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      06-23-2013, 12:58 PM   #69
CanAutM3
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Quote:
Originally Posted by NISFAN View Post
Layman's term maybe, but wrong to a drive train engineer.



No, I unapologetically use the engineering definition. If I were to go by 'EVERYONE's beliefs then I would also have to close mindedly accept that 'Torque wins races' or other nonsensical definitions. Just to recap, a turbo engine responds to throttle input EXACTLY the same as an NA engine, afterall it actually is an internal combustion 4 stroke engine.



If you had used torque in your argument you would have been onto something, but totally failed with the horsepower reference. Lag on a modern turbo system at peak horsepower revs would be negligible. I know you probably used it for a more forum friendly reference, but down the wrong track. The higher the revs = the higher the exhaust gas energy = lower compressor spool time.

At least you agree that, say, the S63Tu at 4.4 litres even when in 'lag' state will be at least if not better than an s65. Kind of poo poo's the people who believe the F10 M5 F12/13 M6 suffers from lag. I'm pretty sure I feel strong acceleration when driving the M6



Yep, you are definitely biased towards the s65.....comes across really clearly. It is a great engine by the way, and deserves the credit it has received. Sadly it doesn't fit in with the modern way of doing things. You have to move with the times in this industry.



This new engine direction has stumbled on a V8/I6 thing, but probably a bigger factor is the NA / FI thing.

Obviously current M3 owners would like the engine they know and love to move into the next car in some form or another.....but simple facts are, to extract the increase of power required, BMW would have to go against the global trends for economy and emissions, on an already thirsty engine.

On the plus side, there was equally as much debate about the F10 M5 / M6 dropping the s85 engine. Seems like s63tu has gone down well with new owners, with only 'the sound' being a negative.

As for turbo lag, check out race two in this e60 M5 vs. F10 M5 (race two singled out as it was closest start point for the both in terms of reaction time). Not bad for a over 100kg heavier car with 12% less displacement.
I am not sure anyone is debating the fact that the S63Tu makes more power and has a broader power band than the S85 as is clearly demonstrated in the vid you posted.

My personal understanding of lag, or turbo lag, is the delay between throttle pedal movement and power output change. A high revving NA engine with individual throttle bodies will have a very sharp response to throttle pedal movements. Such a characteristic makes the car very enjoyable and easy to control and balance at the limit.

On the other hand, a turbocharged engine will have inherent delay between the throttle pedal application and the power increase. Some operating conditions will make this lag worse. For example going from a fully closed throttle position to a fully opened position, regardless of RPM. When the throttle is closed, very little gases pass through the engine and the turbo spools down. When the throttle is re-opened, there is a time delay for the lower pressure intake charge to enter the engine, go through the combustion cycle, travel trough the exhaust and spool up the turbine; and then for the compressor to push more air in the intake, for the higher intake charge to reach the cylinder and finally for the engine to make more power. With your background, I am sure you are familiar with the various methods used to minimize or counter this delay, like using smaller turbos or exhaust fuel injection to keep the turbo spooling (those lovely pops that rally cars do on rundown) just to name two. The engineers at ///M seem to have to done a pretty good job to minimize this on the S63Tu, but the lag is still there to some extent according to most reviewers.

I am very curious about what technology the ///M engineers will use to minimize the lag on the S55 (electric turbo ??). I am sure they will be very creative about it

Last edited by CanAutM3; 06-23-2013 at 01:54 PM..
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