Removing CATs on Stage 2+/Dual Pulley Cars

[LittleDozer]

Anyone out there use test pipes on a Stage 2+ (upgraded HPFP/E85) or dual pulley car? I'm curious whether there's actually significant gains to warrant it. Turbo'd cars will always see a benefit because higher flow means you can spool the turbo faster, but our cars behave much more like N/A despite being boosted since the SC is run off a pulley.

[Trent212]

I am running test pipes on my car, and I will have my dual pulley file finished from SMS within the next week or so.

Will see what she puts on the mustang dyno. We are thinking in the ballpark of 410-420awhp.

[LittleDozer]

I am running test pipes on my car, and I will have my dual pulley file finished from SMS within the next week or so.

Will see what she puts on the mustang dyno. We are thinking in the ballpark of 410-420awhp.

with long tube headers and no cats your car must sound insane

[Trent212]

with long tube headers and no cats your car must sound insane

It is fun when you hit a tunnel I will say that!

[mrmomo313]

I don't think I make more power with test pipes than a similarly modded car with cats... APR says their stage 3 kit benefits from running catless though...

[waxxonMTL]

I remember on my RB26, a catless exhaust would yeild me between 35-40whp on a dynapack!!! that was huge. spool would be quicker too.. but then I was smoking black every time I was going WOT , smell wasn't that bad but you could tell and sound wasn't that bad either. The real downside was the black smoke and honestly, i felt bad going WOT around many people, so i was rarely shifting more than 5k.

I wouldn't want my luxury refined car to smell bad and/or have black smoke. that's for sure. Any downside for the catless owner ?

[colby7]

Another thing with going careless is the smell. Catless with unleaded gas is pretty rough. Catless with E85 isn't bad at all.

[JD S4]

Another thing with going careless is the smell. Catless with unleaded gas is pretty rough. Catless with E85 isn't bad at all.

corn on the cob

[LittleDozer]

I remember on my RB26, a catless exhaust would yeild me between 35-40whp on a dynapack!!! that was huge. spool would be quicker too.. but then I was smoking black every time I was going WOT , smell wasn't that bad but you could tell and sound wasn't that bad either. The real downside was the black smoke and honestly, i felt bad going WOT around many people, so i was rarely shifting more than 5k.

I wouldn't want my luxury refined car to smell bad and/or have black smoke. that's for sure. Any downside for the catless owner ?

That makes sense since those use turbos. I would just love to see someone dyno same day, same conditions with and without cats. Data doesn't exist on this platform which is a shame.

[BlownOne]

That makes sense since those use turbos. I would just love to see someone dyno same day, same conditions with and without cats. Data doesn't exist on this platform which is a shame.

Thats because its a 12 hour labor job to replace cats on our cars lol. I said somewhere (in the dual pulley thread i think) imo our cars would benefit from relieving back pressure by going catless on anything above a 3:1 pulley ratio and i still think that is the case.

[soltez]

I remember on my RB26, a catless exhaust would yeild me between 35-40whp on a dynapack!!! that was huge. spool would be quicker too.. but then I was smoking black every time I was going WOT , smell wasn't that bad but you could tell and sound wasn't that bad either. The real downside was the black smoke and honestly, i felt bad going WOT around many people, so i was rarely shifting more than 5k.

I wouldn't want my luxury refined car to smell bad and/or have black smoke. that's for sure. Any downside for the catless owner ?

I'm catless and my car only lets out puffs of smoke while making corrections during WOT same as when it was catted (stg2). Sound like that RB26 was running to rich it will also smell more with a super rich AFR. Keep in mind that is a dated port injection engine the DI in our cars burn gas more efficiently.

[LittleDozer]

Thats because its a 12 hour labor job to replace cats on our cars lol. I said somewhere (in the dual pulley thread i think) imo our cars would benefit from relieving back pressure by going catless on anything above a 3:1 pulley ratio and i still think that is the case.

In the JHM test pipe thread they said it can be done in 6 for DSG and 4-5 for manual. Not terrible but still a decent bit of cash to spend for something without data. If you end up with data showing your ported/polished SC makes good gains, I'd think it would suggest relieving the other end would too. It's just weird that 2.5 inch non-resonated downpipes haven't been shown to make any more power on these cars. if those don't then cats might not be significant either. Never know until someone dynos.

