# 83 piston.....Next row right is 83mm 1500cc piston (actual 1493cc) setting in the same 85.5mm 1600cc cylinder.  *Order
...83mm piston & Cylinder kits were offered as 1200cc Big Bore Kits increasing it to 1385cc. but these used a smaller wrist pin diameter.

# 85.5 piston.....Second row left shows the stock 1600cc 85.5mm piston (actual 1585cc) in a 92mm cylinder. Weight of Piston, piston rings & Pin = 513 grams "Mahle" forged & 563/588 grams for cast
Top of Cylinder OD = 93.8mm    Bottom of Cylinder OD = 90mm.  *Order

#87mm piston & cylinders ( not shown ) give slightly thicker cylinder wall thickness and only .039" smaller then the 88's below (lately the 87mm P&C kits have been considerable less expensive then the 88's) 
Top of Cylinder OD = 93.8mm    Bottom of Cylinder OD = 90mm.  *Order

# 88 piston.....Lower left is the 88mm piston that is normally called the 1700cc Kit (actual 1679cc) 
Is the largest P&C kit that can be used without machining the case and heads. Weight of Piston, piston rings & Pin = 654 grams "cast"  Top of Cylinder OD = 93.8mm    Bottom of Cylinder OD = 90mm
 87's & 88's also get a bum rap when the first time engine builder fails to consider that the compression ratio rises as the bore increases. Best keep the compression on the low side. We built a lot of motors with slip in 88's and never had problems if kept in tune.  *Order

.....90mm and 90.5mm pistons & cylinders are produced in several configurations and require the case and heads to be machined. The most popular have the same outside diameter as the 92's thus giving a thicker cylinder wall thickness. Weight of Piston, piston rings & Pin 90.5mm = 542 grams "Mahle" forged
Top of Cylinder OD = 98mm    Bottom of Cylinder OD = 96mm.  *Order

# 92 piston.....Center is the 92mm piston (1835cc) setting in a 94mm cylinder. The 1835cc motor is very popular and for years was considered to produce the most H.P. per Dollar 
92mm P&C along with the 82mm crank will produce the 2180cc motor that has become most popular.
Just be sure the case is step bored and #3 top cylinder stud is deep sunk for maximum strength.  
Weight of Piston, piston rings & Pin = 569 grams "Mahle" forged
 92's also get a bum rap when the first time engine builder fails to consider that the compression ratio rises as the bore increases. Best keep the compression on the low side. 
 We built a lot of 1835cc motors and ran our personal camper bus about 90,000 miles before rust got the better of it. It is twice as important to keep a big motor in tune and refrain from lugging on hard pulls.
Top of Cylinder OD = 98mm    Bottom of Cylinder OD = 96mm.  *Order

# 94 piston.....Lower Right is presently the largest Piston and Cylinder Kit used in the type 1 Bug Motor. This kit due to its size can only be used with the small 8mm cylinder studs. Most builders will recommend the aftermarket 8mm chrome molly head studs. Some engine builders are now cutting the cylinders down to the 92mm  dia. where they fit into the case in order to have more cylinder seating surface and more metal around the case studs. We recommend giving this some serious thought before going this way. 94 slip in's  
 Note: When cutting the 94 cylinder sleeve down to 92 dimensions, the case can no longer be step bored, this straight cut was not good when running 92's and hardily the way to go with 94's  The case gets very thin behind #3 cylinder even when it is step bored. Some builders weld up this area behind number three cylinder, even though bigger problems accrue with case warping. 
  Be very careful when cutting heads for the 94's. Do to the 94's large diameter we recommend leaving the .060 compression step in the heads similar to the late Dual Port heads unless special heads are used.   
 Weight of Piston, piston rings & Pin = 624 grams "Mahle" forged. Top of Cylinder OD = 101.1mm    Bottom of Cylinder OD = 97.25mm.  *Order
 

   Cast piston on left and forged piston on the right. Which is best for you.?

