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Discussion Starter · #1 ·
I'm aware that a tune is "highly recommended" when you upgrade your exhaust. However, I've also been informed several times that It's "dangerous" to run without the Primary/Secondary cats and no tune for it. I've also been informed that the people that informed me of the prior have absolutely no idea what they're talking about.

I reached out the ARK themselves and asked if I needed a tune, and they pretty much gave me a vague "I don't know if it's required, or if you will harm your engine running with a full exhaust and no tune" and that seemed like an odd answer from a company that makes exhausts.

I'm still trying to decide between SFR and BTR for my tune and I'm also waiting to get 3.91 gears and my Injen intake before getting the tune. Should I get the tune now, since I have the exhaust, or am I safe just running around with the exhaust bolted on without a tune?
 

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It's recommended you get a tune after you have everything installed. As the ecu basically learns what you have and can provide better output then if you were to throw a aftermarket exhaust on after the fact.. As for being required to have a tuned ecu for aftermarket add ons...no
 

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That is a load of crap. Who ever told you that is a dumas. While it is a good idea to get a tune to take advantage of the reduced restriction etc, it is by no means requred. It is also not dangerous in any way to run catless 1 or 2 or both without a tune. You will however notice an increased fule-ly smell.
Anyone who would go any kind of catless usually gets a tune.

Most likely it was a blue state tree hugger who just doesnt want you to remove your CATS.LOL.
 

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It's not unsafe and here's the science:

Everything in the stock exhaust system (headers, cats, catback, muffler) is a passive system designed solely to allow exhaust gas to get from the front of the car out the tailpipe - there's nothing ACTIVE, meaning the ECU doesn't care about what happens once combustion is done. You can see this based on the sensors: Cat Temp + O2 sensors... that's it. Intake has IAT, MAF, Throttle body sensor, bank adjustments, injector duty, etc etc etc. Exhaust is meaningless to the car except for emissions and maintaining stoich ratio.

All aftermarket headers have a bung for primary O2 sensors which are before any catalytic converter, same as stock headers. These are used to determine whether the gas is being burned at the correct stoichiometric ratio - stock headers are pre-cat, aftermarket headers with no cats are effectively pre-cat. Zero change in how those operate. No need to 'adjust' anything on the ECU for that.

Tuning is about putting more power down with supporting mods. It's not about making it 'safe' and it's not required by any stretch. Running a straight-pipe exhaust without a tune does not mean your engine is going to flood or explode or lean out and snap a rod.

If you want to get pedantic about it, running a tune could be considered less safe. The manufacturer tune is designed with a pretty sizable safety margin to allow for low quality/low octane gas, high altitude operation, high air temperatures, etc. without ever having detonation - if you get knock on a stock tune, it's because something is severely wrong. On a tune, the safety margin is decreased, which is the price of making power.

I encourage you to get all your mods done before you get your tune. You're safe running the exhaust pre-tune for as long as you like. Tune for the highest octane that is READILY available for you... I could have tuned for 94 octane but chose 91 because 94 can be hard to find outside my area. Good luck
 

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Discussion Starter · #5 · (Edited)
That is a load of crap. Who ever told you that is a dumas. While it is a good idea to get a tune to take advantage of the reduced restriction etc, it is by no means requred. It is also not dangerous in any way to run catless 1 or 2 or both without a tune. You will however notice an increased fule-ly smell.
Anyone who would go any kind of catless usually gets a tune.

Most likely it was a blue state tree hugger who just doesnt want you to remove your CATS.LOL.
It was actually my grandfather who used to build 1/8th mile dragsters back in the 60s, I don't think he Qualifies as a blue state tree hugger, considering he's got coal-rollers and a big block camaro project car. :lmao:

It was also a few mechanics have brought it up that it "Could mess something up, such as burning up the valves". I'm not mechanically inclined, but I can grab a wrench and follow instructions.
 

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Discussion Starter · #6 ·
It's not unsafe and here's the science:

Everything in the stock exhaust system (headers, cats, catback, muffler) is a passive system designed solely to allow exhaust gas to get from the front of the car out the tailpipe - there's nothing ACTIVE, meaning the ECU doesn't care about what happens once combustion is done. You can see this based on the sensors: Cat Temp + O2 sensors... that's it. Intake has IAT, MAF, Throttle body sensor, bank adjustments, injector duty, etc etc etc. Exhaust is meaningless to the car except for emissions and maintaining stoich ratio.

