Darton Sleeves are simply the best in performance. Found in everything from the most serious all out race cars to high performance street cars. Dartons has solve many of the issues surrounding cylinder strength, coolant flow and wear issues. Although Darton lists ASTM 536-84 as their base line ductile iron, their material exceeds all the mechanical specifications by a wide margin. Darton currently produces variations of ductile iron but the base line performance material equals 130,000 psi tensile, 280-290 Bhn hardness and 5-6% elongation.Terra Firma bring the very best in engine rebuilding for your RB26 with these Darton Sleeves for your Nissan Skyline GTR.