This Karmann Ghia came from the factory with either a 1200 cc or 1300 cc air-cooled flat-four that made between 34-49 horsepower and 60-69 lb-ft of torque. The largest Type 1 flat-four VW made was a 1600 cc and could only be increase to 2276-2322 cc with a lot of grinding inside the case resulting in some thin walls. So if you want to go bigger, you get yourself an ARPM case from the mid-80’s like this Karmann Ghis is running. The case allows for a larger bore and stroke with proper clearance for camshaft and custom Siamese barrels. This particular engine is a turbocharged 2989 cc flat-four making 300 horsepower to the wheels. The engine features 90 mm stroke, 104 mm bore, JE pistons, Carrillo rods, Pauter 1.4 roller rockers, FiTech carb, and AEM EMS4 EFI system. The pistons and rods are based on Chevy small-block V8 parts and the crank was custom ground to accept the SBC-style rods. The heads are also special, featuring rare angle porting, 50 mm inlet and 40 mm exhaust valves, and heat resistance coating on the inside and outside. See more photos and details in the build thread.
Source: Pro-Touring
Just some clarification. The largest Type 1 engine built by VW was 1585cc, called the 1600. The largest air cooled flat four was the Type 4 at 1970cc called a 2.0L.
Thanks for pointing that out. I updated the article.