Hello chaps

 

What do you think is the best size injector upgrade for the zed tt. 555cc or something a little higher????

Depends entirely on what power you want - basically dependant on turbo size. Don't forget anything higher than 400bhp and you're looking at upgrading to forged internals too :)

pistons and con rods, whatabout the crank/cam shafts, is it best to do the whole lot.

What sort of bhp will the 555cc max out on?? i guess i would need to ugrade pretty much everything in the engine to allow for running greater bhp safely.Best start saving some more pennies

on other thing, on smithy,s web page the forged pistons come in two sizes?? why exactly is this???

basically look at the flow level of the injectors i.e 555's and thats the power the will max out at.

The different sized pistons are for different compression ratio's, slightly bigger cc's and for people with damaged or worn liners.

so the larger sized piston will give a slightly higher compression ratio???

No, piston design/headgasket thickness affects compression ratio. Larger bore means increased engine capacity - usually up to about 3.1L