So I decided to venture out and take a stock set of pre cats and remove the cats, thus making precat deletes. This way it also uses the stock heat shield to keep the oem look. I am just sturring up some interest as I would be offering a trade in service.

I did install these and the power gains were there and amazing. With this service I will be offering new head gaskets and defoulers for a proper install. I would post pictures but it's essentially a stock set of precats just hollow.

I am thinking $200 plus shipping and I would need your stock oem ones back with no cracks or anything less than normal use so I can trade them with the next customer.

got pics?

just kidding, thats a great idea bruce.

Definitely a great idea.

So why wasn't this considered before. There has to be some downside, no?

Genius.

Thank you all. No downside, only up IMO because you can throw the heat shield on and keep the oem look just hollow for track purposes and create a sleeper.

Not sure why no one has thought of this. I mean it is a pain to remove the cats and clean them out. Other then that, it's a hollow tube.

my buddy has done it.
its not a "new Idea" and isnt as efficient as a "straight pipe"

but props for turning it into a service!

That is true is your looking to squeeze out all performance and horsepower... The difference Between this and straight pipes is very minimal though. Cat delets maybe 10 hp, these maybe 7-8.

Stock pre cats I've seen fail, when these cores crumble it gets sucked back into the engine so instead of buying new cats, these are also an option for you.

That's a very interesting idea. I have a Toyota MR-2 and when those cars were built, the precats had a nasty way of breaking down prematurely and trashing the engine. The owners of these cars either replaced the OEM precats with a header (like I did) or took out the factory header with the precats, essentially destroyed them, cleaned out the head completely to get rid of any residue, and reinstalled the header. As a result, no further engine failures. The main cat is still in the car, intact.

The cars with precat deletes will still pass emissions (as mine has) since my header is encased in the OEM heat shields, and in NJ, it's basically an OBDII code check and driving over a camera to make sure the main cat is still there. Since the precats only help with emissions during the warm up of the engine, they really don't do a whole lot otherwise, and in this case, the decatted header will look OEM, so the emissions check should present no issue. Overall, it sounds like a good idea.

I know that the PCDs cause some rasp; do the de-cored cats rasp as bad? I would think not since they are made of thicker steel.

Are you cutting these apart and rewelding them or just knocking the substrate out from the ports?

I'd love to see a dyno comparing these with PCDs...

Not trying to be a negative Nancy, as I'd probably do it myself if I thought mine were bad, but couldn't purposely tampering with OEM emissions and sending them back get you in a little trouble? It's one thing if you sell a new part as "off road only" but deliberately destroying OEM parts for a profit... just saying, if I were to do it I'd probably ask people to label it as scrap metal or something.

As far as performance, it should get most of the gain but the outlet is smaller than the PCDs. Also cars I've heard with gutted cats vs straight pipes don't sounds as good, just kinda sounds a little more hollow.

I will post up with how it sounds in a bit when we start it.


Anyone can sell things, like how they sell pre cats. It's designed for race/offload purpose. Install is on the buyer and they take the same risks as installing pre cats. I will look into it but I don't see how companies sell pre cats and headers for cars and not get in trouble. I am selling these as off road purpose and track. This is the catch 22 where some shops don't like tampering with cats and installing them, but to me I'm selling a pipe thats hollow, but ask for the stock one back from there track or off road car.

I like the idea I would possibly be interested. GL Bruce.

I would be interested too.

Well tested it out. Not one bit of rasp, with a slight bit more throaty exhaust note. As said before it seems as if the thicker walls killed the rasp. Also no codes with our set up.

They're installed on my buddies car and its pretty much stock with an intake. Before it felt like a nice pull, but driving the car after with the hollowed pipes was a difference. Enough upgraded pull to feel a difference. Im not talking WHOA thrown back into seat but the force on take off was defiantly harder than before.

Do you have a pics of the O2 defoulers that you are using? specifically the size of the hole.

Are you banging the cores out with a hammer or cutting the cats apart and pressing out the cores?

This has been an ongoing thing for YEARS. Gutting cats is not new at all. I would be interested but 200 bucks is pretty steep just to gut a cat. I would think 200 if I DON'T send you my cats is a good price since if I were to purchase new PCD's I get to keep my stock parts to re-install if I sell the car or don't pass emissions for some reason.

Also I would only be willing to spend that money if I could see before and after dyno sheets as it has been proven time and time again that there is very minimal gains by gutting your cat.

I very highly doubt you are getting anywhere close to 8hp gains with this but if you are my interest would be hightened. Dyno comparisons have been done with numerous cars gutting cats and usually only get 1-2 hp gains max.

Not to high jack...But not sure if that is safe for the car...Hollowed out pre-cats vs Deletes are alittle different...Heard about the danger of precat subtrates falling out being dangerous..Maybe someone can chime in and explain this better...

^you didnt read the thread, batman.

