But, do we move enough air?
Let's see.
8250 rpm has 4125 intake cycles per minute.
4125 intake cycles of 350cc each equals 1443.75 liters per minute.
We want to have availability of 125% volumetric efficiency if we can get it, so 1443.75 x 1.25 =1804.6875 liters per minute is needed.
There's 28.3 liters per cubic foot of air. So, we divide 1804.6875 by 28.3, and we get 63.76 cfm.
However, we only get about 2/3 of a revolution on the intake cycle to get that air in, we have to multiply that by 1.6 to get that same amount in in that shorter time period. So then we get 102 cfm needed to feed this engine at 8250 rpm at 125% volumetric efficiency.
Okay, so we have 160 cfm, but it doesn't flow 160 the whole time, because we have the valves getting open, and then closing down. So, we can look at the average flow rate over the whole lift cycle which is typically about 2/3 of the peak flow rate. I don't have the chart in front of me right now.
So, 66% of 160 is 105 cfm estimated average flow out of this head.
We need essentially 102 cfm to feed it, and we are averaging about 105 cfm over the lift cycle, which gives us just a little more than we need, just in case.
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Okay, now let's look at the port size.
Our 1.25" port gives a minimum cross sectional area of 1.227 square inches.
A very well ported head that flows exceptionally well can utilize a mach index of up to
0.6 of the speed of sound before choking. That's about the limit. We strive to size our ports to reach our mach limit at the approximate maximum rpm that we plan to reach, in normally aspirated(N/A) trim.
So, let's see how we did.
When we input the Super Meteor engine specs into the mach index calculator, along with the .040" overbore size of the piston, at 8250 rpm, and .500" lift, and a 1.227 sq. in. port size, here's what we get.
**Intake Port Mach Index**
Your bore size is 2.8 inches with a stroke of 3.54 inches
and with a valve diameter of 1.5 inches and cross sectional area of 1.227.
Running a valve lift of .500 inches at 8250 RPM,
Your intake port velocity is 307.22 fps
Your intake valve mach index is
0.59------------------------------------------------------
I think that's looking good to me.
So, we can feed the engine the right amount of air to hit 8250 rpm at 125% volumetric efficiency, which is plenty of available air.
And, we can reach the target rpm of 8250 in N/A trim, just a hair below the choke speed, so that we get the fastest moving air possible at the time that we need it.
Everyone following that?
You ain't getting that kind of work off anybody else doing these engines.