rebore to 1.9 help

[paul-murphys]

im wondering if there would be much gain in having engine rebored to a 1.9 i have to get oversized pistons an was going to go 1mm over sized, to go to a 1.9 i believe need engine to be rebored to 83mm but then in future wont have any chance of reboring engine again if have problems, what sort of gains would i get from having engine go from 1.8-1.9? and would i also need to change the compressison ratio? many thanks for any help

 

[whootish]

there are some small torque gains to be had from oversizing but i wont set the world on fire.
standard piston size is 81mm so 1mm oversize is only 0.5mm off the wall taking it to 82mm bore. this will still give you scope to take more off if you have any problems

 

[rockmonkey69]

If Im not mistaken 82mm isn't 1.9L displacement, I think it's 83mm that gives 1.9L without a stroker, as for the compression ratio most run a lower compression from the standard to give more headroom on boost. Increasing the displacement will give you a bit more torque off boost and make it more driveable.

I wouldn't bother boring it to 1.9L unless your going for a big turbo setup though, the 1.8L spools anything up to a gt28rs fine and some say the 2871r too, remember the bottom end is just a pump, the head makes alot of difference and our heads flow quite well. Plus the standard pistons all handle a fair bit of power anyway. I'm in the process of sourcing parts for my rebuild and I've just decided to keep the standard pistons, just going forged IE rods and new rings with a rehone.