a technical discussion, engine efficiency Options

[r_towle]

so, I have been thinking (not always a good thing)
If an engine is basically an air pump, and the objective is to make it as close to 100 percent efficient, why is the exhaust valve so much smaller than the intake valve?

Forget emmisions, forget fuel delivery, just want to understand why this is so...it is so on most engines...

Rich

[r_towle]

So, taking this knowledge, how can we apply it to analyse the current stock cam profile and how is effects the djet FI system..

Mainly, in a higher HP motor, there is more lift and more duration, and overlap.

I know its all in the combo....

But the question here is what is the true restriction on the cam in a stock FI system, and why.

Without a dyno in my garage, I would like to understand the settings of the FI cam and how they can be changed, and what will happen once these changes are made.

I understand that the MPS is looking at that vaccuum/pressure inside the plenum to determine how much fuel is needed,

With a different sized valve setup, and a different cam profile, it seems that you could maintain a proper Air Fuel ration while increasing the airflow through the system..

The trick is to keep the MPS happy and within range.

Lets say that the MPS is designed to read only a certain set of readings, anything outside that pre-determined set of numbers will make the car run lean or rich.

So if we increase head flow, the car will run lean,,,outside of range of the FI system...

But, if we increase airflow, and increase overlap, we might be able to maintain the same pressure inside the plenum...now the issue would be that the cylinders need more fuel....this could be done with larger injectors and increased fuel rail pressure.

Does this make sense...

I am trying to look at the cam profile, or a change to the cam profile...

Possibly a better flowing head, and or larger valves...

What are the effects, and where can the djet system be taken to...realistically.

Let me give an example, merceded has a 4.8 liter djet driven motor from the 70's....taking four injectors, one could in theory build a 2.4 liter and run it with the proper air fuel mixture.

The readings would be outside of the range of the MPS.
now, can we change the cam/valve size/head flow characteristics to bring the manifold pressure back into range, or is the pressure going to increase or decrease with more air (larger pistons or stroke...)

Rich