Quote:
Originally Posted by DrFerry
Why would Honda spec a 5W30 oil viscosity for their S2000 and BMW spec a 10W60 oil viscosity for the S65 E9X M3 when the rod bearing clearances are similar?
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The Honda S2000
Honda S2000 (F22C1)
Engine capacity - 2 ltr
Engine power - 237 hp
Hp/ltr - 118.5
Redline - 8000 RPM
Preferred oil spec - 5w30
Rod bearing clearance variance - 0.02-0.06mm
Crankshaft pin/rod journal diameter - 49.988mm
Clearance to Journal Size Ratio - 0.008mm
S65 specs
Engine capacity - 4 lts
Engine power - 414 bhp
Bhp/ltr - 103.5
Redline - 8300 RPM
Spec'd oil - 10w60
Nominal rod bearing clearance - 0.0381mm (0.00150")
Rod bearing clearance variance - 0.0292 - 0.0508 mm (from BE's S65 wiki for the later Alu/tin shells, which apparently have a slightly higher minimum)
Crankshaft pin/rod journal diameter - 51.9786-51.9887 mm (official specs posted in the S65 wiki)
Clearance to Journal Size Ratio - 0.0007mm
Source Assimilator1 's thread:
https://www.m3post.com/forums/showthread.php?t=1827360 |
I would venture to guess it’s because the majority of the wear and tear on the engine comes from cold startup / first start of the day. 10w60 I bet remains on the parts longer after shut down, hence leaving more lubrication on parts leading to lower cold start wear. I think it’s also why the higher mileage cars seem to have LESS problems. Ask the boys with cars from Maranello the bills they get when they first turn them over after winter storage
Again, this is what I’d like to call my opinion and not fact based statement backed by a multi-million dollar research project to confirm
Cheers,
e46e92