Custom built exhaust

[fourbanger]

Just wondering if anyone else here has had their exhaust custom made.

I cut my cat and resonator out and changed the muffler all in 2 1/4" stainless steel pipe. Unfortunately, the sound isn't all that great. Has anyone used 2 1/2" pipe? How's the sound?

Anyone have any suggestions about the sound? It's bassy enough at the low end, it's just that at the high end it sounds too metallic, like a damned rice rocket.

[asianwitattitude]

hey wsup, ok this is my plan, after all my dents are fixed in my car, im gonna take this sebring muffler righT? its a big ol 4" can, its huge, and it was loud on my friends 4bangin mitsu lancer :P, after that ima go buy some 2 1/4" piping cuz 2 1/2" you'll probably lose power with that little back pressure ya knoW? but ima keep the cat on..im not bout to get a $2500 fine aite? so jsut do that..get a good intake filter with heatshield and you should be set. the sound should be real nice, i cant wait

[fourbanger]

hm..

the idea was to get away from the 'ricer' sound and get a more civilized, agressive tone... btw, it's not illegal here to go around without a cat, so, wth. hehe...

Anyone here running without a cat? I really wanna get a better sound for the car without losing performance. 2 1/2" pipe making me lose power? I thought the whole backpressure thing was a myth (At least according to UUC Motorwerks - )

So anyways, 2 1/2"?

[asianwitattitude]

well i mean if you can take your cat off by all means..do it but it only adds power...makes exhaust flow better and a **** load louder..better be careful if your not into the ricer. by the way the ricey sound is usually hard to get rid of on a 4bangin bmw. i mean you can get a really low tone exhaust and still have the riceyness at the peak rpms but good luck. and 2 1/2" is way too big for a 4banger. trust me. its not just a myth. how can it just be a myth if EVERYONE says backpressure is needed. if you think about it, you cant just have your exhaust with no back pressure, otherwise the best performing exhaust would be the exhaust that doesnt have a pipe...just straight..header to the air. i dunno thats what i'd think..

[fourbanger]

"how can it just be a myth if EVERYONE says"
um... everyone says the greek gods are a myth, does that mean they're not? just because everyone says something is true, doesn't mean it is...

btw, did you even read the article? it all makes perfect sense... and considering the fact that I'm already running a low backpressure configuration with more power, then maybe everyone is wrong. I just wanna fix the sound anyways.

'nother question. Anyone know the specs for the stock pre-96 headers? I know they're 4to1, but i don't know the diameter or the material or anything...

[asianwitattitude]

well if you dont need backpressure, why have piping and a muffler at all?

[fourbanger]

Sound quality.

maybe some of us don't have a problem running a loud car, but the common individual does have a problem with such noise out of their transportation.

now, running with no piping is a risky proposition, especially with a modified engine, considering backfires can throw out nice big ol' flames. That's something you wanna toss out the back or to the side (I believe the team PTG M3 GTR's have em to the sides).

I know people who like to go offroading in the 4x4's and they all disengage the exhaust when they're out in the woods.

[J!m]

Before the sound restrictions all the big-V8 drag cars ran 'open headers'. You want the SLIGHT backpressure to keep the valves from burning, but you also want that spent gas the hell out of the engine. You don't want to run any engine without some pipes from the head. Having them 'tuned' is not for sound (although they typically sound better) but it's for improved scavenging of gasses.

Some tracks still allow open headers. It's typically been better than any exhaust, but the technology available seeems to indicate otherwise...

I had a '67 Plymouth Belvedere a few years ago. That was a monster. It had a 0.060" over-bored 440 (453 C.I.) and the largest cam I could install without notching the pistons (0.513" lift and 292 degree duration if memory serves) and about a Billion dollars in other mods... But I learned a great deal about pipe diameters of the primary tubes, exhaust pipe diameter, mufflers... (my primary tubes were 1 5/8 inch, collected to 3" head pipes running back to reducing cones into 2 1/2 inch Flowmasters and 2 1/2 inch tail pipes. It was not much quiter than the 3" head pipes with no mufflers... I had no H-pipe on this car, as I was not in need of any torque.) That particular motor was rev-happy. I shifted at 6500RPM (insanely high for a big-block) and it was still pulling HARD. I just did not have the balls to rev it any more. I had visions if push rods coming through the hood....

BUT, that was for an American V8 built LONG BEFORE the cat was invented...

For a high-revving (American V engine, you want large diameter PRIMARY tubes and exhaust tubes, at the expense of low-end torque. An H-pipe is typically added to enhance the low end torque. This is popular on 5.0 Mustangs. Since the 1.9 has no torque, I would go with smaller primary tubes and exhaust, with a "try-Y" design header. ( [2 into 1 + 2 into 1] into 1- doest this make sence?) But I have no idea if one even exists. If you can find an EXCELLENT TIG welder, he (or she) may be able to make a 2 into 1 pipe that fits onto the stock header, essentially creating a 'try-y' header from the stock header.

Now, for the pipe, you will have to experiment with different diameters and a dyno to find the best size for the flattest (and highest) torque curve.

This is why exhausts cost so much. Not for the materials, but the R+D.

[bimmerboi318]

my friend had a 93 camry v6 and the flexible y-pipe broke. we took it off completely so the exhaust was pouring right out of the manifold. it sounded like a monster truck and had NO POWER WHATSOEVER. so all i can guess it that it needed some backpressure to create power. although you have to remember thats before the O2 sensor(s) so they cant really operate and the mixture may be off.

[JedzE36/5]

2 1/2" pipes. seems a little big to me unless you are FI. but anywho, i am running my stock cat, but i have 2 1/4" pipes from the cat to a Magnaflow High Flow resonator, and that goes into a Magnaflow muffler. real deep tone throughout (except when the engine is cold, then there is a slight twang at HIGH rpm). nothing bad though.

[schussey]

i'm not running with a cat, pity for the person behind me in traffic, the smell is unpleasent, haha

[k2fattyti]

depending on what your goal is and what other mods you do will determine what size piping will be suitable for your application.

marko

[Bill Strong]

Wow... not a lot of real science in here is there?

I suggest getting and reading the book Scientific Design of Exhaust & Intake Systems
by John C. Morrison, Philip Hubert Smith, Phillip H. Smith

It was written in the 1950s and 1960s. But the basics and the science is proven. It is the absolute basis for exhaust design. read that book, learn it, and then make good choices on exhaust design.

If the sound is too loud I would suggest adding some small flow through resonators ahead of the main muffler. You will need to do some playing with different sizes, but by adding a resonator you will change the note of the car without sacrificing performance.

One aspect you need to look at is how the Europeans do muffler systems. Before the world went green, most engine over 1600 had a pre-muffler about where the Cat sits in todays cars. Then they may have had one or two resonators after that before the main muffler. On rally setups they usually had one pre-muffler and then a main muffler. I bet that is all you need.
On the 1.9 liter I would actually use a 2.5" pipe for high RPM track usage, on the street I would use a 2.25 as that will be slightly quieter and provide the flow speed at low RPMs for good torque.
Keep bends to a minimum and please use mandrel bends