Flow Rate of Stage 3 cylinder head?
Turbo Mini Forums

Im doing my theses on fuel Injection and at the moment Im working out the CFM or Litres/min or air flow so I can size the throttle bodies for the System.
Ive tried looking everywhere and cannot find a CFM figure or graph for a big valve stage 3 head, the valve sizes are 36mm Inlet and 29mm Exhaust.
I'll post more information on where I am in the project and if I can help you with any parts that need working out. It will be a N/A 1380 , 286 cam , running a canems ECU and ITBs.

any help would be appreciated,

Thanks

Ciaran

stage 3 dosnt mean alot without its exact specs mate its just a term for companys to sell a head. all can be different and not one will flow the same as another... well not exactly.

Right ill go out and measure the Area of the inlets. and have a look at the valves

Nobody really quotes CFM figures for their heads, if you want that you will have to measure it yourself i would guess. Can be done with a vacuum cleaner and a manometer.

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I had a quick measure and worked the CC or Cm3 of the Intel ports to be 83.5 cm3.
Now I had to guestimate the shape of the area behind the straigh run.
valves are Inlet :36mm Exhaust :29mm

The ports look well worked too and the combustion chanbers are opened well up.

Do I need any more information to work out the actual CFM? the Theoretical CFM @3,000 RPM is 73.09 CFM

Humm i need a manometer? Ill get onto my supervisor and ask if I can get hold of one.
So there is no way of working it out on paper, just to get a ballpark figure?

Get hold of a copy of Vizards book. it has many flow curves for different cylinder head modifications.

Either way, the best way to size throttle bodies is to consider the whole inlet system and the asociated wave dynamics. You could start with a given velocity and work out the size based on the CFM, but that would not be the optimum.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I have vizards book, I was looking through it, but it doesnt have a CFM for my exact head. Would using the theoretical CFM be adequate for sizing the TB? although the figures do seem a little optimistic, but looking at the CFM for other larger CC engines they seem to be accurate.
I was thinking of finding the max CFM and picking the nearest Throttle body that gave this figure?
However considering the VE of the 5 port is probably quite poor, the actual CFM must be a fair distance from the Theoretical.

Quoted CFM values for heads is just for comparison purposes. They are based on a given pressure drop. I've seen 2.5", 10" and 25" H2O quoted in the last few days alone.

If I was sizing a throttle body long hand from first principles, I would start with maximum piston speed and bore to port area to derive a peak velocity in the port. If that velocity is reasonable then size the TB to match the port.

Then test the TB bore and runner length against Helmholtz theory to ensure that the area/length combination is going to give you peak torque in the right place.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Thanks man, Ill go work that out.