I don't think the answer MUST be no, to be frank. I haven't dissected the OEM cat (or any cat for that matter, not even in high school biology), but in theory, if the pattern for the flow through the cat was correct, it could actually keep there from being any pressure drop through that section of the pipe. To oversimplify it, as long as the area is kept the same, there won't be a pressure drop. Of course, in reality there are friction forces along the walls as well, so realistically the area through the cat would have to be larger, but in the end, it IS possible that they could have engineered the cat to not cause a pressure drop through the pipe, and in fact it would make sense that they would do so.

Again, I am not trying to say one side is right and the other side is wrong - I'm just playing devil's advocate and trying to apply the principles of fluid flow I remember from college.

 

Exactly!

The preasure will drop and increase with or without the cat.

 

The honey comb is designed the way it is in order to keep the pressure drop relatively low and to straighten out the flow. The hollow camber will allow the exhaust gases to expand more, also it won't flow through in the same way it would with the cat.

 

Normaly I would agree but our cat is made/shaped more like a two-stroke expansive chamber with a nice taper than most cats.

 

Correct, hence if a test shows reduced flow, here is the reason.

Do you think an independent tester (Import Tuner) is going to lie?

They are not promoting any product and the don't get a kick back from the EPA.

 

Interesting discussion .
Firstly I agree with Turborx8 that with a turbo the stock midpipe with gutted cat works very well .
As far as NA goes i would still lean towards it providing improved performance even though there is that expansion and contraction business going on .
If you gut your cat and get a torch and shine it down there you will see very smooth transitions - especially the exit .
My money would be on it improving the performance N/A by just as much as any other midpipe out there .....

 

Actually, knocking out the honeycomb in an OEM cat for N/A applications such as the one on the 8 will rill rob horsepower. I know what you're thinking, bullshit, right? Do a search and find out.

EDIT: Wow, nvm, the information as to why it reduces power is already in this thread.

 

sorry you fail.

and this was dyno'd.

lets put an end to this ignorant nonsense. next thing you know, people will say turbos reduce horsepower because they disrupt exhaust flow. its proven!

 

+1 Agreed
Now I wish someone dyno their 8 to confirm it either way.

 

You may be running way too rich - do you have an AFR gauge to check ?

My backfiring has got better as my tune got better . Still get it a bit though .....

 

Like I said, in turbo applications it is probably negligable, but I wonder if he would pick up more power with a proper midpipe. Your being extremely ignorant by denying something that's in plain black and white. I don't see how you can be so sure of yourself with ZERO PROOF

If some one can prove me wrong that in NA applications a gutted cat is better than a proper midpipe, I will delete all of my posts in this thread.

 

^+1. The only people presenting anything other than what they THINK are the people who agree that gutting the cat is not an improvement. People hear the difference and automatically assume they feel it too.

 

but gutting your cat actually loses power it's been dyno proven by lots of people.

Bose - this original assertion is hopelessly wrong, and I don't see you bringing these 'dynos' to back it up.

prove me wrong that in NA applications a gutted cat is better than a proper midpipe,

Nobody claimed that a gutted cat beats a 'proper midpipe', and it seems you are now trying to weasel out of your first erroneous statement.......

 

http://www.importtuner.com/tech/impp...ion/index.html

Here AGAIN is the proof I bring to the table, yes it is not mine but it is proof none the less, how does this make me hopelessly wrong? I'm not trying to 'weasel' out of anything I'm trying to be more clear as I feel you and other's are not comprehending what I'm saying, or your just that stubborn, either way I don't care it's your cars do what you want. How about you guys go cut some coils off your springs too.

 

That is to generalize that gutting the cat will have negative effects. Some cars, whose cat's are removed gain horsepower, I.E, the Rx-8, Mazda 6, Honda civic. I would like to name more, but I've done that and I noticed a big gain in the 6 and the civic.

I'm not stating that you are wrong, but it varies and depends on a bunch of stuff.

 

There is a difference between gutting a cat and removing it with a proper pipe that's my point, that's been my point. I never said removing a cat is bad, it just depends on how you do it.

