hey man, relax....
try to look up denso website for the OEM spark plug heat range for the mitsu eterna
if u cant find it, the spark plug with heat range of 6 should be okay...heat range 6 is quite general ....dun matter whether denso or ngk or hks...all same.
plus doesnt matter if ur car turbo or non turbo....
reason for OEM heat range is they are optimum for ur car engine, u use too high like heat range 7 or 8...problem lor....unless ur car super turbo or something...if not a 6 should be be very safe...
toyota camry/hondas all 6.
evos,subarus r 7 ...
if u still have problems, i suggest u get a range from 6 to 8 n try each one.
good luck bro. one thing, u can also try to lookup denso/ngk website for ur engine code number perdana 6A12ttb ...should have lah....
cheers