just to share some proven very useful info in exhaust tuning, especially for NA, i dont think this technique is applied anywhere in most exhaust shops here, most of us have only this in mind when modding exhaust system " how much and how fast the exhaust/ muffler/ pipe can flow".

nowadays, when u ask how to modify exhaust, u get typical answer like " manual use straight flow, auto use s-flow", "pickup use 4-1, top speed use 4-2-1". honestly, i think even auto can use straight flow which is better and get faster than stock pickup, achieve top speed easier than stock and the car is snappy. just swap to a smaller pipe and put straight flow in, definitely better than using large pipe than fit in 3 bullets to restrict it, waste of money on large pipe and the 3 bullets

fact is, the most important factor contributing to highest gain in exhaust system is " pressure wave tuning ", go to ur local exhaust shop and ask them this, im sure most of them will say its not related or dont have any idea. ive searched through all local auto forums, not one ever open this discussion so lets start now coz in exhaust modding scene in the states, they put extra effort on pressure wave tuning rather than having the highest flow coz its quite easy to figure out which is "when in doubt, always use smaller pipe size".

a quote that i really like in exhaust tuning:
there is more to this, search them up for more detailed info like determining collector length before terminate to resonator for ur engine. im just here to open some new perspective in exhaust tuning

actually what the best to achieve from exhaust mod?
for me its power increase, power band adjustment and sound.

and when we say about modding exhaust, its all about controlling the backpressure right?

i'm interested to know where is the nearest shop i can look for you, i'm based on klang/subang area.

what i'm trying to achieve on my 1.3L Auto 1st Gen Myvi was i like to drive in cornery road likewise touge or something. most of the time will speed between around 60km/h to 130km/h ish so is the correct place to increase the power and torque is on midband?

i'm currently on a hotbits 4-1 extractor with stock piping and muffler, and the muffler seems to abit crack on sudden full throttle between 2k-3krpm. and even more on load, it sounds like exhaust leaking.

and I dun wan the normal bassy and low pressure sound found every where on the road for the exhaust note. I wan something less usual, not particularly noisy or high note, but more tight/strong pressure/higher velocity, mid note and mid volume and sound lounder >3k rpm

whats the recommended setup for this? i only know that sound is primary affected by rear muffler, anything in the middle i do not know the function except for siliencing/muffling the volume

hehe touge spec engine is nice to drive across LDP/ MRR2 right? im having the same mindset too fast rpm climb at cornering exit, highest torque output across 2.5k - 4.5k for kelisa is what i need for non-track application. i dont bother with 5k power and above for a small engine, i keep tuning practical hehe

my usual place is torque gear and supercircuit in sunway, i like the workmanship but the price can be reasonably high. if small simple stuff i go to wai heng sunway instead coz its cheap. but if u know the design and spec, what u can do is go to cheap exhaust shop (wai heng, wei yip) and supervise them to do it. check welding finishing making sure no leaks after finish, basically be a b****y boss checking everything before u finally pay, i hate doing that coz seems disrespectful to the workers so judging by the work needs to be done, i select the desired shop

yes indeed bro, diameter tuning unlocks probly 40% of ur exhaust potential, its the length of ur header and downpipe to first bullet that makes the big difference

try this, if u r on 4-2-1, assuming extractor length is 15" like mine, then use 37" downpipe length and put ur bullet there. if header length is different, just makes sure header+downpipe length = 52". +- 1 inch is ok.

use 1.6" piping for downpipe, this will flow good up to 4500rpm on myvi engine. with myvi exhaust open BBDC at 30 degree, 52" of header+downpipe would give u boost at myvi peak torque 3200 rpm. for max boost effect, ur bullet internal pipe volume has to be minimum 2X engine cc i.e. 2.6L of bullet volume

if 4-1 then 52" starting from extractor flange to end of downpipe then put bullet there.

i tested this theory on kelisa, 34" downpipe to boost at 3500rpm, i felt boost at 3400rpm which made me happy coz it was really close to my approximation.

try this first and let me know the result, then i can propose something more to lengthen the boost duration

oh yeah, avoid openpodding ur intake, it does not do good for touge tuning, keep ur airbox, modify it to let airflow in easily up to ur rpm habit and call it a day. once air can flow easily thru ur airbox, there is no need for aftermarket drop in. use oem filter that was highly R&D-ed, designed and tested purposely for myvi

i actually stay quite far in desa petaling area hehe

the technique im practising is consistent with theory of using extractor for scavenging during valve overlap, except i study into details as how to approximate at what rpm u want this to happen at maximum by playing with pipe length

i referred to several tuning books, fluid dynamic students and race enthusiasts in U.S for months to fully get the concept, only now i apply coz budget not high so still got long way to go

i dont mind to meet up when got free time, then i'll share this technique so u understand better and can apply it urself

what im trying to say is there is no need for rigid stereotype like "if u r on auto, u lose power on straight flow", this gives wrong impression to first timer like i was when i was a total noob. i think auto can use straight flow provided that the piping size is small enough to keep flow velocity fast at low rpm. Since shift point for auto is around 2-3k rpm at lower speed, its hard to take benefit from big pipe big diameter muffler with stock auto gbox. same goes to manual, if its bad on auto it is also bad on manual coz given the same engine, power should be almost the same, only that manual can cope better coz it has more control over the rpm range, i can just shift gear at much higher rpm to take advantage of big pipe but its not gonna be fun to drive even in fast moving traffic.i remember someone quoted "true enthusiasts are really looking for fun, not just speed" which holds true IMO