All aftermarket headers have a bung for primary O2 sensors which are before any catalytic converter, same as stock headers. These are used to determine whether the gas is being burned at the correct stoichiometric ratio - stock headers are pre-cat, aftermarket headers with no cats are effectively pre-cat. Zero change in how those operate. No need to 'adjust' anything on the ECU for that.

Tuning is about putting more power down with supporting mods. It's not about making it 'safe' and it's not required by any stretch. Running a straight-pipe exhaust without a tune does not mean your engine is going to flood or explode or lean out and snap a rod.

If you want to get pedantic about it, running a tune could be considered less safe. The manufacturer tune is designed with a pretty sizable safety margin to allow for low quality/low octane gas, high altitude operation, high air temperatures, etc. without ever having detonation - if you get knock on a stock tune, it's because something is severely wrong. On a tune, the safety margin is decreased, which is the price of making power.

I encourage you to get all your mods done before you get your tune. You're safe running the exhaust pre-tune for as long as you like. Tune for the highest octane that is READILY available for you... I could have tuned for 94 octane but chose 91 because 94 can be hard to find outside my area. Good luck
Thanks for the information, yes I also noticed that the censor was pre-cat, but I was also wondering why a pre-cat censor would throw a CEL with the cats being removed (Information from ark themselves). I'm going to tune for 93 down here in America, but it makes me question the possibility of road trips, as 93 isn't available everywhere, so maybe tuning for 91 would be ideal. I live in the middle of the divide, and from what I've heard finding good quality fuel in the west side of the country is difficult and most people settle with 87 or mixing race gas.

This also makes me feel better, because I rather spend a few more bucks on a custom tune than to have one of the two companies send me a canned tune not built for my mods.
 

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Thanks for the information, yes I also noticed that the censor was pre-cat, but I was also wondering why a pre-cat censor would throw a CEL with the cats being removed.
It's not the primary that throws the code - you get the CEL because the secondary O2 sensors after the primary cats measure the efficiency of the primary cats. When you pull codes you literally just get "Catalytic Converter Efficiency" errors on both banks when you have your aftermarket headers on.

That's why there's no CEL when you pull out secondary cats and throw test pipes in - there's no O2 sensor behind them to measure their efficiency. If we had an ungodly 6 sensor setup, then we'd have CEL's for putting test pipes in.

Tunes will do some funky stuff to make the emission & evap system seem to not set to ready state, that keeps the CEL from appearing but allows other issues to still present a CEL. It's kinda like the car is always thinking it's still warming up so it ignores the cat efficiency readings.
 

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Tune not required, but recommended.

replacing secondary cats won't do anything...
Replacing primary cars will make the check engine light come on, but won't really do anything for driveability.
 

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It was actually my grandfather who used to build 1/8th mile dragsters back in the 60s, I don't think he Qualifies as a blue state tree hugger, considering he's got coal-rollers and a big block camaro project car. :lmao:

It was also a few mechanics have brought it up that it "Could mess something up, such as burning up the valves". I'm not mechanically inclined, but I can grab a wrench and follow instructions.
Cool,................you won't burn up crap with pump gas.

An aggressive tune, made waay too lean could mess up your valves, but not pump gas and your oem tune.

Rather than cite who we know, what they know, mines bigger than yours............blah blah. I'll use the ultimate factual evidence,...experential example.

I have had a SOLO exhaust on my 3.8 with no cats stock tune since July,..shes perfect.
( as I'm installing her turbo). Yuk,yuk.

My BTR ECM is tuned for 94 with meth. I will be running 98 with PURE meth,...net is about 117 octane protection. Yes, I fuel mix, EVERY tank full. (Its fun).

( If the pic loader was worth a damm this is where I would load a pic of the 2 55 gallon drums in my garage. 1 with Tolulene, and 1 with Methanol).
 

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It's not unsafe and here's the science:

Everything in the stock exhaust system (headers, cats, catback, muffler) is a passive system designed solely to allow exhaust gas to get from the front of the car out the tailpipe - there's nothing ACTIVE, meaning the ECU doesn't care about what happens once combustion is done. You can see this based on the sensors: Cat Temp + O2 sensors... that's it. Intake has IAT, MAF, Throttle body sensor, bank adjustments, injector duty, etc etc etc. Exhaust is meaningless to the car except for emissions and maintaining stoich ratio.

