There was barely any increase in sound, I was shocked! :Eyecrazy:

The increase in power was very noticeable and its not all in my head so it must be significant. Gotta love free horsepower!

The only problem I am having is when I let off the gas my exhaust system pops. If I am accelerating and I let off fast it sounds like a gun shot!

I thought if I recirculate my BOV it would solve the problem but it only helped a little.

What can I do to solve this issue?

beware of the flair my dude..its normal...no cat..=flmaes

crunk sed it

So this is normal?

Damn, I had no idea. lol

Hate to be the bearer of bad news, but gutting your cat actually loses power it's been dyno proven by lots of people. But the popping is normal without a cat.

Hate to be the bearer of bad news, but gutting your cat actually loses power it's been dyno proven by lots of people. But the popping is normal without a cat.

no.

and especially not when turbo.

Where is the proof?

Import tuner and Car and Driver have dyno graphs to prove otherwise.

It causes turbulence in the exhaust stream, blocking more flow than it frees up.

Hate to be the bearer of bad news, but gutting your cat actually loses power it's been dyno proven by lots of people. But the popping is normal without a cat.

loses power? im callin shenanigans until i see some info's

Where is the proof?

Import tuner and Car and Driver have dyno graphs to prove otherwise.

It causes turbulence in the exhaust stream, blocking more flow than it frees up.

so you are saying that if you take an obstruction out of an otherwise SMOOTH pipe there will be MORE turbulence?

ok bill nye.

btw, which one of us has seen the inside of our catalytic converter? :uhh:

http://www.importtuner.com/tech/impp_0904_hollowed_out_catalysts_make_power_fact_o r_fiction/index.html

Here's a link.

The pipe isn't smooth, You hollow out the cat which is a larger diameter than the rest of it, the exhaust gas is allowed to expand in that area then when it's forced back into the smaller diameter pipe causing lots of turbulence.

I've seen the inside of a lot of cats, what's your point?

http://www.importtuner.com/tech/impp_0904_hollowed_out_catalysts_make_power_fact_o r_fiction/index.html

Here's a link.

The pipe isn't smooth, You hollow out the cat which is a larger diameter than the rest of it, the exhaust gas is allowed to expand in that area then when it's forced back into the smaller diameter pipe causing lots of turbulence.

I've seen the inside of a lot of cats, what's your point?

You can't really compare a miata to a turbo rotary. :uhh:

http://www.importtuner.com/tech/impp_0904_hollowed_out_catalysts_make_power_fact_o r_fiction/index.html

Here's a link.

The pipe isn't smooth, You hollow out the cat which is a larger diameter than the rest of it, the exhaust gas is allowed to expand in that area then when it's forced back into the smaller diameter pipe causing lots of turbulence.

I've seen the inside of a lot of cats, what's your point?

i've heard this as well.

The only problem I am having is when I let off the gas my exhaust system pops. If I am accelerating and I let off fast it sounds like a gun shot!

I thought if I recirculate my BOV it would solve the problem but it only helped a little.

What can I do to solve this issue?
My N.A. pops a couple of times when I let off of the throttle. As far as I can tell the cat is still in good shape.

gutted my cat and picked up 20 hp on my turbo setup.
So .....

gutted my cat and picked up 20 hp on my turbo setup.
So .....

That's about how much my butt dyno tells me too. :lol:

Well I may be wrong about it on turbo cars but there are exceptions to every rule. I want to see proof, your butt dyno doesn't mean anything. Lets see your dyno.

I see a lot of people telling me I'm wrong but no one has any proof to show me the contrary. That's all I'm asking.

And either way gutting your cat is for Honduh drivers.:lol::lol::lol:

all race cars have no cat i belive

all race cars have no cat i belive

First, that would probably depend on the rules of the racing league. Second, if they didn't have to have a catalytic converter, I seriously doubt they would take the stock cat + resonator combo and gut the cat. There are quite a few different RX-8 test pipes out there for a reason...

I never said having no cat causes turbulence. I know that some race cars don't have cat, but they have a proper race pipe. Like Zeon said they wouldn't just ghetto rig it up.

Gutting your cat yields more power because it eliminates an airflow/exhaust restriction. Every schoolboy knows this.

I would bet the exceptions are people who have chunks of partially melted honeycomb in their "gutted" cats.

The turbulence argument makes some sense, but would the expansion of the exhaust cause more restriction than the honeycomb. Going catless is like saying FTW, but getting more power is a beautiful thing > : )

That's about how much my butt dyno tells me too. :lol:

No butt involved, butt a DynoPak was.. :)

The stock tune is rich, to prevent the cat seeing peak temperatures.

So it uses more gas, for less power, 'for the environment'......

If you tune the car for max economy OR power, the cat has got to go - burned out, gutted or replaced - keeping it is not an option.

S

I'm not a scientist, and I am not going to try to act like I am right either way, but honestly, thinking about the expansion/compression causing more turbulence makes sense to me in a way. I mean, when you think about, if the pipe gets wider, there will be a pressure drop - and then when it gets smaller again, there will be a pressure increase. Thus if you have a big empty chamber in the middle of an otherwise constant diameter pipe, it could increase back pressure. However, if you keep that flow going at a constant velocity, it will not create pressure drops within the pipe. Every race pipe I can remember seeing has been of a constant diameter - that isn't coincidence.

Again, I'm not saying I know all the answers, I'm just trying to think back to some of those horrid fluid mechanics labs I had to do as a junior.

thinking about the expansion/compression causing more turbulence

The point is not "is there a restriction?"

- obviously the diameter change will affect the flow, but even with the catalyst intact, the gas still has to expand then recompress......

The question is "is the empty chamber more restrictive than the SAME cavity filled with pounds of ceramic" to which the answer must be no.

