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Hi, everyone... In honor of my late wife (and a form of retail therapy), I've been trying to fix up my TransAm how we always wanted to, but never had the time.
1998 A4 WS6 TransAm @~60,000 miles
About a year ago I put in Long-Tube Headers (race version, all EGR/AIR/Cat deleted) with an off-road Y-pipe mating up to a Borla catback, which I currently have removed and just dumped at the rear axel until I can get an electric cut out (the Borla is generally too quiet for my tastes.) As much as I enjoy the sound of the engine through the headers,
1. It sounds God awful when it hits the Y-pipe between 1800-2500RPM.
2. The exhaust smell at a stop light is awful (and likely dangerous). I always have to turn the air on full blast with the windows down when stopped.
I imagine both of those problems will largely be eliminated with the cutout/Borla (because the cutout will be before the Y pipe, and the Borla will obviously muffle a lot.) HOWEVER, I was thinking I should get an aftermarket high-flow catalytic converter welded in at the same time I do the cutout. I only lose a handful of horsepower, right? I'd rather my passengers be safer than have +1.5HP at the top end. I'm not worried about Rear O2's and stuff (obviously), I just need something that won't impede flow much, but still makes the exhaust more inert and safe. Can I just get any aftermarket cat, or do I have to find out the size of my Headers/Ypipe? (I got it for free from a friend who switched to forced induction, so I have no idea what size it is.) Is there a brand that is popular among LS1Tech drivers, that has been reliable for many people? I've included a picture of the headers/Ypipe I received (I had the custom muffler at the end cut off so that it could mate up directly to my Borla.)
Why not get a catted Y-pipe with hi-flow cats in it? Easily available! Plus, a cat for each bank will flow better overall, and lose fewer HP than a single cat. That Y-pipe in the pic looks VERY pieced together! lol
Why not get a catted Y-pipe with hi-flow cats in it? Easily available! Plus, a cat for each bank will flow better overall, and lose fewer HP than a single cat. That Y-pipe in the pic looks VERY pieced together! lol
I'm extremely poor. The less money required, the better. I thought I could put it where the Y merges into 1... but now that you mention it... that wouldn't get hot enough to be useful, would it? I guess I'm kind of SOL...
I'm extremely poor. The less money required, the better. I thought I could put it where the Y merges into 1... but now that you mention it... that wouldn't get hot enough to be useful, would it? I guess I'm kind of SOL...
Someone reported that after a run, they measured the temp inside the I pipe where they had put in their converter and it was 1000 degrees, only need 600 degrees to activate it.
Catalytic Converters DO NOT render the exhaust output inert/safe for you to breathe, CO2 is still being emitted in high enough levels to poison/kill you.
The smell is hydrocarbons, You can't smell carbon dioxide.
Are you interested in selling the Borla catback? Any pictures?
Sorry, sir, I'm not. I would have never bought such an expensive cat-back myself, but it literally came with the car (and I had no idea until I started messing with the exhaust... it was one old lady who owned it, 32,000 miles when I bought it. Literally almost everything else was stock on the car.)
Originally Posted by clinebarger
Catalytic Converters DO NOT render the exhaust output inert/safe for you to breathe, CO2 is still being emitted in high enough levels to poison/kill you.
The smell is hydrocarbons, You can't smell carbon dioxide.
I wouldn't try breathing in exhaust, but reducing what some might "accidentally" breathe for a half a second from a gust of wind is the point. Me putting the Borla back on should force the exhaust all the way to the back of the car, and not have it dumped right underneath the cabin anymore, also. (Except for when the cutout is open, obviously.)
Your problem is you're running open exhaust and it's dumped under the car. Make the exhaust exit behind the car and get a muffler on there
AKA put the exhaust back on and your problems will cease.
The sound will change with the exhaust back on, it will be louder now than before since you have long tubes and no cats now.
Y pipes do cause a bit more resonance that H and X pipes so if you want the tone different you can try changing mufflers or switching to an H or X (recommend X)
Since you said you are low on money I would focus the funds on getting a muffler on there (if there is one already skip that) and getting a pipe that exits beyond the car.
There's a reason cars fail state safety inspections with dumped exhaust, the exhaust comes into the cabin.
Your problem is you're running open exhaust and it's dumped under the car. Make the exhaust exit behind the car and get a muffler on there
AKA put the exhaust back on and your problems will cease.
The sound will change with the exhaust back on, it will be louder now than before since you have long tubes and no cats now.
Y pipes do cause a bit more resonance that H and X pipes so if you want the tone different you can try changing mufflers or switching to an H or X (recommend X)
Since you said you are low on money I would focus the funds on getting a muffler on there (if there is one already skip that) and getting a pipe that exits beyond the car.
