Max Engine Revs?

Nuttzz

I was driving with a friend yesterday in his C5 and I noticed that he would regularly bring his engine up to 40x RPM before changing gears, he wasnt overtaking or anything just standard N7/M50 driving, is this normal, what is normal? Personally I would change at 30x.

fletch

Yeh if I wasn't pushing it I'd change up as soon as possible, prob around the 3k (or less) mark also. He's jus wastin fuel lettin the revs climb to 4k.
Although...I do remember a report on Top Gear that said it can often be more economical to rev the engine...i.e. to get up to cruising speed quicker. This way you spend less time accelerating and more time with the engine in 5th gear.

unkel

The faster a car accelerates, the more fuel it consumes

Seth Brundle

yes, but you arrive at the required speed quicker - would it balance out against accelerating slower but therefore taking longer, i.e. is the rate of acceleration against time proportional?

Chimaera

The economy point is one I've often thought about myself. It's hard to tell really - I suspect taking it easy works better for lowish speeds in and around town, but for open road driving it's better to settle down at cruising speed as soon as possible.

In any case, it's fun to feel the surge of acceleration from revving the engine hard, especially in the lower gears.

ButcherOfNog

With a cold engine, around 2000rpm, once its warmed up, 4500rpm. If overtaking, 7000rpm.

Furp

It depends on the engine and drivetrain and of course the car.

I read an article before but can't find it now so I could be wrong.

Anyway the article was about these fuel efficiency races where you had to get as far as possible on a certain amount of petrol and the most efficient way of doing it was to accelerate hard to a set speed as quickly as possible then turn the engine off and coast until the speed became too low then turn the engine back on and accelerate again.

Also take in mind that every engine and car has a sweet spot where it is most efficient, on my car I think its going about 50-55 mph in fifth gear, doing this speed my mpg hits almost 50mpg if I have a long enough fairly straight section of road where I can keep the same speed. above and below that speed and revs my engine is less efficient, btw my car is a 1.8L Primera. I prefer to accurate quickly and get up to cruise speed when I know that I'm not going to have to stop a couple of hundred feet down the road.

In passenger airplanes they try and accelerate & climb and get up to cruise speeds as quick as possible to save on fuel. Of course with all the regulations on noise levels they have to compromise and try and make the acceleration and climb as efficient for the regulations and passenger comfort. sorry a bit ot.

fletch

ButcherOfNog wrote:

If overtaking, 7000rpm.

What are you drivin? A v-tech civic or motorbike, theres no necessity for that kind of revs.

Seth Brundle

fletch wrote:

ButcherOfNog wrote:

If overtaking, 7000rpm.

What are you drivin? A v-tech civic or motorbike, theres no necessity for that kind of revs.

a bike?

unkel

Furp wrote:

In passenger airplanes they try and accelerate & climb and get up to cruise speeds as quick as possible to save on fuel

The highest acceleration of an airplane is when it is still on the runway. The reason for this high accelaration is that to get airborne, a certain air speed needs to be reached. Also obiously, the runway length is limited

Once airborne, acceleration is still not that high. The reason the plane climbs as quickly as possible is that the fuel savings flying at a high altitude are enormous because of very low air resistance due to lack of oxygen

fletch

kbannon wrote:

a bike?

Well that makes sense now

The Clown Man

I would often take my car up to 4500 revs on a normal acceleration. If overtaking I would go to 6500 - 7000. I would try to keep the revs around 2500 - 3000 when cruising.

But seriously, that's just the way the car drives. Other cars I have driven would feel strained at 4000 but the Alfa just seems to be in it's elephant at around 3500 - 4000. (And that's when the power really kicks in! )

Not to mention the fact that going 80mph or so would take the revs to 4000 in 5th gear and you can hardly notice it's higher than usual.

mike65

Most efficient gearchanges take place at or near max torque.

Mike.

ButcherOfNog

fletch wrote:

What are you drivin? A v-tech civic or motorbike, theres no necessity for that kind of revs.

2.2vtec prelude, no point having it and not using it