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      10-01-2012, 04:50 AM   #395
NISFAN
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Quote:
Originally Posted by swamp2 View Post
I don't see much harm in labeling this all lag. Lag comes from impeller inertia, friction, efficiency, load and plumbing losses. The boost threshold is simply an rpm range where flow does not produce significant turbo rpm, flow and pressure. Both create a perceived lag in throttle response and rapid onset of vehicle power feeling like some "extra" amount of throttle has been applied.
Yes there is harm in collectively calling this lag. It means that engine builders are tackling a problem that shouldn't require the effort that goes into it.

Most anti Turbo protagonists whine about a low rev limit and that an M engine should have a high rev limit. Well turbo charging does not limit the revs. There are plenty of Nissan RB26 engines (inline 6, 2.6litre) revving to well over 10,000rpm Turbo charged, producing in excess of 600hp. You have to understand with those engines that the powerband only starts at 3,500rpm, but if driven correctly on a track, you would never go below 4000rpm so never out of boost threshold region. This concept is very sporty and such a rewarding sensation when you get it right in rif=ding that Turbo charged wave of power.....
.....but because all the NA enthusiast whining, engine designers are building low boost threshold twin /triple turbo systems with a compact rev range overall. Not fun to drive.

Quote:
Originally Posted by swamp2 View Post
It is also unknown if an implementation of and electric turbo charger (or perhaps supercharger) will exist on the car and it is also unknown if it will target lag or lowering of the boost threshold or both.
A compressor driven fast enough to produce boost needs a MASSIVE amount of power (a supercharger requires in excess of 30hp to drive). A 12v system and dinky little electric motors are physically incapable of producing the power required....so you can discount ideas of an eletric supercharger right now. In fact I see this electric turbo concept as a free alternator driving system not the other way round. Garrett tried electric assisted turbo chargers years ago, fact is a Turbo needs to be spinning at over 100,000rpm in order to produce positive boost pressures. Assisting to 50,000rpm or so doesn't really warrant the additional expense and weight for the miniscule reduction in lag.



Quote:
Originally Posted by swamp2 View Post
That is what I figured you meant anyway and of course it makes sense. It is however not a particularly lucid way of thinking about engine performance. Either way you slice it, it is better to not have lag.
I don't understand, all normally aspirated engines have lag from idle to redline....so to you a half and half engine is not acceptable?

A sporty set up turbo charged S65 would produce 4 litre S65 NA torque and power to say 3000rpm then produce 5.5 liter S65 type power and torque to the redline. You saying you would prefer just plain NA 4.0 litres all the way?


Quote:
Originally Posted by swamp2 View Post
Also more power at any rpm is always better. These are nothing more than tautologies! One other very relevant point is that most production turbo engines are much smaller displacement than a competitive NA engine or the NA engine they have replaced. Typically to have a less expensive engine and to improve fuel economy. The makes them notoriously down on torque when not producing significant turbo pressure. Hence why turbo lag and rpm ranges outside of the boost threshold are more annoying.
I agree that Turbo engines are smaller displacement. That is why you need to design a Turbo engine from the start (and probably why Turbo S65 is no go). Torque is actually a product of length of stroke (leverage of the combustion power on the crank) so a torquey engine can be produced with smaller displacement. But ultimately, it is the gearbox that converts the engine torque to useful wheel torque. There are no doubts that a Formula 1 car is pretty fast, also in a straight line? F1 engines produce less torque than many family run abouts. Power is what counts, geared to produce the right torque at wheels.

All this aside I don't understand the debate on engines costing less. Of course ANY manufacturer will persue cheaper engines, doesn't mean they are selling the M power theme down the river.

And by the way, the reason all the others have dropped Inline 6 in favour of V6/8's .....this is to do with crash test performance. Much more difficult to stop a long engine from being pushed into the cabin area.
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