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Tuning for pops on decel

Posted by Sam's GSX, Apr 28, 2019

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  1. Sam's GSX

    Sam's GSX Proven Member

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    Ok, so after searching around, I found out how to tune for pops, the one thing that confused me was people said to do -5 timing at low load, so I changed 33 to 28, that didn't do anything haha, but when I figured it out, I retarded it to -2 in the lowest load (0.3 I believe) and turned idle switch while moving off, now my question is, is this bad for the car? Some people say to watch your exhuast valve, how? If this is bad, I would love to know the science behind why. Thanks
     

    Street Build 508  4

    1997 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM
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  2. curt-s

    curt-s Proven Member

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    By exhaust popping what I think you are looking for is unburnt fuel igniting in the exhaust after the valves.. basically what you would want is a very small amount of fuel to be injected on decel but not ignited by spark.

    By enabling an artificially high fuel cutoff (or disabling idle switch while moving) and using retarded timing flows gasses still in combustion past the valves and turbine, acting as a low load antilag with all the usual component stresses, and pistons trying to drive the crankshaft against the movement of the vehicle in a net negative power manner.

    I just dont think our engine control software was designed for this particular all show no sense operation.
     
    Last edited: Apr 28, 2019

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    1991 Eagle Talon TSi
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  3. 91dsm

    91dsm Proven Member

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    Ive been wondering if there was a way to tune for this as well. My old car popped a lot on decel. It started happening right after I swapped my ecu to set up ecmlink. At first I thought it had something to do with my tune but I actually went as far as temporarily swapping my ecmlink with an eprom chip programmed with a stock 2g image and the pops still persisted. Turns out it was just the ecu itself which was strange because it had no other issues that I noticed. I got a lot of compliments on the backfire. It was similar to the way an srt4 backfires but it louder.
     

    Street Build 327  1

    1995 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM
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  4. motomattx

    motomattx Proven Member

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    When combustion happens in the exhaust manifold and turbo housing, the force from the uncontrolled explosions can push the exhaust valves back open into the pistons, this is how you can do damage with antilag/popping.
     

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    1995 Mitsubishi Eclipse GST
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  5. Crackerman

    Crackerman Proven Member

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    You can also richen up the higher rpm (3k + rpm) high vacuum cells on the map, it will dump excess fuel on decel with throttle shut.
     
  6. motomattx

    motomattx Proven Member

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    Without an air source it wont do a whole lot, just dumping fuel will just foul your O2 sensor and wash out your piston rings/water down your oil, I wouldnt recommend it as far as just randomly dumping fuel just to harass other people with banging anyway, it just invites police to harass you and makes the public dislike compact cars even more.
     

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    1995 Mitsubishi Eclipse GST
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  7. EVLGSX

    EVLGSX Proven Member

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    What is up with guys actually wanting their car to sound awful????

    Im reminded of "tuning for pops and bangs" a few weeks back LOL!!!!

    Shotness
     

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  8. Crackerman

    Crackerman Proven Member

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    I didn't say turn on the Injectors like fire hoses... I said richen it up. In most cases the pops come from rich exhaust hitting atmosphere oxygen at tail pipe anyways. Plus you get some fire!
     
  9. Sam's GSX

    Sam's GSX Proven Member

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    Oh ok I see how it could hurt, I'll try more fuel on normal timing, then with negative timing (I'm guessing that would be loud as hell, which I don't want) and I have multiple tunes, this is going to be one for if I am in a situation that I want pops, and how they are right now are not harassing anyone, they are just nice soft deep pops. Thanks guys
     

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  10. ec17pse

    ec17pse Freelancer

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    Oh here we go, i wanna sound like a crappy german car, (german cars suck) anyway i shall leave this here. They call this over run, its aweful sounding

    Seem to use this alot recently. Haha pops and bangs not far from people wanting flames but you get the idea from the pic

    flames.jpg
     

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    1997 Mitsubishi Eclipse GST
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  11. arrowhead

    arrowhead Proven Member

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    Keep tuning for pops and you are going to get a very loud one in your bank account.
     

