lol

Before I start I want to say I never have to do emissions tests here in Arkansas.

The PO for my 400 had an exhaust custom made with an X-Pipe and he said he kept the cats coming straight from the exhaust manifolds because these cars don't run as well cat-less. Is this true?

sj408

iTrader: (6)

Lol, it will run fine catless. Never had a 400 model but many v8s, They do fine catless as they dont require as much backpressure as their smaller counterparts.

Theres always little wives tales that people hold true, kinda like when people tell me about how much harder it is to turbo an automatic.

lol

Thanks, I've ran every car I've ever owned catless but this is my first V8 so I wanted to be sure before I did anything. Better safe than sorry.

Tam4511

iTrader: (9)

I just straight piped my exhaust yester day and it runs great, if it does throw codes just get a o2 sensor defouler

INTIMAZY

iTrader: (5)

ANY car runs better catless. "Necessary" backpressure is a myth stemming from halfassed leaky cat-deletes that screwed with upstream O2 sensor readings in closed loop.

sj408

iTrader: (6)

Not trying to start an argument, but your wrong. Ever thrown a 3 inch exhaust on an n/a 4 cylinder? Youll soon consider backpressure "necessary" . Yeah it will run but once you start diminishing exhaust velocity youll notice huge down low power loss on the butt dyno.

Yes, cars do run better catless. Yes, your car will run good with less backpressure but there is a certain threshhold at which you start to diminish power instead of gaining.

Even v8's need a certain amount backpressure, if you dont believe me go drive a 4.6 with open longtubes and 3 inch collecters. Couldnt beat a ups truck in a race.

INTIMAZY

iTrader: (5)

Backpressure does NOT equal velocity.

Just the first google result that pops up.
http://www.hondacivicforum.com/forum...ts-wrong-3064/

As an aside,
It's really funny that you chose "4.6 with open longtubes and 3 inch collecters." That's exactly the car in my garage right now getting prepared for NASA this year.

My roadrace toy is a 01 Cobra with exactly the setup you mentioned (4.6 with ARH longtubes and turndowns). Laid down just under 310rwhp on a stock motor with that exhaust setup you described.

Was only good for 265rwhp on factory manifolds and exhaust with all it's "backpressure" goodness

Most days of the week, I CAN beat a UPS truck, I assure you

sj408

iTrader: (6)

a 4v is different but you ever driven a 2v with open headers? blehhhhhhhhhhhhhhh, and yeah your right, backpressure doesnt equal velocity. But what i was trying to get is its like blowing through a straw vs blowing through a toilet paper tube, if you open up an exhaust too much using the theory that no back pressure is good then your likely also to forfeit low end power .
I noticed that alot of people dont notice they lost low end because of the increased noise.

But your right, likely my wording mixed my own train of though up

In regards to your link, every honda ive ridden in who went and slapped a 3 inch exhaust on a nearly stock engine felt like ****. ZERO pull down low. Regardless of what honda tech says.

I had a pi swapped 96 with long tubes, Custom x and SVO side exhaust, full bolt ons tuned cams, nt555's blah blah blah. I laid waste to the 01 cobras i came across. That being said that car felt like utter horse**** with open headers.

bigwes

I think back pressure is important as well. if your exhaust is too big on a NA motor then your going to lose back pressure. I had a Stock GS4 and I put I 3" exhaust and I definitely felt a lost in the low end. Plus, 01 Cobras aren't N/A. so of course headers and a 3" exhaust isn't going to make you lose power.

INTIMAZY

iTrader: (5)

01 cobras are actually NA.

Supruxes

iTrader: (2)

Fun fact of the day.

sjc2467

You do not need backpressure. What you do need is velocity (which is completely different, and certainly not increased by backpressure). With minimal backpressure and appropriate sized exhaust, the suction created will improve cylinder scavenging. This is good for power, but bad for emissions and gas mileage, as a bit of unburned fuel may be sucked into the exhaust (depending on how much valve overlap there is). (You will not notice the difference in gas mileage, with stock cams.)

To maximize velocity, just be sure to match the exhaust size with the power output (don't just stick on the biggest pipes you can fit, like most people do).

So: removing cats will not hurt anything. However, most (honey-comb style) cats these days are not very restrictive (unlike the old pellet filled ones a few decades ago), so gains from removing the cats will be minimal (probably not noticeable unless you're trying to get 1-2 more horsepower on a dyno).

Also, keep in mind that regardless of your state's emissions laws and testing, removing or modifying (gutting) a cat is a federal offense, with pretty severe punishments (if you get caught--which you won't).

INTIMAZY

iTrader: (5)

Clean400

iTrader: (2)

I would keep them in. If your car is close to stock you only lose maybe 5whp at most from them. With the SC400 if you unrestrict the exhaust you will lose low end but gain top end. It depends what you want. I would have a manual transmission or high stall torque converter before opening up an exhaust. That way even if you loss low end grunt you would still make up for it.

INTIMAZY

iTrader: (5)

I think the main point most miss is that cats do NOT in any circumstance HELP velocity. If this was a tubing diameter debate, there would be much to speculate on. Ditching a early 90's era converter is mostly positive with very few minuses (odor, legality being two of the biggest concerns). A well designed cat delete with a constant diameter straight through the catback lets a motor breathe better with improved economy and power.

Again, I reiterate, done properly. I'm not talking about a hollowed out or cut-and-weld delete that disrupts airflow even worse than a honeycomb would.

These cars did no come with 'modern, high-tech cats' and there is still a pretty decent amount of power to gain even on the low-flow truck motored 400's. Combined with a better catback and intake work, I wouldn't doubt you can pick up 15rwhp.