DECAT exhaust without a TUNE. Is it safe? - Page 2 - Rennlist Discussion Forums



DECAT exhaust without a TUNE. Is it safe?

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Old 03-17-2017, 09:33 AM   #16
bondjockey
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I heard it from Kevin at UMW who knows more than most of us put together.
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Old 03-17-2017, 10:47 AM   #17
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Well, that stinks I guess. So much for those claimed 40HP power gains.
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Old 03-17-2017, 12:05 PM   #18
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There are torque limiters in place, but there is wiggle room in there and it will add power and torque even if the ECU dials it back a touch from the maximum it could produce. I still think it is worth it for the sound alone, as the stock exhaust is quite sterile. An off the shelf Cobb stage 2 map is incredibly conservative and would fix that problem and the CEL for the catless exhaust. It can be uninstalled whenever you like and the logging functionality is superb. Many people learn that their "pristine" car isn't exactly running as well as they thought it was after they get a loggable tune as the stock ECU is quite dynamic in its corrective abilities
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Old 03-17-2017, 01:13 PM   #19
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Bond made some great points and there are several nice options which is great for the community. Each has its own character and features so good talk with someone knowledgeable or willing to help can help you make the right choice.

On the subject of the car de-tuning itself...This is true to an extent. The car has load and air flow limits as well as other settings in the factory computer that it's looking for. If it goes above any of those it will bring itself back to what it calls ok. Which is what gets raised and adjusted when you do a performance tuning calibration. At the same time there are absolutely gains to be had. Perhaps not maximum without tuning but the car benefits from a better flowing, lower exhaust gas temperature/pressure exhaust system. We've been able to verify this on the dyno as well as 1/4 and 1/2 mile testing. You're also reducing weight with some systems like Kline which is always good. The car has thresholds and it's never going to be running 100%. This could do with the fuel, altitude, load and many other variables so you're sort of helping it be more efficient and run sort of at a maximum level if you will. We have even done stage III for example on many 991.2 cars. With full exhaust only we gained 2 to 5 mph on the Vbox as well as on the track on various cars at various locations in up to 1/2 mile testing. So I could guarantee it will make a difference although again with tuning you would open up more potential. Then of course there is the sound regardless

As far as not getting a CEL there are some tricks. Different spacers in different configurations or of course tuning. My lines are open feel free to reach out I have a few specific things in mind I know people have tried that work.

Sorry for the long and I hope it helps…I'd be glad to help anyone with any questions!
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Old 03-17-2017, 01:39 PM   #20
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That's only in 997.2 cars with the Siemens's ecu. 997,1 cars with the Bosch unit don't suffer this fate.
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Old 03-17-2017, 02:41 PM   #21
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On top of the sound you will feel it. But vbox it and i guarantee you it's there and will show. Especially the way VTG cars build heat. What was your no tune reason if you don't mind me asking?
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Old 03-17-2017, 02:52 PM   #22
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It really all comes down to Warranty. I'm not willing to take a chance on them turning me away, not yet at least.

Quote:
Originally Posted by SamboTT@ByDesign View Post
On top of the sound you will feel it. But vbox it and i guarantee you it's there and will show. Especially the way VTG cars build heat. What was your no tune reason if you don't mind me asking?
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Old 03-17-2017, 03:07 PM   #23
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I hear you. We have lots of friendly dealerships on the list that we have built relationships with through the years. A large % of our bit kits are installed at dealerships actually. Let me know if I can help.
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Old 03-17-2017, 05:32 PM   #24
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On the 997.1TT Bosch ECU, power in terms of HP will only extend to the limiters and boost setpoints. In a perfect world this engine will make 480HP.. Folks running 91 octane will NEVER reach the rated HP on a STOCK engine. The recent dyno day, proves this point. a optimistic dyno operator will prove me wrong (LOL)

There are four Conditions that will limit power on this platform..

IAT
Power output limiters
Turbine housing Temps
KNOCK

The most significant power robber is KNOCK from poor fuel, low octane>the ECU responds in BLOCKS to pull power 10 to 15HP can be robbed from your engine.

IAT's also play a similar power robbing, not to the extent generally, but once you reach the limiter>interventions do come into to play... timing, boost, and fueling corrections happen.

If the turbine temps hit the limiters> you can see 30HP of output cut>instantly..

When looking to install a exhaust, most have two wishes.. Sound and tone improvements (personal taste) and then engineering>>a significant reduction in back pressure.. The factory piping has a 65mm diameter. 70mm piping is considered the minimum.

A well designed exhaust system, will reduce back-pressure. On this platform with VNT nozzled turbines we reduce temperature but more importantly lower the pressure delta. The result is a boost output, "lower" and "sooner" in the RPM curve. When you have Boost, your gain is torque.

So, for a STOCK ECU file, torque will be available sooner or greater.. Until we reach the limiter.. Generally, on the dyno with everything STOCK and on pump gas, with stock IC's one will never go over 18 WHP.. Due to limters and one or all of the above FOUR conditions that I wrote previously. Disclaimer>>Race gas, or runs in Sub zero weather or phantom ecu flashes will always alter the results..

