Has anyone done a dyno run with aftermarket headers and the primary cats behind them?
Has anyone done a dyno rune just cutting out the primary cats?

I want the HP gain but I haven't found a credible dyno run with just aftermarket headers and the primary cats moved back but still installed. More snake oil I suspect. I want to keep my car smog legal.

 

Don't believe anyone has done that. The primaries are part of the stock exhaust manifold. Moving them and relocating them would mean cutting them out of the manifold, thereby destroying the manifold and cutting the exhaust system behind the Header and welding them in. What about the secondaries. Leave those in too? IMHO, your suggestion is really not practical.

And, BTW, in California ANY modification to the stock exhaust system - is not legal.

Lou

 

I'm sure no one reinstalled the factory cats after getting headers and exhaust.
Everyone that put cats back on their car went with aftermarket cats.
The factory cats are so restrictive gutting the cats on the headers make almost as much power as having aftermarket headers.
Check out the thread below for more on what I'm talking about.
https://www.clublexus.com/forums/is-...-with-isf.html

 

Exhaust modifications are legal in California, as long as it is cat-back...yes I know I'm potentially opening up another can of worms here. The pipe leading from the cat to the muffler, the muffler itself is open to change. Even better if there's a carb number on it, but I'm not sure that's required. When I lived there it was not. In 2019 Cali also past a law regarding how loud the exhaust could be (95 decibels). How do they measure it? I doubt they have decibel meter to check, so basically they can ticket you and you'd have to fight it.

As to what the OP listed, you can do all that work, but you cannot relocate the cats and be legal. When you move the cats from the factory location it will be an illegal modification. This was even true when you swapped a motor into another vehicle, the location of the cat, had to be in the same spot that it would have been on the motor originally.

http://www.californiacarlaws.com/exhaust-noise/

OP if you want to keep your ISF smog legal then you pretty much can only do a "cat-back" exhaust, beyond that any modification involving the ecu, intake, headers will not in the strictness sense be smog legal. Even then if you get a cop that wants to give you a hard time you'll be getting a ticket for the exhaust. Now people have gotten away with just the obdII readiness testing, but technically it would not be smog legal. Suspension work, brakes, knock yourself out.

 

^^^^On an ISF, a cat back exhaust removes the second set of cats. Don't think that's legal

Lou

 

A "cat-back" exhaust on the ISF could just be the mufflers, or again anything that's behind the secondaries. Technically in California if you want to go through the trouble, you can cut the pipe behind the secondaries and custom an exhaust from there on back and be legal as long as it's under 95 db. Though honestly I'm not sure if there's an off the shelf exhaust that does so.

Honestly though, for all the potential hassle California will put you through, just enjoy your 416 horsepower.

 

Catback means just that- behind the cats. All the cats. If you remove the secondaries, it's not just a catback.

I'm thinking I can pass the visual if I relocate the primaries- I know the guy and he's been doing my cars for years now. If there in there he might OK me. Of course he might not.

What I don't know is what the benefits are of just headers with the primaries still in place but moved back. My guess is not much. A convenient test that many of these header sellers neglect to mention. I love the videos- they pull out the factory header and talk about how bad the primaries are and literally completely ignore the giant bulge that is the primary cat just inches away. Do they really think the Yukihiko gnarled up those primaries because he didn't know what he was doing? That's why I call them snake oil sellers. They're simply lying. Who would pay $2,000 for 15 hp? The horsepower is corked up in the cat. And I'll bet for emissions reasons, those cats needed to be right where they are.

The reason gutting cats is not quite as good is because of the backpressure the turbulence in the cavity that is created at higher flows. And once the cat's are gone, yes, a real nice header would really help. But not before. Plus many performance cars today absolutely stink without cats. It's really bad. So I don't want to go there.

Maybe nitrous! Regardless first mod is going to be limited slip diff.

 

That is not correct. A cat-back exhaust system for an ISF means behind the primary cats. All ISF 3rd party cat-back exhaust systems eliminate the secondary catalytic converters.



