Catalytic Converter.

[QuickSilver 0]

I made a new topic about it so that people know what im on about, as I didnt know the name before, its to do with the catalytic converter again, now I have a question for anyone whos just removed theirs, on any car really, and stuck pipe in instead, Ive been told that it will sound like total sh*t, but Ive also been told the complete opposite, has anyone had any experience with this??? What does it sound like after its been removed?? car in question is an 88 e30 320i.. so twin exhausts, help would be appreciated.

Cheers.

[tibbs.james 1]

I did this to my E30 320i

it didn't seem to make any performance difference, and with the stock muffler it made it sound horrible at low revs but it sounds great at 4000+ RPM. My stock muffler is well on its way to being totally stuffed though

[QuickSilver 0]

Likely to bark at certain engine speeds, most systems run a resonator, which is in fact an "anti resonator" it damps out resonance in the pipe / exhaust system. It is very vehicle dependant some will sound okay others will sound sh*t if there is no "resonator"

The cat performs a similar function. I cut my cats out and replaced them with coby "resonators" was just fine, slight increase is depth of exhaust note.

sweet as, thats exactly what I thought, where abouts can one get ur hands on a coby ??? second hand one would be fine and also, what about preventing the merge into one pipe as its losing hp??

Edited April 17, 2007 by QuickSilver

[QuickSilver 0]

but the pipes are quite close together, any ideas on that??? theres a small clearance between the two, and last I recall is that their alot wider than standard piping.

[hotwire 352]

but the pipes are quite close together, any ideas on that??? theres a small clearance between the two, and last I recall is that their alot wider than standard piping.

My experience with cats/ resonators same as 3 pedals. You can put a fluted resonator (same shape as a coby) in which takes out the noise completely & virtually replicates the cat but without the restriction.

Is your cat single in or twin in? They can be either. If twin in - you would need to modify pipes to either be two into one each end or spread them to run two resonators in parallel.

[QuickSilver 0]

it goes like this, twin, then merges into one, and then comes out in one, and merges back into two, why???!?!?! whats the point of a twin pipe exhaust if their gonna merge it into one half way, pointless ! The fact of the matter is, it doesent bother me that i have the cat, im not an enviromental terrorist out to cause global warming, all I want, is a NONE restricted exhaust system, maybe its just me, but merging it into one is a bit ridiculous, does anyone agree??? i COULD spread them to run them in parallel or is there such a thing as a twin coby??? or a twin resonator of such, sound doesent bother me, infact SOME sound is nice, but i dont want an "empty tin can" type sound if u know what I mean, that sort of empty rattle, I like the low rumble of my 6, the only thing i dont like, is the catty rattling away underneath because its stuffed,

note to those wwho would know, I have a twin in and twin out ansa exhaust, this obviously aint stock, and is more beefy than stock, having said that does anyone have any ideas how it would sound with the cat removed now knowing what exhaust i have?? (sorry to repeat the question, totally forgot to mention exhaust) or does it not matter?

Cheers.

Edited April 17, 2007 by QuickSilver

[Jazzbass 1]

Cat out - coby in!

I liked the change on my 318 and my 325.

Will you?

I have no idea - cars seem to behave differently to similar mods.

Just do it and find out.

Its cheap and cheerful.

Plus you get that cool paint smell while the red/orange coby paint burns off...

[QuickSilver 0]

i think the merging and diverging business is stooopid whats the point? another problem is the way its connected, its got brackets, on both IN pipes so its bolt on bolt off, but on the exit end of the cattz, theyve diverged the pipe without the brackets, so i have 2 brackets entry and none on exit welded... so i cant just bolt on and off, otherwise i would be switching and swapping to get the right combo but noooo i dont have a welder so its annoying !

[Silver Fox 43]

Ok, going down to my little 318, it also has twin pipes down to a collector under the car. Again, why? Would it make sense for me to run twin pipes all the way to the back, or not, and if not, why?

