Stage 2 map but retain secondary cats

E4EVL

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On UK/euro spec cars we have catted downpipes but also secondary cats/OPF which is a bit of a pain. I’ve seen very little posted out there around this as most of the tuning posts come from the US but I’m looking at the idea of a catless downpipe but I don’t know what to do about the secondary’s.

No one at the moment seems to offer a secondary cat replacement pipe as there’s little demand. I don’t want or need a full cat back exhaust system as I quite like the stock sound, it’s not mega restrictive and I’m not spending four figures for nothing so it’s not an option, please don’t even go there.

That said, there are however three potential options on the table as far as hardware is concerned but I don’t know the impact in terms of tune. So...

1. Run a catless downpipe and retain secondary cats (my ideal solution)

2. Run a catless downpipe and have a custom section fabricated to cut out the secondary cats and sleeve it but ultimately easily reversible (ballache)

3. Run a catless downpipe, cut the secondary’s open and smash the internals our, re-weld shut, irreversible (rough tactic!)

Now... option one is the route I want to go down ideally if the feedback I get from tuners supports. I appreciate it will restrict the system somewhat having the secondary cats still in place but if the impact is minimal and it won’t prevent me from running a stage two 93 octane (98 RON) tune then I’m good to go. If we’re talking only talking 1-2% hp/torque impacts then I’ll keep them, if it’s a greater impact I may reassess.

I know Litchfield motorsport here in the UK are offering a stage 2 tune where they cut the secondary cats open, smash the core out and re-weld them shut which yes... it serves a purpose and does the job but when it comes to resale or more importantly MOT time (our annual roadworthy test including emissions), the instant they see that welded up it’s a fail. Yes there are friendly testers out there if you can find them but I can’t be bothered with the aggro. The fact they’ve removed them would suggest better power gains but I’m not going to ask directly as I’ll just get the BS sales pitch.

Long story short, what are the implications if any of running a stage 2 map with decat downpipe but secondary’s still in place?
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geert.bieseman

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My European car (Belgium) is currently running just a catless downpipe, standard turbo and a "stage2" tune.
You can read/follow about it if you like in my thread.

Which kind of horsepower gains are you looking for in the end?
Mine is running 520HP at the engine on 93 octane (98 ron).
And that already makes the car really really quick. You can't use that kind of horsepower on the standard tires, let along when its wet :)


I will be going for a "hybrid turbo" soon (in and outlet housing stays stock, but complete different center housing. I already got the pcitures, but i am not allowed to share them).
When that comes, the secondary cat will be removed once they notice that it becomes the restrictor to add horsepower. They created (or will be creating) their own custom one to replace it by.


My thread will be updated as soon as they got time again for my Supra.
 
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E4EVL

E4EVL

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I remember seeing your thread actually, it stuck out because your figures breached the 500hp barrier and by a significant amount on standard 98RON fuel which is something none of the US cars have done without additional mods/ethanol and they don’t have the restriction of secondary cats so I was mind blown and in all honesty, somewhat sceptical unless the boost levels were jacked up significantly?

I’ve come from a standard 510hp AMG GTS so I’m looking for something probably 480-500hp running on 98RON as it’s readily available at the pumps but I wasn’t going to be running a custom tune like yourself due to expense and hassle.

In my mind, the plan was to run with bootmod3 and a stage one OTS map. Drive it like that until March/April time and then add the catless downpipe and switch to an OTS stage 2 map so I’m not having to fork out loads of cash whilst still getting reliable quality. That said, I assume those maps were created for US cars which don’t have the secondary cats and that’s where my hurdle comes in. I know anything can be done if it’s custom tuned as it will be adapted to take the secondary’s into consideration but I’m looking for something off the shelf with support that I’m not expecting to break on me.
 

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While you can run Stage 2 power levels with a Catted or Stock Downpipe. One should not do so if they regularly track the car or do far more spirited driving than an average person. The Cat creates backpressure, which in turn creates more heat. so sustained use at high levels (long, frequent, multi gears WOT pulls) can increase heat to where turbo wear can increase or worst case scenario something fails.
 
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E4EVL

E4EVL

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While you can run Stage 2 power levels with a Catted or Stock Downpipe. One should not do so if they regularly track the car or do far more spirited driving than an average person. The Cat creates backpressure, which in turn creates more heat. so sustained use at high levels (long, frequent, multi gears WOT pulls) can increase heat to where turbo wear can increase or worst case scenario something fails.
interesting... so essentially I either need to wait for someone to develop an OTS map for euro spec cars retaining the secondary’s, have a customer tune or take the plunge. I may have to see if someone can fabricate a cheap-ish mid pipe. To be fair it’s only a V band and straight piece of pipe with a sleeve...
 

