# A quick port question...

Discussion in 'Archived Threads 2001-2004' started by TommP, Apr 2, 2002.

1. ### TommP Extra

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Does anyone know what the effective length of a 90 degree elbow is?

I'm using two 4 in. ports in a Tempest based design and, due to the enclosure configuration (size constraints), I think I'm going to have to put a short radius elbow on each one. I just don't know how much length to figure for each elbow to get the tuning where I want.

Tom

2. ### Patrick Sun Moderator Moderator

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Rule of thumb: shoot for measuring the distance through the middle center line of the port bend.

3. ### Ron D Core Stunt Coordinator

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You will want to consider the volume of the port to get the right length, just add the volumes of every peice. For the torus, you'll have to measure the radius of the arc somehow and find the volume of the quarter torus. You can plug the dimensions of the elbow into the torus volume equation and divide by 4. Then you add the cyclindrical pipes and the required volume of them to obtain the proper length. Of course you can do what i would do and guess.

4. ### Ron D Core Stunt Coordinator

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Sorry if that didnt make much sense ^

5. ### TommP Extra

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Thanks guys. Both methods come down to measuring the radius of the arc thru the center line of the elbow (R in the picture below). You need this length to calculate the volume of the torus, so no need to calculate the volume and then convert right back to length by dividing by x-sectional area. Is this making sense to anyone?
Any suggestions on how to best measure the radius of the center line arc?

-Tom

6. ### TommP Extra

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I guess what I'm saying is if you have to measure the radius of the centerline arc to find the volume, just use that radius to calculate 1/4 of the circumference of a circle with an equal radius. That gives you the effective length of the elbow.