Pistons for Waterboxer: The Whole Story

This article provides some background on the original Volkswagen piston design and the current state of affairs regarding piston and cylinder options available since the original German pistons became no longer available (NLA).

All waterboxer engines were fitted with cast aluminum pistons and all were the same 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 cavity (dish) at the top and the position of the wrist pin relative to the top of the piston, referred to in the industry as "compression height."

The 1.9 liter piston had a larger compression height (wrist pin further from the top) than the 2.1 liter (wrist pin closer to the top). This was because the crankshaft stroke (also known as “throw”) was 7mm (piston travels 3.5mm further up and 3.5mm further down) longer on the 2.1 than on the 1.9 (76mm instead of 69mm, respectively), so the wrist pin had to be moved 3.5mm closer to the top of the piston. The dish at the top of the pistons were also totally different in both volume and shape—the 2.1 having a much more advanced design.

Fun fact: There was a high compression (10.5:1) version of the 2.1 liter engine offered in Europe (code DJ) instead of the common 8.6:1 compression ratio (MV code) engine North American delivered Vanagons were fitted with. The DJ featured a piston with a smaller dish volume, which created the higher compression. This was, in fact, the only internal difference between the DJ and MV engines.

The original German-made pistons and cylinders were top-notch. They could always be counted on to be made of the correct materials, fitted with top quality piston rings, and (most importantly) were consistently made within the necessary specifications. When we started building engines in the mid 2000s, they were already very scarce. So we, like other engine builders at the time, turned to aftermarket offerings from either Brazil or China. We immediately found issues with both offerings right off the bat.

The first, most obvious problem was with the compression height: The dimension used did not place the piston flush with the top of the supplied cylinders. The originals  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: 

Check out the gap between the top of the piston and the straight edge in the picture above. It is not fully understood why aftermarket pistons were made this way, but it might have something to do with how old-fashioned, cast iron engine blocks were typically 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 at the time had the compression height all wrong. In fact, to this very day, some are still inconsistent in this area, as well as other very important specifications. More on that topic HERE.

Incorrect compression height 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 (MV code) engine, if the compression height was off by the typical 1mm, the 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 ends up too far away from the cylinder head at TDC. 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 proper "squish" is not guaranteed to be correct, potentially reducing the efficiency of the combustion chamber. 

Another problem with all the aftermarket piston options is that they come with rings of inconsistent quality. So, not only do you end up with an engine that runs poorly (can't even make 90 HP), there is a good likelihood they will consume oil, and won't last very long, in general.

Lastly, the fit between the piston, the cylinder and the rings on the samples we have measured is inconsistent at best, downright wrong at worst. If piston/cylinder fit is too loose, it can cause “piston slap” noise. If too tight, it can cause seizing if even slightly over heated. This also makes for inconsistent ring gaps, too tight and the ring can seize in the cylinder and break the top of the piston clean off, too loose and you end up with too much crankcase pressure (“blow by”) and/or oil consumption. Any of these issues result in some sort of shorter life.

For these reasons we came up with our own, proprietary, custom 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 have four different pistons made for each of the four displacements we offer, made exactly to correct specifications, every time. All of our custom pistons have a dish volume of 48cc, but each has a different compression height for the stroke we use for that engine displacement.

The piston we use in our 2200, 2300, and 2450cc engines are 96mm diameter, and are fitted to original-design cylinder. The 2700cc engine uses a 100.95mm bore, and utilizes brand new, custom made, GoWesty-design cylinder. All our cylinders are carefully bored and honed  for a perfect piston/cylinder clearance, every time, in our proprietary torque plate system which places the cylinder under load during honing to insure the cylinder will be straight once installed.

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 2704.0. The compression ratios for each are 8.8:1, 9.0:1, 9.4:1, and 10:1, respectively.


Above is a photo of a JE forged piston with ceramic coating on the top and an anti-friction/piston-to-cylinder-clearnace-maintaining coating on the sides

We use two companies to make our pistons: Silv-O-Lite for cast pistons and JE for forged pistons. We started out with forged pistons in all of our engines even though they were over-kill for the lower performance examples. As the volume of engines we produced increased, we reached a point where we could justify having our own, proprietary casting and forging. All the while, it was possible to further refine an already excellent German piston design by using state of the art alloys and a more modern "slipper skirt" shape. By contrast, the “competition” is still just copying the original, 30+-year-old design piston, and doing a poor job at that.

Fun (sad) fact: The first batch of cast pistons we received and used in our own engines had a higher than normal failure rate, and we ended up having to replace about 10% of them under warranty. Ironically, it had nothing to do with the switch from forged to cast, but rather was a problem with the coating that was used on the sides!

In summary:

Various volumes measured in our machine shop: 
Original German 94mm piston dish: 47cc 
Brazilian-made 94mm piston dish: 43cc 
Chinese-made 95mm piston dish: 48.5cc 
Silv-O-Lite and JE-made 96 and 100.95mm piston dish: 48.0 
Cylinder head (2.1 type-yes, 1.9 was slightly smaller) 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 2.2 liter engines built with cheap aftermarket pistons and cylinders: 
Typically Chinese-made 96mm piston, 425 grams 
76mm crankshaft stroke 
2200.4cc actual displacement 
137mm connecting rod 
up to 2mm piston/cylinder head clearance 
8.5:1 compression ratio: too low 

GoWesty rebuilt engines: 

GoWesty standard 2200cc engine: 
Silv-O-Lite brand 96mm cast piston, 376 grams 
76mm crankshaft stroke - OEM crank
2200.4cc actual displacement 
Rebuilt 137mm connecting rod 
1mm piston/cylinder head clearance 
8.8:1 compression ratio, 87 octane OK*

GoWesty 2300cc upgrade: 
Silv-O-Lite brand 96mm cast piston, 382 grams 
79.5mm crankshaft stroke - welded & counter-weighted OEM
2300.6cc actual displacement 
Rebuilt 137mm connecting rod 
1mm piston/cylinder head clearance 
9.0:1 compression ratio, 89 octane OK*

GoWesty 2450cc upgrade: 
USA-made, forged JE brand 96mm piston, 358 grams 
84.5mm crankshaft stroke - welded & counter-weighted OEM
2445.3cc actual displacement 
New Scat brand 137mm connecting rod 
1mm piston/cylinder head clearance 
9.4:1 compression ratio, 91 octane required*

GoWesty 2700cc upgrade: 
USA-made, forged JE brand 100.95mm piston, 466 grams 
84.5mm crankshaft stroke - NEW Scat brand made from solid billet
2693.2cc actual displacement 
New Scat brand 137mm connecting rod 
1mm piston/cylinder head clearance 
Intake and exhaust ports hand-enlarged on a CNC machine
10:1 compression ratio, 91 octane and GW-EFI 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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