VE Calculator For Cylinder Porting

I used the forum’s VE calculator to work out the ideal barrel length for my Gen 9. Great little calculator it is too. :+1:

Apparently to get a ratio of about 1.7:1 I need a barrel length of about 425mm using a 7.3 inner. I don’t want to go that long, I want to keep it at it’s current length of 350mm. So I’m looking at porting the 100% cylinder.

Using the calculator to work out porting I get this figure :

I take it to mean I should have 57.45mm of full cylinder, from the end of the porting to the cylinder head?

To the back of the cylinder head but yes

VE given our constraints on projectile consistency and behaviour is more of a guide than a holy grail.

I measure from the front of the cylinder not the cylinder head , because that is the way a ported cylinder you buy is measured


Okay, cool… thanks :+1:

I know it’s hypothetical, but my ratio is sitting at 2:1 atm, which is a figure I see quoted as the sweet spot. Is that 0.3 change to ratio likely to be value added? :thinking:

Yeah, on that cylinder length thing…

Is the cylinder length in the calculator the total length of the cylinder or the length of the piston travel i.e. effective cylinder length? I tried the calculator using both and got some very different figures.

In you instance I personally would make it 58mm , I have a setup with a 350mm 7.3mm id barrel and at 58mm it is close to perfect.
Expect a quiet shot that will sound like it’s gutless but on the chrono will surprise you and the piston will no longer flog your cylinder head stressing the front of the box :+1:


Ah, thanks, Rattler… saves me experimenting and getting it wrong. :+1:

Looks like the dremel’ getting a bit of light exercise this morning. :sunglasses: Cheers, guys.

@zeHamish Great resource, that VE calculator. :+1:

I suggest you go back and read this entire thread again, it gives my explanation for measuring from the front to maintain a standard that is easy to use without any calculations.

Oh also with porting a tear drop shape is best but not essential…
The tear drop shape port lets the compression load up more gradually instead of a sudden wack where the porting finishes


Oh yeah, I’ve read that thread a few times over… :+1:

I’m assuming the teardrop shape would be with the wider part to the rear of the cylinder?

Yes just like this one


Easy bit of filing there… thanks mate :+1:

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Now that is going to test your dremelling skills :rofl:

thats what wire wheels are for :slight_smile:

I use chainsaw and needle files… do it by hand mostly, that way I can take my time and sneak up on it. :+1:


Chainsaw files, that is… haven’t gone hulk on one with a chainsaw… yet :rofl:


Well, you were bang on in your prediction, Rattler…

Can’t qoute a FPS figure yet, but feels like it’s increased… range, accuracy and grouping is pretty tight now at 20 -30 metres. It does seems to cycle smoother, and is definitely a little quieter.

Good result all around :+1:

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Pics or it didn’t happen, Just saying noidea

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The most reliably accurate porting calculator I use is…

Rattler hail first


Haha what happens when you discover I am full of Shiite laughing (1)