i made a spacer .100 thick and put it under the jug, then put the jug in a lathe and took .100 off the top. this raised the ports and gave very good over all power with a nice bump in lowerer rpm power. it's one of the best running engines i've built.
this engine also had an expansion chamber exhaust and porting.
put as thick a spacer under as you can without exposing the top of the piston to the intake port, then take an equal amount off the top of the jug.
this is exactly what you want to do !!!!!!!!!!
i went to nappa and got 1.6mm gasket paper as my stock base gasket was 1mm .
ripped off my stock base gasket and added the 1.6 one i made . then decked .6 off the jug via sand paper and glass.
this raised the ports by .6 and maintaned the compression raio
just make shure your top piston ring does not go into the intake port at BDC... i did some porting and i took a little off the top of my intake and i can just barley see the top ring in my intake port now !!! close with the raised jug but wow what a diff !!!
i would do this again if i buy a new gt5 ...
pull the head and jug rip off the 1mm base gasket and add a 1.6mm base gasket
deck the jug .6 then port the h3ll out the intake bottom and sides leaving the top of the port just cleaned up, port the h3ll out of the bottom of the exhaust and its sides to just clean the top you already raised it lol.
then deck the head down to about 6.5 cc for around 10.5:1 comp and done !!!
grind your transfer port ramps and exhaust ramp
instant race motor !