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08-22-2008 02:42 AM  12 years ago
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blending

rrNovice

mccoll, sc usa

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cruise control and fuel savings
wonder how many barrels of oil we could save if the cruise control would not drop to a lower gear and speed up as we go uphill? why can not the car makers fix the cruise control to stay at a constant speed uphill as on level road? i put my foot on the gas pedal and ease it down and this stops the speed up. just an idea for saving fuel.
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08-22-2008 07:59 AM  12 years ago
Rob_T

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The very first cruise controls were nothing much more than a clamp on the throttle cable so the engine power output remained fixed. The car slowed down going up hill and sped up going downhill. Now they sense road speed and try to maintain constant speed, but because they only react once the car starts to slow down they often over react and cause the transmission to "kick down".

In my motor home, going up a hill drops me to about 2.5mpg as the cruise control kicks down all the way from fifth gear to second. A little anticipation and the same hill can be done at 4.5mpg and avoiding so many down shifts. (It's not fun when you see a sign that says 10% uphill next 3 miles, and you think "there goes anther gallon" )
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08-22-2008 08:08 AM  12 years ago
GimbalFan (RIP)

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Big Coppitt Key, FL

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wonder how many barrels of oil we could save if the cruise control would not drop to a lower gear and speed up as we go uphill?
Most likely your engine gets better mileage by downshifting the trans than it would if it remained in a higher gear. Older cars' transmissions did this by sensing a lack of manifold vacuum -- newer vehicles' gear selections are controlled by the onboard computer, and all of them downshift for good reasons. Under a load, an engine is more efficient at lower gear ratios.

Ever try to pedal a bicycle uphill in high gear?
op-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-thwop-t
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08-22-2008 09:02 AM  12 years ago
Tintin

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Akershus, Norway

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Just buy the right car....

Mine started to do this when I had I reprogrammed for more power, however just at certain speeds. At others the needle won't fall at all and consequently it doesn't speed up afterwards. Had the program adjusted and now the "problem" is almost non-existant.

At certain speeds I sometimes slip it into manual and shift down before it has the chance to drop speed, then the cruise can keep it at same speed uphill.

It's all about rpm vs load, at to low rpm you won't have the torque to maintain speed, if your computer is to slow to pick up on speed change it wil drop.
“Getting an inch of snow is like winning 10 cents in the lottery.”
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08-22-2008 12:40 PM  12 years ago
SSN Pru

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Taxachusetts

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blending, what kind of car is it.
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08-22-2008 01:24 PM  12 years ago
blending

rrNovice

mccoll, sc usa

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umdpru= it is a 2006 chevy impala.
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08-22-2008 01:42 PM  12 years ago
scatbass

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Hiram, GA

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Try a manual transmission. Gets better mileage, plus it doesn't exhibit this stated issue.

Mike
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08-22-2008 04:33 PM  12 years ago
Sig Dawg

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Yorkton, Sask., Canada

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They need to downshift due to a lack of torque at low rpm on modern gas engines. High HP sells cars, and few people actually even consider the torque number. Turbo diesel is the way to go, Gobs of torque at low rpm, as the load increases the turbo gives more boost and no need to downshift.

Also I hate the way gas engines smell under heavy load, give me diesel anyday
Jason
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08-22-2008 04:33 PM  12 years ago
SSN Pru

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Taxachusetts

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second that scatbass.

Every automatic i have seen sucks on cruise control after my manual tranny car.
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08-22-2008 05:40 PM  12 years ago
Tintin

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Akershus, Norway

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Actually Sig that extra torque you get on a diesel is used to lower rpm even further, sp you still need to shift. My turbo kicks in at abt 2000 rpm, but I cruise at 1500 rpm.“Getting an inch of snow is like winning 10 cents in the lottery.”
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08-22-2008 08:09 PM  12 years ago
Sig Dawg

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Yorkton, Sask., Canada

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Actually Sig that extra torque you get on a diesel is used to lower rpm even further, sp you still need to shift. My turbo kicks in at abt 2000 rpm, but I cruise at 1500 rpm.
My torque peak of 246 ft.lbs is at 1900 rpm, and I cruise at 2100 rpm, even pulling a 1200 lb trailer going up a steep grade my car doesn't downshift with a total vehicle weight of around 5000 lbs. This is with a 2 liter engine. Running at 100 kph (60 mph) I have a consistent 4-6 psi of boost.
Jason
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08-22-2008 09:00 PM  12 years ago
Tintin

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Akershus, Norway

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At 2100 mine wouldn't shift either as I'm getting close to max torque, but I don't have that much rpm in 6th at 100 kph, 1.9 litre, 400 Nm.“Getting an inch of snow is like winning 10 cents in the lottery.”
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08-23-2008 10:14 PM  12 years ago
TachyonDriver

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Chipping, Lancs, UK

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Give me big block torque anyday, unless I was running a Tatra 813 etc, then diesel is good

I heard it said somewhere "If you get decent torque then the horsepower will look after itself "

Non of the above means that you should let an engine labour in a high gear though.

I loathe poxy little 4 cylinder engines, unless they're in a motorcycle. However, seeing as I'm not in the market for a V8 at the moment I will readily admit that 3rd class driving is better than 1st class walking

Tach.
Little Spinning Bundle of Joy® DON'T DISS THE DINO!!
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08-24-2008 06:47 AM  12 years ago
Rob_T

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Horsepower equals performance - torque equals a choice in gear ratios. Most engines with high torque at low RPMs have a flatter power curve than high revving engines , which means being in the right gear is less critical.

I once had a car that had absolutely constant torque between 2000 and 6000 RPM (it was turbocharged and the wastegate was controlled to keep the torque constant). That was a really nice car to drive...
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