I'm not the one to ask... But aircooled.net says;
The aircooled VW engine uses cylinder sets that are removable; they are not cast into the block like most engines. This makes them fairly easy to replace. I will refer to “machine in” and “slip in” piston/cylinder sets. “Machine in” sets require engine case and cylinder head machining before they can be used, since they are significantly larger than the original sets. “Slip in” sets do not require any machining, since they use the stock VW case and head hole sizes and increase piston size by “thinning” the walls of the cylinder.
36-40 HP engines are small, and you should not attempt to build a performance engine from these starting points. Prior to 1966, Beetles and Ghias came equipped with these engines. The 1300/1500/1600 engine should be the basis for all performance modifications. The cylinder hole in the case is the same for all 3-engine sizes! Both the 1500 and 1600 engine use the same bore size in cylinder head, but the 1300 cylinder head is smaller. This means that a 1500cc engine can be upgraded to a 1600cc engine by simply installing the 1600cc piston and cylinder set! The 1300cc engine can also be upgraded if you bore the 1300 cylinder heads out to the 1600cc size, or replace them with the 1500 or 1600 cylinder head.
Almost all piston and cylinder sets are available in two versions: short stroke (these are considered “A” pistons), and long stroke (these are considered “B” pistons). A pistons are used on up to 76mm stroke engines and B are used on 78 and longer stroke engines. The difference between the two versions is the location of the wrist pin hole in the piston. Be sure to get the matching set for your crank and rod combo.
77mm, 83mm, 85.5 mm: Stock VW engines (aircooled type 1 1300/1500/1600 cc) came stock with these piston sizes, respectively. Slip in piston and cylinder sets are available in ‘size upgrade’ of 87mm and 88mm, but we do NOT recommend them EVER, PERIOD. There are NO special cases or exceptions to this recommendation. Aircooled.Net doesn’t sell or support applications that use the ‘size upgrade’ slip in sets on 1300/1500/1600 cc engines. When slip ins are made, the cylinder walls are thinned so that the larger piston will fit. The cylinder walls become too thin to maintain their integrity as the engine gets hot, and the piston, cylinder, and piston ring seal breaks down. Overheating and loss of power are the result.
88mm: The next bore size up from stock is the machine in 88mm set. These work VERY well, but you are looking at a lot of machining (this costs approx. $100) for a very small displacement increase! If you’re going to go to that work or expense, you should opt for the larger piston set! However, 88s are very good for busses and type 3 engines, since these engines run hotter than beetles, ghias, or buggies/rails.
90.5mm: This is a very common bore size. You are finally beginning to get a substantial displacement increase for your $. These sets have the same cylinder wall thickness that a stock 1600 cylinder has, so they are VERY reliable. These are an excellent choice, and routinely last 100K miles or more.
92mm: For 30 years, this piston was essentially a “slip in” set for the 90.5 bore size. It works ‘okay’ for low mileage race applications, but it’s prone to the same problems as the 87/88mm slip in combination. However, now the 92mm P&Cs are available in the old version (which we recommend against), but also in “Thick Wall” versions, with a 94mm register at the top, and EITHER a 94mm register at the bottom, or a 90.5/92mm register at the bottom. These 92s are ultra reliable, and are an excellent choice for convertibles, busses, and type 3s.
94mm: NOW we’re talkin’! 94mm cylinders have the same cylinder wall thickness as the stock 85.5mm set (1600cc). A slight drawback, however is that since the fin area is the same, and the engine is now larger, these do run slightly hotter than stock or 90.5 piston sets. When these were first introduced, I did not trust them! 92s had problems, so how were 94s going to be better? Well, the jury is in and 94s work. Reliability is very good; you can expect about 50K miles before a tear down and replacement is needed. Some sets have gone over 100K miles when low compression and sane driving are exercised. The machining for 94s costs slightly more than 90.5s — in addition to “boring”, you must have the case “decked”, so they do cost a little more to build (even though the piston set is about the same price as the 90.5mm). The additional displacement is definitely worth it!
Once you’ve got all your engine components selected, you will almost always need cylinder spacersand/or head gaskets to set the engine’s deck height. Some guys will do a bunch of fancy math to try and tell you what spacers to get, but our experience is that the best way to determine what spacers you need is to mock your engine up and then measure! Real world beats theory every time!
http://www.aircooled.net/vw-performance-engines/
