period of time when both exhaust and intake valves are open at the same time. This sends a pulse of air back through the intake, which disrupts the movement of the venturi plate in the fuel distributor. This movement therefore disrupts fuel flow to the engine, resulting in overall poor operation. If you really want to keep your car as a daily driver, stick with either the stock cam or the mild ones referenced above.
Now some general notes and definitions regarding camshafts:
Duration: Measurement of how long a valve is lifted off its seat in degrees. The g-grind cam has a duration of 283 degrees, so of the full 360 degrees of cam rotation, any particular valve is open for 283 of them. Too much duration can cause the above referenced valve overlap, which is detrimental to low end power and idling characteristics on CIS equipped cars.
Lobe Center: Measurement in degrees between the peak of the intake lobe to the peak of the exhaust lobe. The smaller the measurement, the more valve overlap, since the the cam lobe peaks are closer together. Volkswagen stock cams generally have lobe centers of about 110 degrees.
Base Circle: Diameter of the short end of the cam lobe. Wider base circles mean the valves open slower since the "ramp up" (profile) to the lobe peak is smoother. Reground cams have a smaller base circle, and can literally make the valve lifter jump off the cam during high rpm operation.
Lift: Measurement in inches in how much the valves are opened. Lift is determined by subtracting the base circle measurement from the lobe height measurement. The g-grind cam has a lift of 0.423". High lift cams can cause several problems, including binding of the valve springs, or damage to the valve stem seals caused by pushing the valve stem retainer into the seal. High lift cams may require grinding the lifter bores for clearance.
Adjustable cam sprockets provide a means of moving the torque peak of the engine up (by retarding the camshaft timing) or down (by advancing the camshaft timing). They don't give you any additional power, but do allow you to tailor the torque of the engine to suit your tastes. I think most people buy these because they look trick.
Ignition
If you have a stock electronic ignition, leave it alone. There isn't anything you can do to improve its performance. If you have an older points/condenser distributor on your car, it is highly recommended that you swap it out with a hall-sending electronic version. You'll go through a rotor about every 20k miles, but you won't have to adjust points ever again!
Plug Wires: Stock Bosch OEM wires are about the best you can find. Save your money when aftermarket wires are concerned, because you won't find any HP increases here. If you've just got to have a trick-looking set of wires, call Rapid Parts and order a set of "Blue Ignitors." These are the only replacement wires that are as good as the Bosch units.
Spark Plugs: Platinum plugs do make a difference. Some people complain that the electrodes on the Bosch Platinums wear into the plug, therefore increasing the gap. I've had a set of Bosch plugs in my car for quite some time, and can vouch that this is in fact the case. There are several manufacturers that make platinum plugs now, so there's a wide selection out there.
Recurved Distributors: Some will say a recurved distributor (otherwise known as "European" distributor) makes no difference. It is most likely because a dyno run showed no gain in horsepower, which would be true at the full load conditions at which dyno tests are run. A recurved distributor will make a discernable difference at partial load conditions since what they do is bring on more ignition advance sooner. These units can be purchased from Autotech (which is a proper Bosch OEM European distributor) and from Rapid Parts (which send a used unit to a shop and have it recurved). The main difference between the two is price, since the Autotech unit is about twice as much as the Rapid Parts unit.
Ignition Coils: The coil that came with the car is fine. Leave it alone, especially on cars with electronic ignitions. Eurorace used to sell a hotter coil for breaker ignition (points) cars, but spend your money elsewhere.
Tricks That Don't Work
Everyone wants to find a magical store of untapped horsepower in their engine. Many look to several "tricks" that are relatively cheap, but really don't do much good. The problem is, Bosch is pretty good at designing fuel injection and ignition systems, and they've pretty much over-engineered everything to begin with.. Here are a few so-called tricks that I know of:
1) Replacing the warm-up regulator: Whether you have k-basic or k-lambda fuel injection, replacing the warm-up regulator will provide very little gain. Some advocate using one from an Audi 5000, others will say swapping with a "load sensitive" unit will give some gains. Both are supposed to be effective because they provide a lower control pressure to the CIS system, which in turn richens the mixture. On K basic CIS, this is perhaps more true, but with K-jetronic, the lambda system is just going to try to bring the mixture back to stoichiometric (14.7:1) anyway. Regardless, fuel system enrichment will only provide nominal benefits to highly modified or Turbocharged engines. Remember, on K-jetronic systems, the full throttle switch puts the system in open-loop operation and richens the mixture anyway. Spend your money on maintaining the system you have rather than messing with its components. The only exception to this rule is using a Audi 4000 or 5000 turbo warm-up regulator, as these units have a vacuum port on them that richens the mixture under boost. The are regularly available used on eBay, but are quite expensive to purchase new. Use of this regulator will negate the need to use a pressure switch to place the CIS system in open-loop operation.
2) Using the cold start valve for added fuel: This is another "enrichen the mix" trick. Problem is, the cold start injector was never intended for continuous operation, and injects fuel into the intake manifold at a single point. General atomization of fuel is poor, and distribution evenly between all four cylinders is unlikely. Resist the temptation.
3) Lower temperature thermostats and fan switches: Really a bad idea if you live in a cold climate. VW engines are designed to operate at about 200 degrees F (95 C). Reducing the operating temperature of the engine will reduce its efficiency, increase engine wear, and reduce drivability.
4) Advancing ignition timing: This trick will only work on CIS-E systems with knock-sensor ignition. Minimal gains to be found on other systems.
5) Removing the pre-heat hose from the intake: The reduction in cold weather drivability make this modification a bad choice. Minimal, if any gain in horsepower found here.
6) Drilling the air filter housing: Air intake into the filter housing has never been identified as a limiting factor in engine breathing on the A1 cars. If you feel like you must do something here, just make sure the intake tubing is free of debris and keep a clean air filter handy.
Your best bet is to make sure your ignition and fuel injection systems are maintained properly to assure peak performance. Don't mess with a good thing.
