How much CSA will be ideal

[DrillDawg]

How can anyone decide on the port csa without knowing the max valve window csa for their head?

[user-30257]

How can anyone decide on the port csa without knowing the max valve window csa for their head?

How can people overcomplicate something so much when porting a head.

[Rick360]

Rick, Stan's data on the CSA chart/graph i can assure you was not pulled out of thin air. I am sure that the data within the chart/graph was figured out (established) over the years thru trial and error (R&D) with engine combos. The VE calculation, the same way, it is based on Bore and stroke and proven combos (some of the engine pieces not mentioned but assumed to ideal like carb, intake, camshaft, exhaust system). I am not saying charts/graphs are 100% accurate BUT they for the most part pretty darn close, AGAIN....established on (been there-done that).

Actually his chart/formula is based on a combination of math and other peoples empirical data.

It is based on the cfm demand at peak piston speed to determine a port velocity. Then converting that velocity back to a theoretical flowbench cfm at 28"wc velocity. So there is some math, some assumptions and some empirical correction going on.

Does the peak piston cfm demand give the best indication of port size requirement? Air is moving into the cylinder for many degrees after the piston is going the other direction.

How do you know what the VE will be to determine the port size? Is that a target or a result?

Is your engine/heads/porting like those who's empirical data was used to convert to flowbench data?

The Engine Pro program written by Patrick Hale (sold here now on Speedtalk) was written using thousands of dyno tests from many different types of engines. He took that data and analyzed it to correlate the variables and created formulas to predict performance etc. I've found it to be a good guide for engines like yours. Here is the recommendations page from it. The flow and cam specs were adjusted to get peak HP at 8750 which is what these are based on.

371ci.jpg

Rick

[digger]

So it's like a graphical representation of pipemax ?

[swampbuggy]

Rick.....what about intake duration (OR) can it be figured from the information you supplied ???? If so i don't know the formula, Thanks for your input Mark H.

[Erland Cox]

I have never seen a big port hurt torque and hp.
But this is on 4 cylinder engines where I can adjust the runner length for bet hp and totque.
I think that you are wave tuning the engine with port velocity on a single 4 barrel V8 engine.
A smaller CSA makes the wave travel back and forth slower so the engine tunes as if the port was longer.
With a bigger port it takes less time for the wave to arrive back to the valve so the engine can tune at to high rpm.
Intake valve open waves.

Erland

also on the engines you deal with you probably cant get aftermarket castings that are a lot bigger? youre probably restricted to what material is in there to begin with so you physically cant remove enough material to see the effect to any great degree

There are bigger factory heads for the 230 engine, casting 405 and 531 that are big enough stock for over 200 hp.
Then you can remove 3mm of aluminum from the port walls without breaking through.
A completely stock 531 intake port flows 189 CFM and it can be taken up to above 260 CFM.
Exhaust to above 190 CFM.
Intake port area can be taken up to around 2,25 square inches feeding 36 cubic inches.
Flow velocity changes wave traversion time during valve open.

Erland

[Erland Cox]

If you take a high powered OEM engine that's tuned on SD, take a look at the tables in the ECU you might find that the VE is mapped at up to 140%.
If you choose the right engine to look at?

A smaller CSA makes the wave travel back and forth slower so the engine tunes as if the port was longer.
With a bigger port it takes less time for the wave to arrive back to the valve so the engine can tune at to high rpm.
Intake valve open waves.

Erland

Changing the CSA changes the amplitude of the wave, not the speed of the wave.
In changing the amplitude you also change the frictional losses so the wave will also change it's decay time.

It does not change the speed of the wave itself but the wave is travelling outwards against the flow and inwards with the flow.
At the rpm of maximum hp the mean flow velocity is around 0,6 Mach.
So the wave will travel outwards with 0,4 Mach and inwards with 1,6 Mach.
It will take the wave 4 times longer going out than going in.
This is a simplified explanation but it shows roughly what happens.

Erland

[swampbuggy]

DrillDawg, when you say max. valve window area is that A.K.A. valve curtain area at max.valve ???? Mark H.

[DrillDawg]

bbc, 2.19 x .90 / 2 x .9855 x 3.14 = 3.05 - (.34375 / 2 x .171875 x 3.14) = 2.957241211sqin. compared to 3.8squin port entry.

[user-23911]

If you take a high powered OEM engine that's tuned on SD, take a look at the tables in the ECU you might find that the VE is mapped at up to 140%.
If you choose the right engine to look at?

A smaller CSA makes the wave travel back and forth slower so the engine tunes as if the port was longer.
With a bigger port it takes less time for the wave to arrive back to the valve so the engine can tune at to high rpm.
Intake valve open waves.

