Revs, how high do they go?

[youngsyr]

Limpet said:

The R6 is an interesting case as Yamaha gave the 2006 model a 17,500 RPM redline which the marketing team made quite a big deal out of. A few months later when bikes started hitting dynos with calibrated tachometers connected to them, it was discovered that the engines were actually limited at 16,200 RPM. The rev counter was very optimistic. Quite an embarrassing position to put yourself in as a manufacturer, all things considered.

My early 90s Kawasaki ZZR600 would pull a genuine 14,000 RPM. Bike engines have been capable of these kind of revs for a quarter of a century now, and with excellent reliability and longevity.

Can someone please explain to me why a bike engine should rev higher than a car engine?

I understand turbos and superchargers limiting rpm, but what about naturally aspirated engines? Why doesn't the family Focus rev to 12,000 rpm, for example?

Is it simply due to the reliability of valve train components? If so, why do bikes rev so high?

[skene]

youngsyr said:

Can someone please explain to me why a bike engine should rev higher than a car engine?

I understand turbos and superchargers limiting rpm, but what about naturally aspirated engines? Why doesn't the family Focus rev to 12,000 rpm, for example?

Is it simply due to the reliability of valve train components? If so, why do bikes rev so high?

Reciprocating mass as I under stand. I.e there's less weight in a bike engine. The largest sports bike high revving engines are only 1.3s. Also with such high revs the torque delivered wouldn't really be enough to move a large car. Although they seem to be okay in westfields caterhams etc.

[youngsyr]

skene said:

Reciprocating mass as I under stand. I.e there's less weight in a bike engine. The largest sports bike high revving engines are only 1.3s. Also with such high revs the torque delivered wouldn't really be enough to move a large car. Although they seem to be okay in westfields caterhams etc.

Thanks. Unfortunately, neither makes much sense to my simple mind though: F1 cars rev to 18,000 rpm and weigh around 600kgs, so why does torque profile limit the rpm to less than half that in a smart car, for example?

Also, reciprocating mass - there are plenty of econoboxes with smaller than 1300cc naturally aspirated engines, so why aren't these high revving like bikes?

Don't get me wrong, I can understand why car engines don't rev to 18,000 rpm outside of F1, but I don't understand why they're usually limited to around 7,000 rpm. BMW make a big deal about my M3 revving to 8,500 rpm, but that is nothing compared to the average bike.

[Captain Muppet]

youngsyr said:

Limpet said:

The R6 is an interesting case as Yamaha gave the 2006 model a 17,500 RPM redline which the marketing team made quite a big deal out of. A few months later when bikes started hitting dynos with calibrated tachometers connected to them, it was discovered that the engines were actually limited at 16,200 RPM. The rev counter was very optimistic. Quite an embarrassing position to put yourself in as a manufacturer, all things considered.

My early 90s Kawasaki ZZR600 would pull a genuine 14,000 RPM. Bike engines have been capable of these kind of revs for a quarter of a century now, and with excellent reliability and longevity.

Can someone please explain to me why a bike engine should rev higher than a car engine?

I understand turbos and superchargers limiting rpm, but what about naturally aspirated engines? Why doesn't the family Focus rev to 12,000 rpm, for example?

Is it simply due to the reliability of valve train components? If so, why do bikes rev so high?

Bikes can't use much torque, because they flip over (unless you make them very long, which has implications for cornering). So you can design them to produce power without much torque, which means lots of revs.
Or looked at another way - race rep bikess are marketed/raced at a particular engine capacity, and need the maximum headline power number and revs really help here.

You can fit high reving naturally aspirated engines in to cars, but then the internet bangs on about how gutless they are and refuses to use the right gear.

[youngsyr]

Captain Muppet said:

youngsyr said:

Limpet said:

The R6 is an interesting case as Yamaha gave the 2006 model a 17,500 RPM redline which the marketing team made quite a big deal out of. A few months later when bikes started hitting dynos with calibrated tachometers connected to them, it was discovered that the engines were actually limited at 16,200 RPM. The rev counter was very optimistic. Quite an embarrassing position to put yourself in as a manufacturer, all things considered.

My early 90s Kawasaki ZZR600 would pull a genuine 14,000 RPM. Bike engines have been capable of these kind of revs for a quarter of a century now, and with excellent reliability and longevity.

Can someone please explain to me why a bike engine should rev higher than a car engine?

I understand turbos and superchargers limiting rpm, but what about naturally aspirated engines? Why doesn't the family Focus rev to 12,000 rpm, for example?

