Exhaust fabrication

[94touring]

Another shop project!  Well one I've already done on another car, the bus, which yielded fantastic results. I have read and listened to a lot of what Vizard has said on a variety of topics, one of them being exhaust.  He used a super turbo muffler and was able to reduce noise yet retain maximum exhaust flow.  There's more involved to get "open header performance and factory exhaust sound" which has to do with a collector box 8 times the volume of a cylinder, but I'll skip that for now. In fact on the bus I did the best I could do to get 8x a cylinder with the biggest resonator I could fit, and it worked very well according to the wideband and my ears. Anyways, on the 1425cc Inno, the 1.75 OD exhaust is fairly restrictive, so bumping the headers up to a 1.875 ID outlet.  The current ID of a 1.75 OD exhaust was about 1.6".  The headers choice on an engine is more important for power curve than the rest of the system.  You actually don't want any back pressure past the header, contrary to internet folklore.  The size of the header however, in conjunction with cam and head choice, determines exhaust velocity and where your power band will be. It all has to work together to achieve the poweband you want. Once you've established the best combination of cam, head, and header, it's really just a matter of flow verses how much noise your mufflers will make to retain your optimal header choice. Aside from Vizards findings, I talk frequently with probably the top engine builder in Sweden to swap ideas and pick his brain. He confirmed the 8x cylinder theory as it really works.  Now I'm not going to try and stuff a box that big under the mini, and odds are it wouldn't fit.  What I can do is use the turbo muffler as I did on the bus and another type of resonator with wave length cancelation pipe.  Tuning pipe if you will.  Now depending on the length of the tuning pipe may not even work on the mini, and I haven't sat down with a calculator to do the math to determine what rpm range it will hit it's target. Measured everything out and it will fit as a standard resonator will, so worst case is it provides the same noise reduction.  Best case I get significantly less drone.  As for the turbo muffler, it will give a better exhaust note.  It really made a difference on the bus, which previously used a muffler similar to what minis use. Better yet, it flows!  The exhaust piping from the 1.875 ID header outlet will remain 1.875 ID to the resonator, then bump up slightly as smallest ID for the resonator is approximately 2.13 and about 2 inches given the internal lip on the turbo muffler. I just happened to have an extra muffler in the shop to use so already had the inner dimensions of the muffler construction.  I bought the appropriate mini exhaust tip and should be able to get all the angles setup in such a way it all looks "mini".  I will take a comparison before and after with a decibel app to see what if any noise reduction I get. The wideband will tell me the effect on performance.