[BlownOne]

In the JHM test pipe thread they said it can be done in 6 for DSG and 4-5 for manual. Not terrible but still a decent bit of cash to spend for something without data. If you end up with data showing your ported/polished SC makes good gains, I'd think it would suggest relieving the other end would too. It's just weird that 2.5 inch non-resonated downpipes haven't been shown to make any more power on these cars. if those don't then cats might not be significant either. Never know until someone dynos.

Well shit 6 hours is wayyy better than 12, but still a decent amount of cash in labor on top of the cost of the test pipes. Yea man I think you're right...if my ported blower picks up power like I expect it to, going catless should show improvements too. I really think until now, nobody was running enough pulley for it to make a difference. I also think that every little bit will help maximize efficiency of our setups.

It's very strange because I've never heard of any forced induction car not gain power from ditching cats. I will probably end up doing it by the end of the year so I'll keep everyone posted.

[rubicant5x]

Is anyone throwing codes with the test pipe or does the tune really negate what the O2 sensor would see as a cat-less condition?

[mrmomo313]

Is anyone throwing codes with the test pipe or does the tune really negate what the O2 sensor would see as a cat-less condition?

My APR tune had a test pipe file that coded out the CEL but still had soft codes for cat efficiency on both banks. My GIAC tune does show the CEL on the dash. I'm going to ask to see if they can code it out when I get a tune revision...

[Trent212]

Is anyone throwing codes with the test pipe or does the tune really negate what the O2 sensor would see as a cat-less condition?

I had a code for a while on Apr file, but got it reflashed and it went away.

[lowjonathan]

i am gutting my cats next week as preventive measure of the cats failing on 30k mileage dual pulley set up.

on my prev evo x, gutting the cat + 30hp more under same set up.

Pro
more power, better flow, louder exhuast note when WOT, preventive measure for failing cats, zero replacement cost.

Con
some smell during idling (probably can lean the AFR thru custom tuning).
CEL might pop up after 500km (02 spacer might do the trick for untuned ride or self clearing CEL)

[LittleDozer]

i am gutting my cats next week as preventive measure of the cats failing on 30k mileage dual pulley set up.

on my prev evo x, gutting the cat + 30hp more under same set up.

Pro
more power, better flow, louder exhuast note when WOT, preventive measure for failing cats, zero replacement cost.

Con
some smell during idling (probably can lean the AFR thru custom tuning).
CEL might pop up after 500km (02 spacer might do the trick for untuned ride or self clearing CEL)

You should dyno before and after! I'm tempted to get rid of mine because I think they've been failing since going stage 2. Ran low fuel pressure for a bit and I think it damaged them. Exhaust rattles sometimes when I'm WOT. Now dual pulley and it concerns me.

[lowjonathan]

You should dyno before and after! I'm tempted to get rid of mine because I think they've been failing since going stage 2. Ran low fuel pressure for a bit and I think it damaged them. Exhaust rattles sometimes when I'm WOT. Now dual pulley and it concerns me.

yeah but my dyno wasnt accurate coz last dyno session only with CTS pulley at 411whp on mustang.

but after that i did my KI crank, the decat gain might not be accurate.
end of day, defintely there are gains. It just that gain versus money spent might be on the high side.
and zero replacement cost on the cat in the future.

[CrownSeven]

i am gutting my cats next week as preventive measure of the cats failing on 30k mileage dual pulley set up.

on my prev evo x, gutting the cat + 30hp more under same set up.

Pro
more power, better flow, louder exhuast note when WOT, preventive measure for failing cats, zero replacement cost.

Con
some smell during idling (probably can lean the AFR thru custom tuning).
CEL might pop up after 500km (02 spacer might do the trick for untuned ride or self clearing CEL)

You're going to kill your perfectly good cats? Thats like getting rid of a perfectly good set of tatas because they might go bad some day, but hey -to each their own.

Definitely do a dyno, I'll be surprised if you see a significant increase in power, but who knows. Good luck!

edited for poor grammar (too many cognacs will do that)