Ott 928 V² Pipe, or Ott Pipe

Not USA street legal without cats. Cats can be added by removing the straight pipe section behind the V² and inserting cats such as Random Technology SuperStainless P/N 702500. Random Technology does not have a picture of the 702500 cat on their web site, but their 8100 series universal cat is the same size. Picture of their 8100 cat.

I have noticed several different designs for the center of the V² in the V² pipe. Some have the pipes meeting at near 90 degrees to each other with only a short gap between them. Others are made from tubing bends laid side by side with a section cut from the outside of each bend with the tubes joined in siamese fashon.

Not efficient scavenging V²s

While these are probably effective to some degree, and cheaper to build, they are not configured for most efficient scavenging. I suspect they are made that way because the usual front engine V8 has the transmission joined to the rear of the clutch housing and there simply isn't room available for a proper V² designed for good scavenging. We are fortunate in that the 928 allows plenty of length in the cat area to have a nicely designed V² where the tubes meet with about 20 degree included angle on both inlet and outlet and still have enough room for cats. Burns Stainless is one of the premier exhaust design and fabrication companies in the US and probably the world. You can check their design of the V² section here. Burns Stainless V². Note how the inlet and outlet angles are very narrow with a constriction in the center. Their V² sections are really two Y collectors joined together.

The book, "Four Stroke Performance Tuning" has a section on exhaust where the author, A. Graham Bell, explains the design of the venturi merge collector. The V² section is two of these merge collectors joined together at the constriction point. The inlet pipes merge at an angle of 9 to 12 degrees each for an included angle of about 20 degrees. A scan of that page from his book illustrates the design. My point is that when experienced exhaust designers design a Y merge, or V² section, they do not use the wide angle V² or siamesed bend sections joined on the outside.