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**black asp** · 03-03-2016, 03:46 PM

Re: What is "Power", what is "Torque"..??

Originally posted by rakeshchn View Post

Thanks Divya, Rachit and John! Your answers definitely gave me a little bit more insight into the relationship between torque, power and RPM. So contrary to what I thought as engine RPM should be always dependent on rider input via throttle, it looks like the torque or power can influence the RPM and override the throttle input. Correct?

Also I guess you can sense that my initial question partly remains unanswered still, which is the mechanical part of it. That is the when the bike is climbing uphill and is losing torque and there by RPM, you are lazy and dont want to downshift yet and give it all to the throttle. Mechanically this should open the butterfly valve and cause more air-fuel mixture to go to engine, right? Or is there any mechanism by which carburettor limits air flow irrespective of the throttle valve position?

well if that be the case then if i open the throttle fully when the bike is parked and engine turned off then my entire fuel in the petrol tank will be gone inside the engine

CHEERS

**RohIIT** · 03-03-2016, 03:48 PM

Re: What is "Power", what is "Torque"..??

Originally posted by rakeshchn View Post

So contrary to what I thought as engine RPM should be always dependent on rider input via throttle, it looks like the torque or power can influence the RPM and override the throttle input. Correct?

Also I guess you can sense that my initial question partly remains unanswered still, which is the mechanical part of it. That is the when the bike is climbing uphill and is losing torque and there by RPM, you are lazy and dont want to downshift yet and give it all to the throttle. Mechanically this should open the butterfly valve and cause more air-fuel mixture to go to engine, right? Or is there any mechanism by which carburettor limits air flow irrespective of the throttle valve position?

Power is a function of torque . P=(2*3.14*engine rpm * Torque ) /60

When you are driving on plain ground , it need lets say 12hp to keep up the speed.

But key factor here is mass , as F=M.A
When you go up the hill a component of mass (cos component ) acts downwards. ( Please refer to forces and mechanics for this )
Due to this effective weight of bike is increased to 1.5times ( roughly speaking)
Now the 12hp which was carrying you in plains will suddenly feel powerless.

Regd your question , you need high amount of torque to pull you up the hills. Now this is very flexible as it depends upon how gearing and gear ratios are set and how power curve of engine is.

When you give full throttle under load ( i.e climbing ) you will see even though you are going WOT bike isnt going. This is because at that moment wheels are not generating torque to push the bike upwards ( read higher gears ) Hence you downshift to attain more torque and lesser speeds.

There is no limitation in carb or FI that limits butterly to open completely.

**Bibhu** · 03-03-2016, 03:49 PM

Re: What is "Power", what is "Torque"..??

Originally posted by rakeshchn View Post

Thanks Divya, Rachit and John! Your answers definitely gave me a little bit more insight into the relationship between torque, power and RPM. So contrary to what I thought as engine RPM should be always dependent on rider input via throttle, it looks like the torque or power can influence the RPM and override the throttle input. Correct?

Also I guess you can sense that my initial question partly remains unanswered still, which is the mechanical part of it. That is the when the bike is climbing uphill and is losing torque and there by RPM, you are lazy and dont want to downshift yet and give it all to the throttle. Mechanically this should open the butterfly valve and cause more air-fuel mixture to go to engine, right? Or is there any mechanism by which carburettor limits air flow irrespective of the throttle valve position?

The carb does not/can not limit airflow in the manner in the way you are describing. The suction of air is dependant on the movement of the piston in the cylinder, simillar to a syringe. So when the piston movement decreses, because the crank can not turn freely, because it has to turn the gears with more force going uphill against gravity, the intake suction decreses and causes the bike to stall.

Sent from my XT1033 using xBhp Connect mobile app

**RohIIT** · 03-03-2016, 03:51 PM

Re: What is "Power", what is "Torque"..??

Originally posted by black asp View Post

well if that be the case then if i open the throttle fully when the bike is parked and engine turned off then my entire fuel in the petrol tank will be gone inside the engine

CHEERS

Fuel air mixture enters into engine , when piston goes down and inlet valve is open. This creates suction in chamber which takes in Air fuel mix.
Thats why if one cannot start bike due to weak spark , it is required to open spark plug and move piston to clear chamber as it filled with unburnt Air fuel mix

**black asp** · 03-03-2016, 03:55 PM

Re: What is "Power", what is "Torque"..??

