Turbo to TMIC silicone pipes to replace OEM I've seen this covered twice, here by Marky: http://www.clubsub.org.nz/forum/index.php/topic,31651.0.html and here by nickmcgill: http://www.clubsub.org.nz/forum/index.php/topic,6105.0.html The OEM pipes smallest internal diameter, primary and secondary is 28-30mm at the bend, The smallest internal diameter in the silicone is 36-38mm not to mention the ribs and corogations. Which is 7.065cm3 compared to 11.335cm3, with an air velocity of 10m/s cha