[BG22M3]

Originally Posted by Indo Rider

Lol, thanks for attempting to teach a lesson, but I call BS. Take your "destroying engines" fear mongering elsewhere. I'm interested in a technical discussion with someone who actually knows what they are talking about, I'm confident it's not you.

Take advice as you please. Been a tech for 16 years now. Google it. My answer is 100% facts. Talk to any tuner or racer. Good luck.

[evidence]

I could be wrong w the G8x DME, but traditionally only the pre cat sensor is used for AFRs. Post cat is narrowband and just says or rich/lean. It's used to make sure the pre sensor is tuned right. Unless someone knows if the post sensor on this platform differs.

At any rate, changing most things in the intake and exhaust stream (as long as diameter stays the same to keeps flow characteristics fairly even) without a tune is.. "fine", but I would not label it as "safe". Mods push the ECU further outside of its base calibration and closer to its limits. In most cases this will be fine, but enough of them and/or in the right circumstance, and you'll hit the limitations of the fuel trims and the car won't be able to correct back to optimal.

Imagine a seesaw where one kid keeps getting fatter. It's generally fine and you can still use it w the small kid working harder. Once one kid gets fat enough, it no longer works. Where that limit is on the G8x would be the question. On other platforms I've worked on, fuel trims are limited to 20% outside of the base calibration (EDIT: looks like at 30% our DME will go into limp mode)

[Indo Rider]

Originally Posted by evidence

I could be wrong w the G8x DME, but traditionally only the pre cat sensor is used for AFRs. Post cat is narrowband and just says or rich/lean. It's used to make sure the pre sensor is tuned right. Unless someone knows if the post sensor on this platform differs.

You are correct, pre-cat is bosch LSU 5.2 (wideband), post-cat is bosch LSF Xfour (switching).

[Indo Rider]

Originally Posted by DieselG80XC

Jb4 has no control over fueling it relys on the ecu to trim fueling as necessary. I believe something with the catless DP throws the trims way off.

OK, so here's the log. AFR spiking like that after the shifts doesn't seem too atypical from most logs I've seen (my own and from what other people post). Short term fuel trims (unless maxxed out) are always going to bring AFR to target. The question might be whether they can do it fast enough if long term trims are off.

Not sure what you mean be trims being way off, you think LTFT is way off?

Also, why does the additive target jump from nothing to the map2 level in the middle of the pull, that's weird no?

[evidence]

It would take a few minutes of STFTs being non zero before LTFTs changes, and it would slowly step towards STFTs being 0 by modifying LTFT in small increments. The stepping of trims also means STFTs can be slower to respond in realtime if LTFTS are not calibrated.

So if you reset the learned calibrations (which bm3 etc can do) and then rip on the car right away with mods, you can definitely have a bad time. Say 20% off of base trims is the limit. if LTFT is 0%, STFT has +20% room. If LTFT is learned at +12%, STFT still has 20%, making your max higher at 32%.

This is the reason why running mods without a tune can get you into trouble. You're left with less of the FT window for the car to work w because you didn't retune the base calibration to near 0.

[Indo Rider]

Originally Posted by evidence

It would take a few minutes of STFTs being non zero before LTFTs changes, and it would slowly step towards STFTs being 0 by modifying LTFT in small increments. The stepping of trims also means STFTs can be slower to respond in realtime if LTFTS are not calibrated.

So if you reset the learned calibrations (which bm3 etc can do) and then rip on the car right away with mods, you can definitely have a bad time. Say 20% off of base trims is the limit. if LTFT is 0%, STFT has +20% room. If LTFT is learned at +12%, STFT still has 20%, making your max higher at 32%.

This is the reason why running mods without a tune can get you into trouble. You're left with less of the FT window for the car to work w because you didn't retune the base calibration to near 0.

Everything you say here makes perfect sense. Log above shows STFTs not maxxed, in that particular example.

The big question in this thread seems to be whether running catless downpipes creates an insurmountable challenge for the stock tuning that will "destroy the engine", as one poster suggested.

If the short blips of high AFR post-shift as shown in that log above are really thought to be cause for concern, I'd like to see someone's log running catless downpipes with a flash tune to see the difference.

[evidence]

Originally Posted by Indo Rider

The big question in this thread seems to be whether running catless downpipes creates an insurmountable challenge for the stock tuning that will "destroy the engine", as one poster suggested.

If the short blips of high AFR post-shift as shown in that log above are really thought to be cause for concern, I'd like to see someone's log running catless downpipes with a flash tune to see the difference.

Yeah and there just isn't a black and white answer. Your engine isn't going to inevitably pop a rod, but the car isn't going to run exactly as the calibration expects. Anytime you run mods without a tune you are inheriting a small amount of risk. Most of the time you'll be fine.

Short blips of lean AFRs, extra heat, small amounts of knock all start to add up. These engines can take a beating, but if you're serious about power and longevity, get a tune.

Of course more power lessens the longevity of a motor also, but at least it's more fun for all the trouble

[DieselG80XC]

Originally Posted by Indo Rider

OK, so here's the log. AFR spiking like that after the shifts doesn't seem too atypical from most logs I've seen (my own and from what other people post). Short term fuel trims (unless maxxed out) are always going to bring AFR to target. The question might be whether they can do it fast enough if long term trims are off.

Not sure what you mean be trims being way off, you think LTFT is way off?

Also, why does the additive target jump from nothing to the map2 level in the middle of the pull, that's weird no?

It’s not from my car, my car had OEM downpipes but in comparison typically by the time im in 5th gear my afr is in the 12s-11s

[Tethys]

Originally Posted by DieselG80XC

It’s not from my car, my car had OEM downpipes but in comparison typically by the time im in 5th gear my afr is in the 12s-11s

I just looked at my graph on my downpipe and JB4 car and mine is the same way, at or around 5th my afr is down in the 12s.

[DieselG80XC]

Originally Posted by Tethys

I just looked at my graph on my downpipe and JB4 car and mine is the same way, at or around 5th my afr is down in the 12s.

I guess it’s not all cars I’ve seen a few that have been really lean idk what would cause the difference between them.

[Tethys]

Originally Posted by DieselG80XC

I guess it’s not all cars I’ve seen a few that have been really lean idk what would cause the difference between them.

Good question, I sent my logs to Terry Burger and he said they were fine as well. Not sure what would cause different cars to react differently.

[andyho123]

Originally Posted by danniexi

bad batch of gas?

had that happen to me once when driving on the highway and i was passing a vehicle. the car started stuttering and threw codes. i freaked out a bit since it was on a mini road trip. filled up at a gas station, cleared the code, hasnt appeared since.

S58 stock (no tune, no downpipes).

Was it also superknock code?

[andyho123]

The superknocking cylc 2 code came back. I checked plugs and coil and they are all good. Again, car never go into limp mode or cut power. Still shadow codes. Also, I remembered that these downpipes have built in minicats inside. IDK if that is the possible cause for this code.