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Old 1st August 2006, 18:17   #16
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I dunno but everytime i acc in first (on the Vtec) and let go of the pedal, the car literally trws me onto the steering. Thats the kind of deceleration i get.

I feels it's mass, speed, gearing and engine capacity (cc per cylinder) that matter. Aerodynamics too, but at high speeds.

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Old 7th August 2006, 09:07   #17
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Quote:
Originally Posted by turbo_c
I'm really bad at math guys... and I hated Physics formulae... but I did have to mug a few, so...

Momentum = Mass * Velocity

Hence momentum is directly proportional to mass...
We all agree that the car has more mass (weight) than the bike, so the car will have more momentum than the bike too. It would take more force to stop the car than it would for the bike.

Coming to the source of the force (wow, it rhymes ) ... assuming that both are running 4 stroke petrol engines, their compression ratios would be similar, hence the intake resistance with the throttle closed would be similar as well. Also, if we assume that the bike has a 4 cylinder engine (I'm sure the Hyabusa does!), then we can safely assume that the amount of engine braking is similar too.... If we select similar gear ratios on the bike and the car, still the bike would "feel" like it has more engine braking because what you would feel is the RESULT of the engine braking; you would feel the deceleration of the bike...

Since the bike requires a lot less force to stop it (because it is lighter), it would decelerate faster, hence you would feel that it's engine braking is stronger.


- T u r b o C -
Right said…. momentum is the main reason.. I would like to add to the comment 2 things
Firstly it’s the Engine RPMs + Momentum that do the trick. If you are on a bike in 5th gear and at a speed of 60 KM/h the RPMs would be around 4500-4750 (depending on the engine capacity…and gear ratio because of it) If you are on a car at that rpm and that speed it would be in its first gear. So you will feel same breaking as you feel on the bike. (Theoretically). For the RPMs funda you can try comparing even Zen with Esteem. Esteem has a tall gear ratio so you cant feel much of an engine breaking while you can feel it on zen. Running both of them at same rpms and speed will result in similar engine breakings while running on same speed while on different rpms the results will differ.
Secondly there is a role of clutch/pressure plates. Usually when the clutch plates are new you will feel more engine brakes.
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Old 7th August 2006, 22:32   #18
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Two reasons:

1. Engine size: A 150 cc engine running at 60 km/h is revving much harder than a 1500cc engine doing the same speed.

2. Combustion chamber: A bike depends quite a lot on manual position of accelerator for the combustion of petrol. The moment the accelerator is withdrawn, petrol drastically slows down into the combustion chamber. While the car engines are similar, they are constantly fuel injected for the driver to notice any such decrease in energy.

3. Gearing: Bikes have very short gearing (typically 1:10.5) compared to cars. This is necessitated by point 1.

Lot of other points too long-drawn out to be readable in a forum

Last edited by theMAG : 7th August 2006 at 22:35.
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Old 8th August 2006, 06:26   #19
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Quote:
Originally Posted by drifter
Quote:
Originally Posted by WhiteKnight
Have you noticed that Diesel engines slow down faster when you lift the accelerator.
Infact i have noticed the exact opposite? In which car have you noticed this?
Drifter
The engine's compression stroke requires the most energy.
A speeding car has a lot of kinetic energy stored in its momentum.
Engine braking, dissipates that kinetic energy by using it for successive compression strokes.

Letting up on the accelerator pedal in a diesel car starves the engine of fuel. In that condition, the engine's compression strokes, (two out of four in every revolution), feed on the momentum of the car and dissipate it.

The car's forward momentum continues to turn the crankshaft and compress air inside the engine's cylinders. So engines which have higher compression and are therefore harder to turn, will provide the most engine braking.

Diesels IMHO will therefore provide superior engine braking to petrol engines.

But even this engine braking must be enhanced when the vehicle is a heavy trailer truck.

Compression brakes (aka Jake brakes)

The compression stroke dissipates the vehicle’s kinetic energy, by compressing the air in the cylinder. At this point the compressed air may release some energy by pushing down the piston and speeding up the truck again.

Back in 1987 in Everett, Wa, I was introduced to the compression release engine brake. This is a feature on heavy diesel trucks. It has a solenoid-mechanism to open the exhaust valve at the top of the compression stroke.

