Air compression and all that stuff

Hey guys,

So I’ve been doing some learning and I’ve decided it’s time to learn about cylinder ports, cylinder percentages and volumetric efficiency ratios. I’ve done some searching and have found answers to most of my questions but I’m still a little clueless on some. I also just need to confirm some info.

So from what I’ve read porting a cylinder is primarily used on shorter barrels where you would not need an entire cylinder of air. So why exactly do you port a cylinder? My guess is to suck air in quicker, which would be helpful for high FPS builds?

I was also going to ask what the hell cylinder percentages are but I think I may have figured it our while typing this. So a 100% cylinder is a cylinder without ports correct? And then 80% is 80% of the cylinder being used because the other 20% is ported? If this is right, it’s impossible to have a 100% ported cylinder right?

Also, volumetric efficiency ratio, 2:1 right?

Sorry it’s so long, but your help is greatly appreciated.

A short answer…

Ve is the ratio of the cylinder volume to port : barrel volume

So where we use shorter barrels, if were wanting a 2:1 VE we need to port the cylinder to reduce its volume

It’s done so that you’re not shoving excess air through the barrel which as the theory goes, screws up the trajectory as it exists the barrel


Is it advantageous to have air still rushing past the gel when it hits the hop up?
If so, would you include the distance to the hop up in the calculations?

Doesn’t make that much of a difference but I do it from cylinder head to porting on my hopups

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To a point… if the air stops before the gel meets the hop up, that is bad… I am guessing if the air stops while the gel is in the hopup, it wouldn’t help the cause either…

I would suggest the volume of air be enough to push the gel out of the hopup and a tad more to keep it movin’ along… but having 3x the amount of air needed to get it out of the hopup is counterproductivepop

That’s why ports, holes and slots in cylinder are popular…fart