pops and bangs

[oscar]

hope you get it the way you want it soon. remember it's a lot harder to get turbo cars to pop and bang because all cylinders flow out onto the turbine of the turbo and then down the exhaust wheras a naturally aspirated (non turbo) car just gets popped out the downpipe to the exhaust. the turbo can act in lots of ways as a dampener of sound, but this isn't always true. once the omex is in, and you cut the spark (set the rev limit) it will bounce of it, and when you take your foot of it will bang like a motherfu...er lol

 

[waitey]

Some launch controls don't pop and bang at all so I still think it won't.

Oscar the focus ST pops and bangs as standard and doesn't need a pop and bang map so does a corsa VXR and R56 cooper S all of which are turbo.

 

[oscar]

Some launch controls don't pop and bang at all so I still think it won't.

Oscar the focus ST pops and bangs as standard and doesn't need a pop and bang map so does a corsa VXR and R56 cooper S all of which are turbo.

like i said waitey, the theory is that the turbo itself has a dampening effect on sound as it is the initial restriction faced to exhaust gasses. being a 1.2 economy turbo the exhaust passageways in the manifold won't be very big. that's two disabilities straight away that a GT owner would need to work around. launch control is merely software which incorporates ABS and a host of other things to ensure maximum traction is met of the line, after a few tries it will figure out the optimum point for the clutch and programme itself with those parameters in mind and launch you with those settings saved. a rev limiter is another kettle of fish, all this does is cuts spark at whatever RPM you set it too. the cutting of the spark allows an unburnt mixture of air and fuel to escape the cylinder, and to be ignited by either the red hot exhaust manifold or the next exhaust pulse which is what creates a pop and a bang. all you need is the spark to be missed which i don't believe you can do on the standard ECU in which case i'd be confident enough to say the Rev Limiter will do it's job just fine.no doubt the focus ST will have a much tuner friendly ECU where cutting spark can be programmed on initial over run or 'lift of', no doubt the cars you've mentioned will have that programmed into the over run parameters

 

[oscar]

quick add on thomas lol. there are 2 types of rev limiter, there is the type where the fuel is cut and the type where the spark can be cut. with a spark cut, unburnt fuel will be dumped into the exhaust which is what results in that loud gunshot type bang. With the fuel cut rev limiter (like on the GT's ECU) unburnt fuel won't be dumped into the exhuast which will drop the revs but will feel like a hesitation and produces no pops or bangs. the omex cuts spark, so would be ideal for what you want it for. have you driven your GT through the rev range yet and tried lifting of in 3rd gear at clost to rev limiter? i'd be certain with advanced spark, on the over run it would pop! i forgot to tell you, but i was hoping you'd realise that the rev limiter will only make it pop and bang whenever you are holding the car on the rev limiter (so with the inbuilt software, when you wanted to launch as you buzz of the limiter it will pop and bang like mental!)

 

[thomasged]

Yeah mate the only way I can get it to pop just now is change just before it hits the limiter, cheers for all the info, launch control will defo fix the problem tho

 

[singlespeed]

Okay ive got my car back for the remap, he advanced the ignition timing yet he says he still couldnt get it to pop! Could it be the baffles in the ktec backbox stopping it? The cars decatted so I dont see any other reason why it won't? Ive had a couple of pops but only when ive hit the limiter, please help haha?

Wouldn't that give the mixture more time to burn before the exhaust valve opens, so probably less likely to pop :?

If its been advanced through the range, is it now using the knock sensor to save destructive detonation from damaging the pistons/valves by the mixture reaching a critical pressure before the piston has started to desend on the power stroke.


I think its completely pointless to deliberately map it in. Mine does it a little bit, but it certainly wasn't mapped to do it on purpose. Not that I'm into the mapping yet... If your wanting to have the fuel mixture burning when the exhaust valve is starting to open, to allow some unburnt fuel into the exhaust, wouldn't it be better to delay/retard the spark when the throttle is closed at high RPM?

 

[oscar]

neil has a strong point, but the trouble in doing that would be a complete loss of performance. any spark that happens ATDC (after top dead centre) is really a false economy. the basics of advanced / retarded ignition is that the more load on the engine (higher RPM), the more you will want to advance the ignition timing (when the spark occurs). when the piston travels up on the compression stroke, just before it reaches the top of the piston at TDC (top dead centre), the ignition will send the spark to the spark plug just before it reaches the top of the stroke as it moves onto the power stroke. the reason for this is that optimum combustion doesn't take place instantly. like an explosion, it needs to spread throughout the combustion chamber like an explosion and by the time it's at TDC the combustion is already taking place, pushing the piston downwards on the power stroke. retarding the ignition (this is after the piston has passed TDC, so is now on the downwards power stroke) would result in a noticeable loss of power and your engine would feel very hesitant, although as neil says this would cause backfires or pops and bangs but i'm fairly sure the siemens ECU doesn't allow for that.


i think the moral to the story here is that the only way you can get your car how you want it is by lots of messing around! curiously, do you like what your mates car does with the omex rev limiter w/ launch control?

