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# How do I adjust port length when rounding ends? (1 Viewer)

#### Joe Ku

##### Stunt Coordinator
I am currently building the Audax Center channel. The plans call for two 5"long 2"id ports with streight cut ends. I want to use a 1/2" roundover on the exit and a 1/4" on the entrance. Do I keep the total length 5" including the rounded sections? Or do I use 5" plus the roundovers (total of 5.75")? Or something in between?

Thanks for any input you can give me, I am hoping to glue it up tonight or tomorrow, I will post pics when I am finished of course.

#### Joe Ku

##### Stunt Coordinator
Got the answer, thanks guys, if anyone is curious here it is

2"id port
1/2" roundover is equal to .62 inches on streight port
1/4" roundover is equal to .28 inches of streight port

so the short answer would be it doesn't matter much at all.

#### Chris Carswell

##### Supporting Actor
What is 3/4" & 1" roundover is equal to?

#### Joe Ku

##### Stunt Coordinator
Here are the numbers I have, I would like to know if anyone disagrees,

2"dia port
1/4" radius = .28" of streight pipe
1/2" radius = .62" of streight pipe
3/4" radius = 1.03" of streight pipe
1" radius = 1.52" of streight pipe

3"dia port
1/2" radius = .58" of streight pipe
3/4" radius = .93" of streight pipe
1" radius = 1.33" of streight pipe

4" dia port
1/2" radius = .56" of streight pipe
3/4" radius = .88" of streight pipe
1" radius = 1.24" of streight pipe

What these numbers indicate is that if you use a 2"port with a 1 inch roundover on one end you would shorten the port length by .52" to account for the port rounding.

#### Chris Carswell

##### Supporting Actor
Hey Joe,
Thanks for running the #'s .

Are you sure about the shortening part? IIRC, you add length to a rounded port.

#### Joe Ku

##### Stunt Coordinator
I'm never sure of anything... with that said, The numbers I listed are based on equivelent volumes, the example I gave will maintain the same volume of air in the port. However I think you may be right about lengthening instead of shortening because of the inverse relationship between port length and diameter.

Could someone who has used a precision port clairify this?

#### JoelTW

##### Stunt Coordinator
I have the precision port 4", I think I "shortened" the inner section by about 5-6" due to the large radius flare

#### Dennis XYZ

##### Stunt Coordinator
I've always, as a rule of thumb, counted half the flared part in the total length. Example, the sim calls for a 12" port and I'm using flares on both ends with a flare radius of 1". Make the total length after the thing is assembled 13". Of course, in practice, I usually start with them extra long and trim them until I get the tuning I want.

Adire seems to confirm my rule of thumb with their port kits. I think they have about a 1" flare radius.

1. Trim center tube to 5" shorter than the calculated vent length.
2. The vent should be 1" longer than the calculated vent length when assembled.

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