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      07-04-2013, 05:05 AM   #138
NISFAN
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Drives: BMW M2
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Quote:
Originally Posted by CanAutM3 View Post
It is the second time you bring this argument and it is flawed. By adding a turbo to an engine you increase both the intake and exhaust plumbing thus decreasing the efficiency of the flows. So no, you will not have the same throttle response.
OK, lets look into this.....

At low engine speeds (where turbo lag is greatest, might even be below boost threshold) the air ducting is under very little strain as it is sized to flow far greater volumes. You are telling me that a charge cooler is going to offer a noticeable pressure drop in this operating range?
The Compressor is again sized to flow far greater volume than this too, and it will be rotating offering some assistance even if not compressing at this stage.
Exhaust side is the same thing, a turbo exhaust will be large enough to flow peak NA volumes plus the extra volume in boosted mode, so likely to be at least 50% greater flow capacity than an NA system, yet we are only flowing less than 30% of full NA volume in this scenario.

Due to these reasons I doubt you would feel any decay in throttle response. A stock NA engine has restrictions in the form of the Hot film Air mass sensor, and Cat boxes. These will still be the restrictions on a Turbo application.

Now I am not saying these restrictions make no difference, but I am saying that on a fly by wire throttled car which doesn't snap open like a cabled system, the drive by wire is more likely to be controlling throttle response than other factors.

Lets look at a more taxing engine operating parameter, perhaps going WOT in the upper 1/4 of the rev range?
Well in this range turbo lag will be in the order of 0.1 seconds in a properly sorted application. That is 0.1 seconds more than standard NA fuelling lag until you feel 'pushed into the back of your seat' boosted torque.

Not much of a penalty there.

Sure the turbo engine will have a CR of something like 10:1 instead of an NA 11.5:1, which drops response a tiny bit. You may also assume that the Turbo engine will have bigger injectors with lower resolution as a result of. But we are grasping at straws here.

You mentioned you work on aircraft. You will know a much greater (by large magnitudes) factor in response......PIO (Pilot induced oscillation), yes that thing that has crashed multi million dollar F22 prototypes.

This same factor afflicts even the best racing drivers. Do yourself a favour and look at the pedal cams on someone driving say an M3 round a track. If you can show me a progressive-on-full-off throttle pedal driving style I will concede and say 'Turbo engines are not for this guy'. Fact is you won't find this driving style, racing is all about 'feeling' how much power you can apply, how much steering angle you can get away with, how much brake pressure you can apply. All analogue inputs made by a human, and totally drown out a tiny lag here or there, after all most NA drivers will describe NA engines as 'instant response' yet we know it isn't instant, it is just too small for them to feel it.
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