5 Speed or 6 speed, Whats the difference?

[Rodimus Prime]

The entire Diesel range for Land Rover?

Which by the way when cruising at 110km/h (~68mph) in 6th gear is running at roughly 1200-1400 rpm, seriously low, but then again it redlines at about 4000rpm i think.

In petrol cars, higher RPM generally means more power, since (again, as a rule of thumb) Power = torque x revs. But higher revs has more losses etc. In a diesel engine, the torque band comes in really early and fairly large, meaning low power (low rpms). Low rpms is more efficient. That is why loads of torque early on is good for pulling heavy stuff.

ok minor correctoin on their to explain hp.

Hp= (Torque x RPM)/5252. This also explains why most cars have more horse power than they have torque and that is because peak torque is after 5252 rpm. In a diesel where all the power is lower in the RPM they will not make as much horse power. Reason high RPM are used is because you can get a lot of horse power for quite a bit less torque.

 

[Fearless Leader]

wow thanks all this really helped my understanding.

 

[twoodcc]

ok minor correctoin on their to explain hp.

Hp= (Torque x RPM)/5252. This also explains why most cars have more horse power than they have torque and that is because peak torque is after 5252 rpm. In a diesel where all the power is lower in the RPM they will not make as much horse power. Reason high RPM are used is because you can get a lot of horse power for quite a bit less torque.

thanks for that

but why 5252?

 

[Rodimus Prime]

thanks for that

but why 5252?

you know I never really ask why. I just have always just accepted it as part of the formula I used when I need to calculated it which is few and far between. Before I posted it I did check to make sure it was the correct number. I also just double checked and made sure so it is 5252

 

[twoodcc]

you know I never really ask why. I just have always just accepted it as part of the formula I used when I need to calculated it which is few and far between. Before I posted it I did check to make sure it was the correct number. I also just double checked and made sure so it is 5252

hmm. ok. interesting.

so do you know why diesel engines use lower RPM?

 

[Rodimus Prime]

hmm. ok. interesting.

so do you know why diesel engines use lower RPM?

well one reason is diesel from what I understand is diesel burns very different than Unleaded fuel and the engine run on compression.

 

[twoodcc]

well one reason is diesel from what I understand is diesel burns very different than Unleaded fuel and the engine run on compression.

oh yeah, i remember that. my dad told me that diesel burns longer than gas.

 

[iGav]

so do you know why diesel engines use lower RPM?

There's absolutely nothing to stop manufacturers producing a diesel engine that revs to similar levels as petrol engines.

But in doing so you'll somewhat reduce diesels double-advantage over petrol engines, namely the bundles of low speed torque, and fuel efficiency.

my dad told me that diesel burns longer than gas.

Diesel also produces more energy when it is burned.

 

[Rodimus Prime]

There's absolutely nothing to stop manufacturers producing a diesel engine that revs to similar levels as petrol engines.

But in doing so you'll somewhat reduce diesels double-advantage over petrol engines, namely the bundles of low speed torque, and fuel efficiency.



Diesel also produces more energy when it is burned.

there is Diesel fuel can not burn fast enough for some of the much higher reving petrol engines. Example of this is look at high end sports cars and race cars you will noticed none of them run on diesel. The reason for it is it just can not burn fast enough to make the hp. Even fast spinning diesel engines are no where near as close as a petrol engine. This is noticable in how slowly diesel engines can rev up. They just can not do it very fast and this would be under no load they are very slow at reving up when compared to a petrol engine.

Plus diesel uses compresion to ignited compared to petrol which uses a spark. Start cranking up the rpm and you can started getting it to ignited early.

Top it off diesel engines are a lot heavier than petrol engines so cranking up the RPMs on them starts getting a lot more difficult. The engines have to be stronger because of the added stress of how they work. But it means the pistons are heavier and at higher RPMs it gets a lot larger to move them.

 

[iGav]

Example of this is look at high end sports cars and race cars you will noticed none of them run on diesel.

Audi R10.

Peugeot 908.

The reason why diesel isn't more widely used in racing cars isn't a technical one, such engines are simply not permitted in many races series.

The reason for it is it just can not burn fast enough to make the hp. Even fast spinning diesel engines are no where near as close as a petrol engine. This is noticable in how slowly diesel engines can rev up. They just can not do it very fast and this would be under no load they are very slow at reving up when compared to a petrol engine.

Plus diesel uses compresion to ignited compared to petrol which uses a spark. Start cranking up the rpm and you can started getting it to ignited early.

Top it off diesel engines are a lot heavier than petrol engines so cranking up the RPMs on them starts getting a lot more difficult. The engines have to be stronger because of the added stress of how they work. But it means the pistons are heavier and at higher RPMs it gets a lot larger to move them.

I remember reading a quote from the head of engine development from Honda when they launched their first diesel engine a few years back for the European Accord, and he said exactly the same thing as me.

From an engineering point of view, it is perfectly possible to get a diesel engine to rev to similar levels of a petrol engine (now I'm not on about F1 engines here, more your average road car)... but there's simply no point, as the losses exceed the net gain.

 

[Counterfit]

and when you drop it to 5th, the RPMs go up, giving you more power! ha!

That's not the main reason downshifting lets you accelerate better. Read up on "mechanical advantage".

 

[twoodcc]

That's not the main reason downshifting lets you accelerate better. Read up on "mechanical advantage".

but it still does

 

[Rodimus Prime]

Audi R10.

Peugeot 908.

The reason why diesel isn't more widely used in racing cars isn't a technical one, such engines are simply not permitted in many races series.



I remember reading a quote from the head of engine development from Honda when they launched their first diesel engine a few years back for the European Accord, and he said exactly the same thing as me.

From an engineering point of view, it is perfectly possible to get a diesel engine to rev to similar levels of a petrol engine (now I'm not on about F1 engines here, more your average road car)... but there's simply no point, as the losses exceed the net gain.

but both those race cars you listed run at low RPMs and put out a lot more torque than HP. HP is where acceleration comes from. Diesel just can not run at high RPMs with out losing way way to much power in the trade off. the Fuel does not burn fast enough.

 

[Lord Blackadder]

Like I said before, a 6 gears is not inherently better than 5 - in fact, the ideal transmission would have just one ratio. In such a scenario, the engine would produce its maximum power and torque throughout its power band.
Imagine a 150hp/160lb-ft engine that produced that amount of power/torque at all engine speeds between 800-6000 rpm.

More gears generally means that your engine is less flexible, and needs the extra ratios to stay in its optimal power band. OR (as memntioned previously), an extra gear is added to give better fuel economy at freeway speeds. Sometimes, a car's entire transmission uses tall ratios that hurt performance but improve fuel economy (as in the old Civic HX), or uses very short ratios that are suitable only for racing.

but both those race cars you listed run at low RPMs and put out a lot more torque than HP. HP is where acceleration comes from. Diesel just can not run at high RPMs with out losing way way to much power in the trade off. the Fuel does not burn fast enough.

Horsepower alone does not determine acceleration. When you accelerate from a stop, look at your tach...as the car begins to move the engine is spinning much more slowly than the speed at which it makes its maximum power, unless you always rev your engine to 5k+ rpm every time you set off...the torque of the engine has more to do with the rate of acceleration than the power.