Cylinder spacers are used to achieve proper deck height when using stroker crankshafts and/or longer connecting rods. Using spacers is one accepted method to lower CR and works very well on VW engines. Compression Ratio Recommendations, GB 801-CR, GB 801-DECK, and GB 801-HEADS are mandatory reading. Do not use paper gaskets for sealing under the barrels with or without shims/spacers. Seal only with high temperature RTV silicone sealer, such as GB 9000B. Install a small bead of GB 9000B against the cylinder diameter and the cylinder flat surface (spacer or shim if any) so it seals the cylinder to the spacer or shim (if any) to the case all together. Be clear that this must only be done at final assembly just before the heads are to be torqued.
How to calculate the approximate spacer and/or shim amount when the stroke is changed: Subtract original stroke from new stroke in mm, then multiply by 0.0197. This gives spacer measurement in thousandths of an inch. Remember, this is only if case height, rods and new stroke are exact. Whenever possible check deck height first by a trial assembly, or order additional shims to space out cylinders as necessary. Never run less than 0.040" (1mm) deck clearance with quality crankshaft and rods. Poor quality cranks, rods, and/or line bored cases often require up to 0.060" deck to clear in race applications. Always allow 0.050" to 0.060" deck clearance on street engines. I have run a deck clearance of as much as 0.250" to lower compression with no adverse affects, however the heads should always be Semi-Hemi cut first. How to mathematically calculate deck:
New Stroke 82. mm
Original Stroke - 69. mm =13. mm
Multiply By (formula) x 0.0197
= The Spacer size 0.256"
As you can see, the amount of spacer to get back to the original deck height is 0.256 inches.
Note 1: If you change the rod length and/or cut the case deck down to get a full seating surface, such as with a hole cut for 92mm or 94mm size pistons, you must add and/or subtract the full amount of these changes. Shorter rod subtract, longer rod or case cut down add.
Note 2: The above measurement will be mathematically correct, but not necessarily physically correct when you put the engine together. This is due to many unknown variances. This will only get you close to the stock deck height. If you are going to lower the CR, as you must for today's pump gas, you must calculate how much more spacer you will need in addition to the above amount. If you don't know how to achieve this, the calculation formulas are listed in our GB 770 instructions and/or in GB 801-CR on compression ratio vs. today's fuel and how to make your engine live and provide better cooling with more power.
Note 3: The recommended procedure is to pre-assemble the engine to achieve actual measurements with our GB 751 deck tool, then order the proper spacers. Steel spacers are stackable. With the availability of spacers in about every 0.020" thickness you have no need to stack more than one spacer to achieve any deck required. If not, it may require that you have custom spacers made.