Is it simply due to the reliability of valve train components? If so, why do bikes rev so high?

Bikes can't use much torque, because they flip over (unless you make them very long, which has implications for cornering). So you can design them to produce power without much torque, which means lots of revs.
Or looked at another way - race rep bikess are marketed/raced at a particular engine capacity, and need the maximum headline power number and revs really help here.

You can fit high reving naturally aspirated engines in to cars, but then the internet bangs on about how gutless they are and refuses to use the right gear.

So presumably F1 engines only rev so high because of the cc limit?

If there were no limit, would we see huge capacity, (comparatively) lower revving engines in F1?

[jon-]

^ Spot on. Don't forget power (bhp) = Torque x RPM ÷ 5252

[Chewykneeslider]

OK, 101 on power and torque.

Have you ever wondered why the powerful F1 cars you see on TV have such tiny driveshafts? They look to be about the same size as those you get on your Eurobox, but they can transmit 700BHP or whatever.

Its simple, because the torque produced by an F1 car won't be that different from most road cars.

Power = torque x rpm.

Torque is the twisting force at the wheels, and if you can produce the same twisting force at 20,000 rpm as you can at 10,000 rpm then you have double the power.

People have mentioned on here that most piston engines are limited by their mean (rms) piston speed which is about 25m/s.

If the mean piston speed stays constant, the only way to get higher rpm and therefore power, is to reduce the stroke length to keep the piston speed within sensible limits.

My ancient TR6 has a 74mm bore and a 96mm stroke, my Ducati has 92mm bore and 68mm stroke. They both produce similar power, but the Ducati only has 904cc from 2 cylinders, where the TR6 needs 2500cc and 6. The huge difference in the feel to drive/ride of these engines is down to the number of cylinders, and the torque figures.

[paranoid airbag]

Economy? A fireblade engine returns fairly poor mileage when it's only got a motorbike to push - worth it for something that's more used for fun where light weight and throttle response matter but not a daily driver. Fairly noisy too, and would a superbike engine really last the hundred thousand miles - even if neglected - that a car engine will?

edit: also, what Capt. Muppet said about people being unable to understand gears

Edited by paranoid airbag on Monday 29th July 12:29

[john2443]

youngsyr said:

So presumably F1 engines only rev so high because of the cc limit?

If there were no limit, would we see huge capacity, (comparatively) lower revving engines in F1?

I suspect it would make a bit of difference but not huge - an 4 litre engine doesn't give 4 times as much power as a 1 litre and it weighs more per hp - maybe there would be an advantage in having say 10% more cc and less revs but it certainly wouldn't be better to have twice the cc and half the revs.

[rohrl]

I was quite surprised to learn from a guy called Scott that the rev limit on the Audi RS5 is just 4500rpm. That might sound more like the figure you'd expect from a 1.9TDi but I am assured that the car's definitely an RS5.

[b14]

rohrl said:

I was quite surprised to learn from a guy called Scott that the rev limit on the Audi RS5 is just 4500rpm. That might sound more like the figure you'd expect from a 1.9TDi but I am assured that the car's definitely an RS5.

Ha... red lines at 8500rpm.

Edited by b14 on Monday 29th July 12:13

[rhinochopig]

rohrl said:

I was quite surprised to learn from a guy called Scott that the rev limit on the Audi RS5 is just 4500rpm. That might sound more like the figure you'd expect from a 1.9TDi but I am assured that the car's definitely an RS5.

nice cross thread pollination.


Back on topic, isn't the limiting factor valve speed rather than piston speed at high RPMs, i.e. you get valve bounce so need to ACTIVELY open and close the valve rather than rely on springs?

[sovietspybob]

I believe it's as much to do with the flame front of petrol as anything, petrol will only burn so fast which is why F1, motorbikes & the S2000 all only go about the same speed as each other.

There's also valve issues which is why F1 use pneumatic valve springs as they don't rebound like metal springs do. Then there's desmodromic but that seems a bit over complex compared to pneumatic.

[xRIEx]

youngsyr said:

skene said:

Reciprocating mass as I under stand. I.e there's less weight in a bike engine. The largest sports bike high revving engines are only 1.3s. Also with such high revs the torque delivered wouldn't really be enough to move a large car. Although they seem to be okay in westfields caterhams etc.

Thanks. Unfortunately, neither makes much sense to my simple mind though: F1 cars rev to 18,000 rpm and weigh around 600kgs, so why does torque profile limit the rpm to less than half that in a smart car, for example?

