[paras211]

why do bikes rev higher than cars? is it just coz the engine is small its easier to rev higher or is there more to it?

i mean even not so performance oriented bikes rev till 9k


one more question didnt want to start a new thread
what is different about avation fuel than normal fuel? i remmeber seeing gautam singhania putting some blue fuel or some thing like blue(not kerosene i am sure) in his lotus at the speed run a few years back. when it was held at bandra

[revtech]

ill answer the latter part for you.aviation fuel are mainly of three types

100 (green)
100 low lead(blue)
jet fuel (red)

they are of a slightly higher octane.most other high octanee fuels in india are with addiitives while these are pure.

[paras211]

so without additives is better??

[ananthkamath]

small-capacity bikes rev higher because they need to have higher specific power output in order to maintain decent driveability.

they can afford to have higher rev limits because they have a small stroke compared to most car engines and so the piston speed & acceleration is much lower at a given rpm.

[badri]

Higher RPM of a bike engine is due to

1) Small stroke ( piston speed is limited.Hence smaller stroke-faster rpm)
2) Lighter rotating internals ( like crank)
3) Lesser valve movement/spring rebound.Hence higher cycles per sec

If you get rid of valve springs ( by means of pneumatic valves), have smaller stroke and light interernals you can have a car engine revving as high as a bikes ( F1 engines by cosworth ran over 20000 rpm in the last race with Williams)

[veyron1]

Actually, any engine can have a high rev-limit, provided it has a low stroke, and the design specifications to support it (valve height, weight, roller specs, flywheel weight, etc.) . High performance Hondas have always been rev-happy, straight out of the showroom. Modded Skylines have been known to have 10K redlines, without reliability issues.

Litre class engines and upwards do not rev that high. It's just the 600cc sportsters that have been known to rev above 15K; like the new R6...

Originally Posted by ananthkamath

small-capacity bikes rev higher because they need to have higher specific power output in order to maintain decent driveability.

Actually, even though they have high specific outputs (most surpassing 150 bhp/litre), driveability/rideability is affected a lot by their torque curve. Most of the sportsters aren't that rideable below 5K (a big pain in city traffic), because of their peaky torque curves..

[Mpower]

Originally Posted by veyron1

Litre class engines and upwards do not rev that high. It's just the 600cc sportsters that have been known to rev above 15K; like the new R6...
..

..and 400cc inline fours rev even higher. 250 cc inline fours (kinda rare but do exist) take it up to another level. All driven by the same logic.

[kuttapan]

@paras - The primary reason for bikes to have high revving engines is lack of torque. The small capacity bikes make piddly amount of torque, so they need to rev high to produce decent power. power is a function of torque and rpm.

If you notice, Bullets don't rev high(less than 6k rpm), as they have oodles of torque, but still produce the most power(among Indian bikes). There are other reasons why a Bullet does not rev high, but that's not relevant here.

Another thing is, high revving engines usually have shorter stroke, compared to the lazy engines. Also, push rod engines generally rev lower than OHC engines.

[ajitkommini]

Originally Posted by revtech

ill answer the latter part for you.aviation fuel are mainly of three types

100 (green)
100 low lead(blue)
jet fuel (red)

they are of a slightly higher octane.most other high octanee fuels in india are with addiitives while these are pure.

Aviation fuel for piston engined aircraft is high-octane petrol with a low flashpoint. Jet fuel (Aviation Turbine fuel) is a kerosene based fuel

[paras211]

flashpoint=ignition point??

[vinya_jag]

Was not sure on where to post this question. Mods please move this to the appropriate forum.

1. Bikes redline close to 11000 RPM while cars can not do more than 7000. Why is this?
Is it because the single cam in car cannot withstand any more from all its cylinders? And the bike with only 1 cylinder and a smaller cam can hold more?

2. Cars produce their max torque at very low RPMs and bikes at higher RPMs.
Is this because they are tuned to work that way?

3. My Bike sounds more relaxed (Low frequency) even at 6000 RPM but my car at 6000 RPM is singing in all its glory.
Is this because the 4 cylinders in my car alternate in a way and the sound produced is a superimposed sound of all 4 engines which make it sound higher Frequency?

Any more details on how the car engines and Bike engines differ in terms of material quality, sound deadening, NVH etc

[vina]

I don't know whether it has been answered elsewhere, and the questions interest my curiosity too. Here are some guesses:

Originally Posted by vinya_jag

Was not sure on where to post this question. Mods please move this to the appropriate forum.

1. Bikes redline close to 11000 RPM while cars can not do more than 7000. Why is this?
Is it because the single cam in car cannot withstand any more from all its cylinders? And the bike with only 1 cylinder and a smaller cam can hold more?

Part of the reason would have to be the heavier crankshafts etc. that the bigger engines have. Higher the reciprocating mass, higher the forces for a given rpm and hence to be within the limits of materials you may have to limit the rpm.

But this is just a guess.

Originally Posted by vinya_jag

2. Cars produce their max torque at very low RPMs and bikes at higher RPMs.
Is this because they are tuned to work that way?

Even race cars generate torque at higher rpms - all Honda street cars too generate it at higher rpms (relative to other cars)

It is the question of the application - and hence the tuning.

Originally Posted by vinya_jag

3. My Bike sounds more relaxed (Low frequency) even at 6000 RPM but my car at 6000 RPM is singing in all its glory.
Is this because the 4 cylinders in my car alternate in a way and the sound produced is a superimposed sound of all 4 engines which make it sound higher Frequency?

One thing I can definitely tell you - no amount of adding/subtracting multiple waves (or different amplitudes and phases) of a given frequency is going to result in a wave with a higher or lower frequency.

The car engine is louder - doesn't mean it has higher frequency, loudness is NOT frequency.

Originally Posted by vinya_jag

Any more details on how the car engines and Bike engines differ in terms of material quality, sound deadening, NVH etc

there are obvious other differences e.g. bike engines are generaly air cooled, almost all of them are petrol (NATO is trying to build a diesel bike to simplify their logistics - they use diesel in all other vehicles), but I guess you knew these.

[hdnivara]

*BUMP*

The Ninja ZX12R has a 1.2 litre engine producing a whopping 160bhp! But most pf the 1.2 litre engines in cars produce somewhere close to 90PS (Swift)

What makes the Ninja produce so much power?
I am not much into technical things, but, I do understand the previous discussions here: Smaller stroke, single cylinder - so smaller crank and stuffs. But, are these that substantial which would lead to such a difference in power?

[vina]

Originally Posted by hdnivara

*BUMP*

The Ninja ZX12R has a 1.2 litre engine producing a whopping 160bhp! But most pf the 1.2 litre engines in cars produce somewhere close to 90PS (Swift)

What makes the Ninja produce so much power?
I am not much into technical things, but, I do understand the previous discussions here: Smaller stroke, single cylinder - so smaller crank and stuffs. But, are these that substantial which would lead to such a difference in power?

I don't know the specs but let me venture a guess - it produces its peak power at much higher rpm than the 90ps cars with 1.2L engines.

[hdnivara]

Exactly and adding another reason: the compression ratio.
The CR of the Ninja should be much higher that the 1.2L cars.

Any other besides these two?