Repiping and hiflow cat

[89CivicHatch]

alright similar to the topic "hi flow cat- headers" i got my hi flow cat and repiping done to a 2 1/2 i got a good exhaust and also when i got this done i would think it wouldn't fart no more! but i was wrong it just got f***ing loud like so loud i can't drive my car because it hurts my ears! i'm not joking either. but my question is why the hell is so loud i got a dc headers and hi flow cat with a 2 1/2 repiping done it flowing nice but yet it still farts a little bit. so my question is why is it farting and so loud?

[S Q A D]

youve completely modified everything dealing with the exit of your exhaust gas .. you took ouT all of the restrictive pieces that make the exhaust exiting quiet ... it's gonna be loud for the simple fact that you took out your cat .. have headers and 2.25 all the way back .. !! its GONNA be loud anyone could have told you that ... kinda wierd you cant handle your own exhaust .. :?

[Charles]

Install a resonator of some sort. Unless you are FI, your pipe is a bit big.

[zc87crx]

ya as charles said unless ur going FI 2.5 is a lil big for N/A...if ur going N/A i think the ideal pipe size is 2.25

[Charles]

I've got 2.25 all the way back. The ZC header is smaller than 2.25. Do you recommend a different header?

[zc87crx]

not meaning to jack the thread but ...ya evenentually cuz on the older motors a header and a straight pipe those are good bang for your buck investments

[89CivicHatch]

no i can handle it just didn't think it would be that loud but i got a high flow cat with the piping done and later on i'm going to turbo it so in long i think i'm benefits me don't you think

[S Q A D]

yea it does ... i say leave it .. let it be loud ..

[89CivicHatch]

thx

[S Q A D]

i have 2.5inch piping also ... its loud .. but i like it ..

[custom_junky]

You want quite, check out rs-s exmags, suppossedly they are extremely quite mufflers, and are not nearly as restrictive as a reagular, i don't think you'll loose any horse power, but it will be quiter.

[89CivicHatch]

thx sorry it's a 2.25 piping and also my question that hasn't been answer why is it still farting? can any one tell me that

[Rexinre]

I got 2.25 and its loud, but not all that bad!

[dragman99]

it's farting because you have no backpressure. the exhaust system you have now is good for a fully built d series motor with close to 300hp. that's why it is farting. i can't belive this exhaust system helped you one bit. i mean, i'm sure when you stomp it at 70mph it pulls a little harder but when you stomp it from dead stand still it probably doesn't pull as hard. my recomendation is either put a cat on it or downsize to a 2 inch pipe. ok everybody, disagree with me now.

[ahedau]

because you have no backpressure

werd

this from the 2001 SCCA FSP National Champion...

On some of the Honda Civic boards I frequent I see the common suggestion to people new to the fold is that they invest in an intake, header and exhaust first. Then I often see questions asked such as "Which cat-back system is best for my car?" or "What is a better exhaust size, 2 inch or 2.5 inch?" In general I think what people want to know is "What should I look for when evaluating what exhaust system is best for my car?"

Well, first I encourage all of you to take a long hard look at the "big picture" before you go much further. Not that there is anything necessarily wrong with the mods suggested, but I don't normally read anything in the messages about what you plan to do with the car (other than daily driving).

For instance, if running the quarter mile is what appeals to you, then you should probably concentrate on maximizing the peak horsepower your powerplant produces. On the other hand, if autocrossing or road racing is your thing, then you probably want to concentrate on maximizing the breadth of your torque curve (creating the maximum area underneath the torque curve). These two goals require different approaches.

Even if all you are doing is making darts down a drag strip, I would much rather have a car that hooks up well off the line, handles tight and straight down the track, and stops nicely after the lights than one that makes buttloads of power that I can't harness comfortably.

For what should you be looking when buying a cat-back exhaust? Well, the key to a well-functioning exhaust system is the balance between minimal obstruction while maintaining exhaust gas velocity. By doing this the engine can evacuate as much of the spent air/fuel gasses as possible from the combustion chamber enabling it to pull in more of the power-producing fresh air/fuel mixture for the next combustion stroke (I won't even get into the details of overlap and the additional power enhancing abilities it introduces when combined with a well functioning exhaust system).

If you are building an engine that only needs to perform well over a small range at high RPMs, then this it's relatively easy. Since the amount of time between the firing of cylinders is small at these engine speeds, the flow of gasses is relatively consistent (with only small low pressure gaps between pulses of exhausted gasses). All you need to do is provide a passage large enough to avoid restricting the flow.

Conversely, if you are building an engine that you want to produce power at a large range of engine speeds, then it gets tricky. While you want to minimize obstruction, you also want to maintain the speed of the exhaust gasses even when the engine is turning at lower speeds.

Chemistry tells us that the gasses that are being exhausted have mass (albeit, lower than the mass of an equal volume of a liquid or a solid). The gasses are being expelled from the combustion chamber primarily due to the upward stroke of the piston with the exhaust valves open, pushing the gasses out into the exhaust manifold at a speed relative to speed of the piston. Thus we have a mass moving at a measurable speed, and Physics tells us that means we have momentum...the gasses moving out of the exhaust system have their own momentum and will continue moving until met with an equal or greater force.

Some of that momentum is fighting against the unavoidable friction of the barrier zone of the gasses "rubbing" against the inner surface of the exhaust pipes. There is not much you can do about that other than ensure that the pipes are as smooth as possible (one reason you want mandrel bends rather than crush/crimp bends).

