change jet after a 13.5:1 piston???????

[shamisc]

I just installed the ported head and piston in my sig. I was running 180mj before the head and piston, and my mech told me to go to a 185 and remove the sparky. I thought it ran good the way it was. Does someone have close to the same set-up as me? What main do I need to run? The plug was on the light side of tan with the 180. Now I'm:
2 1/2 out on screw

3rd clip on needle

stock pilot???

185 main

[speedfreaksguy]

Increasing the compression will not require a bigger jet, but porting and removing your end cap will. I run a 13.5 compression piston with a 185-190 main jet. I also use a bigger (can't remember off hand) pilot and the HRC needle. Do you still have a stock exhaust and cam??

[Colby@C&DRacing]

Comp is one of the main factors in jetting. A higher comp piston will require more fuel. Fuel keep the piston cool. You will need to increase the main and pilot jet size