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interesting... so essentially I either need to wait for someone to develop an OTS map for euro spec cars retaining the secondary’s, have a customer tune or take the plunge. I may have to see if someone can fabricate a cheap-ish mid pipe. To be fair it’s only a V band and straight piece of pipe with a sleeve...

realistically, most people with these cars sporadically use WOT and they are not tracking the car to the extent of having that OPF or second cat you're talking about will hurt anything. It just depends on the vehicles use. Normal spirited driving i don't see being an issue. Legit road course racing or Drag constantly or street race constantly i can see eventually causing issues.
 

geert.bieseman

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I remember seeing your thread actually, it stuck out because your figures breached the 500hp barrier and by a significant amount on standard 98RON fuel which is something none of the US cars have done without additional mods/ethanol and they don’t have the restriction of secondary cats so I was mind blown and in all honesty, somewhat sceptical unless the boost levels were jacked up significantly?

I’ve come from a standard 510hp AMG GTS so I’m looking for something probably 480-500hp running on 98RON as it’s readily available at the pumps but I wasn’t going to be running a custom tune like yourself due to expense and hassle.

In my mind, the plan was to run with bootmod3 and a stage one OTS map. Drive it like that until March/April time and then add the catless downpipe and switch to an OTS stage 2 map so I’m not having to fork out loads of cash whilst still getting reliable quality. That said, I assume those maps were created for US cars which don’t have the secondary cats and that’s where my hurdle comes in. I know anything can be done if it’s custom tuned as it will be adapted to take the secondary’s into consideration but I’m looking for something off the shelf with support that I’m not expecting to break on me.
Indeed, mine is a 100% custom tuned.
True, I think they are the only one in Europe who went that high in power (think it still is a 'European record'). They even double-checked on another tuners dyno to prove that indeed had these power levels :)


I have to say, they pushed the limits. But those guys know what they are doing (20 years experience in tuning GT-R and Supra).
Most tuners stopped around 480HP at the engine for 98RON


But it is a great deal for me: I don't have to pay for all the R&D hours, only the parts.
Downside: For the R&D... this meant I didn't have my car for around 2 weeks and the risk of blowing the engine (still can happen in the next phase). I knew the downsides upfront (they were honest about the possibilities), but still, an awesome deal :)

I drive it daily and where I can, I go on the throttle :).
Currently driven around 3500 kilometers with that tune.



According to me, there are UK tuners who offer the same service, don't they?
Or do they ask really expensive prices?
 

geert.bieseman

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realistically, most people with these cars sporadically use WOT and they are not tracking the car to the extent of having that OPF or second cat you're talking about will hurt anything. It just depends on the vehicles use. Normal spirited driving i don't see being an issue. Legit road course racing or Drag constantly or street race constantly i can see eventually causing issues.
True, but as you said... 99% of the people will not do that and will only go maybe 2-3 times a year on the track.
And those that weekly hit the drag (mostly not happening in Europe), will already have a tuner like yourself to tell them what they should think about :)


You see that on real track cars... engine abuse will always wear out parts and eventuelly end in engine failure (unless engine taken apart x-amount of times). Ferrari/Lamborghini can't handle lots of track abuse either, they are not meant for that :)
 

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On my previous F80 M3

I ran a stage 1 tune on my car with full bolt ons, tuner just added the CEL delete option for the DP's

It was around 20whp less than the typical pump gas stage 2 tunes and was very reliable

Why not do something similar?
 
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E4EVL

E4EVL

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On my previous F80 M3

I ran a stage 1 tune on my car with full bolt ons, tuner just added the CEL delete option for the DP's

It was around 20whp less than the typical pump gas stage 2 tunes and was very reliable

Why not do something similar?
I didn’t actually think that would be the safest or best way to do it in all honesty and that fuelling would have been out on a stage 1 with decat leading to overboosting/fuel cut
 

a90moe

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I didn’t actually think that would be the safest or best way to do it in all honesty and that fuelling would have been out on a stage 1 with decat leading to overboosting/fuel cut
Air/ Fuel ratio was on the safe side

I am currently running a full exhaust and a catted high flow downpipe on my Supra with a stock tune

If anything on a stock tune with a DP, car is reaching optimum boost levels much easier

Our ECU's are very intelligent and adapt well to basic bolt on's
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