KiwiBirkin Posted February 22, 2009 Share Posted February 22, 2009 Im in the middle of pulling my orignal Birkin exhuast apart to build a new one that will be a side pipe exit and not out the rear, the 4 headers come out into a 4 into 1 that ends with a 2 1/2" flange, im getting a S/S muffler built and would like to know if I should stay with 2 1/2" pipe all the way to the side mount exit or should I reduce it down to 2". The car is running a 1600x flow with twin weber 40s, I dont know if any work has been done to modify the engine when it was installed by Birkin at the factory in 1996. Cheers KiwiBirkin Link to comment Share on other sites More sharing options...
Ian7 Posted February 22, 2009 Share Posted February 22, 2009 Hi Kiwi Don't want to sound "unhelpful", but there really is no way to answer that question with that little amount of data. There is way more science in exhaust design and tuning than most people realize. Whoever designs your exhaust needs to know - - > the state of engine tune, rpm you want it optimized for, length and diameter of the primary headers, (they alone could be far from optimum), length and diameter of any intermediate piping, back pressure in the intended 'muffler' (if any) at different volume flow rates, etc etc for street use, you can't go far wrong with sticking with the collector outlet dia of 2.5 inches for the remaining pipe; I wouldn't think you should step back down to 2" after the 2.5 collector. cheers Link to comment Share on other sites More sharing options...
KiwiBirkin Posted February 22, 2009 Author Share Posted February 22, 2009 Hi Ian7 The car will only be used for street use and you have been help full really ill stick with 2 1/2" all the way through. Link to comment Share on other sites More sharing options...
slomove Posted February 22, 2009 Share Posted February 22, 2009 I would second the 2 1/2" recommendation. For a stock engine the exhaust won't be the bottleneck and I guess it will not matter then. If you ever upgrade you will be happy to have it a bit more free exhaling. Not very scientific but necking it down to 2" is counterintuitive. Link to comment Share on other sites More sharing options...
11Budlite Posted February 24, 2009 Share Posted February 24, 2009 I'll add my two cents on Birkin exhausts. My 2001 Birkin has a 2.5" collector pipe ending at a 2-bolt flange that attaches to the front of the muffler which has the same 2-bolt flange but the ID of the muffler and tailpipe is 2". Obviously this is not optimum for exhaust flow with the 1/4" step all the way around the circumference of the muffler flange. This has been one of the few disappointments (along with the wiring and stock seats) that I've had with the Birkin. It also seemed like some of the exhaust packing was blown out so I decided to replace it with something a little better. I decided to go with a side exit exhaust that's 2.5" all the way through, repackable, and very light. I'm hoping it'll sound a little better too. Bruce :7drive: Link to comment Share on other sites More sharing options...
Davemk1 Posted February 24, 2009 Share Posted February 24, 2009 I converted my Birkin from the stock rear exit 2" exhaust to a 2 1/2" with a side exit. More power, less fumes and a good bit lighter. A win-win deal. I used a DNA stainless muffler and all stainless pipe. It works very well. dave Link to comment Share on other sites More sharing options...
KiwiBirkin Posted February 25, 2009 Author Share Posted February 25, 2009 Well I made the new exhaust today and fitted it up tonight at work, I made a 450mm dia x 550mm long muffler with a chamberd system as i have to get the noise level down to 94db to pass the 6 monthly car checks here called a WOF (Warrent Of Fitness) I made it 2 1/2" in let and out let as suggested. Next thing is im getting the system from the front flange painted at work in a paint called sermatel (spelling could be wrong) which is heat resistant paint we use on aircraft engines in the hot areas, then Im haveing made a S/S heat sheild to 3/4 wrap the exhaust from the flange to the end of the muffler and im having Birkin laser cut in to it. Drove the car home from work and first thing I noticed is the nice sound the 1600 xflow now makes and there is lots more power down low and the flat spot i had on the low end power has gone away, in all a much better sounding car with more power. I have included some pics of tonights effort at work, I fabricated every thing my self and fitted it up, its still a work in progress and is about 50% complete, ill post another pic when its painted. http://www.usa7s.com/aspnetforum/upload/1607982858_DSCF0004.JPG http://www.usa7s.com/aspnetforum/upload/1524107229_DSCF0002.JPG Link to comment Share on other sites More sharing options...
scannon Posted February 25, 2009 Share Posted February 25, 2009 Well I made the new exhaust today and fitted it up tonight at work, I made a 450mm dia x 550mm long muffler with a chambered system as i have to get the noise level down to 94db to pass the 6 monthly car checks here called a WOF (Warrent Of Fitness) Wow. You fabricated your own muffler. I'm impressed, I can't recall anyone making their own muffler from scratch before. Skip Link to comment Share on other sites More sharing options...
KiwiBirkin Posted February 25, 2009 Author Share Posted February 25, 2009 Ah cheers Skip It wasnt too hard really as im a sheetmetal worker and had all the tools need to make one, all they really are is a round tube with either a straight through pipe packed with fiber glass or S/S wool or a pipe that runs through but gets offset a few times to make the exhaust quiter and then packed wiyj S/S wool again . I would have liked to make one fully from S/S but where i work now we dont use S/S so I couldnt get my hands on any. Link to comment Share on other sites More sharing options...
KiwiBirkin Posted March 4, 2009 Author Share Posted March 4, 2009 Well the exhuast is finished and on the car, im pretty pleased with the look and the diffrence it made to the car, the final touch was to spray the heat shield with gun metal gray paint as it was looking tatty, next year ill rplace it with a S/S heat shield with BIRKIN laser cut into the side. Link to comment Share on other sites More sharing options...
scannon Posted March 5, 2009 Share Posted March 5, 2009 Kiwi, It looks great. Are you happy with the sound and noise level? Skip Link to comment Share on other sites More sharing options...
KiwiBirkin Posted March 5, 2009 Author Share Posted March 5, 2009 (edited) Yes Skip Im very pleased with it, now it sounds how I thought a lotus would sound with a 1600 xflow, the noise level up to 4000rpm is fine then after that it gets a real nice growl So far the wife hasnt complained to me about it all and tells me its not giving off as much heat as the old system either. Edited March 5, 2009 by KiwiBirkin Link to comment Share on other sites More sharing options...
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