| Been a while since I've done any new work to my personal Z and have been wanting for about a year now to build a new exhaust setup. I've had an idea in mind for a particular configuration that I haven't seen before and have been curious about its performance advantages and the tone it produces. Finally got around to ordering the part and spent a few hours this weekend putting it all together. Quick history: I completed the build of this car in early 2006 which took nearly two years from start to finish. The exhaust was fabricated entirely from the cylinder head back to the muffler tips. 304 stainless steel was used for everything except for the tubular manifolds which were made from 321 stainless as well as the downpipe tubes. The rest of the tubing is 3" in a seperate tube system. Each exhaust pulse running the entire length and going out the muffler, as shown: 
This setup worked very well but it has always been on the loud side and with a very low resonance, also having a bit of rasp to it when at WOT. So I purchased one of these: Borla silencer, 4" inlet and outlet, 304ss construction:
 
.... and then got to work fabricating the exhaust to incorporate this into the midsection of the exhaust... Midsection has been cut out and the two ends tacked together. The inlets and outlets of the silencer are round which I put into the vice and squeezed to form an oval shape. A collector to bring the two 3" pipes into the 4" ovaled inlet was fabricated, tacked, and then final TIG welded. Then a collector for the outlet of the silencer was also made to join to the pipes leading out to the mufflers. 
The difference in sound is quite amazing. :) By bringing all of the exhaust pulses together into a common section and shortening the resonating tube section, the exhaust tone has taken on a completely different exotic tone. The previous setup with the long seperate 3" sections act like a trombone stretched out to its full length, thus lowering the resonant frequency of the exhaust tone. With the silencer being placed much closer to the engine it has shortened the leading runner length much like drawing back on the trombone slide. Each exhaust pulse is now only traveling in a 3" diameter tube for less than half of the previous distance and then opening up into a much larger cross section. This larger area reduces backpressure further up in the exhaust system thus leading to better pressure drop through the turbine wheel. The car has notably better spoolup response as a result. But this arrangement has further benefits. With the exhaust pulse traveling down a shorter 3" length and then opening up into a 4" dia section, and then shortly thereafter opening up into two 3" pipes, the restriction to flow is significantly reduced. As the cross section increases, the velocity of the gases decrease, which has lower frictional losses with the tube wall. Just like what we see with the larger intake piping. So at high revs the engine will experience less backpressure in the exhaust - allowing it to evacuate the exhaust out of the engine with less effort - more energy left in the crank. The sound level is also reduced since each exhaust pulse is now going through a silencer and then out both mufflers. In addition, since the gas velocity is much lower she no longer has that raspy buzzing tone through the midrange. Here is a video of what the car sounded like with the previous exhaust configuration: [ http://ashspecz.com/events/Gainesville2-12-06/DSCF1854.mpg ] and here is what it sounds like now (sorry for the poor video quality, the camera was doing something strange) Also, the clutch isn't slipping - the tires just aren't holding the power in 3rd. :)
[ http://ashspecz.com/Image%20Gallery/2011NewExhaust/Videos/P1240077.AVI ] [ http://ashspecz.com/Image%20Gallery/2011NewExhaust/Videos/P1240078.AVI ] I have dyno results from previous tunes with the old setup so we can compare it to the new setup. I should have results to post up later this evening once we have the time to strap the car down and make some pulls.
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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AshsZ-II Ultimate Street Z - New Exhaust Fab >> - 
