Hey I got a 1991 polaris Indy trail with the 488 fan cooled. Looking to shave the heads to up compression. What is the best way to calculate compression ratio? Looking to get a before measurement so I know how much I can take off the heads. Any help would be appreciated
Put a piece of solder bent in a L shape down the plug hole and hold on to it and than pull motor over than measure the squished part and than you know how far you can cut them, but you will see no performance gains and you will just have to run higher octane gas, you cant really do anything with those motors, just leave it alone
Like Polaris said. More power means the engine makes more heat. The limiting factor is getting rid of the heat. When hot-rodded, those engines don't last long.
Its a 1991,first clean and sync the carbs,change the fuel lines and check the carb boots for cracks.
,if it has more than 2500 km on it,,changing the piston and rings, may help you a bit.
Other than that,,cleaning your clutches,changing the clutch spring,adjusting the track tension down, greasing the suspension and gearing are other options if you want almost ski lifting trail performance up to 45-50mph
If you are looking to go faster in the top end,,you may be better off getting a new sled.
( shaving...most machine shops will know that stuff,,I've done it by hand measuring the cc, and clearances shaving the thickness of the gasket seemed to work;I mostly did it to true the heads.)
Polaris performance