What is more realistic vs a dyno sheet is using a Driftbox. Run your 60 to 130 times. Run your 0 to 60 times.. The "better" dataloggers will provide quartz locked timing (mine does)..

Tuning the ECU will gain more power vs a exhaust change. But tuning with a Exhaust system will net you more POWER..

If tone and decibel are required, the simple DRILL bit HACK can be utilized. DIY are all over the forums. Look at the 996TT... Results will vary... I'd purchase a used "known" exhaust to experiment with... Or find a Rennlister and hear/drive/ride in the car... WE have almost every city covered..
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Old 03-17-2017, 06:19 PM   #25
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Thank you for such detailed response.

To clarify... because of the four conditions set by the ECU, from your experience, we're limited to 18WHP gain no matter what mods we add. The only way around that would be to tune?
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Old 03-17-2017, 08:02 PM   #26
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Quote:
Originally Posted by Kevin View Post
On the 997.1TT Bosch ECU, power in terms of HP will only extend to the limiters and boost setpoints. In a perfect world this engine will make 480HP.. Folks running 91 octane will NEVER reach the rated HP on a STOCK engine. The recent dyno day, proves this point. a optimistic dyno operator will prove me wrong (LOL)

There are four Conditions that will limit power on this platform..

IAT
Power output limiters
Turbine housing Temps
KNOCK

The most significant power robber is KNOCK from poor fuel, low octane>the ECU responds in BLOCKS to pull power 10 to 15HP can be robbed from your engine.

IAT's also play a similar power robbing, not to the extent generally, but once you reach the limiter>interventions do come into to play... timing, boost, and fueling corrections happen.

If the turbine temps hit the limiters> you can see 30HP of output cut>instantly..

When looking to install a exhaust, most have two wishes.. Sound and tone improvements (personal taste) and then engineering>>a significant reduction in back pressure.. The factory piping has a 65mm diameter. 70mm piping is considered the minimum.

A well designed exhaust system, will reduce back-pressure. On this platform with VNT nozzled turbines we reduce temperature but more importantly lower the pressure delta. The result is a boost output, "lower" and "sooner" in the RPM curve. When you have Boost, your gain is torque.

So, for a STOCK ECU file, torque will be available sooner or greater.. Until we reach the limiter.. Generally, on the dyno with everything STOCK and on pump gas, with stock IC's one will never go over 18 WHP.. Due to limters and one or all of the above FOUR conditions that I wrote previously. Disclaimer>>Race gas, or runs in Sub zero weather or phantom ecu flashes will always alter the results..

What is more realistic vs a dyno sheet is using a Driftbox. Run your 60 to 130 times. Run your 0 to 60 times.. The "better" dataloggers will provide quartz locked timing (mine does)..

Tuning the ECU will gain more power vs a exhaust change. But tuning with a Exhaust system will net you more POWER..

If tone and decibel are required, the simple DRILL bit HACK can be utilized. DIY are all over the forums. Look at the 996TT... Results will vary... I'd purchase a used "known" exhaust to experiment with... Or find a Rennlister and hear/drive/ride in the car... WE have almost every city covered..
Thanks for the wealth of info here.
Are there any major differences for a 997.2TT?
Are there any downsides or risks to reliability if going catless without a tune?
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Old 03-17-2017, 08:52 PM   #27
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Yes, major engine design change>>Engine management change.. Bigger turbochargers, better intercoolers and other features..

I don't understand the logic why folks feel that you need to go Catless for street driven daily drivers (Especially in California, Washington, Colorado, New York, New Jersey, Conneticut and 12 other states) The condition is more problematic when you have a STOCK ECU.

If you are tracking your car >>that's a different story..
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Old 03-17-2017, 09:02 PM   #28
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Yes, 18WHP per the conditions that I have mentioned. And yes, in some parts of the world we have magic gas that will prove my statements wrong. Run 60 to 130's or write down your 1/4 mile trap speeds on each set of mods and/or upgrades.
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Old 03-17-2017, 10:30 PM   #29
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Quote:
Originally Posted by Kevin
Yes, major engine design change>>Engine management change.. Bigger turbochargers, better intercoolers and other features..

I don't understand the logic why folks feel that you need to go Catless for street driven daily drivers (Especially in California, Washington, Colorado, New York, New Jersey, Conneticut and 12 other states) The condition is more problematic when you have a STOCK ECU.

If you are tracking your car >>that's a different story..
Agree on this point. I'm not a patchouli smelling composting toilet hermit, but I feel an ecological obligation to run with at least high flow cats (still OEM at present). Catless can sound a bit better, and you might get a few more horses, but I struggle to see these gains as outweighing the stench produced.
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Old 03-17-2017, 10:46 PM   #30
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Good info Kevin, but I believe the Siemens unit in the 997.2 is a "smart" ecu, or at least smarter than the Bosch unit. For ex, if you ad an exhaust to a .2 the ecu sees the reduced back pressure/increased power and pull timing, or other maneuver to save the engine. I'm not sure the Bosch would adjust for back pressure on an exhaust alone change, Kevin would know for sure.
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