Dyno Testing Bolt-Ons
Putting the four most popular performance additions to the test
Without question, the most often asked question to our Tech Talk column is about basic bolt-on performance items, and how much performance can really be achieved with these components. Of course, we’re talking about the big four — a header, mechanical advance distributor, high-ratio rocker arms, and dual single-barrel carbs. The combination of these items has been a great way to increase the performance of an otherwise stock 1500 or 1600cc air-cooled VW engine for decades, and is a great way to get a taste of better performance from your VW without having to disassemble your engine.
Before we begin, however, it’s important to note that any modifications should only be made to a healthy, good running engine. If in doubt, you should check your engine’s compression to be sure it is up to spec. While the VW engine is very tough, and can easy handle performance increases when in good condition, increasing the output of a tired, worn engine will only speed its demise.
Our test engine is a bone stock 1972 1600cc engine with its original 34 PICT-4 carb and twin pea-shooter exhaust, inside a ‘72 Super beetle with stock transaxle. But before we changed anything on this engine, we drove down to San Marcos, California where Kris Lauffer of VW Paradise put it through the paces on their Dynojet Research chassis dyno. While this dyno regularly sees 200+ horsepower street engines and 700hp+ Pro Mod engines, it is accurate enough to test our tiny 1600. And when the rollers stopped, it showed that the engine was producing a whopping 40.84 horsepower and 67.03-ft.-lbs. of torque at the rear wheels. Not bad for a stocker.
Once back at Hot VWs’ office/workshop, the bolt-on work began. The first item we changed was the rocker arms, which were switched with a set of BUGPACK 1.4:1 high-ratio rockers. Since the stock rockers have a ratio of only 1.1:1, these new units lift the valve higher, allowing more air flow — just like a performance camshaft, but without the installation hassles. These particular rockers required shorter pushrods, but others on the market cam be used with the stock pushrods. Once installed, we measured the lift at the valve and it came to an impressive 0.424-inch. Note: all of these bolt-on modifications in this article can be performed with the engine still in the car, however, we removed the engine for photographic purposes.
Next came a Bosch mechanical advance distributor, which was later timed at 32° at full advance. In order to time the distributor properly, we also used an EMPI full-size degreed pulley. This was followed by an EMPI header, topped-off with a performance muffler from Kymco Automotive Racing.
The final item on our list was a set of dual single-barrel Weber carbs with center-pull linkage, which really made a change to our engine compartment. After firing the engine, adjusting timing and carbs (main jets seemed close), and taking a few test drives, we were ready to hit the dyno again
So, what did this combination do? back on the Paradise Motorsports dyno, after Kris Lauffer checked things and verified timing and valve lash, the engine was ran again, but this time the output was considerably different — would you believe 54.71 horsepower and 73.92-ft.-lbs. of torque? That’s a 34% increase in horsepower (13.87) and 10.3% increase in torque (6.78) by simply bolting on performance items. And while the numbers show the increase in performance, they don’t describe how much nicer of a driving experience they deliver. And ... it can all be done in an afternoon! For those struggling in today’s economy, these modification don’t necessarily have to be out of reach. While buying new parts ensures that they will perform properly and be in good condition, many of these items are available used at VW swap meets and on on-line auction sites, making them in-reach to many who have had to tighten their budget belts. Some parts may have to be cleaned-up, inspected, and in some cases repaired, but you may be able to realize substantial savings. You might notice that some of the components used in this article were in “used’ condition, but performed flawlessly for our test. Enjoy the performance.