S

thinking about the expansion/compression causing more turbulence

The point is not "is there a restriction?"

- obviously the diameter change will affect the flow, but even with the catalyst intact, the gas still has to expand then recompress......

The question is "is the empty chamber more restrictive than the SAME cavity filled with pounds of ceramic" to which the answer must be no.

S

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.

thinking about the expansion/compression causing more turbulence

The point is not "is there a restriction?"

- obviously the diameter change will affect the flow, but even with the catalyst intact, the gas still has to expand then recompress......

The question is "is the empty chamber more restrictive than the SAME cavity filled with pounds of ceramic" to which the answer must be no.

S

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.

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.

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.

gutted my cat and picked up 20 hp on my turbo setup.
So .....

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!

:rant:

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 .....


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

The only problem I am having is when I let off the gas my exhaust system pops. If I am accelerating and I let off fast it sounds like a gun shot!

I thought if I recirculate my BOV it would solve the problem but it only helped a little.

What can I do to solve this issue?

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 .....

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!

:rant:

:uhh: 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.:banghead: 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.......

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_0904_hollowed_out_catalysts_make_power_fact_o r_fiction/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.:banghead:

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

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.

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".

. The only dyno evidence I've seen in this thread backs up the assertion that gutting the cat is actually detrimental to power ...................

Missouri (the Show Me state).

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


Where did you read that ?

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


Where did you read that ?

http://www.importtuner.com/tech/impp_0904_hollowed_out_catalysts_make_power_fact_o r_fiction/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 fuck 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 shit that's in the air in you engine.

Oh wait, Import Tuner did a test on this: http://www.importtuner.com/tech/impp_0905_intake_removal_decrease_power/index.html
But they don't know anything do they.:jerkit:

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......

Noticeable and quantifiable are extremely different. You can notice something that isn't truly there. Maybe my butt dyno just isn't as finely tuned as others.

Again, the only real data I've seen in this thread shows that the gutted cat produces less power. I'm not sure how people can still argue this fact without bringing real data to the table.

And Bose, very interesting test with the filters as well. I agree that there's no way in heaven I'd remove the filter from my car!

http://www.importtuner.com/tech/impp_0904_hollowed_out_catalysts_make_power_fact_o r_fiction/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.

Id imagine it really depends on the shape & size of the cat, but without that media in the cat, you lose all the spaces/honeycomb that would straighten out the airflow, so you should get some more turbulent flow with the cat gutted. This may cancel out any gain from opening up the space in the cat

Ether way, id like to see proof of loss or gain, especially with the gains you claim on the gutted cat... I doubt itd be much if any

Why the fuck 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 shit that's in the air in you engine.

Oh wait, Import Tuner did a test on this: http://www.importtuner.com/tech/impp_0905_intake_removal_decrease_power/index.html
But they don't know anything do they.:jerkit:


Relax and take your meds. Just an example of restriction.:lol:

If you read the article it says it's not a restriction, a proper filter will suck in more air than an open air box.

Fluid dynamics? Whats that?

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.....

I did this at the track last weekend and lost 3mph which is a good amount of loss hp. I did atleast 5-8 runs with it out. Also did another 3-5 runs with the airbox propped open. You have to try stuff to seee if you can gain a extra MPH or .1 E/T.

OK sooo I guess I'm just going to have to try one for myself. Why does everyone seem to hate the OBX midpipe? I dont want to search. Anyone have one?

Fluid dynamics? Whats that?

:lol:

Fluid dynamics and vibrations/resonance.

I did this at the track last weekend and lost 3mph which is a good amount of loss hp. I did atleast 5-8 runs with it out. Also did another 3-5 runs with the airbox propped open. You have to try stuff to seee if you can gain a extra MPH or .1 E/T.

Agreed, You have to try stuff to see if it works. My drag bike works better without a airfilter but It also has a pretty big stack on it.

Well, Just ordered a mid pipe. I'll get back in a few weeks...

I guess my point of view is if you have the cash to go turbo you have the cash to at least get an rb pipe.. having a mid pipe is just as useful as a BOV IMO.

Maybe I'm off but I would much rather sell my stock cat for $200 and buy a $125 mid pipe.

Well, Just ordered a mid pipe. I'll get back in a few weeks...

Midpipe numbers are all well and good, but that won't settle the gutted vs. non-gutted CAT debate.

I guess my point of view is if you have the cash to go turbo you have the cash to at least get an rb pipe.. having a mid pipe is just as useful as a BOV IMO.

Maybe I'm off but I would much rather sell my stock cat for $200 and buy a $125 mid pipe.

I did not gut my cat because I could not afford a midpipe.

The reason was because I need to keep my car as quiet as possible (cops in my area are bad) and the only way to accomplish that was to gut the OEM midpipe.

I could have gone with a Mazsport midpipe but I did not like that you need spacers for the cross members.

Midpipe numbers are all well and good, but that won't settle the gutted vs. non-gutted CAT debate.

But it will settle the gutted cat vs. midpipe issue.

I did not gut my cat because I could not afford a midpipe.

The reason was because I need to keep my car as quiet as possible (cops in my area are bad) and the only way to accomplish that was to gut the OEM midpipe.

I could have gone with a Mazsport midpipe but I did not like that you need spacers for the cross members.

hmmm well to each their own I suppose.

OK, its been awhile now since I installed a catless midpipe. I gotta admit theres more top end power. To the point where the vehicle revs past the redline(Easy) and sometimes kicks on the fuel shut off on late. The only minus was there was a rasp sound at around 2000 rpm. Belive it or not I got 90% of the rasp out by wraping the pipe with header heat wrap tape.

i think that happens because the wrap is muffling a bit, where as the stock pipe is thicker, but i am just talking out my ass