There's a reason cars fail state safety inspections with dumped exhaust, the exhaust comes into the cabin.
What you're saying makes sense, but I don't have to pay anybody to reinstall my cat-back/muffler. I can do that part in my driveway (I've taken it off, put it back on after the headers, and then took it back off when I hated how quiet it was.)
I wanted the cut out to be closer to the engine for sound, but you're right, that wouldn't solve my problem of exhaust in cabin when it's open. I suppose I can get the cut out farther back, a little before the muffler, and cat as close on the I pipe as I can after the split.
Tsp catted y will reduce the smell a bit but putting on your catback will help out even more. When I went from tsp catted y to there ory I noticed a bit more exhaust smell. I'm running slp catback. How much smell also depends if you sitting in traffic, wind ect.
Technically enough CO2 in a closed environment can kill you as it displaces oxygen. It just won't happen outside.
True. But the discussion involves catalytic converters, which convert CO INTO CO2. And CO will kill you even mixed with pure oxygen, because it is POISONOUS. CO2, as you said, kills by displacement, not poisoning.
i think i bought jet hot longtubes with tsp catted y pipe and the only negative was the high flow cats slip into the tubes like coke cans and would NOT pass a visual inspection. cheers!
I went with a magnaflow high flow spun cat in the I pipe after a QTP e-cutout. Absolutely love my exhaust set up. The car still smells like a muscle car (not some prius). But it is not dangerous in the cabin at stoplights like it was without the cat as you mentioned. I used to get light headed if the wind blew the wrong way and that does not happen anymore.
p.s. I dyno tested open cutout vs thru cat and muffler. a negligible 1hp 1ft/lb difference confirmed.
I went with a magnaflow high flow spun cat in the I pipe after a QTP e-cutout. Absolutely love my exhaust set up. The car still smells like a muscle car (not some prius). But it is not dangerous in the cabin at stoplights like it was without the cat as you mentioned. I used to get light headed if the wind blew the wrong way and that does not happen anymore.
p.s. I dyno tested open cutout vs thru cat and muffler. a negligible 1hp 1ft/lb difference confirmed.
I was running the LT Headers with no cats out the 3in true dual over the rear Speed Engineering exhaust system. Car has stg 2.5 heads & cam along with a DSC-1 which is almost as noisy as the exhaust...so you could imagine the sound and the drone would be enough to drive anyone crazy. I constantly tried to keep the car between 2000-2500 rpms anything above that the sound begins to get annoying after a while. I added Kooks Green high flow cats and it really helped the overall sound not to mention it brought the smell down good enough to where I don't smell like a mechanic all day. They are pricey about $300ea.
I'm waiting to re-tune to see how much its really taken from the car. Ive heard noting but good things about these high flow cats and they seemed to do the trick both tone wise and overall smell that emits. Tone is way better with the high flow cats in my opinion, doesn't sound like *** clapping anymore. I'm not in my 20s anymore but back in my earlier days I wouldn't have changed a thing and let that car roar.
I have some Dynatech high flow converters for sell if you are interested? They have about 65,000 miles on them. PM me if you are interested and ill give you a price with shipping.
I was running the LT Headers with no cats out the 3in true dual over the rear Speed Engineering exhaust system. Car has stg 2.5 heads & cam along with a DSC-1 which is almost as noisy as the exhaust...so you could imagine the sound and the drone would be enough to drive anyone crazy. I constantly tried to keep the car between 2000-2500 rpms anything above that the sound begins to get annoying after a while. I added Kooks Green high flow cats and it really helped the overall sound not to mention it brought the smell down good enough to where I don't smell like a mechanic all day. They are pricey about $300ea.
I'm waiting to re-tune to see how much its really taken from the car. Ive heard noting but good things about these high flow cats and they seemed to do the trick both tone wise and overall smell that emits. Tone is way better with the high flow cats in my opinion, doesn't sound like *** clapping anymore. I'm not in my 20s anymore but back in my earlier days I wouldn't have changed a thing and let that car roar.
How many inches of ground clearance under the cats? I typically see these mounted just after the headers on Y pipes and I can't imagine clearance being good in that location without some floor board modification.
I have 2 of the Kooks GE-307540 which were half the price as the Kooks Green and I plan to put them in the I-pipe for optimal clearance, in the area behind the passenger seat. There's a fallacy that they don't get hot enough in the I-pipe to activate but someone measured the temp and they work just fine there. I also plan to use DMH low profile dual cutouts on the Y. Car is going to be so quiet and not smell with great ground clearance until someone pulls up next to me revving their rice and I press the electric cutout button and blow everyone's ear drums out including my own.
12-20-2017, 04:37 PM
"High flow" catalytic converters? 
