View Single Post
      01-01-2008, 08:39 PM   #41
Lieutenant General
swamp2's Avatar

Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

iTrader: (1)

Originally Posted by ArtPE View Post
the torque of this engine is pretty well maxed out...but it doesn't's all about gearing...

this tells me that you will be hard pressed to get more torque than it's rated 295...

by extending rpm's, they can extend the HP line, but it will still droop, so although they can extend the torque, it will not increase...

want more torque, get a bigger engine engine...or lower gears
This is not entirely true. Sure torque is intricately linked to displacement but there is significant variation in specific torque (tq/l). Consider the E46 M3 vs E46 M3 CSL:.

…….hp/tq/redline/hp peak@/tq@peak hp
M3: 343/269/7900/7900/228

Although the S54 was fairly maxed out (highly stressed) at 106 hp/l and 83 ft lb/l the M boys still found room for improvement. Although the CSLs peak tq only increased by 1.5% its tq increase at peak hp went up by almost 5%. Note that the rpm at which the peak hp is obtained did not change! This was accomplished almost entirely through improvements to “breathing” (intake/exhaust). Which is more important during very spirited driving when the car will typically be above 5000 rpm? Since the S65 is “only” producing 105 hp/l and 74 ft lb/l, I suspect there is substantial room for more. I’d expect the CSL to have AT LEAST: 450 hp, 8500 rpm redline, 300 ft lb AND 270 ft lb at hp peak (vs. approx 258 ft lb at peak hp in the base S65).

A bit more on redline: The S65 is really quite oversquare compared to the undersquare S54. The bore to stroke ratios are 1.2 vs. 0.94. A B/S of about 2.0 allows F1 engines to get very close to 20,000 rpm. We have heard rumors of BMW S65 durability testing at 9-10k rpm. The piston accelerations of the S65 do not even match those of the S54 until 8700 rpm. Furthermore, the S65 has smaller and lighter pistons. Putting all of this together if BMW was happy with the stress and safety factors in the S54 connnecting rods/pistons/crankshaft/etc. at 7900 rpm they should be equally happy going to at least 8700 rpm in the S65.