Also, reciprocating mass - there are plenty of econoboxes with smaller than 1300cc naturally aspirated engines, so why aren't these high revving like bikes?

Don't get me wrong, I can understand why car engines don't rev to 18,000 rpm outside of F1, but I don't understand why they're usually limited to around 7,000 rpm. BMW make a big deal about my M3 revving to 8,500 rpm, but that is nothing compared to the average bike.

As well as the good replies above, it's also about usability.

An engine's powerband is usually defined as the rev range from where peak torque is made to where peak power is made (I'm assuming for engines where peak power is higher up the range than peak torque). An engine with a wide powerband is generally easy to drive, power is available wherever you are in the rev range and gear selection is less important; with a narrow powerband, gear selection can become extremely important, and outside of the powerband the engine can struggle to accelerate if in an inappropriate gear.

A 'normal' family road car needs to be driveable more than it needs to be powerful (given the mass of the vehicle), so a wide powerband is more important.

A race car (or bike) is generally driven as hard as possible and is designed to be kept in the powerband (down to gear ratios/final drive ratios selected for specific corners). The old 2 stroke 125 GP bikes had peak torque at, say, 11,250 rpm and peak power at 11,500rpm - a powerband 250rpm wide. At tight hairpins they may need to slip the clutch in first gear just to be able to accelerate away.

A road superbike/sportsbike doesn't necessarily get driven at 10 tenths all the time, but because of its low mass (a fifth or less the mass of a car) it doesn't need a huge amount of torque/power to potter about, so it still remains driveable outside of its powerband.

Bike engines in kit cars have different final drive ratios that take into account the greater mass (so a bike engine with a top speed of 175 in a bike might give a top speed of 120 in a bike-engined car (BEC)). There is often split opinion BEC vs CEC. Again, BECs are generally better for going for a blast where you are driving it hard, race car style, where you stay in the powerband; for a better all-rounder, CEC is generally preferred.

[TREMAiNE]

Ozzie Osmond said:

General Madness said:

Publicly available production model cars, bikes, quads any mode of transport for road use.

Need to check out those Mazda rotaries. 9,000+ rpm.

No pistons which have to keep making 180 degree changes of direction.

My RX8 R3 will to 10,000 rpm off the bounce. Apparently they're capable of hitting as high as 13,000.

[Mave]

Chewykneeslider said:

OK, 101 on power and torque.

Have you ever wondered why the powerful F1 cars you see on TV have such tiny driveshafts? They look to be about the same size as those you get on your Eurobox, but they can transmit 700BHP or whatever.

But there's no gearbox between the wheel and the driveshaft; so if you're putting down 700bhp then it's only road speed and wheel diameter which affect driveshaft torque. Engine configuration doesn't come into it.

[Captain Muppet]

sovietspybob said:

I believe it's as much to do with the flame front of petrol as anything, petrol will only burn so fast which is why F1, motorbikes & the S2000 all only go about the same speed as each other.

There's also valve issues which is why F1 use pneumatic valve springs as they don't rebound like metal springs do. Then there's desmodromic but that seems a bit over complex compared to pneumatic.

Traditional steel valve springs can work just fine at 22,000rpm and beyond.
They just need the valves to be small and light and the cam lift and open ramps to be gentle.
Or you just make the valve strong enough to take the shock load and increase the spring force to control bounce, but that increases friction, which is bad.

[Kozy]

It's the stroke. It's all in the stoke.

Short stroke = High RPM.
Long stroke = Low RPM.

Both will have the same piston speed, and it won't be higher than 25ms unless it's got a life expectancy rated in minutes.

Ultimately, the power of an engine has little to do with the capacity or the stroke, and boils down to bore and number of pistons, or more simply, total piston area.

[Huff]

TREMAiNE said:

My RX8 R3 will to 10,000 rpm off the bounce. Apparently they're capable of hitting as high as 13,000.

One thing to note about the wankel - the output shaft is geared up to 3x the rotor speed. So in a Mazda with an output shaft speed of ~8000rpm the rotor is only actually spinning at about 2600rpm.

(The gearing is required partly out of efficiency and rotor tip seal wear considerations, but also because the rotor runs an eccentric cycloidal path and gearing its inside face to a central shaft the only way to get a concentric rotary motion out of the thing)

[Mave]

Captain Muppet said:

Bikes can't use much torque, because they flip over (unless you make them very long, which has implications for cornering). So you can design them to produce power without much torque, which means lots of revs.

Huh? I guess you're talking about torque at the wheel? For a given power and speed, how do you reduce torque at the wheel?