Originally posted by Bibhu View Post

The carb does not/can not limit airflow in the manner in the way you are describing. The suction of air is dependant on the movement of the piston in the cylinder, simillar to a syringe. So when the piston movement decreses, because the crank can not turn freely, because it has to turn the gears with more force going uphill against gravity, the intake suction decreses and causes the bike to stall.

Sent from my XT1033 using xBhp Connect mobile app

so if i twist the throttle when bike is stationary then petrol won't go in the engine resulting in poor fuel economy?

**RohIIT** · 03-03-2016, 03:59 PM

Re: What is "Power", what is "Torque"..??

Originally posted by black asp View Post

so if i twist the throttle when bike is stationary then petrol won't go in the engine resulting in poor fuel economy?

If bike engine is running (read on and making sound ) then yes FE will suffer
If bike engine is off ( read off and not making sound ) FE wont be affected.

**Bibhu** · 03-03-2016, 04:01 PM

Re: What is "Power", what is "Torque"..??

Originally posted by black asp View Post

so if i twist the throttle when bike is stationary then petrol won't go in the engine resulting in poor fuel economy?

If the bike is stationary and turned off, then your mileage would be 0/0.

Sent from my XT1033 using xBhp Connect mobile app

**black asp** · 03-03-2016, 04:02 PM

Re: What is "Power", what is "Torque"..??

Originally posted by RohIIT View Post

Fuel air mixture enters into engine , when piston goes down and inlet valve is open. This creates suction in chamber which takes in Air fuel mix.
Thats why if one cannot start bike due to weak spark , it is required to open spark plug and move piston to clear chamber as it filled with AFR.

please explain this?? as far as i know AFR refers to air fuel ratio i think u meant to say the un burnt charge(air fuel mixture) in the combustion chamber that was not scavenged as the piston didn't move

**rakeshchn** · 03-03-2016, 04:04 PM

Re: What is "Power", what is "Torque"..??

Thanks to all of those who pitched in to answer my questions! It all makes sense to me now. You guys are awesome!!

**black asp** · 03-03-2016, 04:04 PM

Re: What is "Power", what is "Torque"..??

Originally posted by RohIIT View Post

If bike engine is running (read on and making sound ) then yes FE will suffer
If bike engine is off ( read off and not making sound ) FE wont be affected.

Thanks for the clarification will keep the highlighted things in mind mate

CHEERS

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**RohIIT** · 03-03-2016, 04:07 PM

Re: What is "Power", what is "Torque"..??

Originally posted by black asp View Post

please explain this?? as far as i know AFR refers to air fuel ratio i think u meant to say the un burnt charge(air fuel mixture) in the combustion chamber that was not scavenged as the piston didn't move

Stoichiometric AFR required is 13.5:1 to 16.5:1

If you disable ignition circuit of bike and try to crank , engine will fill with unburnt charge. Now if you reconnect ignition circuit and crank again,it would either not start or one needs to go WOT and crank bike . Under some cases removal of plug is required and cranked once or twice to empty the chamber.

**black asp** · 03-03-2016, 04:10 PM

Re: What is "Power", what is "Torque"..??

any limit on how loud the sound should be??

CHEERS

----consecutive posts auto-merged-----

Originally posted by RohIIT View Post

Stoichiometric AFR required is 13.5:1 to 16.5:1

If you disable ignition circuit of bike and try to crank , engine will fill with unburnt charge. Now if you reconnect ignition circuit and crank again,it would either not start or one needs to go WOT and crank bike . Under some cases removal of plug is required and cranked once or twice to empty the chamber.

My question was wats the AFR u meant in the post ya i do know the ideal stoichiometic is somewhere between 14:1 to 14:7 but didnt get the AFR stored behind in combustion chamber part

CHEERS

**John P Daniel** · 03-03-2016, 10:32 PM

Re: What is "Power", what is "Torque"..??

Originally posted by black asp View Post

My question was wats the AFR u meant in the post ya i do know the ideal stoichiometic is somewhere between 14:1 to 14:7 but didnt get the AFR stored behind in combustion chamber part

CHEERS

AFAIK, the fuel does not completely exit the combustion chamber compared to air if ignition does not happen. This may be due to fuel condensation on the walls and absorption by carbon. This increases the fuel content, requiring external effort to generate the spark as mentioned.

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What is "Power", what is "Torque"..??

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