CAT replacement pipes

[chriswtx]

Just FYI for everybody. I took off my CATS today and replaced them with straight pipes. My Comptech exhaust measures 2" as do the straight pipes. The stock CATS measure 1.75" on the intake side and 1.625" on the exit side. That looks like a big restriction to me at 8000rpm. I have seen post both ways, they make 10-12hp and others say there is no difference. well the measuring tape dose not lie. And from what I have learned from hp and engines, less restriction makes hp on top end and that is where are cars like to run.and dont forget about the 25lbs the cats weight. The pipes weight 5lbs thats 20lbs less weight on my car and hopefully some more hp. Remember power to weight is what it is about and this adds to both sides of the equation. Hehe!! Just posted this for information only so make your own conclusions.

 

[docjohn]

This topic has been extensively discussed and I'm too exhausted to get into it again but use the "search" my friend!

 

[chriswtx]

i did the search thing for about 2 hours before I purchased the pipes but nobody had posted any actual measurments of the pipes and CATS. So I thought I would. SO there...

 

[peiserg]

someone quite recently mentioned removing the cats with a forced induction engine yielded 13hp with back to back dyno pulls. i bet with an NA engine the gains are in the 1-2HP range, if anything...

 

[fastcat99]

Of course, the tradeoffs are vastly increased air pollution (goodbye ozone layer) and or course more noise pollution.

Let your conscience be your guide.

 

[pach]

An properly tuned EFI motor without cats can still run fairly clean. It can pass the average emissions sniffer test (both idle and rolling). Im sure Chris's NSX pollutes less than a 1983 Buick Riveria w/ cats.

 

[chriswtx]

I know our cars burn cleaner without cats than 40% of the cars on the road, plus the 3000 miles I drive a year cant have any inpact on polloution.

 

[nsxtasy]

well the measuring tape dose not lie.

A measuring tape does not measure horsepower. That's what a dyno (dynamometer) is for.

I know our cars burn cleaner without cats than 40% of the cars on the road

Not true.

the 3000 miles I drive a year cant have any inpact on polloution.

Of course it does. Just because you're selfish and you're breaking the law, doesn't mean that you can kid us by saying things that just aren't true.

 

[chriswtx]

I dont know about where you live but in texas they check emissions and if you fail you are only required to spend up to $100 to fix it (ie. oil change, spark plugs, wires)and if its not fixed you get a waiver and away you go...So their is a couple million cars blowing smoke out their tail pipes everyday and the government doesnt care. So thats why I said the little I drive my car is not going to impact where I live.

 

[Guttiensx]

hey chris, this is jeremy from houston...how do the 'no cats sound and how much did it cost to do that?

 

[nsxtasy]

I dont know about where you live but in texas they check emissions and if you fail you are only required to spend up to $100 to fix it (ie. oil change, spark plugs, wires)and if its not fixed you get a waiver and away you go...So their is a couple million cars blowing smoke out their tail pipes everyday and the government doesnt care. So thats why I said the little I drive my car is not going to impact where I live.

What you mean is, since there are other people around you breaking the law and polluting the environment, it's okay for you to do it, too.

I bet that you most of the cars in Texas are passing the emissions inspection, and that any one of those cars emits less pollution driving 30,000 miles than an NSX without the catalytic converters does in 3,000 miles.

 

[fangtl]

Question, is your car running richer now? Is there any additional blackness on the rear bumpers?

 

[sjs]

Question, is your car running richer now? Is there any additional blackness on the rear bumpers?

More likely leaner, no? But I'm guessing negligible either way once the ECU adjusts and no difference at all in closed-loop.

 

[sjs]

Of course, the tradeoffs are vastly increased air pollution (goodbye ozone layer) and or course more noise pollution.

Let your conscience be your guide.

To fastcat99 and all those opposed to this on some sort of moral grounds, I could ask countless questions along the lines of:

~ Do you drive more miles than absolutely necessary? If so, why?
~ Do you accelerate faster than necessary? Why?
~ Do you drive a car that is less efficient than other available options? Why?
~ Have you done any performance mods to your NSX Why?
~ Do you watch auto races? Why?
And on, and on, and on…

It seems safe to assume that you own and drive an NSX because you enjoy it more than you would an Honda Insight or equivalent. Does your conscience bother you? Let’s face it, we all live in glass houses on this and the difference a few (or even many) enthusiasts make by pulling cats could barely even be calculated. So don’t expect an intelligent person who is inclined to examine the facts to take such criticism very seriously.

 

[Yellow Rose]

Texas Clarification

I dont know about where you live but in texas they check emissions and if you fail you are only required to spend up to $100 to fix it (ie. oil change, spark plugs, wires)and if its not fixed you get a waiver and away you go. So thats why I said the little I drive my car is not going to impact where I live.

You either don't know the whole story or intentionally did not share it. If a driver goes through specific steps and still cannot get his car to pass inspection, you are granted a "one-time-only" exemption for just that vehicle for twelve months. So no, you don't just get a waiver and off you go for as long as you own the car, as you have implied.

As far as no impact on where you live, you are living on borrowed time. Counties between Austin and San Antonio are next to implement rigorous tail pipe sniffing. So even if you drive a few thousand miles per year, w/o cats your car will fail inspection. It may pass the CO and HC but will fail the NOX miserably.

