What are the Positives & Negatives of removing Catalytic Converters?

[NSX123]

What are the Positives and Negatives of removing Catalytic Converters?

1)Apart from Not passing emission tests, polluting the environment and the illegal nature of not having cats.. are there any other negatives?

2) Are there any back pressure issues?

3) Any loss OR improvement in low end, mid range or top end power?

4) Is it true that fuel economy improves when the cats are removed?

5) Is the NSX considerably louder with the cats removed (on and aftermarket exhaust system)? 10 20 50 100% louder???

Cheers

 

[nsxtacey]

I think the sound depends if you have non oem headers and exhaust. I think somoene on here had oem headers and exhaust and put on test pipes and didn't notice any sound difference. I'm getting a set soon.

 

[nsxtasy]

1)Apart from Not passing emission tests, polluting the environment and the illegal nature of not having cats.. are there any other negatives?

Those are the biggies. And they will make your car smell noticeably bad.

3) Any loss OR improvement in low end, mid range or top end power?

No significant improvement on a normally-aspirated car.

4) Is it true that fuel economy improves when the cats are removed?

No.

5) Is the NSX considerably louder with the cats removed (on and aftermarket exhaust system)?

Yes.

 

[SmknVTEC]

nsxtasy,
So you are saying that having no cats on the car won't improve hp or times? How about racing cats? I know those are lighter but, I thought they should not restrict as much airflow as the factory cats do.

 

[nsxtasy]

So you are saying that having no cats on the car won't improve hp or times?

On a normally aspirated NSX, that's correct - no significant difference. That's what people who have tried them have found.

How about racing cats?

Same...

 

[Bob Kenney]

I am in agreement with Ken; there is no significant increase in HP. There is however a small increase in the max HP.
If my memory serves me correctly, there has been quit a long discussion about this in a recent thread where one of the posters actually dynoed his car before and after test pipes. A small increase was noted but most felt that few HP gained was not worth the hassle. He also noted the car was noticeable loader; he did not define "noticeable" in terms of a percentage.

 

[AU_NSX]

5) Is the NSX considerably louder with the cats removed (on and aftermarket exhaust system)? 10 20 50 100% louder???

Removal of the cats results in a 20% increase in exhaust db on a NA car.

 

[ctrlaltdelboy]

my personal experience with DC headers and DC exhaust when switching between python hi-flow cats and test pipes was:

noise measured at 4,500rpm at 0.5 metres from exhaust tip

with hi-flow cats = 99dB
with test pipes = 103dB

with dB measurements, every additional 6dB represents a doubling of the volume, so in my case the increase from 99dB to 103dB means the car is making approx 167% of the noise when decatted compared to using the hi-flow cats - not quite double, but indeed significantly louder.

the car certainly seemed somewhat quicker without the cats during the limited time that I drove it like that, but I never did any back to back dyno tests to back that up (butt-dyno readings only :biggrin: ).

I now keep the cats in, as 103dB prevents me from driving at the majority of racing circuits here in the UK

 

[btcog82]

I have mine removed, and my...what a gorgeous sound with an Ark DT-S exhaust!!! Hope your not behind it though, the fumes are kinda' hullicinagenic and mezmorizing...Ok, I need to go get a hit.

 

[docjohn]

Louder exhaust would be the only real reason to use test pipes unless you are squeezing every last hp out of a fi settup.That and as Ken likes to point out : placebo effect!:redface:

 

[drewdeezee]

somoene on here had oem headers and exhaust and put on test pipes and didn't notice any sound difference.

Yes, I tried that. The stock muffler does a damn good job of muffling. It didn't sound any louder with the test pipes.

 

[Tanto2]

Many years ago Comptech found 6 NA HP on their flywheel dyno with w/test pipes when using their I/H/E combo. You usually get about 12-15 on 5.7L v-8's, so the numbers sound right. And the more you pump, the more you will get. If you have that intake/header/exhaust combo, IMO you WILL notice a seat of the pants difference. I have actually done this before and after test. Placebo baloney. Engines like to breath- period. The smell comes FROM the cats. Some engines suffer low rpm stumbles unless the FI is re-calibrated. The NSX does not have this problem. The logarithmic scale thing is misleading. The sound at high rpm is 15-20% louder and thats a good thing IMO. The only downside is you may have strange resonance sounds with certain aftermarket exhausts. My system presently has none, but I have had them with other exhausts. And if memory serves, you lose 17#. I say pull those damn things off if you can, your engine will love you!

