Going catless

[Dzmitry]

Originally Posted by Teseo

You will have the smell also

Not really. I have a cat-less header with a stock front pipe. If I'm not mistaking, the header cat is more focused on cold start emissions as it heats up faster being next to the engine and all. It has far less cells doing the work. Once the car is warmed up, the rear cat is doing the majority of the work.

I only ever smell fumes when idling for a minute or two on cold start. I never smell fumes once I get going and especially once the car is warmed up. I don't do much idling during my drives of course, but the car has had to sit in traffic for at least 10-15 minutes in a single spot during traffic from accidents in the past. Never smell anything.

[Clipdat]

Have you ever driven behind your car while someone else drives it?

[norcalpb]

Originally Posted by Dzmitry

Not really. I have a cat-less header with a stock front pipe. If I'm not mistaking, the header cat is more focused on cold start emissions as it heats up faster being next to the engine and all. It has far less cells doing the work. Once the car is warmed up, the rear cat is doing the majority of the work.

I only ever smell fumes when idling for a minute or two on cold start. I never smell fumes once I get going and especially once the car is warmed up. I don't do much idling during my drives of course, but the car has had to sit in traffic for at least 10-15 minutes in a single spot during traffic from accidents in the past. Never smell anything.

So you are saying the primary cat has less cells than the secondary cat? Could be true, but seems to be counterintuitive.

[Ernest72]

Originally Posted by Teseo

You will have the smell also

And somehow I have none running this setup for the last 4 years. YMMV.

[x808drifter]

It's also illegal as hell but YMMV.

[Dzmitry]

Originally Posted by Clipdat

Have you ever driven behind your car while someone else drives it?

I have not, but the concern here was for the smell personally, not to those around you as far I understood from the comment. But I honestly have a feeling those behind me don't smell anything either. If I don't smell anything after idling for 15-20 mins in the car, it's unlikely anyone else is smelling anything.

[Dzmitry]

Originally Posted by norcalpb

So you are saying the primary cat has less cells than the secondary cat? Could be true, but seems to be counterintuitive.

Trying to dig this information up, I thought I recall this being discussed in the past. But based on what I described, it doesn't sound counterintuitive to me. The rear cat does the big work once the car is warmed up. The front cat is there to assist emissions during cold start as it warms up the quickest. I'll see if I can find where I heard or read this, it's possible I got it wrong. I'm sure someone on the forum knows the answer to this.

EDIT: To add to this, the rear cat is quite a bit larger in size, likely definitely having more cells. Also, tons of people have confirmed that if you remove the rear cat, you will have a smell compared to removing the front cat.

[norcalpb]

Originally Posted by Dzmitry

Trying to dig this information up, I thought I recall this being discussed in the past. But based on what I described, it doesn't sound counterintuitive to me. The rear cat does the big work once the car is warmed up. The front cat is there to assist emissions during cold start as it warms up the quickest. I'll see if I can find where I heard or read this, it's possible I got it wrong. I'm sure someone on the forum knows the answer to this.

EDIT: To add to this, the rear cat is quite a bit larger in size, likely definitely having more cells. Also, tons of people have confirmed that if you remove the rear cat, you will have a smell compared to removing the front cat.

I just don’t see how if the secondary cat does the majority of the work, why it wouldn’t be called the primary cat? Also why would there be 0 sensors on the secondary cat? Seems like you’d want a measurement post secondary cat if it was what really cleaned things up, instead of just post primary cat.

I’d be curious to see where you read this stuff as I could easily be wrong too. Just want to learn more about this stuff.

[Clipdat]

Originally Posted by Dzmitry

EDIT: To add to this, the rear cat is quite a bit larger in size, likely definitely having more cells.

Do you have a side by side photo?

[RToyo86]

There is definitely added smell by deleting the header cat, but no where near as nasty as fully catless. I mostly notice it in colder weather under harder throttle when I crack the window. AFR is richer which makes sense.

Fully catless is near unbearable by comparison in the same exact condition. the entire cabin reeks of fumes, where the single cat I get a bit of a smell but it doesn't linger and goes away immediately

[Capt Spaulding]

Originally Posted by RToyo86

There is definitely added smell by deleting the header cat, but no where near as nasty as fully catless. I mostly notice it in colder weather under harder throttle when I crack the window. AFR is richer which makes sense.

Fully catless is near unbearable by comparison in the same exact condition. the entire cabin reeks of fumes, where the single cat I get a bit of a smell but it doesn't linger and goes away immediately

The thing I find difficult to see is the cost / benefit of ditching the cat or cats. How many horsepower does going catless free up compared to the environmental and personal comfort costs? Does going catless enhance drivability? Comfort? Reliability?

I realize everyone’s calculus is different, but for me with a street driven vehicle - particularly one that is already in 100hp/liter territory - no thanks. And for those whose calculus differs, okay, ditch your cats. But if you wind up in trouble with the authorities, I will snicker a bit.

[RToyo86]

Originally Posted by Capt Spaulding

The thing I find difficult to see is the cost / benefit of ditching the cat or cats. How many horsepower does going catless free up compared to the environmental and personal comfort costs? Does going catless enhance drivability? Comfort? Reliability?

I realize everyone’s calculus is different, but for me with a street driven vehicle - particularly one that is already in 100hp/liter territory - no thanks. And for those whose calculus differs, okay, ditch your cats. But if you wind up in trouble with the authorities, I will snicker a bit.

I can make a case for a catless header on a street car but not the front pipe. Just deleting the header cat is not noticeable 90+% of the time. I only really notice it during the winter and on cold starts in the garage.

Having gone back and forth from stock to a UEL header and tune, back to stock then onto my current JDL made me notice how I changed my shifting habits with the header/tune. Definitely some drivability perks.

Header sort of unlocks 4000-6000rpm range as usable shift points around town under moderate/harder acceleration as the engine doesn't feel dead when you hit the next gear at 3000-4500rpm(the "dip"). Not something I noticed until going back to stock again and realizing how much I shift at those RPMs every day.

Engine still makes all of its power above 5000rpm, but don't feel like I need to rev the nuts out of it all the time to keep the engine happy.

[Dirty Harry]

^100% agree with this. I have after market catted headers (HKS GT-Spec), with a custom dyno tune and it is the low down torque where you notice it most. Top end is a little better, but you can become a little more “shift lazy” cruising around town as you have the extra torque down low.

As for going catless headers, I wanted to stay legal.

OP, I wouldn’t go from aftermarket catted to aftermarket catless as the gains would be negligible and you definitely won’t be legal then. Not sure about how it affects the snap, crackle and popping. If you really wanted that, you could probably get it added via a tune.

[Dzmitry]

Originally Posted by Clipdat

Do you have a side by side photo?

I do not unfortunately aside from having the exhaust apart myself in the past. Here are some photos I found from a quick search that give a pretty good visual of size difference.

https://www.ft86club.com/forums/showthread.php?t=134526
https://www.ft86club.com/forums/showthread.php?t=63714