 

[singlespeed]

I'm not saying to retard the ignition in general, just whilst your off throttle at high RPM. As you say, theres no point in globally retarding the ignition timing.

The time it takes to burn the mixture is pretty much fixed to a period of milli seconds, irrelevent of the RPM. The piston also lingers at the top (and bottom) of the stroke as the crank is vertical, so theres a point where high cylinder pressures would just be trying to push the crank out the bottom of the engine, rather than continue to rotate

At idle/low RPM, the ignition spark is timed arround 10-14deg Before Top Dead Center, so the burn will be well under way ready to push the piston down as it passes over TDC and the burn is still finishing as the piston decends. With higher RPM, the piston will be spending less time near TDC, so the ignition timing needs to be advanced so the burn has progressed enough that theres high pressure as the piston is just passing TDC... Although, not so much pressure that the mixture reaches an explosive phase instead of continuing to burn. Hence, the balancing act of getting maximum power from the mixture without causing damage from detonation.

When your off the throttle, it wouldn't really matter if the spark was well after TDC as your not trying to generate power... However, completely cutting the spark and rellying on the exhaust manifold being hot enough to cause a bang may work but would be optimistic (how often have you seen a manifold anywhere near glowing)

 

[oscar]

Gasoline (petrol) −43 °C (−45 °F)[3] 280 °C (536 °F)

in a Si engine, the exhaust manifold is usually around 600 °C -1,000 °C so the flashpoints have been superseded, the moment the exhaust valve is opened and the air / fuel escaped, it will reach it's flashpoint and combustion will take place. remember back in the good days of WRC when the turbo cars would backfire and create an almighty bang?? although that would be anti lag, the same thing is happening although you couldn't achieve anti lag effects on a factory ECU. the temperatures in the exhaust is what's causing the backfire or pops and bangs as thomas called them. i was just actually thinking in depth about this but one of the reasons why newer cars do not backfire, is because most fuel injected cars shut down the fuel injectors after so many seconds of decelerating. this prevents raw fuel from entering the exhaust, it's a safety measure built into the ECU ........ think that could possible be the suspect the more that i think about it. this parameter is strictly non mess with'able at least in the twingo

 

[Brad133]

All I've had is my back box chopped and it pops nicely on downshift or with a few Taps of the throttle when in neutral, any more would just be a pain

 

[singlespeed]

Gasoline (petrol) −43 °C (−45 °F)[3] 280 °C (536 °F)

in a Si engine, the exhaust manifold is usually around 600 °C -1,000 °C so the flashpoints have been superseded, the moment the exhaust valve is opened and the air / fuel escaped, it will reach it's flashpoint and combustion will take place. remember back in the good days of WRC when the turbo cars would backfire and create an almighty bang?? although that would be anti lag, the same thing is happening although you couldn't achieve anti lag effects on a factory ECU. the temperatures in the exhaust is what's causing the backfire or pops and bangs as thomas called them. i was just actually thinking in depth about this but one of the reasons why newer cars do not backfire, is because most fuel injected cars shut down the fuel injectors after so many seconds of decelerating. this prevents raw fuel from entering the exhaust, it's a safety measure built into the ECU ........ think that could possible be the suspect the more that i think about it. this parameter is strictly non mess with'able at least in the twingo

I think you missed or skipped over the main bit that I was thinking about.
If your giving the mixture enough time to fully burn by keeping a high degree of advance, there wont be any air or fuel left to spontaneously combust in the exhaust... however hot it is.

Anti lag was firing way after tdc, to produce minimal torque/power but still give a large volume of exhaust gas to keep the turbo spinning

 

[singlespeed]

Ive been having a look at my ECU file, more out of curiosity for how its programmed and what the ECU can do, than wanting to play about with variables as thats why it was at RS tunning for the mapping.

However, reading up on the crackle map and comparring my parameters, its clear that the over-run fuel cut off is keeping mine quiet from pops crackles above 2000-2200RPM whilst off throttle gets an occasional burble <2200RPM...

Disabling the fuel cut would leave the injectors flowing the small amount of fuel with the relevant spark advance programmed in the base mapping, and therefore give some fuel for burning in the exhaust at the expence of higher fuel consumption (marginally as the fuel flow is small) and higher exhaust valve/manifold temperatures and the possible heat related damage

 

[Martin_172]

on my old one running fastchip software the new owner added a k-tec cat back, the cat was still fitted and it used to pop like mad on gear changes when you got some temperature in it!

 

[thomasged]

Got sent twin coil launch control instead of single, but the guy reckons if I wire the 2 pulse wires in it should be fine, any ideas? Sounds dodgy to me haha

 

[oscar]

nope, send it back. get what you paid for or full refund, assuming it was advertised as single coil and not twin!

 

[thomasged]

Yeah exactly what I thought, didnt see why they would make a single if the twin fitted both haha

 

[thomasged]

What colours represent what on the coil pack plug, I have green orange and purple?