The St170 needs these according to the Denso guide

http://www.globaldenso.com/cgi-bin/g...me=&cc=&FF=100. The detail button doesn't give much info though unfortunately. If you want a 27 heat range version, of the ITV24, have a look at these

http://www.opieoils.co.uk/p-4120-den...lug-itv27.aspx