Cal Club Autocross Forums

Our '99 Miata has 95K on it. Is there a "standard" when to replace the Cat?

Do Cat's get "clogged" up and decrease performance?

Is there a legal aftermarket Cat that's better or cheaper then what we can get thru the Mazda Speed program?

How much horsepower gain should one expect when adding Formula V to the gas tank? :ibrightdea:

Not knowing how a stock Cat compares to the aftermarket, Andy Hollis found a fairly small increase going from a 200k cat to a "performance" cat. I think that you are stuck with a stock cat in stock class. That being the case, IMO, replace when you no longer pass smog. YMMV.

You should convert it to Federal spec -vs- CA spec. The federal cars don't have the pre-cat for cold starts. The pre-cat is what gets fouled. It'll still pass a sniffer and will not throw codes. Basically you have to get a header for a car destined for somewhere other than CA.

It is still stock legal too.

http://forum.miata.net/vb/showthread.ph ... ht=Pre-cat" onclick="window.open(this.href);return false;

Mako Koiwai wrote:Our '99 Miata has 95K on it. Is there a "standard" when to replace the Cat?

Well, the Feds have demanded since 1996 that a catalytic converter be warranted for 8yrs, 80k miles. Also with the advent of OBDII, you will know about anything amiss with the cat long before it becomes more of a back-pressure issue than it was from the factory; that second o2 sensor is there to monitor the emissions post cat. If there is a problem, you will have a check engine light and it will be a code for something like "warm-up catalyst efficiency below threshold" or some such. Now if you are racing in stock class, you can't change it to anything other than a "stock replacement part" as I believe it's worded. I think your next step up would be to SP (are 99's legal for STS2 yet?). There you can change to a header.

If its lying belly up and doesn't bite you when you kick it, your cat may need replacing.

I always suggest a pound adoption.

Zak Gutmann wrote:

Mako Koiwai wrote:Our '99 Miata has 95K on it. Is there a "standard" when to replace the Cat?

Well, the Feds have demanded since 1996 that a catalytic converter be warranted for 8yrs, 80k miles. Also with the advent of OBDII, you will know about anything amiss with the cat long before it becomes more of a back-pressure issue than it was from the factory; that second o2 sensor is there to monitor the emissions post cat. If there is a problem, you will have a check engine light and it will be a code for something like "warm-up catalyst efficiency below threshold" or some such. Now if you are racing in stock class, you can't change it to anything other than a "stock replacement part" as I believe it's worded. I think your next step up would be to SP (are 99's legal for STS2 yet?). There you can change to a header.

I still stand by my statement about a federalized 99 Miata being stock legal.
Do it Mako.

Federalizing the black and blue MR2 (the white one and the solid black one started life in Nevada and Ohio, respectively) required not only dropping one of the two cats, but also dropping the CA O2 sensor, changing the computer to a 49-states one, and getting the appropriate 49-states sticker. Before anyone turns me in to CARB, that car currently lives in North Carolina...

Just a note for anyone who might be casually reading this thread and thinking that federalizing a car is just a matter of cutting out the second cat. (That's not, of course, what Sebastian implied...just wanted to underline that in some cars, it's a bit more involved...)

Sebastian Rios wrote:

Zak Gutmann wrote:

Mako Koiwai wrote:Our '99 Miata has 95K on it. Is there a "standard" when to replace the Cat?

Well, the Feds have demanded since 1996 that a catalytic converter be warranted for 8yrs, 80k miles. Also with the advent of OBDII, you will know about anything amiss with the cat long before it becomes more of a back-pressure issue than it was from the factory; that second o2 sensor is there to monitor the emissions post cat. If there is a problem, you will have a check engine light and it will be a code for something like "warm-up catalyst efficiency below threshold" or some such. Now if you are racing in stock class, you can't change it to anything other than a "stock replacement part" as I believe it's worded. I think your next step up would be to SP (are 99's legal for STS2 yet?). There you can change to a header.

I still stand by my statement about a federalized 99 Miata being stock legal.
Do it Mako.

An NB Miata would need a new exhaust manifold, ECU, midpipe, and engine wire harness just for starters. Yes, it would be legal if you do it correctly, but it's cheaper to go find another car.

Regarding cats, read this link for the basic rules on replacement: http://www.car-sound.com/04basics/04epa.asp
On a stock Miata, the under-floor cat flows fairly well so there's not much reason to replace it. For the Cal-spec front cat, (a.k.a maniverter) my testing has shown that costs you about 8rwhp. Unfortunately, there is no legal replacement for the front cat available other than OEM. This is why the fastest C/S Miata starts with a 49-state car.

[quote="Mari Clements"] required not only dropping one of the two cats, but also dropping the CA O2 sensor, changing the computer to a 49-states one, and getting the appropriate 49-states sticker. quote]
EGR valve was different too.

Are these things one can just order from Mazda Motorsports?

Mako Koiwai wrote:Are these things one can just order from Mazda Motorsports?

Should be able to get it from them. However, I would not expect to find 8hp as was said in a previous post. People I know that have done the 50 to 49 state coversion found 2hp. Do you think 2hp, or even 8hp, are going to make up the difference in that car?

Thanks A Lot!!!

Yours Truly ... Karen & Mako

PS - Yeah ... we know ...

Steve Lepper wrote: An NB Miata would need a new exhaust manifold, ECU, midpipe, and engine wire harness just for starters. Yes, it would be legal if you do it correctly, but it's cheaper to go find another car.

I recently did this on my '99 as the pre-cat was causing a CEL. I needed a federal exhaust manifold, an O2 sensor wiring harness extender from Racing Beat and a bung welded to my downpipe at a muffler shop to relocate the second O2 sensor aft of the retained second cat. Total cost was $100 for the manifold + heat shield, $80 for the wiring harness and $30 to the muffler shop. I also sprung for a $10 socket for removing the O2 sensor. No more anoying CEL! I guess I did my swap on the cheap and maybe it is not 100% SCCA legal but functionally its a complete conversion. If someone wants to protest me, whatever!

Thomas Smith wrote:

Steve Lepper wrote: An NB Miata would need a new exhaust manifold, ECU, midpipe, and engine wire harness just for starters. Yes, it would be legal if you do it correctly, but it's cheaper to go find another car.

I recently did this on my '99 as the pre-cat was causing a CEL. I needed a federal exhaust manifold, an O2 sensor wiring harness extender from Racing Beat and a bung welded to my downpipe at a muffler shop to relocate the second O2 sensor aft of the retained second cat. Total cost was $100 for the manifold + heat shield, $80 for the wiring harness and $30 to the muffler shop. I also sprung for a $10 socket for removing the O2 sensor. No more anoying CEL! I guess I did my swap on the cheap and maybe it is not 100% SCCA legal but functionally its a complete conversion. If someone wants to protest me, whatever!

I doubt you would ever have a problem locally. In a divisional, maybe... at Nationals or a Pro, definitely.

Oh, and good luck getting it smogged.

Jason Isley BS RX8 wrote:

Mako Koiwai wrote:Are these things one can just order from Mazda Motorsports?

Should be able to get it from them. However, I would not expect to find 8hp as was said in a previous post. People I know that have done the 50 to 49 state coversion found 2hp. Do you think 2hp, or even 8hp, are going to make up the difference in that car?

If that's all they got, they're doing it wrong. I'd be interested to see their data... every Miata I have tested before/after has been between 5 and 8 hp.

Steve Lepper wrote:
If that's all they got, they're doing it wrong. I'd be interested to see their data... every Miata I have tested before/after has been between 5 and 8 hp.

Did you test a new 50 state setup to a new 49 state? Or just take used stuff of a high mile car and replace it with new? We have not even seen 8hp gains removing cats and replacing it with strait pipe. You must have a very optimistic dyno.

Steve Lepper wrote: I doubt you would ever have a problem locally. In a divisional, maybe... at Nationals or a Pro, definitely.

Oh, and good luck getting it smogged.

So to be SCCA Stock legal, everything must be changed out including the ECU, and wiring harness?
For smog, do you say good luck because it's visually obvious or because you may run into a smog shop that is a stickler, it should still pass the sniffer and not throw CELs right?

Sebastian Rios wrote:

Steve Lepper wrote: I doubt you would ever have a problem locally. In a divisional, maybe... at Nationals or a Pro, definitely.

Oh, and good luck getting it smogged.

So to be SCCA Stock legal, everything must be changed out including the ECU, and wiring harness?
For smog, do you say good luck because it's visually obvious or because you may run into a smog shop that is a stickler, it should still pass the sniffer and not throw CELs right?

Yes. Regarding SCCA, a Cal-spec car has a different wire harness, and since the two O2 plugs are plainly visible under the hood, it would be an easy protest. Can't legally modify it, so you'd have to swap it. You also need the Federal emission sticker: see below for more about that...

Regarding smog, there are a couple of problems.
First, as was mentioned earlier, you need the correct, 49-state smog sticker to go with the conversion. Problem is, in order to purchase these you have to provide the vehicle's VIN, and the dealer won't sell you one that is not for your car. One of the reasons this is done is to prevent exactly the kind of emission system conversion (they call it "tampering") you're trying to accomplish. Maybe you could buy them more easlily through Motorsports... I haven't yet tried that route as I had another way around that issue.

When you go for a smog check, you converted car will already be in the CARB system with the VIN listed as a Cal-spec car, so when you show up for a Smog Check and the tech tries to enter your car as Federal, you will fail. Doesn't matter what the tailpipe result is, because you won't even get that far. Only way around this is to know a friendly tech that will look the other way and still enter the car as Cal-spec, or make it a trailer queen that never needs plates.

