How accurate is this statement?

[Syringer]

1) To optimize efficiency, you need to run the engine at optimum RPM's. This is exactly what hybrid cars do - when they run the engine, they run it at optimum settings, and get the most power per liter, and end up qith 90 mpg. Of course, they use a few other tricks (charging when breaking, no gas wasted when "idling") Anyways, this optimum is rarely at the minimum RPM's.

(When I get to my lab, I could find some old data.. and put up a nice graph or something.)

2) There is the "choking" effect. If you're in too high of a gear, and hence to low of RPM (i.e. not putting enough hp's etc.) the engine start injecting extra gas.. which adds power.. but kills efficiency. (Again, for good emissions and low consumption.. you want to run lean.. for extra power.. you want to run rich.. unfortunately, the two don't work together. It's either one or the other.)

 

[Syringer]

..

 

[PowerMacG5]

I thought hybrids worked by powering the wheels using an electric engine, with a gas generator to charge the batteries.

 

[Transition]

Originally posted by: Syringer
1) To optimize efficiency, you need to run the engine at optimum RPM's. This is exactly what hybrid cars do - when they run the engine, they run it at optimum settings, and get the most power per liter, and end up qith 90 mpg. Of course, they use a few other tricks (charging when breaking, no gas wasted when "idling") Anyways, this optimum is rarely at the minimum RPM's.

(When I get to my lab, I could find some old data.. and put up a nice graph or something.)

2) There is the "choking" effect. If you're in too high of a gear, and hence to low of RPM (i.e. not putting enough hp's etc.) the engine start injecting extra gas.. which adds power.. but kills efficiency. (Again, for good emissions and low consumption.. you want to run lean.. for extra power.. you want to run rich.. unfortunately, the two don't work together. It's either one or the other.)

For maximum efficiency and motor longevity you want to run a naturally aspirated motor at gasolines stoichiometrix ratio of 14.7:1 Lean = Bad

 

[Crucial]

Originally posted by: Marauder911
I thought hybrids worked by powering the wheels using an electric engine, with a gas generator to charge the batteries.

Thats a negatory.

 

[Transition]

Originally posted by: Marauder911
I thought hybrids worked by powering the wheels using an electric engine, with a gas generator to charge the batteries.

Hybrids like the Honda Insight use the electric motor to deliver additional power when needed. If sufficient power is being delivered by the gas engine the electric motor will not turn on. The electric engine uses regenerative braking to recharge the battery pack. Hybrids fuel efficiency ratings are more efficient in stop-and-go environments then highway driving since the constant stop-and-go is powered largely by the electric motor.

 

[PowerMacG5]

Originally posted by: Transition

Originally posted by: Marauder911
I thought hybrids worked by powering the wheels using an electric engine, with a gas generator to charge the batteries.

Hybrids like the Honda Insight use the electric motor to deliver additional power when needed. If sufficient power is being delivered by the gas engine the electric motor will not turn on. The electric engine uses regenerative braking to recharge the battery pack. Hybrids fuel efficiency ratings are more efficient in stop-and-go environments then highway driving since the constant stop-and-go is powered largely by the electric motor.

I see. Thanks for the info.

 

[frostgiant]

I don't know a whole lot about cars, but I will try:

1) Yes, every engine has a "optimal" RPM (usually 3000 ish). But there is NO WAY a hybrid gets anything close to 90 mpg. I just read a story that hybrids gas mileage is much lower than advertised. Back to optimal RPMs, most cars are geared for the optimal RPM in high gear to be around 60mph, so if you drive faster than that, you get worse mileage.

2) This would go back to the engine having an optimal RPM. If I am going say 20 mph in 3rd, my engine would be going at a lower than optimal RPM for 3rd gear and thus worse gas mileage. Also, you wouldn't have much acceleration when speeding up from 20 mph.

Part of the reason hybrids get such great gas mileage is smaller engines and they are light weight.

 

[thomsbrain]

all i know is at 30 mph, i need my foot on the gas in 3rd, and if i take it off the gas, the tranny kicks into 4th and it will just cruise along without any extra gas. that's at 1500 RPM in a torque-less 4-banger.

 

[Syringer]

I was always under the impression that lower rpms will result in better mileage. So is this not true?

 

[MrScott81]

i thought so too, but i don't know jack about cars

 

[UNCjigga]

Seems to be right. In that 'Top Gear' Exige video the driver (sorry I'm not fan enough to know his name) states that the Exige's Toyota engine uses a dual-cam where each cam has a different role. One cam is the 'efficient' cam which is active up to about 5000 rpm, but then near 6000 rpm the 'power' cam kicks in, and the ecu tends to keep the engine at or above 6000 rpm after that to keep the 'power' cam engaged.

It sounded flaky to me at first, but I guess I believe it...