As long as the precat matrix is destroyed and the hollowed out header is cleaned out, typically with water and compressed air, it should be no problem. The precat matrix is typically very friable, so it breaks up /disintegrates easily and should be easy to remove completely.

I did read it, get off my nuts...I don't wanna catch crabs

then you would know that the whole point of the thread is to hollow them out.
which would leave nothing inside the tube; hence the term hollowed out.

The precats are the main catalytic converters in these cars. They take care of 95% of the emissions, and that's why they're monitored by the ECU. The third cat is just in place to make the car achieve ULEV status. There's no o2 sensor on this cat for that reason; it's just not crucial in adhering to the Clean Air Act. Some people in California have passed the sniffer without the third cat in place, but they wouldn't have a snowball's chance in hell of passing without the precats.

Nah...Really? Thanks Sherlock....HFC are a better option and safer

^how are HFPC's safer than a hollowed out OEM cat? it's essentially the same thing.

Well for emissions purposes and air quality they are...

this is a feeler "service" thread.
he wants to provide a service/another option for people that cant afford the HFC's or PCDs.

this is not for COMPARING the two.

I agree that one isn't any "safer" than the other, but they're hardly the same thing. One is hollow, one contains a low count substrate.


As far as the price, I don't see the value at $200, unless "looking" OEM is important. $200 is pretty crazy money to bust the substrate out of two cats.

What are PCD's going for, like $350? Then you can flip your stockers for over $200 to someone who has cats that failed and you're down $100-150 with proven PCD's. I'm sure these will make some power, but not what the PCD's will. Velocity of the exhaust coming out of the heads will be impeded compared to PCD's. you've got the smaller openings and then all that increased pipe volume that's going to slow down flow.

Has anyone scrapped stock cats? They might go for $100+ at a junk yard, at least $50. That'll offset some of the cost, or have them cut and straight pipe welded in instead.

Actually the precats are not the main source of emission reduction- that job remains with the main catalytic converter. The precats reduce emissions when the engine is warming up, and after its warm, they do nothing. That's when the main cat is most effective, and with the main cat still intact, it will still pass emissions (as long as the car is warmed up and if it's going to have a 'sniffer' test- mine has passed this way before NJ went to just an OBDII check and check to make sure the main cat is present. If it's just an OBDII check and main cat presence check as in NJ, the precat delete won't be noticed. As I have said, I have personal experience with my other car (the MR-2) and it has the same setup (O2 sensors in bungs on the precat header). With the precat matrix gone, there's no OBDII codes and the main cat is still present, doing its job. My car has been like this for about 6 years, and it's passed NJ emissions consistently. Unless they take off my heat shields on the car, it will never be noticed by anyone (and the heat shield removal is a bit of a job in itself on the MR-2).

There's a lot of MR-2 owners in California that have done the precat delete and the car still passes emissions testing. The setup in the MR-2 is just like any other car made currently. Granted, by taking out the precats, what you're in essence doing is bringing the car from ULEV status to LEV status. If you remove all of the cats, then it won't pass emissions.

I know the MR-2 is not an Acura TL, but the setup is the same.

^ The price vary in condition wise. They make good $$ on these.

They are, which is why hollowed out they aren't there to fail.



These cats are ceramic, worth nothing In scrap. You may get $50-100 and sit on them for months as type s ones are a bit more free flowing and desirable and go for $150 ish. Also IMO I wouldn't spend anything on used being that it takes almost 4 hours to install with the risk of not knowing if they failed. Same with things like app sensors/alternators etc. it's always better to go new. If your just trying to fix the car and sell it working, you may find a buyer.

I was thinking it would be a lot harder but I would be at $120 plus shipping. It does take a while and I am also including the defoulers. Again no codes and yes it's not ass efficient but you cant tell me it's 1-2 hp. These cars are very restrictive so gaIns will be there..

They a ceramic cats, not worth anything. If they werent, junk yards buy them for $40-50 or so.

Precats have rasp and won't pass emissions. These are oem look, no rasp and gains are there from my install last night on my buddy's car.

Please get that car on a dyno!!!! I have all parts to do it

Unfortunately the car we installed it on got into an accident. I already have a custom fabbed exhaust so I can't install these on my car. I would be interested in giving a set away for free for a stock set if they Dyno there car before and after...

I'm down I have a stock set with 65k miles still good and I just dynoed my car a week ago so lmk and ill ship mine back to you

I guarantee that I will be interested in this in the near future

what? i dont get it

^you're going to have to spell out what you dont get.
this thread in general?
the mod in question?
the service he is providing?
what dont you get?

Ack, I have my stock Base precats and I'm in NJ if you're interested in buying them (or bartering). One needs a new stud because the nut was seized and I had to cut a stud off.

i don't see why anyone can't do this themselves. all you need is a screwdriver and a few hours.