[Vwdiesel] something worth trading the A4 in for

Val Christian val at mongo.mongobird.com
Fri Jul 4 21:17:35 PDT 2008

> "Power robbing transmission" my boot! Typical manual transmission is 95% 
> efficient, and improves prime mover efficiency by allowing it to operate 
> within its peak efficiency and power bands more of the time.
> You could drive a normal car without a transmission, but you'd need a 
> single step-down (or really tiny wheels) and some way to decouple the 
> engine from the wheels while stopped. These two alone would introduce 
> the same level of power loss as a gear-gear transmission/differential 
> and dry clutch. Electric motors, granted, get around the decoupling 
> necessity.
> Oh, and your engine would need to be able to produce 100% of the hp 
> necessary to begin accelerating the vehicle's mass at low RPM points, as 

	Not hp, rather torque.  A gas turbine is an example of 
	an engine which has high torque at low output shart RPMs.
	Diesels are not as good, but they do have more torque at 
	lower RPMs, favorably impacting drivability.

	However gas turbines near output shaft stall, are not 
	as efficient as diesel engines.  

> opposed to being able to wind it out to its peak HP point to do your 
> standing acceleration.
> In other words, you'd need a V8 to move a Rabbit around.

	No, you simply need a configuration where suitable torque is
	available at low wheel RPMs.

	HP is needed for acceleration, but it's also needed for 
	max cruise (drag) and hill climb (lift).  

	A 48 hp Rabbit, heading into a 50 knot wind, is speed limited
	due to increased aerodynamic drag on the Rabbit.  With a 
	50 knot headwind, don't expect a road speed much over 60 mph.

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