Here is a compression chart.................
Approximate Cranking Compression
These pressures are estimates based on fresh stock bore, piston, porting, and deck height.
It is recommended to check your compression after installation.
Sea Level 1000' 2000' 3000' 4000' 5000'
18cc 197 178 171 170 165 145
19cc 183 167 160 158 152 137
20cc 169 156 149 146 140 129
21cc 156 145 138 134 128 121
stock 130 125 118 112 106 100
Sand Mountain Nevada is at approximately 4000-4500' depending on where you are at. So on stock bike the difference is approximately 33 #'s and on a modified bike the difference is more drastic 42 #'s. But you need to check it at either end............... :beer: