camshafts

[NoHachi]

VE is volumetric efficiency: aka the % of the cylinders displacement that the engine actually manages to inhale. Usually this is less then 100% because of pumping losses in the system. Using clever design and harmonic tuning of all runners, racing engines sometime exceed 100%VE. For engines with a form of forced induction 100+% VE is normal.

A normal way of plotting a VE graph would be running the engine of another engine (in fact using it as a pump) and measuring the amount of air going through the system at all rpms...nobody does this though..

Another method is making a graph of dutycycle vs RPM while keeping the lambda constant at one. You then know the mixture and the amount of fuel injected. A crude VE graph can be calculated from this information.

A VE graph is THE single most informative piece of information you can have on a engine. It is THE way to determine a stable idle point for a wild cammed engine. It is also an enourmous informative tool to determine where exactly you place the RPM/Map intercepts (sampling grid) to prevent wrong mixtures through interpolating errors in the ECU.

You get a nice look into the working of the engine, you see every peak in VE where the runners are harmonically increasing the VE..pretty neat. Especially when combined with a computer simulation. you can then make predictions of the locations of peeks and vallies in advance. usually thats enough to determine which peeks are exhaust related and which come from the intake. These can then be worked so that they take place at the same point (=max VE).

[wouter86]

very very interesting.VE just means "vulgraad" right?

So when i use camshaft with a higher duration, it means that the that the engine is having it`s highest VE on a higher RPM right?

More VE means more torque, if the amount of torque stays the same but is available at a higher RPM you make more power right? say you go from 150 NM at 5000 RPM to 150 NM at 6500 RPM you would have an increase in power or am i wrong?

Thank you man you are really helping me with this kind of info

[NoHachi]

Yes thats correct. The cams have one optimum flow point where they are setup to allow the biggest body of air into the engine without any reversal or blowthrough effects. Think of it as a big hump in the VE curve.
The effects of intakes and exhaust are seen in local peaks in the VE curve, but vallies as well. At some points the air bouncing around in the intake and exhaust (stated a bit simply for clarity) helps air in and out of the engine, but at some points it works against it. So you see that the Big hump (peak VE at peak torque) is increased in places and reduced a little bit further on.

Here comes the difficult bit: If you tune the VE peak from the cams onto the place where there is a VE vally due to intake and exhaust design, then peak VE may actually be lower then before. Think of it as an example of the systems design in engines, everything has to work TOGETHER.
One more reason to not just slap some parts onto the engine.

Be aware of one thing though: the ecu has a version of the original VE plot in its memory. It knows that when its at X RPM at a certain MAP pressure it has to be flowing X amount of air. When you start to deviate to far from this value the ECU just tries to interpolate from what in already knows. This doesn't have to work, basically its just guessing. Make sure you monitor Lambda en EGT+knock just in case.