 

I read that link . In summation it said that they saw identical power with the gutted cat . With a test pipe they saw more power up top with a small reduction down low .

Being that was not an RX8 and knowing how much air an rx8 flows - I don't think it proves that gutting the cat on an 8 will give similar results .

 

Alrighty then. I think no matter what data I post your all still going to think the same thing anyways so I guess my words fall on deaf ears, or I guess blind eyes in this case.

Have fun and play nice, and if you can't find a good place to hide the bodies.

 

after reading it I am less confident than i was ............. So I'll concede you do have the upper hand on this . I'd like to see it tested all the same .

I did swap from a testpipe to a gutted cat when I was NA for a while and really liked the tone it gave my Trust catback

 

First off, the car in the import tuner test was a Miata, not a Civic. At any rate.

Shazy, I am not going to say that all cars react to a gutted cat in the same way - there is no doubt that there can be very significant differences. But when you say you noticed a big gain in the 6 and Civic, that's hardly solid evidence. The only dyno evidence I've seen in this thread backs up the assertion that gutting the cat is actually detrimental to power, or at the very least, produces no gain. You can sit here and SAY gutting a cat increases power all you want, but until you offer significant viable data that backs up your assertion, you're just blowing smoke.

It seems logical that they would engineer the RX8 well enough that the cat would be ideally tuned to reduce pressure drops and not impact power. So quite frankly, until I see actual dyno results that a gutted cat produces gains in an NA vehicle, specifically the RX8, I will remain in Missouri (the Show Me state).

 

There is more to it than just a steady state flow...because, at that point in the exhaust its not steady state. Now further on down the line after the muffler, I can see it being more of a "steady state".

Anyways, what I am getting at is when all the innards are removed, you are not just removing something that "restricts", but you are changing the working volume of the chamber. And not only that, but how the chamber itself resonates.

For the same reason the K+N short ram loses power, gutting the cat can lose power as well. Just like the stock intake is tuned to certain frequencies (see Hemholtz), the exhaust is tuned much the same way.

To keep it very simple, the stock intake takes the pulse from the intake port being closed off and "bounces" that shock wave off the stock box just as the next charge is being pulled in. The increases the overall efficiency of the stock intake immensely. Sure the K+N probably performs better on a flow bench (a steady state flow), but is not tuned like the stock intake. All of the applies to the back side of the engine as well with the exhaust. Just be mindful of this.

For turbo applications that might just work. Once the exhaust is passed through the impeller, its smoothed/compressed out much more than N.A. N.A is going to rely on Hemholtz tuning much more than a turbo application in that application.

I'm not claiming that gutting the cat adds or removes power, it may add power in certain ranges and remove power in others...I don't know, but I am saying that it can change it, and it may have an adverse effect.

There is a lot more going on there than just "flow" and "restriction".

 

Wat - detrimental you are saying now !!!!!!! - I just moved to Missouri


Where did you read that ?

 

http://www.importtuner.com/tech/impp...ion/index.html

That's the link to the import tuner article where they test it on a Miata. With the cat intact, they get 104.1 - with the cat gutted they get 103.0. Meaning gutting the cat actually decreased horsepower by 1.1.

I'm not saying that what happens in a Miata has to happen in an RX8, but that's the only hard evidence anyone has presented thus far.

 

I'd like to see a 8 dyno'ed before I become a beliver(Kepping an open mind). Untill then to me it's like removing your airfilter from your stock airbox= more flow.

btw: I have two cats, one gutted and one thats not. I have switched back and forth. Their is almost no differents in noise but the gain is noticeable. If I could gain 1 more HP I would buy a midpipe. Untill then......

 

Why the **** would you remove the air filter. That's got to be the most asinine thing I have ever heard of in my entire life. Even if you gained 10 hp why would you risk getting all the **** that's in the air in you engine.

Oh wait, Import Tuner did a test on this: http://www.importtuner.com/tech/impp...wer/index.html
But they don't know anything do they.