I started fabbing up the exhaust off of the turbos. It will consist of 3.5″ pipe exiting behind each front wheel. I am hoping to be able to keep it tucked into the wheel well. I am also considering using spring retainers for header collectors to allow me to swap between pipe and small 6″ race bullets for when i am doing much street driving. That would allow me to change between open pipe and mufflers in minutes.
I was faced with the choice of buying a box of mandrel bends and cutting them up as needed, or buying straight sticks of pipe and pie cutting it to make up the bends I wanted. The first method costs quite a bit more with each bend ranging from cost of $20 to $40 depending on material, size and degrees of bend. The second method allows for custom bends not available prebent, is more economical but requires much more labor and time. I decided to go with the second option as I knew I was going to require some complex bends to keep it where I wanted.
This is the piece for the passengers side. First I made the initial piece by cutting a 15 degree angle into a short section of pipe and inserting it into the V band half. The fit is very tight ensuring it shouldn’t have any issues sealing once welded.
I inserted each piece until they were about .250″ from the lip of the V band half.
This is the piece for the drivers side. I may go back and shorten it a bit just for additional clearance and to give me a slightly better angle on the pipe coming up.
Then I began cutting small pie cut pieces that will make up the bends.
You can see here how tight the pieces fit together. The key is to cut one side of the pie cut to the same degree as the piece it is mating to. You can keep the other side of the piece at a straight 90 degree. This will allow you to rotate the bend how you desire and allow you to make compound curves.
Each piece is marked with alignment marks and numbered so when I disassemble it for welding, I can line everything back up as it was and weld it easier. You can also see in this photo that using the method for pie cutting I spoke about above allowed me to add a slight compound curve to the pipe to clear the header collector.
I made sure to leave plenty of room to allow for the header wrap that will be covering both the down pipes and the headers themselves.
I also kept this side very short because I wanted to try to clear the existing heater hose ports on the stock LS1 water pump. However, even keeping this radius tight. I barely had clearance from the pipe to the block off cap. So I instead will remove the pressed in pipes and tap the holes and plug them with block off plugs.
With the initial piece bolted in place, I began building the multiple compound curves that will keep the pipe parallel to the header until it drops down behind the wheel.
I started by using very small pie cuts. each with the short end being about .250″ wide. This requires more pieces, but keeps the bends cleaner and smoother.
Once again you can see how tight each pipe is using this method. I am using my 14″ Dewalt chop saw to cut these pipes, which requires a bit of cleanup on each cut, but that also allows me to keep the fit nice and tight.
I stopped there for the night, but will update when I make more progress.