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  12. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    Sam, I know there are some "remarks" in this thread, but I do think the members are meaning that unless you need your car to do this, it really is not good for it and we like to not give bad advice out. You did ask and you got some answers that probably will give you the results, but you should think about making and keeping your car "happy" and it will keep you the same! Good luck my friend!
    Marty
     

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  13. Sam's GSX

    Sam's GSX Proven Member

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    Hahaha, I didn't even realize you could post memes, that was funny. So I'll just keep that tune in the bank, it'll be funny to show some people.
    Thanks guys
     

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  14. EVLGSX

    EVLGSX Proven Member

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    we do need to try and not take ourselves too serious here........

    isnt breaking stones part of the fun, especially when its a wild topic? I know where I hang its constant and healthy

    I think its pretty clear that none of us intend any harm here

    good luck with whatever your goals might be sam
     

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  15. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    Sam seems to be a good natured guy, taking it all in stride. Thanks for putting up with us having a little fun @Sam's GSX :)
     

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  16. curt-s

    curt-s Proven Member

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    just as long as it doesnt turn into "DSMs are unreliable shit. the turbine melted and valves cooked when i did -5 timing at 5k at every stop light"

    I am NOT saying Sam is going to do this. Not at all. It is more of the unfair stigma these cars have for reliability when it is really a case of improper/untimely maintenance, poor build knowledge/implementation, or, although overengineered, we tend to still push them too far. Basically, user error in all cases.
    When the car isnt designed to do something, you need to force it. That is when there are no warranties or guarantees and all the fault lies with the implementer not the product. And even then it still might not work due to design and you break it for no reason.

    This thread just felt like it was going down that road like so many before. I am glad it no longer seems to be the case and I hope any attempts at this are understood to be "at your own peril."
     
    Last edited: Apr 29, 2019

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  17. curt-s

    curt-s Proven Member

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    The sudden changes in rich/normal (assuming targetting stoich in openloop at "normal" vac) might cause severe bucking when on and off throttle.
     

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  18. Crackerman

    Crackerman Proven Member

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    The only time any of us are ever in that portion of the map is when we are off throttle, decelerating from higher rpm.

    Watch the cursor when you rev on it, and yank foot off gas. On link, it runs to the very top right ish (rpm dependent) and rides it to the left, on the very top high vacuum row.

    No normal driving, cruising, drag racing or idling takes place in that portion of the map.... Ever.
     
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  19. randman2011

    randman2011 Proven Member

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    There's a little bit of advice in this, but it's mostly just a relevant story. After selling my RS, I wanted some more exciting exhaust noises on the GSX and tried to go down this route. Since I'm not willing to shut off overrun fuel cut, I never got anything to happen. I even tried cracking the throttle slightly in order to keep fuel flowing and incite some exhaust noises but I just couldn't get it to happen. So I switched to "enhancing" my summer DD, which is a Miata running Megasquirt. Megasquirt lets you set a duration for how long after a throttle closure it waits before triggering overrun fuel cut, so I set timing above 3500 RPM and below 20 kPA MAP to -15 degrees and set the timer to 1.0 seconds. Then it snowed and I never had a chance to test it.

    I got the Miata out of storage earlier this year and drove it to work. I enter the highway via left hand merge, cross two lanes, then exit in 1/4 mile to get to my office, and it just so happened that when the dividing wall dropped off I saw that I was about 3/4 car length ahead of a police officer next to me. Since we're both well below the speed limit due and I'm already ahead of him, I bury the gas pedal intending to complete the pass in front of the cruiser. I let off just as I get into that lane and I look in my rearview mirror to watch the cop just as his whole squad car is illuminated by a large flame that shot out of my exhaust due to the overrun. It was very awkward. It was very embarrassing. It was very not great for my turbo. In addition, Megasquirt's code has a bug (surprise, surprise) where if your fuel cut timer is greater than 500ms, the timer can never actually expire. End result: like clockwork, every 1.0 second I get this disgusting sounding pop and a flame until I get back on the gas. Because the Miata has a relatively quiet exhaust, it sounds more like quickly uncorking a bottle than it does the overrun of a racecar from the 80s. I may be a child at heart but that's just unpleasant. I have since reverted everything back to the previous tune.

