Exhaust x pipe placement?

[jonvolk]

I am going to be building a dual 2.25" exhuast for my inline 6 BMW. There are two separate exhuast headers for cylinders 1-3 and 4-6. I am going to use an x pipe in the exhaust but have not been able to find any information on what the proper distance is to install if from the header collectors. Anyone have any insight?

 

[Warpspeed]

I would assume that when each primary pipe reaches the X there will be an apparent doubling of available flow area, as each individual pulse can then split two ways.

That may well create a small negative reflection back towards the engine. If you try using some of the pipe length formula, something useful might come from that.

 

[Rob45]

In order to calculate the "ideal" place for an X-pipe, you need to know the gas temperature so that speed of sound can be estimated.
Gas temperature of course varies with engine load, so you need to be able to load the engine and measure gas temperature at a variety of locations along the pipe to develop a temperature profile.

You can simply cut and try: as a first cut, I'd try locating the 'X' about 2/3 of the way from the collectors to the rear end, or you might try putting a dual-inlet silencer at that point.