Quote:
Originally Posted by men_in_jean
I know that the 4-valve engine revs high, But does all 4 valve engine generate power only at high RPMs?
From the 4-valve bikes I have seen in India say P135/R15/Ninja 250 all these bikes generate power only at RPM's more than 5-6k. The main reason for my question was that today is you take the P220, it is a torque monster read Indian biking context. It has power through out its RPM range. So if in future a P220 with 4-valve comes out, will it loose the initial grunt it has?
One dumb question. How does 4 valve tech improve mileage of the bike(read so somewhere)??!! Having 2 intake valves will make more fuel to pass to the cylinder which in-turn should reduce the mileage is it not so!? I am pretty sure there is no VTEC technology in for a P135 atleast  |
From what I remember of my Mech engg:
Take a 2 valve engine at low RPM. The air-fuel (AF) mixture enters the cylinder through the intake valve. As this is a single valve, the flow velocity of the mixture is high and it results in better filling of the cylinder with the mixture.
Due to a greater amount of mixture available for combustion the 2V will make good torque at low revs.
Now take the 2V engine at high revs. The valves open and close very fast and a single intake valve does not allow enough time for properly filling the cylinder with the AF mixture. Thus the 2V engine becomes less powerful/torquey at high revs.
Now, take a 4V engine at low revs. Two intake valves will result in a greater area through which AF mix can flow. But a greater area results in lower velocity. Hence the cylinder does not get filled properly at low revs and the engine is not so powerful/torquey.
4V engine at high revs: 2 intake valves provide far better filling of the cylinder than a 2V. And hence the improved top end.
Now, why does the 4V result in better mileage? In the lower-to-mid revs the AF mix intake being lesser than that in a 2V, this would result in better FE. I'm not too sure about its reversal at the higher revs though.
VTEC is variable valve timing and lift electronic control, its job is to alter the valve timing for optimal power at all revs. That is not coming to Bajaj bikes for quite some time I guess.