 

[nsxtasy]

I have actually done this before and after test.

So have other people, who have found absolutely no perceivable difference whatsoever.

I say pull those damn things off if you can, your engine will love you!

Your nose and your ears will hate you. So will the nose and ears of everyone in your neighborhood. Don't do it!

 

[gobble]

I can speak from experience.

For several months last year I had the Comptech supercharger on my car with I(Comptech)/H(B&B)/E(Anytime). To do some air/fuel tuning, I put the Dali test pipes on my car. The car was on the dyno two nights with the cats and one night with the test pipes. The dyno work was done by a guy in Milwaukee that did the tuning when Basch was up here installing his product (the guy knew what he was doing).

There was ZERO difference with the test pipes compared to the cats. The car actually lost a little bit of power in the low end. Besides no gains on the dyno, the car smelled bad and was way too loud.

And think about it for a minute. If there were gains to be made, don't you think there would be lots of vendors selling high flow cats for our car?

 

[nsxtacey]

This is a case of your miles may vary...some say some gain some say no gain...but we can all agree that its louder and it pollutes the air more at least.

I was thinking for a minute per your request..whats the point of high flow cats? Their alot like test pipes in that they're not carb legal, don't do jack w/ hp and they cost more than test pipes. They're just used for at the track when cats are require? Maybe thats why not more vendor makes them
http://www.comptechusa.com/store/250101.html

I'm also wondering about the smell everyone mentioned. Some friends of mine have 360's w/ test pipes and i've driven behind them many times and never noticed a funky smell.

 

[darknezz_ghost]

This is a case of your miles may vary...some say some gain some say no gain...but we can all agree that its louder and it pollutes the air more at least.

I was thinking for a minute per your request..whats the point of high flow cats? Their alot like test pipes in that they're not carb legal, don't do jack w/ hp and they cost more than test pipes. They're just used for at the track when cats are require? Maybe thats why not more vendor makes them
http://www.comptechusa.com/store/250101.html

I'm also wondering about the smell everyone mentioned. Some friends of mine have 360's w/ test pipes and i've driven behind them many times and never noticed a funky smell.

can't smell any bad odor.. since i'm the driver :biggrin:

 

[DocL]

I used test pipes when I had an HKS exhaust and the car sounded great. When I installed a Taitec JGTC Parallel exhaust the car was obnoxiously loud so I put the cats back. I don't know if there was any power gain, but my car dyno'd 250.8 rwhp and 193ft/lb tq without the cats. I haven't dyno'd with my current set up, but I don't think there is going to be much of a difference.

If you want to do it for $hits and giggles, then I say do it. But be preparred to accumulate a lot of soot on your rear bumper.

 

[02#154]

I'd have to say that I'm of the opinion that removing cats from an NA NSX would likely produce *measurable* HP. I mean, just looking through a cat, I can't see out the other side and I can't imagine that's good for performance. That said, I know that catalyst technology has increased a great deal since they were first put into wide use in cars and the tests I've seen on NA cars, the measured gains are minimal, if any. So I don't think that it would be felt or that it would make a difference at the track. I highly doubt it, though it's just an educated guess. You could probably find the same amount of performance by taking out the tools in the trunk.

The bottom line to me is that it's just not worth it to run no cats on an NA NSX. Even assuming you free up 10HP which is a big "IF", if you get pulled over and the officer checks for cats, if they're not found then they can impound your car (at least that's how it is here in CA). Just not worth it to me.

Oh, and my first-hand experience with cars I've owned (not NSXs):

1) I couldn't feel any difference
2) there were no additional smells emitted in the exhaust
3) there was a lot more soot on the rear bumper

That's all I have to say about that.

J

 

[titaniumdave]

I used to run test pipes on my CTSC low boost set up and it would dyno 1 RWHP more with the test pipes when compared to stock cats. I ran test pipes because I used leaded race gas mix to keep from pre-detonating on the track on hot days because there was not enough timing control with the stock ECU. Now I have an AEM, and always run my cats. For 1 RWHP I would rather do my part to not damage the environment as much...

No one has pointed out the one BIG advantage of test pipes, my old car shot flames at shift point on the track!!!:biggrin: Always a crowd pleaser! the cats completely kill the flames...:frown:

 

[95EagleAWD]

Mine's nice and loud and shoots flames on upshifts, even naturally aspirated.

I don't need 'em here, so I don't have 'em.