Erland

Changing the CSA changes the amplitude of the wave, not the speed of the wave.
In changing the amplitude you also change the frictional losses so the wave will also change it's decay time.

It does not change the speed of the wave itself but the wave is travelling outwards against the flow and inwards with the flow.
At the rpm of maximum hp the mean flow velocity is around 0,6 Mach.
So the wave will travel outwards with 0,4 Mach and inwards with 1,6 Mach.
It will take the wave 4 times longer going out than going in.
This is a simplified explanation but it shows roughly what happens.

Erland

Lets do some working out with a real example, lets say a 500cc cylinder (2 litre, 4 cyl or a 3 litre 6 cyl)and that cylinder makes 50 HP N/A with an intake port approx 4.25 cm diameter.
BSFC 0.4 and 12.5 AFR.
You might end up with an average consumption of 20 lbs/hr fuel and 250 lbs / hr air.
That 250 lbs/hr might convert to about 88 cu m/ hr (0.0244cu M / sec).
The intake runner at 4.25 cm dia should end up with an average flow rate of 17 metres / sec.

Speed of sound is 343 M/Sec roughly so 17 m / sec is only 5% or 0.05 mach.


It's pretty much negligible.

So the incoming wave will be mach 1.05 and the outgoing wave is mach 0.95.


Certainly nothing even close to your above figures and if it IS close, the port is far too small.

[swampbuggy]

Thanks DrillDawg for you formula input, it also does some confirming. As to the BBC port data which revels as is commonly known, BIG at port entry, smaller as you move towards the valve. Those in the know are now saying (LESS) taper in the intake tract makes more power, of course the tract must be big ENOUGH for the combonation being used. Mark H.

[Stan Weiss]

Stan, you have 2.02/1.60 valve size listed in your chart?

Jay,
Thanks, but the lines on the graph will not change as valve size is not used to create the graph. That is not to say that valve size does not matter, as it and other things are a factor in which line to select.

Stan

[DrillDawg]

The "csa" determines the torque peak and has to be sized to keep the mach numbers in line. If the mach numbers are to high the cyl. pressure will be lower than the port pressure at bdc and the intake closing can be later to let the pressures equalize, which means you have more of a pumping loss. Valve size, rpm, lift, csa and velocity work hand in hand to control the mach numbers.

[68corvette]

Should not the area decrease, not increase to increase potential volumetric efficiency?
Any sewer can do 100% VE when valve is closed soon enough, but you need air speed to create mass inertia for overfill and to utilize it you need to close valve later.

Head porters job is to size and shape head correctly for target rpm and target VE%.
Depending of the camshaft and induction specs the head size can vary quite much to reach target.
Not everybody are targeting to peaky 130VE% curve.

[Erland Cox]

If you take a high powered OEM engine that's tuned on SD, take a look at the tables in the ECU you might find that the VE is mapped at up to 140%.
If you choose the right engine to look at?




Changing the CSA changes the amplitude of the wave, not the speed of the wave.
In changing the amplitude you also change the frictional losses so the wave will also change it's decay time.

It does not change the speed of the wave itself but the wave is travelling outwards against the flow and inwards with the flow.
At the rpm of maximum hp the mean flow velocity is around 0,6 Mach.
So the wave will travel outwards with 0,4 Mach and inwards with 1,6 Mach.
It will take the wave 4 times longer going out than going in.
This is a simplified explanation but it shows roughly what happens.

Erland

Lets do some working out with a real example, lets say a 500cc cylinder (2 litre, 4 cyl or a 3 litre 6 cyl)and that cylinder makes 50 HP N/A with an intake port approx 4.25 cm diameter.
BSFC 0.4 and 12.5 AFR.
You might end up with an average consumption of 20 lbs/hr fuel and 250 lbs / hr air.
That 250 lbs/hr might convert to about 88 cu m/ hr (0.0244cu M / sec).
The intake runner at 4.25 cm dia should end up with an average flow rate of 17 metres / sec.

Speed of sound is 343 M/Sec roughly so 17 m / sec is only 5% or 0.05 mach.


It's pretty much negligible.

So the incoming wave will be mach 1.05 and the outgoing wave is mach 0.95.


Certainly nothing even close to your above figures and if it IS close, the port is far too small.

You will have to recalculate.
Use this formula in metric: ( Cylinder volume in cc:s X RPM X VE ) / ( 3000 X area in square mm ) = port velocity

My engine has 591 cc:s per cylinder and a VE of 120% and has maximum hp at 6750 rpm.
The port in the throat is 41,5mm, that is 1352,6 square mm.s, 1300 with the valve stem deducted.
That is 122,75 m/sec or 0,36 Mach.
This is assuming that the intake cam has 360 degrees of duration and the same flow at every degree which it has not.

Erland