YACT: why don't automakers make a taller 5th gear?

[andylawcc]

wouldn't that save more gas and create a quieter ride? coz who needs the engine to run at high rpm while coasting on the highway/freeway?

 

[NutBucket]

Well, they design it such that the engine is turning its most efficient RPMs at highway speeds. For my car, its about 2000 rpm which equates about 55mph. At that speed you'll get more then 32 MPG. So that's how its geared.

 

[WinkOsmosis]

I hate that my engine spins at 3500 rpm for 85mph... it could do fine at 2500 but the 5th is too low. Is there a way to swap gears??

 

[Eli]

Engines don't get their best fuel economy at Idle.

If you look at the fuel usage graph for any engine, it's always more at idle.. then the curve goes down, and then rises sharply in the low-mid RPM range.

 

[Eli]

Originally posted by: WinkOsmosis
I hate that my engine spins at 3500 rpm for 85mph... it could do fine at 2500 but the 5th is too low. Is there a way to swap gears??

How do you know it could do it "fine" at 2500RPM?

It's also a matter of power.

 

[m2kewl]

Originally posted by: WinkOsmosis
I hate that my engine spins at 3500 rpm for 85mph... it could do fine at 2500 but the 5th is too low. Is there a way to swap gears??

that's it? mine is over 4500 at the same speed. it definitely needs a 6th gear.

 

[WinkOsmosis]

Originally posted by: Eli

Originally posted by: WinkOsmosis
I hate that my engine spins at 3500 rpm for 85mph... it could do fine at 2500 but the 5th is too low. Is there a way to swap gears??

How do you know it could do it "fine" at 2500RPM?

It's also a matter of power.

Actually its 3500 at 75mph, not 85. I'm just assuming that it can! It's a truck engine, after all.

 

[OrganizedChaos]

listen people rpm does not equal power out put. these are gas engines not electric motors. they do have a power curve

 

[WinkOsmosis]

Originally posted by: OrganizedChaos
listen people rpm does not equal power out put. these are gas engines not electric motors. they do have a power curve

I don't think power has anything to do with this. The average car needs something like 20hp to maintain speed at 70mph. It's about the noise.

 

[Eli]

Originally posted by: WinkOsmosis

Originally posted by: OrganizedChaos
listen people rpm does not equal power out put. these are gas engines not electric motors. they do have a power curve

I don't think power has anything to do with this. The average car needs something like 20hp to maintain speed at 70mph. It's about the noise.

No, that is absolutely incorrect. The wind resistance increases exponentially the faster you go. You would be surprised how much energy it takes to propel you forward at 75MPH vs. 85MPH.

It has everything to do with power. That's the whole purpose of a transmission; to keep the engine in it's optimum powerband. Horsepower doesen't mean much, it's torque that pushes you forward.. and most engines lack torque at low RPM. Of course that's a pretty big statement and there are exceptions.

Like I said, an engine uses more gallons/HP/HR at Idle than it does in the low-mid RPM range. After that, the curve goes up steeply. So you're going to get the best MPG a bit above idle, in the first place.. then you have to take into account engine power.

You just have to trust that the manufacturers knew what they were doing.

 

[Zugzwang152]

Originally posted by: Eli

Originally posted by: WinkOsmosis

Originally posted by: OrganizedChaos
listen people rpm does not equal power out put. these are gas engines not electric motors. they do have a power curve

I don't think power has anything to do with this. The average car needs something like 20hp to maintain speed at 70mph. It's about the noise.

No, that is absolutely incorrect. The wind resistance increases exponentially the faster you go. You would be surprised how much energy it takes to propel you forward at 75MPH vs. 85MPH.

It has everything to do with power. That's the whole purpose of a transmission; to keep the engine in it's optimum powerband. Horsepower doesen't mean much, it's torque that pushes you forward.. and most engines lack torque at low RPM. Of course that's a pretty big statement and there are exceptions.

Like I said, an engine uses more gallons/HP/HR at Idle than it does in the low-mid RPM range. After that, the curve goes up steeply. So you're going to get the best MPG a bit above idle, in the first place.. then you have to take into account engine power.

You just have to trust that the manufacturers knew what they were doing.

or they are conspiring with OPEC.