Over Running Clutch For Extra Mpg

[Catia]

I am all for the over-running clutch feature but with a switch to disable it when desired. I like engine braking for most of my driving, it saves brakes.

Welcome Dexter Henschel! I am from Peach State, and I hope you will enjoy this site as much I did. Again, Welcome.

 

[Dexter Henschel]

One of my college roommates bought a new '62 Studebaker Lark with a 90hp straight six and a three-speed transmission with OD. It was more than a little weird to drive because that OD was accompanied by an overrunning clutch that disconnected the driveline altogether when you lifted off the throttle. On a rather steep downhill stretch, lifting off the gas would produce a surprising amount of acceleration as you backed off the power and the clutch decoupled the engine from the drive wheels, causing your speed to increase in the absence of engine braking. Otherwise it was a pretty decent if slightly underpowered car . . . but you had to be warned about that overrunning clutch before you took the wheel - nowhere else could lifting your throttle foot cause a vehicle to accelerate. Counter-intuitive much? o_O

 

[Dexter Henschel]

The overdrive must have been inoperative on that Lark, otherwise lifting your foot from the gas would cause it to shift into overdrive. Overdrive could be locked out manually, but then it shouldn't freewheel when off the gas.

 

[Dexter Henschel]

I am all for the over-running clutch feature but with a switch to disable it when desired. I like engine braking for most of my driving, it saves brakes.

 

[Dexter Henschel]

One thing about an over-running clutch that might not be good, is the jolt to the drive-train when you press the accelerator to resume speed. You should re-open the throttle gradually to prevent the jolt.

 

[Ty]

I think most people have the idea that fuel usage is simply in direct proportion to engine RPM, but that's not the case. The throttle plate controls vacuum in the intake manifold, not RPM or fuel flow. Those things are a RESULT of manifold vacuum. If you push a car downhill at idle it doesn't use more fuel than sitting at idle, because the result is a big increase in manifold vacuum, so little or no additional fuel is needed to maintain the same fuel:air ratio. That's why I cannot understand the non-existance of vacuum guages in the dash, or the utter unavailability of them in the aftermarket. My old Porsche had one, and it was a good indicator of engine operation and efficiency, (or lack thereof if you drive like I did then).

Because cars don't use throttle plates any more... or rely on vacuum pressure... fuel injection on almost all cars now.

 

[Ty]

View attachment 4733 Welcome Dexter Henschel! I am from Peach State, and I hope you will enjoy this site as much I did. Again, Welcome.

I grew up in Locust Grove, GA once upon a time... spent 17 years there.

 

[skygazer6033]

Ty --- Actually all gasoline engine cars have a throttle plate and manifold pressure. An idle air control valve(IAC) controls air at idle the throttle plate control air from there up. The throttle position sensor(TPS) coordinates with the mass airflow sensor (MAF) and the manifold absolute pressure sensor (MAP) to tell the engine control computer (ECM) how to adjust the bandwidth of the fuel injectors. The MAF keeps the mixture correct regardless of altitude. The inlet air temp sensor (IAT) or manifold air temp (MAT) adjust for temperature. (No choke)

 

[outsydthebox]

Because cars don't use throttle plates any more... or rely on vacuum pressure... fuel injection on almost all cars now.

Hmmm, I was thinking "diesels" don't have throttle plates.

Ty --- Actually all gasoline engine cars have a throttle plate and manifold pressure. An idle air control valve(IAC) controls air at idle the throttle plate control air from there up. The throttle position sensor(TPS) coordinates with the mass airflow sensor (MAF) and the manifold absolute pressure sensor (MAP) to tell the engine control computer (ECM) how to adjust the bandwidth of the fuel injectors. The MAF keeps the mixture correct regardless of altitude. The inlet air temp sensor (IAT) or manifold air temp (MAT) adjust for temperature. (No choke)

Yea, what he said

 

[Elio Amazed]

This is the main reason, tall gears. The 3.8 just loafs along.

01 LeSabre.

OMG look!
It's the cursed sweep-needle gauges!
Where your periphrial vision can usually pick up the approximate position of the dial.
And where the large needles instantly guide your eyes to the stationary numbers during a split-second glance.
Call the cops!