Theres an easy way to go Single into twins Without creating too much turbulence.
Do some careful measuring of teh ID's of your TB's to start. Make sure the ID of yout single leg on your Y Pieces gives the same cross sectional area or a little greater than 2 x the cross sectional area of your TB's. The old DxPi helps here. D = Diameter, and always use Inside measurements.
To split the flow evenly, , you use an Oval shape rather than pure round - with the longer axis of the oval, lying in the same plane as the split. So if your splitting with legs to left & right, the oval's long axis also runs left to right.
So grab your oval feeder pipe, then slide 2 x twin rounds inside it. Yes I know it's not exact, but I havent done the math. Tack weld everything in place.
Through the mouth of the oval, grind away anything that obstructs unnecessarily. thin out the center join, smooth out the dges of the inner pipes. Now you have a 2 into 1.
This is very high on efficiency, but there is always some losses. It's round into round that is turbulent, oval to round much less so.
Thats the basic technique, of course I have left out a whole lot of work that needs to be done in preperation, measurement and fitting.
Cheers
