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Pistons for Waterboxer: The Whole Story (updated 10/14)

When it comes to waterboxer pistons, there are a variety of options available to the engine rebuilder. This article provides some background history on the original Volkswagen piston design and illustrates our personal experience with "off the shelf" aftermarket pistons. While the four pistons we compare below look similar, they are dramatically different in dimension, quality and overall performance and reliability.

All waterboxer engines originally had the same piston diameter or "bore" (94mm). The 1.9 liter engine (1915cc, to be exact) has a 69mm crankshaft stroke, and the 2.1 liter engine (2110cc, to be exact) has a crankshaft stroke of 76mm. The difference between the 1.9 liter piston and the 2.1 liter piston is the design and size of the dish at the top—and, more importantly, the position of the wrist pin relative to the top of the piston. This is referred to in the industry as compression height. The original German-made pistons were constructed so that, when at top dead center (TDC), the piston comes right up to the very top of the cylinder. This is VERY important. See image below:



Original VW German made pistons have not been available for many years now. For while, there was an inexpensive, OEM-Brazil, 94mm replacement available. Currently, there are a two or three Chinese made replacements available. Although all of these are theoretically made to the same standards (materials, construction, clearance) and of similar construction as the original German pistons, the wrist pin bores on all of theme are located 1mm (.040 inches) too high. The result is that, at TDC, the piston is 1mm shy of the top of the cylinder. Check out the gap between the top of the piston and the straight edge in the picture below. It is not fully understood why aftermarket pistons are made this way, but it might have something to do with who old-fashioned, cast iron engine blocks typically were re-surfaced during overhaul—necessitating a different wrist pin location so the pistons would not stick out of (the now shorter) block. For whatever reason, every aftermarket piston manufacturer we have checked made this same mistake:


This creates several problems:


The first is that the compression ratio (the ratio of the total volume above the piston at bottom dead center and the volume above the piston at top dead center) is reduced somewhat. In the case of the 2.1 liter engine, the compression ratio drops from an already low 8.6:1 to an even lower 8.3:1. The result is a loss of power and efficiency. Not good!

Secondly, the piston is 1mm further away from the cylinder head at TDC. The head gasket is about 1mm thick, so now the piston ends up about 2mm away from the cylinder head. All modern engines rely to some degree on the close proximity of the piston to the cylinder head to create turbulence inside the combustion chamber. This is commonly referred to as piston to cylinder head "squish" area. If one uses aftermarket pistons right out of the box, the "squish" effect between the piston and the cylinder head is reduced substantially, reducing the efficiency of the combustion chamber. 

Lastly, another problem with all the aftermarket piston options is that they come very low quality rings. So, no only do you end up with an engine that runs poorly (can't even make 90 HP), they are likely to consume oil from the get go or eventually, and don't last very long, in general.

For these reasons we came up with our own, proprietary, custom, forged piston made from scratch. This was an expensive and time consuming proposition, but by far the best solution. In doing so, we were able to solve all the problems at once. We employed a U.S. company to manufacture a piston for each of the engine displacements we offer, made exactly to our standards. All of our custom pistons have a dish volume of 48cc. The piston we use in our 2200, 2300. and 2450cc engines use 96mm pistons with and the original cylinder carefully bored and honed in a custom torque plate system. Our 2700cc engine uses a 100.75mm bore, and utilizes brand new, customer made cylinders. Each piston design has a compression height such that the piston comes right up to the top of the cylinder, ensuring the combustion chamber can work like it was designed to. The results are highly efficient engines with exact displacements of 2200.4cc, 2300.6cc, 2445.3, and 2693.2. The compression ratios for each are 8.8:1, 9.0:1, 9.4:1, and 10:1, respectively.
GoWesty Piston
Wiseco and JE are two divisions of the same U.S. piston manufacturer. We started out with Wiseco in the begining, then switched to the JE division in 2008, when our volume increased to the point  that we could justify having our own, proprietary forging. With our own forging, it was possible to further refine an already excellent piston design to a more modern "slipper skirt" design.

In summary:

Various volumes measured at Lesco Machine Shop:
Original German 94mm piston dish: 47cc
Brazilian-made 94mm piston dish: 43cc
Chinese-made 95mm piston dish: 48.5cc
Wiseco or JE USA-made 96 and 100.75mm piston dish: 48.0
Cylinder head combustion chamber volume: 15cc
Piston/cylinder head clearance volume, per mm: 6.9cc to 7.3cc, depending on bore

Based on these measurements, the following was calculated:

Original German 2.1 liter engine:

German-made 94mm piston, 427 grams
76mm crankshaft stroke
2110cc actual displacement
137mm connecting rod
1mm piston/cylinder head clearance
8.64:1 compression ratio, 87 octane OK

Other rebuilders 2.2 liter engines:
Typically Chinese-made 96mm piston, 425 grams
76mm crankshaft stroke
2110cc actual displacement
137mm connecting rod
2mm piston/cylinder head clearance
8.5:1 compression ratio: too low

GoWesty rebuilt engines:
GoWesty standard 2.2 liter engine:
USA-made, forged JE brand 96mm piston, 376 grams
76mm crankshaft stroke-stock
2200.4cc actual displacement
Rebuilt 137mm connecting rod
1mm piston/cylinder head clearance
8.8:1 compression ratio, 87 octane OK*

GoWesty 2300cc upgrade:
USA-made, forged JE brand 96mm piston, 382 grams
79.5mm crankshaft stroke, counter-weighted
2300.6cc actual displacement
New 139.7mm (5.5")connecting rod
1mm piston/cylinder head clearance
9.0:1 compression ratio, 89 octane OK*

GoWesty 2450cc upgrade:
USA-made, forged Wiseco brand 96mm piston, 358 grams
82mm crankshaft stroke, counter-weighted
2445.3cc actual displacement
New 137mm connecting rod
1mm piston/cylinder head clearance
9.4:1 compression ratio, 89 octane required*

GoWesty 2700cc upgrade:
USA-made, forged Wiseco brand 100.75mm piston, 466 grams
84.5mm crankshaft stroke
2693.2cc actual displacement
New 137mm connecting rod
1mm piston/cylinder head clearance
10:1 compression ratio, any grade fuel ok, but knock sensor required

*Note: It is a good idea to run 91 octane fuel on all Vanagon waterboxer engines. The price difference between regular and premium, as a percentage of the total price, has never been lower. We recommend premium fuel in all of our engines.

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GoWesty! Camper Products is a privately owned company specializing in parts, accessories, sales and service of Volkswagen (R) campers. It is not affiliated in any way with Volkswagen of America or Volkswagen AG. "Vanagon", "Bus", "VW", "Volkswagen", and "Eurovan" are registered trademarks and should be considered as such throughout our entire website.

 

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