QUOTE(upontheriversky @ Oct 12 2011, 09:42 PM)
mine is close to luqmanz result, with BBDC of 29 degree, these are the results:
tuned rpm - 3000 , exhaust port length+header + downpipe length before bullet = 59"
tuned to engine max torque rpm 4000, total length of 44.5"
i suggest u do it shorter by 2" because this length includes the port length inside ur engine head as well
it's a good start. thanks for providing the estimates for this.
QUOTE(upontheriversky @ Oct 12 2011, 09:42 PM)
im not sure whether im getting this right but since u can hold maximum of 3.5k rpm then shift gear, probably best to tune it to run at around 3k so during upshifting, the rpm will drop to around 3k which is near to the tuned setup rpm so hopefully torque can be sustained longer across gears and rpm without having engine to push extra to climb back to tuned rpm everytime gear changes
but ur engine has 4k and 6k for max torque and max hp respectively so makes me wonder should u tune the exhaust to these rpm? haha but come to think about it, no matter how powerful the engine is, the power delivered to the wheel is still governed by the gearbox so 3k is probably a good start
the same engine runs on sentra manual transmission models, and there are sporty versions of it (ie Spec V models but not available here). hence they're able to hold it at 6k rpm. mine is AT but I guess, if i wanted to hold it at 6k, i'll need to enable the overdrive button and keep my foot on the pedal and hope i dont hit anything along the way. haha. nonetheless, this is more of a family car, haha, I'm less incline to do so especially with our traffic here in KL/PJ.
QUOTE(upontheriversky @ Oct 12 2011, 09:42 PM)
if u are willing to further trial and error, get the longer 59" one first so in case u need more power at higher rpm, just cut it shorter to the next tuned rpm and place the bullet there. if u start shorter then later u will need to add more length in case u need torque at lower rpm, welds will be all over the downpipe area and does not look nice especially these parts are where power is being unleashed the most hehe
yea, agreed. i'll probably go with your suggestion
QUOTE(upontheriversky @ Oct 12 2011, 09:42 PM)
when u look for the 4-2-1, pay attention to the primary pipe size, i have read that good ratio for primary size to port size is around 1.15, i.e. if port diameter is 1.2" then best primary pipe will have around 1.4" in diameter but generally u will see bigger than this so get whichever close enough. also there should be at least 2" of straight line at each primary pipe on the header in line with ur exhaust port, if they are bended down straight away after the flange then its not really good in design. both these features improve anti-reversion of the header design to prevent exhaust gases going back to the chamber especially at idle and low rpm when gases are moving slow
the 1.15" / 1.2" port diameter size that you're refering to is the engine manifold exhaust outlets, did I get this right? this then best fitted with 1.4" primary pipes (ie cyclinders), this will be the extractor head/header that goes to the engine manifold exhaust. is this correct? then it should be 2" in length horizontally on the primary before a curve bend downwards. hope i get this right. I read
here that a good design, the diameters of the extractor to be slightly increased/decrease as it goes to the collector. a bad design is where the exhaust port and engine manifold port diameters the same.
QUOTE(upontheriversky @ Oct 12 2011, 09:42 PM)
pay attention to the merge collectors too, look inside for casting marks and merge quality. good header will have long and smooth merge at every collector i.e. at 4-2 merge and 2-1 merge collectors. smooth long collector improves the flow easeness and most importantly, although pressure wave reflection is weaker but the reflection duration will be lengthened due to the long merge and powerband is wider. short collector will have narrower powerband but in return pressure reflection will be much stronger, good for high rpm take off, not really for speed recovery in city drive
this is good stuff info! powerband means, the ability to expand/hold the torque?
QUOTE(upontheriversky @ Oct 12 2011, 09:42 PM)
so, to sum up:
-4-2-1,
-1.6" stock pipe
-4L bullet/midbox or if u cant fit them under the car, 2.5L or 3L will also do the job if u are not going for 5k and above. 4L makes sure that the tuned length is kept until ur max engine rpm, if u dont go that high, lower than 4L still ok. but make sure u keep at least 0.5" diameter difference between bullet and downpipe. say if u use 1.6" downpipe, try get something like 2.5" bullet which has 0.9" difference. if u use 2" bullet, at one point im afraid the bullet will be considered as extension to the downpipe , the length will go out of tune so efficiency is lost there.
- im not sure the stock muffler is capable of flowing the gas ur engine expelling due to manufacturer noise regulation. they always compromise exhaust efficiency for a lot quiter sound and low cost in muffler design but stick to the stock first and see how the new upgrade does to u, let us know the result and we come up with another proposal for u
actually the 1.6" stock pipe is my own guessing. it could as well be a 2" pipe. as such, i'll need a bullet of 3" diameter. how do you go about calculating the bullet volume? say if it's 15" in length and has 3" diameter? I read earlier at one of your suggestions is to add some pipe of 3" length before and after the bullet if the bullet volume is insufficient. 4L is hard to find for a bullet. as one of the guys found out, the longest length for the bullet is 15".
will try with stock muffler first and if not that good, save some $$ and get a better one. some reviews of matola seems promising.
i've got to ask this, and this maybe silly noob question. why not use the cat convertor as termination box? what are the downside besides noise suppression? how about placing a catcon after the midbox bullet, although logically this is restrictive setup but it's better to have the cat before the midbox.
QUOTE(upontheriversky @ Oct 12 2011, 09:42 PM)
sorry for long explaination but i just thought u deserve to know at least the essentials
hey, no need to be sorry. in fact, i should say thank you for taking time to put this together. i am quite happy with the lengthy notes. these explaination helps me to understand more. now i know why the collector's length is important because it also helps to create a vacuum for the gas to be pushed out as the BBDC cycle goes, types of collectors layouts, cylinder firing sequence and how it relates to the header non-sequential paring. before this, i know nuts about exhaust system! truly good stuff and it's science at work.
This post has been edited by caarzee: Oct 13 2011, 11:50 AM 
Oct 12 2011, 03:44 PM
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haha. 
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