Jason Isley BS RX8 wrote:

Steve Lepper wrote:
If that's all they got, they're doing it wrong. I'd be interested to see their data... every Miata I have tested before/after has been between 5 and 8 hp.

Did you test a new 50 state setup to a new 49 state? Or just take used stuff of a high mile car and replace it with new? We have not even seen 8hp gains removing cats and replacing it with strait pipe. You must have a very optimistic dyno.

That particular test was: same car, same aged parts, (btw, what aging procedure did you use?) before and after, same dyno. Results proven on more than one car. I'm researching and developing my some of my own parts for these cars, so I've spent a lot of time gathering information and testing: one of my upcoming products is an exhaust, so that's why I have a lot of data on that particular subject. In my research, I've tested from very low (4K-mile) to 100K-mile cars. Also tested new Cal-spec and Federal cars. Bone-stock and blueprinted engines, too. I did dyno testing for many years as part of my job, so I'm very familiar with proper test conditions and precedure. I have a database of dyno results for just about all differnt year Miatas.

Steve Lepper wrote:

Jason Isley BS RX8 wrote: Did you test a new 50 state setup to a new 49 state? Or just take used stuff of a high mile car and replace it with new? We have not even seen 8hp gains removing cats and replacing it with strait pipe. You must have a very optimistic dyno.

That particular test was: same car, same aged parts, (btw, what aging procedure did you use?) before and after, same dyno. Results proven on more than one car. I'm researching and developing my some of my own parts for these cars, so I've spent a lot of time gathering information and testing: one of my upcoming products is an exhaust, so that's why I have a lot of data on that particular subject. In my research, I've tested from very low (4K-mile) to 100K-mile cars. Also tested new Cal-spec and Federal cars. Bone-stock and blueprinted engines, too. I did dyno testing for many years as part of my job, so I'm very familiar with proper test conditions and precedure. I have a database of dyno results for just about all differnt year Miatas.

It depends on what we are testing. Typically we take the old original part/configuration as a baseline, then test it against a new version of the old part and the aftermarket replacement part. All of this will be done multiple times in varying orders to try to eliminate anomalies. But we have it easy... Regardless of the product we are testing, we are not selling anything, so we can call a spade a spade.

Steve Lepper wrote:Regarding smog, there are a couple of problems.
First, as was mentioned earlier, you need the correct, 49-state smog sticker to go with the conversion. Problem is, in order to purchase these you have to provide the vehicle's VIN, and the dealer won't sell you one that is not for your car. One of the reasons this is done is to prevent exactly the kind of emission system conversion (they call it "tampering") you're trying to accomplish. Maybe you could buy them more easlily through Motorsports... I haven't yet tried that route as I had another way around that issue.

When you go for a smog check, you converted car will already be in the CARB system with the VIN listed as a Cal-spec car, so when you show up for a Smog Check and the tech tries to enter your car as Federal, you will fail. Doesn't matter what the tailpipe result is, because you won't even get that far. Only way around this is to know a friendly tech that will look the other way and still enter the car as Cal-spec, or make it a trailer queen that never needs plates.

I doubt the smog tech will know you need 2 cats on a CARB 99 Miata. Many on miataforum have passed smog with one cat. I'll take my chances.

Thomas Smith wrote:I doubt the smog tech will know you need 2 cats on a CARB 99 Miata. Many on miataforum have passed smog with one cat. I'll take my chances.

He will know. The computer he uses tells him what should be on the car when he enters the VIN. Good luck.

Jason Isley BS RX8 wrote: It depends on what we are testing. Typically we take the old original part/configuration as a baseline, then test it against a new version of the old part and the aftermarket replacement part. All of this will be done multiple times in varying orders to try to eliminate anomalies. But we have it easy... Regardless of the product we are testing, we are not selling anything, so we can call a spade a spade.

Sounds solid. There are only a few other varaibles that come to mind... I'd be interested to talk with you more sometime to see why our results are different.

Steve Lepper wrote:He will know. The computer he uses tells him what should be on the car when he enters the VIN. Good luck.

And I've personally seen smog machines with a port labeled "Camera". Not used yet, but.......

Steve Lepper wrote:When you go for a smog check, you converted car will already be in the CARB system with the VIN listed as a Cal-spec car, so when you show up for a Smog Check and the tech tries to enter your car as Federal, you will fail. Doesn't matter what the tailpipe result is, because you won't even get that far. Only way around this is to know a friendly tech that will look the other way and still enter the car as Cal-spec, or make it a trailer queen that never needs plates.

Our Black&blue E-Stock MR2 started out life as a Cailfornia car and we converted it to 49 state. The VIN/Cal-spec/Carb system never caused a bit of a problem. Maybe they've changed the system since 2004 when we sold it?

On MR2's the emissions sticker tells the smog tech how many cats the car has. CA=2, 49 State=1