Meanwhile the firing of cylinders results in a series of high and low pressure zones in the exhaust system - pulses of exhaust pressure. At lower rpms the distance between the high pressure zones is greater than at higher engine speeds. Physics tells us that gasses will attempt to flow from an area of high pressure to an area of low pressure until equilibrium is reached. Thus if you have a large low pressure zone behind a high pressure zone, there will be a drawing effect pulling the gasses backwards in the exhaust system which will also diminish the momentum of the exhuast gasses.

On the other hand, if the designers of the exhaust system (and exhaust manifold) can harness these pulses with the proper diameter tubing, primary lengths, and collector dimensions, it is possible to use the low pressure zones from one cylinder to draw the exhaust out of another cylinder...priming the exhuast primary with a vaccum prior to the exhausting of spent gasses and thus enhancing the evacuation of spent gasses to make room for fresh air/fuel mixture. This effect carries on through the entire exhaust system.

So why is a 2.5" exhaust too large for a 1.5-1.7 liter normally aspirated Civic engine? Because even at their highest rpms, they do not produce enough exhaust gasses to fill the inside of a 2.5" exhaust system in order to make this exploitation of the low and high pressure zones possible. What happens instead is you get the pulses flowing into one large low pressure zone and rather than being constrained by the walls of the exhaust tubing and directed to the rear of the car, they end up creating turbulence within the exhaust system which actually serves to create a restriction to the gasses entering the system later.

Note that the volume of a 2.5" diameter pipe is over 150% the volume of an equal length 2" diameter pipe - that half inch amounts to a significant increase in the volume of the pipes.

So in the end, what you really want to look for when choosing an exhaust system is engineering that seems to take these factors into account and avoid all the hype or "style" associated with the F&F crowd. There are a few off the shelf systems that seem to do that, but if you can find a shop or fabricator who is willing to work with you in building a system, then it is possible to build a darn good system with a combination of off the shelf parts - just look for or select mandrel bends and straight-through, perforated (not louvered) resonators and mufflers. Also, look to see if the manufacturer is willing to back up their power claims with dyno charts for cars like yours - most are not.

Stainless steel is fine, but aluminized steel is actually lighter, a little less brittle, equally as rust resistant if finished properly, and costs a good bit less. It doesn't look nearly as nice, but are you looking to go fast or are looking to look like you go fast?

There are some excellent books out there, and not just about Hondas. For instance, check out any of Carroll Smith's books ("Tune to Win," "Prepare to Win," etc.). Then there is the "Auto Math Handbook" and "How to Build Horsepower." One I have been interested in getting my hands on, but have yet to see in a bookstore is titled "Intake and Exhaust Systems: How to Build and Modify" or something like that.

Also check out "The Physics of Racing Series" on the web - http://www.miata.net/sport/Physics. There you will find probably the best collection of information in existence on what it takes to make a car go fast.

and that's the edited version!!! WHEW!!

[89CivicHatch]

thx for that advice but your probly going to think i'm stupid or something but i don't think it is that because it just didn't start doin it, it did with the stock piping? like i said could it be that i may have to rebuild the motor because it so whore down. or maybe i need a new. offtopic(anyone know where i can get a good price zc motor) more advice please

[slammedcivy]

thx for that advice but your probly going to think i'm stupid or something but i don't think it is that because it just didn't start doin it, it did with the stock piping? like i said could it be that i may have to rebuild the motor because it so whore down. or maybe i need a new. offtopic(anyone know where i can get a good price zc motor) more advice please

im not sure what the exact definiton for "farting" is but if it means it cackles like a mofo then i might have an idea but one question first.
does it only cackle on deceleration or at idle>??

[89CivicHatch]

um it does it when i let off the gas! does that help?

[slammedcivy]

um it does it when i let off the gas! does that help?

there is really nothing you can do about it when your decelerating there is raw gas being dumped into the exhaust that ends up igniteing somewhere else in the pipe and makes it fart.
every car would fart if it had a free flowing exhaust

i have 2.5 in straight pipe all the way from my turbo to the bumper and when I let off the gas it sounds like i lit off a pack of bobcat firecrackers.

i guess you have to make sacrafices for more power

[DOG]

Shit. My wife is going to skin me alive. I took her car to get new pipe, hi-flow cat, and muffler. It sounds like it needs to be at Indy now. Loud! I like it, the boys like it of course (10 and 5 yrs old so you know there opinion will be positive.lol). 2" crush-bent piping, Research Technologies hi-flow cat, and a series 40 Flowmaster. no farting and a better sound than most of the coffee can type exhaust Ive seen. Like I said it sounds pretty good for a custom exhaust, but its loud.

[S Q A D]

hahaha nice dog ... teachin the kids @ an early age .. a loud honda is a good honda .. lol :lol:

[DOG]

They get to help me install the header this weekend.lmao. keeps them were I can see them. Nice to be able to get under the car and have someone there to hand you things. A fine tradition passed down through ages. lmao

[slammedcivy]

They get to help me install the header this weekend.lmao. keeps them were I can see them. Nice to be able to get under the car and have someone there to hand you things. A fine tradition passed down through ages. lmao

i need to have a kid. a couple extra hands around would be appriciated

[ahedau]

i need to have a kid. a couple extra hands around would be appriciated
problem is those "hands" have "mouths"