 

[chriswtx]

So much discussion and points of veiw. As with my first post this was for information only. I justed wanted to post the measurements of the cats because no one else had and for those of us who have aftermarket headders and exhaust systems. This was not ment to be a discussion on opionions of right or wrong, just the measurements for the ones who wanted to know. For you tree huggers out there, you can allways install a set of aftermarket highflow cats with 2"in and out, just weld them up in the bigger aftermarket bypass tubes. As for me, once a year when they test, 20min job to switch the cats.

 

[hlweyl]

To fastcat99 and all those opposed to this on some sort of moral grounds, I could ask countless questions along the lines of:

~ Do you drive more miles than absolutely necessary? If so, why?
~ Do you accelerate faster than necessary? Why?
~ Do you drive a car that is less efficient than other available options? Why?
~ Have you done any performance mods to your NSX Why?
~ Do you watch auto races? Why?
And on, and on, and on…

It seems safe to assume that you own and drive an NSX because you enjoy it more than you would an Honda Insight or equivalent. Does your conscience bother you? Let’s face it, we all live in glass houses on this and the difference a few (or even many) enthusiasts make by pulling cats could barely even be calculated. So don’t expect an intelligent person who is inclined to examine the facts to take such criticism very seriously.

Good point!

 

[nsxtasy]

To fastcat99 and all those opposed to this on some sort of moral grounds, I could ask countless questions along the lines of:

~ Do you drive more miles than absolutely necessary? If so, why?
~ Do you accelerate faster than necessary? Why?
~ Do you drive a car that is less efficient than other available options? Why?
~ Have you done any performance mods to your NSX Why?
~ Do you watch auto races? Why?
And on, and on, and on…

None of those things are against the law. But driving a car on public roads after removing the catalytic converters is.

For you tree huggers out there

I don't hug trees. But I do breathe air. I guess you don't, huh?

 

[peiserg]

Well, to be fair, his origional question wasn't really a moral one... but i think the fair answer is you might save some weight, but the HP gains are negligible... you'd gain a hell of a lot more dropping in headers, or cams, etc, and not have to deal with swapping cats back and forth for emissions, or the stankyness... and it is stanky.. my friend has no cats, and jeez, if he idles for more than 3 minutes the whole place stinks.....

 

[sjs]

None of those things are against the law. But driving a car on public roads after removing the catalytic converters is.

I don't hug trees. But I do breathe air. I guess you don't, huh?

I guess I should have been more specific but my comment about it being made a moral issue was in reference to the issue of pollution, not the law. Mind you I doubt many of us adhere strictly to every law on the books at all times, but that's not what I was getting at.

In my case I have a set of bypass pipes on the shelf and two cars that would benefit from them. Someday I'll experiment with them and then decide whether or not to keep them on. Meanwhile, when one of you buys that ultra-low emissions vehicle as your sole transport or starts riding the bus, come back and preach. Have any of you organized a carpool to work or attempted to participate in one?

Point is, we all live by our own moral compass. Any decent person can find things to be proud of, and others where they fudge a bit. Whenever I'm tempted to make some self-righteous speech I pause and consider my own list. I draw a hard line at flagrant things like burying waste oil in the back yard, tossing litter out the car window, and other no-excuses actions against the environment and my fellow man. But I drive my street cars hard and often and my leaded fuel race car as often as possible, and I sleep pretty well at night.

Sorry for the speech

 

[hlweyl]

Well, to be fair, his origional question wasn't really a moral one... but i think the fair answer is you might save some weight, but the HP gains are negligible... you'd gain a hell of a lot more dropping in headers, or cams, etc, and not have to deal with swapping cats back and forth for emissions, or the stankyness... and it is stanky.. my friend has no cats, and jeez, if he idles for more than 3 minutes the whole place stinks.....

Very good point!

Less restrictive exhaust doesn't always equate to more hp.... there needs to be some back pressure in the exhaust for the peak performance. I had no idea of the "stinky" situation

 

[Lud]

Bigger diameter pipes do not mean a power increase. That is why every Civic with a 6" exhaust is not necessarily a fast car.

Unlike many cars, removing cats on an otherwise mostly stock NSX doesn't really do anything for power. This has been shown many times on the dyno. Only if you have forced induction are you going to see any useful power gain (the 10-12 HP gain you mentioned).

It does, as you noted, take some weight off the car. It also makes the car louder (whether that is good or not depends on what you want!) and increases emissions (stinky).

 

[peiserg]

I must respectfully disagree with Lud. I put a 12" diameter cat-back on my civic and dyno'd 395 RWHP with no other mods. oh wait, i forgot my huge wing (20HP increase) and NOS stickers (30HP increase)

 

[Ponyboy]

I thought this a worthwhile mod for me. From experience, the hp gain is minimal, the car is louder, and it IS stinky. Stinky enough to make me wonder, "WTH is that?!" But the pipes are legal in Oklahoma (I know Ken will hate me for writing that), the weight savings are substantial, there is a power increase, and I LIKE the sound.

 

[Guttiensx]

does changing the cats out affect the performace eg....the computer tells the car not to run at its full potential because it might think somethings wrong with the car?