Thread: I Test Drove M5
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  #64  
Old 02-02-2013, 05:55 AM
bm323 bm323 is offline
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Quote:
Originally Posted by solstice View Post
I don't see a reason why NA can't survive in enhusiasts vehicles like M cars. Power is mainly generated from how much fuel ( energy content ) you burn per time unit. There are three obvious ways of increasing the fuel volume per time unit:

1. Increase displacement. Larger combustion chambers will load more fuel per engine cycle.
2. Forced induction. More fuel is forced into the combustion chambers per engine cycle.
3. Increase rpms. More fuel is combusted per time unit when more engine cycles are executed per time unit.

Now, how does these technologies rate in terms of fuel efficiency? The trick is to use minimum fuel when you don't need all that power or to reduce the power needed to move the vehicle.

A turbo engine is normally more efficient than a NA engine that delivers the same power per engine cycle since it's displacement is smaller, i.e when you feather the throttle or cruise it drinks like a NA engine of it's relatively smaller size. When you are running full boost it is likely not more efficient than the larger NA engine that can burn the same amount of fuel per engine cycle as is forced into the turbo engine.

However a high rpm small NA engine with the same displacement as the turbo engine should be able to be nearly as fuel efficient but instead of feathering the throttle the efficiency is achieved by keeping the rpms low.

Also I don't think the race should be lost for a bigger NA engine with low end grunt either. There are technologies to cut out a number of cylinders while going easy on the throttle and thereby provding a turbo like efficiency where the discplacement used is smaller when going easy on the throttle or cruising.

You can also lighten the cars and make them more aerodynamic etc. The transmission can be more efficient by "sailing", i.e no engine breaking and KERS like systems can be used for energy savings.

One obstacle I see for a high performance NA engine is that it requires a lot more skills, have lower tolerances and is in general more costly to develop and manufacture. Now when the genie is out of the bottle on easier and cheaper M turbo power the BMW bean counters can be reluctant to put it back.
Clearly BMW is not thinking along your lines; they are into turbo (for all new M cars) and have it even in 3 cylinder 1500 cc petrol and diesel engines http://www.bmwblog.com/2012/09/14/bm...etrol-engines/

You have persistently been praising your E60 (535i) saying that it was sporty was that not turbo??

And if enthusiast cars should/must be NA, then the new M3, M4, RS6 soon, E63 are all not enthusiast cars!

Last edited by bm323; 02-02-2013 at 06:46 AM.
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