This prevents the compressed air in the cylinder from returning energy back to the piston and the truck.

Compression release engine brakes make a loud machine gun like chattering noise while being used. Residential areas have put up notices banning them: "Engine brakes restricted", etc.

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Old 8th August 2006, 08:39   #20
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ref'g to Ram's post above: http://jakebrake.com/technology/
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Old 8th August 2006, 09:21   #21
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Quote:
Originally Posted by ram
Diesels IMHO will therefore provide superior engine braking to petrol engines.

Compression brakes (aka Jake brakes)

The compression stroke dissipates the vehicle’s kinetic energy, by compressing the air in the cylinder. At this point the compressed air may release some energy by pushing down the piston and speeding up the truck again.

Back in 1987 in Everett, Wa, I was introduced to the compression release engine brake. This is a feature on heavy diesel trucks. It has a solenoid-mechanism to open the exhaust valve at the top of the compression stroke.

This prevents the compressed air in the cylinder from returning energy back to the piston and the truck.

Compression release engine brakes make a loud machine gun like chattering noise while being used. Residential areas have put up notices banning them: "Engine brakes restricted", etc.

Ram
very interesting..wonder why our modern diesels do not have such
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Old 8th August 2006, 09:39   #22
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Quote:
very interesting..wonder why our modern diesels do not have such
That is because we dont need them in cars....only required in heavy trucks...wonder if volvo trucks here have them...

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Old 8th August 2006, 10:08   #23
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Quote:
Originally Posted by drifter
That is because we dont need them in cars....only required in heavy trucks...wonder if volvo trucks here have them...

Drifter
Volvo trucks use something they've branded as the Volvo Engine Brake (VEB).

It comprises two collaborating pieces: a compression brake and an exhaust pressure governor. They call 'em the Volvo Compression Brake (VCB) and the Exhaust Pressure Governor (EPG).

An automotive high-speed diesel produces max. torque between 1500-2000 rpm. The VEB delivers higher braking effect at 1600 rpm and below. It's use of compression braking in conjunction with the exhaust pressure governor makes it quieter (no machine gun sound) and almost instantaneous to use.

What's different about Volvo trucks?
Volvo is one of the world's largest heavy engine manufacturers.
Their engines are manufactured to 10 micron assembly tolerances.
By way of comparison, human hair ranges in diameter from 17 to 181 microns.
That's what gives their legendary reliability, long life and economy.

Besides their innovative use of the exhaust pressure governor, holds the warm air in the cylinders at idle, allowing the engine to idle at 500-650 rpm, saving fuel.

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Old 5th July 2008, 12:44   #24
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Sorry to answer to a 2 year old thread. (I did it once before without being aware of the fact!). However this is a topic that has made me wonder for a long time and I had my own explanation though I could never confirm this. Hence I am posting it here so that may be someone can confirm or contradict.

OK why does an old, conventionally aspirated, Maruti 800 provide more engine braking than a MPFI Maruti 800? Try.

So my take on this is like this. I feel that the difference you are seeing could be between carburetted and fuel injected vehicles.

In carburetted (spelling?) vehicles, as soon as the throttle goes down the slider closes the fuel path and only the fixed amount of idling fuel is supplied to the engine, while in an MPFI engine even when the throttle is cut the amount of fuel supplied to the engine is controlled with other inputs also so that at higher rpms slightly more fuel is supplied even when the throttle is fully cut. This is what I suspect to be the reason, but anyway I could never get a confirmed reply from someone who has authentic knowledge.
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Old 5th July 2008, 16:38   #25
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Quote:
What's different about Volvo trucks?
Volvo is one of the world's largest heavy engine manufacturers.
Their engines are manufactured to 10 micron assembly tolerances.
By way of comparison, human hair ranges in diameter from 17 to 181 microns.
That's what gives their legendary reliability, long life and economy.

Besides their innovative use of the exhaust pressure governor, holds the warm air in the cylinders at idle, allowing the engine to idle at 500-650 rpm, saving fuel.

Ram
[/quote]

Hey Ram,

Thats wonderful news about Braking, Precision and fuel economy. Very very informative.

Thanks.

So long....
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