Where did I get that idea? From decades of reading Race engine building articles by David Vizard, Race Car engineering, and Race Engine Tech, SAE white papers and following OEM engine design changes and understanding the trends. Engines have been running tighter and tighter tolerances for the last 20 years or more in an effort to reduce emissions and improve fuel economy by using thinner and thinner oils. 0w-20 oils are now quite common in modern engines. But don't think for an instant that you could use that thin of a weight in a 40 or 50 year old design.
BTW, Well aware of that guys ramblings. The guy contradicts himself many times over. There is no ZDDP " myth ". It's a fact and well documented. High performance engine builders who work with Flat Tappet engines have known about the issue for well over 10 - 15 years. You can not compare stock valve trains to high performance valve trains. Apples to oranges.
Maximum allowable main clearance of .0028" on L-series is almost double that of S2000 at .0016. How can you say that is almost the same? Journal size and bearing width also play a big part. As does crank finish and crank stiffness. An L-6 is hardly a stiff crankshaft, even with 7 main bearing.
And a Honda S2000 is built a little looser compared to some other Honda engines, because it is built to run very high RPM's. ( 9,500 )
Here is just one example of a more pedestrian engine built by Honda. And this was a mid-1990's Vintage.
Honda D15B7 clearances:
main bearing clearance
No. 1,5 journals: 0.018-0.036mm (0.0007-0.0014in)
No. 2,3,4 journals: 0.024-0.042mm (0.0009-0.0017in)
service limit 0.05mm (0.002in)connecting rod bearing clearance
service limit 0.05mm (0.002in)
Here's some data from a real Engine Building site on bearing clearances. It's a very good read.
And the biggest differences in modern engines is the machining Tolerances they are built to these days. Modern Robotics, CNC machining and Laser measuring ensures that modern production tolerances are dead nuts on. Every time. Something that could not be achieved as accurately or repeatably on the assembly lines back in the 60's and 70's. The tooling just did not exist.
Edited by Chickenman, 07 June 2017 - 11:57 PM.