View Single Post
Old Thu, Dec-03-2009, 06:29:46 AM   #44
Registered User
Join Date: May 2009
Posts: 313
Reputation: 0 elp_jc is on a distinguished road
Location: El Paso, TX

United States


Originally Posted by Cleveland View Post
Since the S65B40 4.0 liter engine revs to 8400 rpms, the tolerances for piston ring-to-cylinder wall clearances have to more conservative than the tolerances for a normal 3-series engine.
Isn't piston speed the real variable? Don't have engine dimensions handy, but a long-stroke piston could be travelling at the same speed at 7K rpm as a short-stroke one at 8,400 rpm, no? Both should generate the same amount of heat, correct? Furthermore, with an appropriate cooling system that shouldn't be an issue anyway. And hey, motorcycles rev to the moon compared to the S65 engine, and mine have never burned any oil.

Having said that, what you said actually makes sense, even if I don't know why. Maybe the S65 has forged pistons that behave differently, or titanium connecting rods, etc. I don't believe our engines even have the former, but as long as oil consumption is not over the top, I don't have an issue with that. Heck, even my 2 new Hondas consume oil too, something that never happened to me before with any new car. My guess is sloppy quality and/or looser tolerances for cheaper costs, but could be wrong. Thanks a lot for your insight buddy .
'08 E92 M3, Silverstone/Black Extended (w/carbon leather), 6MT
Premium/Tech/Cold packages, Ext. Leather, 19s, Pwr Sunshade, Park Dist., iPod/USB, HD radio, Sat Radio, Enhanced Premium Sound, Moonroof.
MODS: P/C black 19s, BMW perf. grilles, body-colored gills, black stock exhaust, reflector delete, euro light switch, alum pedals, ZHP lighted knob, tint.
Jump to top elp_jc is offline   Reply With Quote