Everyone has told me that the collector is the hardest part of the system to get right, so again, why have it? If it's a weight thing, I can live with it if I get increased performance. Any reasoning would be great, why mix all the exhaust gasses together with the resulting constriction that must occur? Thanks.

[QuickSilver 0]

flaws in the creation of the bimmers ... tsk tsk tsk, who thought of the collectors and cattys in the first place. jeeez

my common sense is, two CLEAR pipes the whole way through >= good,

stupid constricters which are eco efficient, go down to one pipe, resrtict performance, over all stupid things, = bad.

clear long twin pipe good.

Edited April 19, 2007 by QuickSilver

[Silver Fox 43]

Is it a flaw, or does it equalise the cylinder back pressure? Maybe it's a mistake to just try to remove the gasses as quickly as possible. I guess if you put uneqal back pressure on the pistons you would upset the engines balance? Does this make sense?

[QuickSilver 0]

completely, upsetting back pressure is possible, but what u dont know, is germany has a law, infact all of europe doesw, which makes the catt MANDATORY so their built like that factory SO, race cars obviously arent worrying about their emissions, they want to win dont they?? i dont think the back pressure will be upset..

another strange thing, is my pipes flatten partway along the car, they properly flatten, not just bent, they get quite thin and close together, before they reach the exhaust they go bak to normal size lol.

Edited April 19, 2007 by QuickSilver

[Silver Fox 43]

Thanks for that, so what about 4 into 2 in a 318, will this give more peak power?

[Silver Fox 43]

Ok, well I've been doing the old google thing, and it seems that the general concensus is that the important bit is the distance from the collector to the first chamber, whether it is a straight thru resonator or a muffler? Seems to be between 8 and 24 inches depending on the motor, and that what you do after that does nothing as long as you don't restrict the gas again, and the outlet from the first chamber is larger than the inlet, as the gases think they have been set free if you do this. You can put a muffler on the end, so long as it flows at around the same rate as the engine, which is hp x 2.2, so if I have a 95 hp motor, if I'm lucky, I should make sure that the muffler flows at around 200 cfm?

This is at variance with what I've been told by some people who should know, in that I was told that any old muffler will do.

Interesting article here on this.

http://www.superchevy.com/technical/engine...st/0505phr_exh/

[QuickSilver 0]

so basically, removing the catty or whatever is there in its place, would not affect tuning??? if im getting this correctly that is... then can someone explain to me why my pipes flatten towards my exhaust if at that point it doesent matter what you do to the pipes, its obviously constricting the exhaust.

[Surge 1]

I thought the only reason for BMW putting twin pipes on the exhaust systems was for ground clearance, and only that. Hell even then the pipes squeeze a about a third near the rear subframe... There's definately room for improvement.

Twin entry twin exit mufflers are apparantly hard to come by now, (Dad couldn't get one on his) so thats often the reason why 325's have twin then to a single.

I've heard so much talk about how BMW exhaust are near perfect from the factory (not too loud, make good power), which to a degree is true - typically speaking the gains from just bolting on a new system don't seem to be as large as per a Japanese car.

With anything there's always going to be comprimise be it just due to the fact of mass production.. It's definately possible to do better in some respects - BMW has done farily well - Most exhaust on 5's and 7's are stainless steel and newer 3's...

[duggybuggy 0]

i have my e36 325 booked in at the local exhaust shop on tuesday, planning to chop the cats (i think theres two of em, anyway) anp stick in a pair of cobys. anything i should know? like, does the e36 not like this kind of treatment, is it really worthwhile etc?

[QuickSilver 0]

I thought the only reason for BMW putting twin pipes on the exhaust systems was for ground clearance, and only that. Hell even then the pipes squeeze a about a third near the rear subframe... There's definately room for improvement.

Twin entry twin exit mufflers are apparantly hard to come by now, (Dad couldn't get one on his) so thats often the reason why 325's have twin then to a single.

I've heard so much talk about how BMW exhaust are near perfect from the factory (not too loud, make good power), which to a degree is true - typically speaking the gains from just bolting on a new system don't seem to be as large as per a Japanese car.

