greg f Posted December 8, 2009 Share Posted December 8, 2009 Interesting reading for sure... I have never measured a loss of cold or hot oil pressure with a properly cross drilled crank. My cars run either Mobil 1 15W50 EP ( yellow cap) or Brad Penn 20W50 oil. Hot oil pressure is right between 4.5 and 5 bar with the oil temperature between 240F and 250F. I have seen an issue with cranks being cross drilled and polished, then having low oil pressure after re-installation. I have found this is due to Porsche overdrilling the crank oil feed holes, creating "dead ends" that are 4 to 10mm too deep. Material from both the drilling and the polishing can become trapped in these dead ends, coming out when the crank gets hot and partially blocking the oil passages and relief valve. Now we pull all the factory plugs, drill and tap the oil passages so that they can be cleaned properly and threaded plugs installed last. Since performing this last step all of the cars here in the NW run 5 bar cold, 4 bar at the end of a race. Joe is mostly correct in his oil dissertation with the exception that he neglects to mention how important oil pressure is. The effect of viscosity is negligible when compared to the effect that low oil pressure has. Higher viscosities are required with higher clearances to maintain the film strength. After polishing a used standard crank will measure much smaller than when it was new, indicating 40wt or higher oil viscosity to me. Greg F Quote Link to comment Share on other sites More sharing options...
dmdirks Posted December 8, 2009 Share Posted December 8, 2009 Hello Greg, Thanks for chiming in on this topic. With regard to cross-drilling, I recall a while back you had recommended drilling the #2 and #3 rod journals only, and drilling them to 3/16". Do you still recommend this, and is this applicable to both the early and late crankshafts? Quote Link to comment Share on other sites More sharing options...
Sterling Doc Posted December 8, 2009 Share Posted December 8, 2009 Just to throw another option and data point into the mix, we just finished the Road Atlanta 9 hour enduro using 20/50 Mobil1 V-twin oil. Motorcycle oils do not have to worry about clogging cats with zinc, and run higher ZDDP contents (around 1,600 PPM, IIRC). D/T high temps in V-twin motors, the the formulations suit our needs well. Like Joe said, durability over ultimate performance. We only had to add one quart of oil over the 9 hours, and had about 50lbs of oil pressure at idle hot. Oil temps were all of 190ish degrees in these 40 degree temps, though! With this oil, the motor made 135 RWHP, so it's not costing a lot of HP. There is a preliminary race report in the MW region section. Once I get it fleshed out, I'll post it up on the Spec site. Quote Link to comment Share on other sites More sharing options...
dmdirks Posted December 8, 2009 Share Posted December 8, 2009 Hmm- that sounds interesting, Eric. I'll have to look into that. Thanks for sharing! Looking forward to reading about the enduro also!! Quote Link to comment Share on other sites More sharing options...
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