What's the difference between Turbo and Overdrive...

[Xenon14]

in a car?

 

[Soybomb]

A turbocharger is a piece of hardware that gives a power and efficiency boost by compressing air. Overdrive is usuaully driving the output shaft of the transmission faster than the input shaft. (think I got that right) Completely different

 

[Xenon14]

So what does Overdrive do exactly? My nissan altima has it, when i turn it off my RPM increases...granted it's less efficient way of driving, but when do i need to use it?

oops, I mean, when i DO use it it's MORE efficient. When it's off the RPM increases.

 

[vi edit]

Overdrive is a "cruising" gear that yields better gas milage at highway speeds.

 

[Supradude]

Soybbomb's got it...

Turbo is actually an add-on to your car that boosts performance and increases acceleration and/or top end depending on type and setup...

To my knowledge, overdrive is just a fancy name for "thrid gear" in some sedans. I recall drivin an older toyota camry that had went from 2-D (4th gear drive) and had no 3... the 3 was in essence the OD...

 

[Viper GTS]

Turbo
Automatic Transmissions (With a section on overdrive)

A turbo is an exhaust powered forced induction system, while an overdrive is a gear-ratio that allows the engine to spin slower than the drive wheels - resulting in low RPM highway cruising.

Viper GTS

 

[DesignDawg]

Always use overdrive in normal driving. The question is when do you NOT need to use it. The answer is when you are driving in mountains, or very hilly country, where having overdrive on would result in too much downshifting. Basically, overdrive is (for simplicity's sake) a higher gear. Like adding 6th gear to a 5-speed. It allows the engine to run at lower RPM, get better mileage.

Ricky
DesignDawg

 

[Zenmervolt]

As usual in car threads Soybomb is right. A turbo is short for turbo-supercharger, and it uses an exaust driven turbine to drive a compressor, which forces more air into the engine. More air means more oxygen which means a bigger explosion, which yeilds more power. Overdrive is simply a gear ratio smaller than 1:1 in the gearbox (note that due to the gear ratio of the differential or final drive the ratio of the entire transmission of a car is almost always more than 1:1, and generally in the area of 2.5:1 at the least). Example:

4th gear ratio; 1:1 (The most common 4th gear ratio)
5th gear ratio; .65:1 (A made-up overdrive ratio)
Final Drive ratio: 3.56:1 (a common differential ratio)

So the overall ratio in 4th gear is 3.56:1, and the ratio in 5th gear (overdrive) is 2.314:1 .

Zenmervolt

EDIT: It should also be noted that overdrive is usually a very large jump in ratio from the gear below it, and generally has no use other than for cruising on a flat road. Because the engine is so much less responsive when the transmission is in overdrive, BMW does not have an overdrive gear in it's 5-speed transmissions, in a BMW transmission, 5th gear is a 1:1 ratio, which also allows all the other gears to be more closely spaced.

 

[Xenon14]

One more question...how does vtec on Hondas work?? my '95 altima has 150hp and my dad's '99 accord has 150hp w/ vtec...his acceleration is much better than mine (even w/ my overdrive off), and to add to that, his car weighs more too.

 

[DesignDawg]

The VTEC doesn't have anything to do with the acceleration difference. That's mainly due to the drivetrain. Hondas have a really snappy first gear. VTEC doesn't kick in until higher RPMS. Like, REALLy higher RPM's, I think. But someone else will have to fill you in on the details.

Ricky
DesignDawg

 

[Soybomb]

Explaining vtec is a tad more complex. You have at least one came shaft in your car (maybe more, not familiar enough with it) As this lumpy stick of metal turns, the lumps cause intake and exhaust valves to open. You can change performance by changing how soon/how long the valves open, but often the tradeoff is worse power at a different rpm range. VTEC is honda's answer to this. Your valves open differently at different rpms. Other car lines have similar systems.

 

[Viper GTS]

VTEC

God, I love that site. I don't think there's anything they DON'T have.

Viper GTS

 

[Zenmervolt]

<<how does vtec on Hondas work??>>

On a most basic level, VTEC alters the lift and duration of the valves, allowing near optimal low RPM behavior without sacrificing high RPM performance. If you look at the characteristics for both the Honda engine and the Nissan engine, you will brobably find that the Honda makes the majority of its HP and torque at a high RPM, while the power and torque of the Nissan tend to fall off as RPM increases. Because under hard acceleration the engine is in the upper part of it's rev band, the Honda is in the best part of its powerband at this point while the Nissan is comparitively wheezing at higher RPMs because it cannot breathe as well as the Honda, whose engine has the valves open longer at high RPM for better breathing. Your Nissan probably beats the Honda to 15 or 20 mph, but once the engine hits the upper ranges of the rev band the Honda has a distinct edge.

Zenmervolt