With anything there's always going to be comprimise be it just due to the fact of mass production.. It's definately possible to do better in some respects - BMW has done farily well - Most exhaust on 5's and 7's are stainless steel and newer 3's...

Problem is, I dont have a 5, or a 7, or a new 3, I have an old series 3 like lots of people do, I do however THINK i got lucky with my twin in and twin out exhaust can we confirm this someone?? lol.

the exhaust in my opinion is not perfect, it changes shapes, diverges and merges, and flattens into 2 VERY small pipes, im sure the newer ones have much improved systems, and the reason for twin pipes in my opinion is not clearance, its 6 cylinders, more breathing obviously for 2 more cylinders,

Edited April 21, 2007 by QuickSilver

[will 169]

Problem is, I dont have a 5, or a 7, or a new 3, I have an old series 3 like lots of people do, I do however THINK i got lucky with my twin in and twin out exhaust can we confirm this someone?? lol.

the exhaust in my opinion is not perfect, it changes shapes, diverges and merges, and flattens into 2 VERY small pipes, im sure the newer ones have much improved systems, and the reason for twin pipes in my opinion is not clearance, its 6 cylinders, more breathing obviously for 2 more cylinders,

Mate, you should stop making statements like the ones above until you have the facts, and not just read out of a book (like some of the know-it-alls we have on this forum), but REAL experience in the REAL world. Your statement about "breathing" is quite flawed.

Exhaust design on a street car is incredibly complicated and is always a compromise. Probably the simplest vehicle to design an exhaust for is a dragster, it is ALWAYS driven flat out so exhaust is designed to work in a very specific rev range for given atmospheric conditions.

The basic resultant of any exhaust design is to create a negative pulse at the exhaust valve at the instant the valve opens and this can be achieved in many different ways. A properly designed single pipe system can easily out perform a dual pipe system and visa versa. All good tuners will tell you that the theory is only part of the design, a good dyno is necessary to confirm the design and fine tune it.

The WHOLE exhaust is important, right down to the point where the gases exit the system, a bad exit will have a negative effect on the system as will header pies of the incorrect diameter or length etc etc. It is all to do with generating that negative return pulse properly. I will state here that I am positive that most these turkeys you see around with these massive exhaust tips are actually stuffing up their power by ruining the exhaust gases' exit. (I saw this on my mate's dyno many times as he experimented with differing exhaust tips).

I was fortunate enough to have a top tuner as a friend when I was racing and spent many hours with him building systems for both my (and others) track and road vehicles. He would always start out with the theory for the particular vehicle, and it was often suprising how much tuning had to be done on the dyno afterwards to get it sorted.

3pedals has highlighted some of the important bits in good design, i.e. collector design, balance pipes etc. The design of the muffler itself is also very important, a so-called straight-through muffler can absolutely stuff up the system if it is designed incorrectly and a conventional type muffler can enhance the performance of the system with correct design.

Temperature of exhaust gases also plays a big part in design, larger single pipes run cooler exhaust gas temperatures than than twin smaller pipes, which can have a positive effect on performance, but in a conventional car, large pipes are often difficult to fit in, hence the tendancy to use twin smaller pipes. (as Surge pointed out).

So there is no right answer, single system or twin, it will not perform if it is not properly designed. Both can work well.

[QuickSilver 0]

thanks for that, makes alot of sense.

Edited April 21, 2007 by QuickSilver

[Karter16 329]

Problem is, I dont have a 5, or a 7, or a new 3, I have an old series 3 like lots of people do, I do however THINK i got lucky with my twin in and twin out exhaust can we confirm this someone?? lol.

the exhaust in my opinion is not perfect, it changes shapes, diverges and merges, and flattens into 2 VERY small pipes, im sure the newer ones have much improved systems, and the reason for twin pipes in my opinion is not clearance, its 6 cylinders, more breathing obviously for 2 more cylinders,

When you say a "new 3" are we talking E90's or E46's?

Cheers

[Surge 1]

From memory E46's do. This is from working in the same building as a warrant shop a while back.. So don't quote me on it!