On 7/8/24 1:52 AM, Jeff Layman wrote:
On 07/07/2024 23:51, KevinJ93 wrote:
On 7/7/24 9:57 AM, Don Y wrote:
In The West, it is not uncommon to find yourself driving through varying >>> elevations (mountains). Relying solely on the engine for braking often >>> won't allow you to comply with the posted speed limits *or* "safe
driving
conditions".
[OTOH, being overly reliant on the brake can lead to brake
overheating and
failure]
My recent cars automatically increase engine RPM by changing gear to
maximize engine braking, in addition to using brakes if necessary.
Some people find that disturbing to have the engine spinning at
4000-5000RPM down steep hills.
A few years after I learned to drive (in 1972!) I was in England's Lake District which has some long and pretty steep hills. Coming down one in
my manually-geared car I decided I could save petrol by turning the
engine off and leaving the car in second gear, using the aid of engine braking to save heavy use of the brakes. What I'd forgotten is that the fuel pump wasn't electric, but was driven off the engine shaft. So as
the engine braking was rotating the shaft all the way down, at the end
of the run not only hadn't I saved any fuel but I'd flooded the
cylinders as well and the engine wouldn't restart until all the excess
fuel had been expelled!
That shouldn't have happened - the float needle valve in the carburetor should cut off any flow from the fuel pump.
The fuel pump typically operated off a cam on the camshaft. It was
spring operated so that if the flow is restricted by the float valve it
would reduce the stroke of the fuel pump - potentially down to zero.
With modern cars going downhill it is non-obvious whether it is better
to put the car into neutral to cause the engine to go to idle where it
stays consuming some fuel or leave it in gear such that engine goes into fuel-cutoff but adds some braking resistance.
kw
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