All aftermarket headers have a bung for primary O2 sensors which are before any catalytic converter, same as stock headers. These are used to determine whether the gas is being burned at the correct stoichiometric ratio - stock headers are pre-cat, aftermarket headers with no cats are effectively pre-cat. Zero change in how those operate. No need to 'adjust' anything on the ECU for that.

Tuning is about putting more power down with supporting mods. It's not about making it 'safe' and it's not required by any stretch. Running a straight-pipe exhaust without a tune does not mean your engine is going to flood or explode or lean out and snap a rod.

If you want to get pedantic about it, running a tune could be considered less safe. The manufacturer tune is designed with a pretty sizable safety margin to allow for low quality/low octane gas, high altitude operation, high air temperatures, etc. without ever having detonation - if you get knock on a stock tune, it's because something is severely wrong. On a tune, the safety margin is decreased, which is the price of making power.

I encourage you to get all your mods done before you get your tune. You're safe running the exhaust pre-tune for as long as you like. Tune for the highest octane that is READILY available for you... I could have tuned for 94 octane but chose 91 because 94 can be hard to find outside my area. Good luck

This post was full of absolutely spot on explanation.

I'd like to add that the only thing that results from pulling cats without a tune - aside from the CEL - is more unburnt fuel at the tailpipe. Catted, fuel-injected cars have additional fuel added to the mix to reduce cat temps. The cat substrate is actually cooled by the extra fuel. When you pull the cats, you tune out that extra fuel as part of optimizing the fuel and spark tables. Power goes up, and fuel consumption can actually break even or give you a gain since you can run much leaner at cruise than with a catted car.


It was also a few mechanics have brought it up that it "Could mess something up, such as burning up the valves". I'm not mechanically inclined, but I can grab a wrench and follow instructions.
People who say that are repeating "wisdom" left over from the carbureted days of thirty-plus years ago, when reduction in exhaust restriction could result in the car leaning out, since most if not all carbs didn't have the technology to respond to the increase in air flow through the cylinder. Its also the basis for the back pressure myth, the "you have to have some back pressure" nonsense that exhaust shop techs like to say.

As I've said before, zero back pressure is the most desirable environment for the exhaust part of any internal combustion event. The exhaust that can approach that number while still offering you the most velocity is the way to go.

The tune is "highly recommended" when you feel like doing it. You're leaving some power on the table until you get it done. The car will still be enjoyable though.
 

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It's not unsafe and here's the science:

Everything in the stock exhaust system (headers, cats, catback, muffler) is a passive system designed solely to allow exhaust gas to get from the front of the car out the tailpipe - there's nothing ACTIVE, meaning the ECU doesn't care about what happens once combustion is done. You can see this based on the sensors: Cat Temp + O2 sensors... that's it. Intake has IAT, MAF, Throttle body sensor, bank adjustments, injector duty, etc etc etc. Exhaust is meaningless to the car except for emissions and maintaining stoich ratio.

All aftermarket headers have a bung for primary O2 sensors which are before any catalytic converter, same as stock headers. These are used to determine whether the gas is being burned at the correct stoichiometric ratio - stock headers are pre-cat, aftermarket headers with no cats are effectively pre-cat. Zero change in how those operate. No need to 'adjust' anything on the ECU for that.

Tuning is about putting more power down with supporting mods. It's not about making it 'safe' and it's not required by any stretch. Running a straight-pipe exhaust without a tune does not mean your engine is going to flood or explode or lean out and snap a rod.

If you want to get pedantic about it, running a tune could be considered less safe. The manufacturer tune is designed with a pretty sizable safety margin to allow for low quality/low octane gas, high altitude operation, high air temperatures, etc. without ever having detonation - if you get knock on a stock tune, it's because something is severely wrong. On a tune, the safety margin is decreased, which is the price of making power.

I encourage you to get all your mods done before you get your tune. You're safe running the exhaust pre-tune for as long as you like. Tune for the highest octane that is READILY available for you... I could have tuned for 94 octane but chose 91 because 94 can be hard to find outside my area. Good luck
An absolute GOAT of an answer.
 
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