X-pipe angle ?

i want to build an X-pipe for my charger.
what is the common angle [if there is one] on most available "pre-built" units ?
30 degrees or so ? 45 ? all are different ? [can't be that much difference can there ?]
the headers have a very short, 3 1/2" collector. should i go 3 1/2" to the X, then 3" from there, or 3" right from the collector ?
TIA !

These are 45 degrees, 4 ", It's what can fit under the car. For the street I just slip on a pair of modified 4" supertrapps

thanks tig.

as to reducing the 3 1/2" to 3", where should that reduction take place ? or should i stay 3 1/2" for the whole system ?

I'd stay 3 1/2" all the way through. With the bullet mufflers there is no noticeable difference in ET and though it's way quieter than open headers, it's still too loud for the street which is why we slip on a couple of supertrapps. We just replace them with turndowns at the track. If you just want a quiet (ish) 2 muffler system, pick your muffler wisely, some are better than others when it comes to flow / silencing.
Edit: You can make em out here

I ran the 3.5 pypes on my wedge. I ditched it for the new engine combo.

P9070002 by Greg Ault, on Flickr

too bad you are so far away. shipping would be a killer.
gives be a good idea of how to do it though.

Nice home made "X",,,I did the same.