2.6L can be equivalent of 3" diameter bullet having 22" length, the volume inside would give approx. 2.6L of air. u can use bullet/midbox if u got the space as long as after tuned downpipe, the piping change of area is significant and volume is close to 2.6L. if u can only have less volume, it will work too but not at its full potential but it will work, it worked for me on 2" bullet giving about 1L only where i need 2L minimum. this technique is derived from 4 stroke bike tuning where they use expansion chamber to increase horsepower

i forgot to mention the tuned part is only at the front (header+downpipe), once u terminate the tuned part with a midbox/bullet/expansion chamber, the piping after bullet to the back does not matter in terms of pressure wave tuning, what u need to do is make sure it flows well to not causing considerable backpressure

ive read experience from people using big bullet as expansion chamber is they tend to get drone so i cant promise u a super silent noise. custom a big body straight flow which has same diameter as ur tailpipe. big body muffles more noise, smaller pipe is even easier to muffle, thats the best i can say coz different people has different taste in exhaust sound. u can custom at supercircuit, i custom 1.6" big body straight flow and the noise is only as loud as typical 2" sflow but speed like a straight did mine there and it is reasonably priced.

A lot of racers in the U.S apply this technique to maintain their car horsepower while having street permitted noise. do a search on David Vizard, he's the one came up with this idea and people loved him for it

problem with my math is, i dont think it works that well with reverse flow muffler due to nature of it to break up the flow for noise reduction, i have confirmed it with some gurus so i dont really favor sflow, if i lose pickup from straight flow, get smaller pipe, thats it

ive bought 3" diameter 19" length oval bullet as expansion chamber but havent fit it yet coz no budget after bought that bullet haha so i cant tell my experience on the noise though..performance wise im quite confident

swirl bullet can scrap la
if wanted to use swirl bullet better use back ur cataliac converter

in ur manual at engine mechanical section. usually there is a table showing engine cc, bore stroke, compression etc, there u will find intake/exhaust timing
dont get confused, 3" midbox and 3" bullet of same length has the same pipe volume, the body cant be counted coz its not free air, it has fibre packing so gas will not pass thru it, only sound waves are absorbed by the packing. what i did was the original bullet is 15" so i added 3" pipe extension at both ends to give 19"

thats the problem with termination box, it can be hard to fit especially for big engines, 2.6L has to fit 5.2L box volume to get full benefit of expansion chamber haha

yea i suggest u custom ur own muffler coz u cant find good quality 1.6" straight flow big body muffler anywhere, minimum size is 2" and since pricing for 2" and 1.6" are almost the same given same body size, better go for 1.6" coz has better silencing and power. supercircuit custom price is reasonable and quality is there

u can use 1.5" after bullet to keep the noise down. If u r using crush bent pipe, connection from bullet to rear muffler is best to make it in straight line as possible, too much bend can make 1.5" act like 1.2", re-do the oem route if u need.

the length of branch resonator is not fixed. u need to know at what rpm ur exhaust is giving the drone and start calculating from there because all cars can have different drone rpm

the progress sounds good

Piping size after bullet = same as downpipe? yes, if u have 2.6L, i think 1.5" should work well too if u want less noise
Distance to place rear muffler = not important. yes, if tuned pipe end is fully terminated, the part after does not matter to wave tuning, only need to make sure it flows well

stainless steel piping retain more heat and longer than aluminized steel if im not mistaken, so it keeps exhaust relatively faster than aluminized one but i suppose the gain difference is minimal

can whatsapp if u want, i havent use msn for ages haha

yea, i could go with u whenever im free, weekend should be good. it depends on ur budget, supercircuit has higher charges than wai heng obviously but i wouldn doubt the workmanship, there is a chinese dude with glasses whom i can trust for touching my car hehe

but im not sure whether they stock normal pipe coz i think they only do stainless and i think they are the only one of many shops that owns a mandrel bend machine

hi luqmanz,

pardon my ignorance, haha.

ok ok, i googled around. first get the vol jisim, and then convert it to litres

so, to get 4L, with 3"diameter bullet, this translation that I need the length of 35.4" for a bullet    haha.

( a ) therefore, if there is a length of 15" bullet, i'll need to join two bullets to make it 30" and adds two 3" length of 3"diameter pipes before and after these two bullets to make it somewhat total length of 36" (ie eq to 4L), or
( b ) should I go with one bullet of 15" length, and extend the pipping of 3" diameter after the bullet to make it 36" in total length (ie 4L), before it reaches the stock muffler, or
( c ) since I have a muffler (and it's not a straight flow), just leave it as one 15" bullet

what would be the logical and economical option?

and thanks for replying in the termination box

thanks.

3. Ignore exhaust pressure wave tuning; it's not a significant issue with a stock valvetrain.

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Added on October 17, 2011, 3:11 pm

If you feel an extra 10-15 HP is negligible ... then you can ignore pressure wave tuning ...

i agree it is not as significant on stock valvetrain when my engine has only 9 degree overlap and results i have got from testing on my own car is not that impressive but it certainly works and thats enough for me. ive seen impressive result helping others with more aggresive cam with this idea when it was opposed and mocked by most exhaust shops i consulted and that means something to me
What matters is the grab of knowledge and know how to apply, coz to be able to apply it to any cars in future, that is priceless, it can save us a lot of money in future mod with bigger more overlap engines. worthiness of things has different meaning to everyone

also to challenge conventional ideas is what makes the forum fun and make our forum looks more sophisticated hehe
what is the diameter of that muffler?