    The Focus RS did this from the factory, and it has become an increasingly popular factory feature on modern performance cars, since they can't seem to offer excitement via any other means. It's a little easier to force when you have VVT on the exhaust cam, but plenty of manufacturers are doing this intentionally and offering full factory warranties, and plenty of aftermarket tuning companies are adding this behavior in via tune and offering some kind of guarantee. It can definitely be done with no real-world impact to reliability as long as you're smart about it. For example, don't retard timing to the limit of the hardware AND richen the mixture by as much as 20%. Police don't like that too much.
     

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  20. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    I love your story!
     

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  21. Sam's GSX

    Sam's GSX Proven Member

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    Hahaha, that's great. For the one day I had the pops, I saw a cop and let off the gas as a always naturally do, and the soft pops got much louder as time went on, luckily when I got to the cop it finally occurred to me to put the car in neutral.
    The last thing I want to do is something that everyone agrees is not respectable, the only reason I had the pops is because I liked them (not enough to keep them haha) and not to show off, some reason I have this car is because I like them, if I wanted to show off I wouldn't have bought this car, I live in a town only jacked up trucks that people have put 20k into at least, and drive by basically unnoticed in a Borg warner s256 GSX hahaha WTF. Anyway thank guys, and thanks for the hours and hours of past posts in the last 2 years that lead me to have this build today, all of my information I owe to this forum.
     

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  22. curt-s

    curt-s Proven Member

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    I should have clarified. Slow speeds, such as when negotiating a parking lot, and high rpm (first gear) with constant load nets me a lower-than-idle vacuum even at just 8.1% throttle. From just one of my logs, -21.5inHg and still in closed loop. In another section of my log I am at 1.8% throttle, still in closed loop, and I net -22.9inHg at 24km/h and ~1600rpm without ever going off the throttle entirely. Given the section of log I'm reviewing, I must have been driving around a parking lot right before I stopped logging because my throttle varies between 4% and 1.8%, vacuum between -20.4 and -22.9, but speed is constant.

    At 22.9, row 1.8 is starting to contribute which would result in a rich low-speed driving condition if it's an artificially high VE (albeit minimal in this case). As driving around a parking lot brings changes in throttle position, doing so in lowest gear could bounce your absolute pressure between rows 1.8, 3.7, and potentially 5.5 and above. Given 3.7 and 5.5 should be tuned correctly for idle and off-idle, that would ultimately cause a bouncing between stoich (from 3.7 & 5.5) and rich (from 1.8). Will you be solely in row 1.8 while the butterfly is open at all? No, likely not. Will it ultimately cause bucking? I don't know, that's why I said could result in bucking but I should have qualified that earlier with a specific condition and not allow it to be interpreted as a "could be anytime." In any event, usually we're already bucking around in first gear in lots trying to maintain speed already (or so I hear..).

    The best way around this then, if that's really the way one wants to go, is to only raise the VE on the row 1.8 cells that are to the right of an obvious RPM that you'd never be driving around in first gear at a constant speed at anyway. Although the drawbacks of dumping fuel this way far outweigh any benefit, being only show or not.
     

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  23. ec17pse

    ec17pse Freelancer

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    Yeah i was just having fun with my meme i found from someone on google LOL, no harm ment my end.

    Honestly though while it may not shoot flames or alot just get a full straight through exhaust system as in zero boxes! I have this and every once in a while it kinda mumbles on down revs and gear changing, its not the full on stuff that happens alot nowadays and thats just with a stock fuel and timing setup, so you can get nice sounds pretty easy just depends on how much noise you want or rather how much bangs your after.

    Im not a huge fan of crackles itself and not if its tuned to do it, if its a nice natural one thats ok and sounds nicer, my old skyline used to do this, after a while it would make nice noises when you was coming to a stoplight and down shifting. Seemed to happen alot more when the exhaust system was very hot after a nice cruise or something. Never shot flames that way but it loved flames when shifting gears oh boy it did!
     

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