  Don't assume that forged pistons is the way to go, just because most most high dollar drag motors use them and since they normally cost more, they must be better then cast pistons. 
  Uniform wall thickness in pistons is very very important. When the piston heats up, the thickness and mass of the piston determines how the piston expands. The more uniform the material thickness then the more uniform it expands. The large lug of metal on right "B" tends to transfer a lot of heat to the pin boss and causes the piston to expand out of round. Also the excessive thickness of the metal at "A" in right photo is also undesirable but because the piston is forged this can not be avoided. The metal density of the ring land and the dome or top of the piston is the main strong point of  forged pistons. When a piston is forged the inside design is limited because the one piece core must be forced into the metal billet and then pulled straight out. You end up with lots of taper from the ring area to the bottom of the skirt. Poor design but the metal is a lot stronger where the cast piston is the best design but cast metal has less strength.

On the left at point "A" the separation of the dome (where all the heat is) and the pin boss helps the piston expand in a more uniform manner. When you mike the piston diameter you will notice it is ground like an egg so as it expands it becomes round at operating temperature. The Key word here is operating temperature
 The big drawback to any Air Cooled motor is keeping the operating temperature constant. It's a lot easer to control the heat with water then with air & oil. Controlling this heat gets harder as HP increases.
 
Notice that ribs "C" can be cast in to help expansion and give more strength were needed.
 Due to the 5 piece collapsible mold, the skirt thickness can also be controlled. Section #1 is removed letting the #2 mold sections be removed which in turn allows the two #3 sections to slide to the center and extracted. The cast metal is not as strong but the design flexibility can greatly improve the strength. 

If your running 14 to 1 compression or Nitrous then the extra strength of the Forged piston top is needed, but for the typical street motor running 7 or 8 to 1 compression, you would be better off with the Cast.

Some of the forged pistons advertise the black anodized finish or graphite coating on the skirt, saying it is a harder surface and reduces piston seizure. Yes the anodized surface is harder & yes the piston will tolerate a few more degrees of heat before sticking. But for all you builders out there that tear down hundreds of motors you know it's the ring land that dictates when the Piston & Cylinders need replacing. And if dirt entered the cylinders do to faulty air filters then nothing will keep it from wearing out. 
 If the Piston sticks in the cylinder then you have other problems and a few more degrees before it sticks, only means you will get 20 feet further down the track before disaster strikes. 
 We anodized Go-Kart pistons 30 years ago and it helped or sales but little else. It's like the farmer said, when he chrome plated his manure spreader, It sure looks nice but it still does the same thing it was designed to do. 

Rings: If you need to replace your piston rings it is best to measure the width/thickness as different manufactures use different ring width. Do you need to replace pistons & cylinders or will rings do the job. *click here. VW cylinders are made of very good material so they have very little in common with most American daily drivers. Normally the wider top rings last longer and do a better job of sealing, plus get rid of more heat. But the wider the ring the more drag ( less HP ) and longer break in time. Some chrome rings never break in properly. The cast rings with a good air filter seem to work best in the VW. Top rings will have a chamfer on the inside and is always toward the top. 2ed ring will have a chamfer on the outside diameter and is toward the bottom. Oil control rings come in the cast or steel segmented type. Formula "V" racers only use the cast oil control rings when only performance is considered. Air cooled Pistons and Cylinders are a lot different then those used in water cooled motors, so don't think water cooled when working with the air cooled motor. The ring gap on the top ring is .012"/.018" and wear limit of .035" The ring side clearance will tell you if rings need replacing or if your wasting your money.
If you drop a fan belt then overheating can collapsed the rings and re-ringing might be needed but normally your VW will need a P&C kit,  not just rings. 

 ** New Aluminum 1600cc or Super Case for  85.5, 90.5 / 92 and 94mm cylinders & stroker cranks up to 86mm... *price & info

To convert mm to inches > multiply mm x .03937 = inches  or  85.5mm x .03937 = 3.366 inches
To convert inches to mm > multiply inches x 25.4 = mm  or   3.700" x .25.4 = 93.98 or 94 mm
**-- Cylinder Base Shims for 90.5, 92 and 94mm ...See #33 -- price & info.

  Piston Pin clearance in bushing = .0004-.0008       --VW  Piston ring  compressor "State size of Bore"  "Quote"  
  Heat piston to 176' F (until piston is to warm to touch and Pin will slip right in.   ...... Wrist Pin Teflon Buttons... order