can anyone please tell me about upjetting..... i have googled it but couldnt find anything useful....

what is upjetting, how is it useful, when it should be done etc....

thanks in advance...

A Main jet is a small metal cylinder, that soaks up petrol through a small hole in the middle of it, so that it can be mixed with air and sent to engine cylinder. This happens in carburettor.

Replacing the Main jet with a bigger jet, is called upjetting.

This is usually done to compensate for increased oxygen flow to the engine.

Air and fuel has a particular ratio called AFR, which should remain constant for best results, in our road bikes.
So, if you fit a High Flow Air Filter into your bike, you should fit a bigger main jet to maintain this ratio...

thanks for the info samarth. got the concept of r125 overtaking the zma.

can we install anti-lag on a bike (pulsar [4 fun]) .. are the kits avail in India ??

thanks

hi bro thanks a lot 4 d details .

i was supposed to meet u can i have ur no plz

Help needed...

Hey guys i wanna know about the working of the bike from scratch i.e. from the injection of fuel to power delivery braking etc etc in video format like in howstuff works. com.. !! (Or even a write up in a sequential fashion with tech details !! )
I did try out in tat site but couldn't get hold of it in a proper way..
Can anyone help me in this regard ???

Questions on 4-valuve tech

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.

Is it really the velocity the reason for a low torque in initial RPM's??!! My understanding is velocity should not differ much for a 4-valve.

And how is it that the AirFuel intake is lesser in a 4-valve?

Sorry if the question is noob!

Well I know the basic stuff, even I'm not the hi-fi engineer but this is the concept: Suppose you are blowing air through a straw. The air will come out from the other end with greater velocity in a thin straw. If you blow through a hollow tube/pipe then the air coming out at the other end will be much slower.

Same applies to engines. A 2V engine with a single intake valve will have a smaller area than 2 intake valves of a 4V engine. So higher intake flow velocity for a 2V. A 2V engine has around 1/3rd combustion chamber head area covered by the valves, but a 4V head covers much more area, hence smoother and quicker breathing. A 4V design also has a cleaner and more effective combustion (not very clear why) and this coupled with lower flow velocity of the AF are probable reasons for better FE.

All this stuff was in Fluid Mechanics and I hated this subject. So, if you find something horribly wrong with the above, pls excuse. Although I'm reasonably sure I've got it right.

Right now i don't know in what CO% setting i am riding but my FE is dropped 38kmpl to 32kmpl. My avg speed is around 70 to 80. Guys also i need to know what is CO setting n how it is done. N how we can check it.
What r the merits & demerits of the same. I own p220dtsi

All 4 v engines don't produce power at high rpms. It depends on the state of tune of the engine. But still it will be higher than the similar sized 2v one. This is due to the fact that the valve train of a 4 v engine is lighter than the 2v one, and so less inertia to mess with. Taking ur eg- of the 220,if u make it 4v its initial grunt will be comparable to 2v with an added bonus of better high end performance, unless u tune it for extreme high end performance.

Also even if the flow velocity varies the flow rate of both 2v and 4v should remain same due to the variation in flow area .

Thanks for the post. Hi guys, Im a newbie. Nice to join this forum.

Function of throttle valve in FI system?

Hello friends
I have the following question:

In FI bikes, the fueling is completely controlled by the ECU right? mostly by controlling the duration of fuel injection at constant fuel pump pressure if I am right..
If this is so, why cant we have the throttle valve, which regulates the airflow, open full time? In carburetor, air flow also decides the amount of fuel sucked in.. But, since this is not the case in FI, can we not regulate the engine speed purely by controlling Fuel Injection and leaving the throttle valve open all the time?

Thanks..

The VTEC system on my Honda VFR800 does not alter valve timing, like it does on many cars. I wonder why they still called it VTEC. Instead each cylinder operates on two valves below 6800 rpm and on 4 above it. The swirling motion of the incoming charge is improved below 6800 rpm, but nothing variable as such. In fact, you can certainly feel the power increase when you cross the 6800 rpm mark, it feels as if a turbo had kicked in, quite nice actually...