Here is the engineer in me…if I had identical materials for the nut and the bolt, then I would need one diameter’s worth of threads to take full advantage (strength) of the bolt. So since we are looking at a 10-mm bolt, that bolt would have to be sticking out past the flywheel 10-mm. Since ARP makes their bolts from 200-KSI material and if the crankshaft was made from 200-KSI material, then all you would need is 10-mm of bolt engagement. I seriously doubt that the crankshaft is made of 200-KSI material. That is some pretty strong stuff! I would be very surprised if the crankshaft was made from 120-KSI steel. Some racing crankshafts are made from 160-KSI steels though. OK…if I have 120-KSI crankshaft, then I would need proportionally more thread engagement to take advantage of the full strength. I would need 200/120*10 or 16.7-mm of bolt engagement. So yes, both ARP bolt sets would work fine. But since the 209-2801 are 2-mm shorter than the 203-2802 I would choose the longer ones just to load the crankshaft threads less. The longer bolts will just ensure that the bolt broke before the threads in the crankshaft got deformed or stripped. The longer bolts are just cheap insurance. Oh, and the longer set of bolts are cheaper than the shorter ones…go figure…better and cheaper!
So…IMHO, the 203-2802 is the preferred bolt over the 209-2801.
Last edited by <@¿@>; 05-17-2012 at 10:55 PM.
Reason: Opinion added