Lou

 

If you modified your exhaust it's illegal regardless if cat back or not. The way the state stated from the link is very gray but when a cop pull you over he can give you a ticket. Smog shop will see the exhaust and not pass even with factory cats. There are many shops that will not care so you might get lucky.
the 95db law been around much longer then '19. The '19 law made it so an exhaust ticket is no longer just a fix it ticket but an actual fine.
Something with a CARB number will be exempted since the manufacturer already submitted it for testing and the product passed all regulations. I don't know of anything for the ISF that have carb number.
They can get you for lowering to. Measuring from your headlights toward the ground you have to be 23" or more.

 

Hah. They can call it whatever they want but that isn't what it is. Just like they call it a header replacement, no mention of the primary cat elimination. Maybe they should call it I want my cats-back. Lol. Catback in every car I've ever dealt with is resonators and mufflers only. That is a good pic. Looks like the midpipe can be removed and reinstalled easily for smog purposes. I'll bet removing the secondary cats keeps the stink tolerable and adds some nice power. I'm sure its covered on the board here.

 

While some manufacturers have called this a cat-back exhaust in the strictest of terms it is not. Technically cat-back, like the name implies, is an exhaust that replaces the exhaust from the cats on back. While some manufacturers may argue that the exhaust is a cat-back exhaust because the primaries are still on the exhaust manifold it does not take into account the secondaries.

Lou we might be debating two different things. You mentioned that "ANY modification to the stock exhaust system - is not legal". That is not true, you could custom an exhaust rear of the secondaries and technically be legal under the way the law is written now. You could change the stock mufflers to something more free flowing and again not be illegal. Again though as long as it does not put you above 95 db. It doesn't make you immune from harassment, and time and cash spent in court, but technically legal. Where you might be correct is that I'm not sure there is any off the shelf exhaust for the ISF that doesn't remove the secondaries.

Modified exhausts are not illegal strictly based on how the law is written, even being given a ticket does not mean it's specifically illegal. The officer writing the ticket is unlikely to have a decibel meter to check if the exhaust does not meet this requirement, they are making a judgement based on their experience. You can contest the ticket and get it tested at the referee station. If it tests below the 95 db limit you will be issued a certificate of compliance, that you can present the court. The question will be is it worth it to deal with the harassment/hassle?

BUT, what the OP is proposing is a different thing all together and would not be smog legal.

 

The way the law is stated is vague beyond max sound your exhaust can produce. It does state no modifications to pollution devices and this is what will be use to say no to exhaust even if cats are left. You can take it to court but the judge will side with the cop. After all if judges start dismissing citations how will cities make money. State ref like the cop will not care and want the car to be stock. No one want to go to the state ref as they know more then the a cop. Cop might miss something but most likely the ref will get you for it. The exhaust laws is written but interpretation by the people enforcing them is a whole other thing.
With the recent take overs and new exhaust law the cops are having a filed day handling out tickets. We can only thanks all the knuckle heads for making it hard for all of us in CA.

 

No doubt to that, it is written vague for that purpose. But if you have the time and cash you can fight it. The way the law is written you can modify the exhaust behind the cats. It will likely require a lot of time and cash, a second car and a lawyer. This isnt anything new for California, they do this on many different fronts, basically making it near impossible or at least financially infeasible for most people.

 

So there is a CARB Compliant Magnaflow CAT, which can be used in place of the secondary cats, that work for up to 2010 ISFs, so far. I know because I just did it. I had them installed on a Borla mid-pipe in the stock location, and I have the RR Bazooka on the back end of the Borla. My mechanic (and smog guy) wouldn't pass the visual without the secondary cats, and I didn't want to deal with finding a shady shop every couple of years. So I found the CARB compliant cats and had them installed. Not cheap, but I don't think I lost a lot of performance (butt dyno says so); they are high-flow cats, they just can't be advertised "high flow" in Cali, another one of our stupid laws.

 

My experience with Magnaflow cats:

https://www.clublexus.com/forums/is-...w-no-more.html

Lou