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Old 07-21-2016, 02:57 PM   #1
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Exhaust pops and bangs

I've got the exhaust bypass mod done a while back, and it's the best money I've ever spent on the car. It's gorgeous.

Sound of it here:
https://www.youtube.com/watch?v=dcsEqFS7yKE
https://www.youtube.com/watch?v=N71oYX-ejZk

On cold, blipping the throttle, or driving in 1st gear to 3,000rpm and letting it coast, makes the exhaust pop and bang on the run down. It sounds incredible, and sounds very 981 spyder like. I'll try to get a video soon.

However, when the engine and exhaust warms up, this goes. The exhaust still sounds immense, but there's no more pops and bangs on the run down (well rarely - you still get the odd CRACK now and then on the run down).

My question is this: is there any way to make the exhaust pop and bang, even when it's warm? I know it's silly and possibly borderline immature, but I adore the sound of it and can't quite work out the physics on why it stops when warm. Any way to make it last even when warm?

Will be interested to hear thoughts. Thanks chaps.
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Old 07-22-2016, 04:32 AM   #2
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Can you share a pic of what your piping looks like now?

I agree that while it may be viewed as immature, popping exhaust is one of life's great joys.
Many times while slowing in 2nd, I will graze the throttle to open the injectors up for a cycle to get some pops out of mine.

When your car is warm, and you slow down in gear (past a certain rpm), the injectors are not operating. You'll see this on an air fuel meter as pegged lean. Tapping the throttle will turn them back on.
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Old 07-22-2016, 05:38 AM   #3
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The ECU calibration most likely keeps the injectors on during run-down while the engine is heating-up to help warm up the cats, but then turns it off once the engine is up to temperature to conserve fuel.

If you have the fuel mileage computer (OBC?), the fuel consumption display will go to zero when the injectors are off. On my old Audi S4, you could figure out when they turned back on by watching this value, which was 0 until about 1500rpm. Of course, you have to be coasting, with your clutch off the pedals and the transmission in gear. This is how it works on a manual transmission car, not sure about automatic.

So it's likely a function programmed within the ECU that would be difficult to change without knowing the right person.
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Old 07-22-2016, 03:13 PM   #4
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Quote:
Originally Posted by alm001 View Post
Can you share a pic of what your piping looks like now?

I agree that while it may be viewed as immature, popping exhaust is one of life's great joys.
Many times while slowing in 2nd, I will graze the throttle to open the injectors up for a cycle to get some pops out of mine.

When your car is warm, and you slow down in gear (past a certain rpm), the injectors are not operating. You'll see this on an air fuel meter as pegged lean. Tapping the throttle will turn them back on.
Haven't got a proper photo unfortunately but I'll get one as soon as I can. It's just a 1" pipe that goes from the pipe after the CAT, straight into the tail pipes, bypassing the back box. Same on both sides.
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Old 07-22-2016, 03:23 PM   #5
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I'm partial to the rumble, too, and I've found that rolling onto the throttle on decelerating just a bit produces exactly that sound.
BTW, you didn't happen to lend a bicycle to somebody in a yellow jersey recently, did you???
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Old 07-23-2016, 12:56 PM   #6
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Oh god not you as well!

My Twitter name is @geraintthomas, the Olympic cyclist is @geraintthomas86, and everyone thinks I'm him
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Old 07-23-2016, 07:37 PM   #7
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+1 for asking. I was wondering also. You are both from Wales? Congrats Froome, Thomas and Team Sky. Vive le Tour.
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Old 07-24-2016, 12:53 AM   #8
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Quote:
Originally Posted by geraintthomas View Post
My question is this: is there any way to make the exhaust pop and bang, even when it's warm? I know it's silly and possibly borderline immature, but I adore the sound of it and can't quite work out the physics on why it stops when warm. Any way to make it last even when warm?
This can be done by ECU manipulation. Popping in general can be produced by let the engine run a little bit rich fat for a short time while you go from the gas pedal. But this has to be done by someone who is knowing what he is doing, because that can also ruin your catalysators.

Regards, Markus
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Old 07-24-2016, 02:48 AM   #9
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Program right, and with enough heat you'll get a nice little fireball, ala 930.
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Old 07-24-2016, 04:59 AM   #10
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I worked with some Formula Mazda`s. They can shoot flames. First thing I was warned about.
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Old 07-24-2016, 05:28 AM   #11
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+1 for asking. I was wondering also. You are both from Wales? Congrats Froome, Thomas and Team Sky. Vive le Tour.
We are yes, and both of us are in his new autobiography. Which is a little weird, lol.

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This can be done by ECU manipulation. Popping in general can be produced by let the engine run a little bit rich fat for a short time while you go from the gas pedal. But this has to be done by someone who is knowing what he is doing, because that can also ruin your catalysators.

Regards, Markus
I may have to look into this! Is it a known thing to do this?
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Old 07-24-2016, 06:39 AM   #12
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Hi,

in general if you know how to remap an ECU you might be able do that. But that means you have to know how to remap; not only to use / install modified tuned files from others.

Additionally i have to say that i havent't done it in person for a 986 and i don't know if the ECU software offers all parameters you'll need.

There might be other ways to get the result by using an additional programmable ECU that adds fuel in specific situations. But in general that is a bit complicated and if you don't want to harm your catalytic converters i would not recommend that.

Easiest way is to buy a car with carburator and no cats. Than to modify intake with a single carburator battery, single open long funnel intakes, modify the exhaust and let the beast run a little bit too fat. Than you have the sound you're looking for.

Regards, Markus
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Old 07-24-2016, 06:43 AM   #13
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I didn't mean I'd do it myself as I'm fully aware that ECU programming is an art form in itself. Would be interesting to see what a tuning garage would have to say about it

Thanks for the information!
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Old 07-24-2016, 12:31 PM   #14
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Get in touch with Paul (owner) at Viezu. Bet he has plenty of his Tuners near Wales if not there already. Tell him I sent you and pass my regards please (Fred, SH/CN)

Plan a good 300 pounds and he'll take you in as a customer I'm sure. Don't be offended if more, worth it, trust me there. In Milton Keynes Aug 22~26 and I want to try your car, I'll lend you my rental in exchange
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Old 07-24-2016, 02:29 PM   #15
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Quote:
Originally Posted by geraintthomas View Post
Haven't got a proper photo unfortunately but I'll get one as soon as I can. It's just a 1" pipe that goes from the pipe after the CAT, straight into the tail pipes, bypassing the back box. Same on both sides.
Reducing back pressure has leaned out the air/fuel mixture causing the pops during warmup cycle. Once it warms up the DME compensates as much as it can to restore the ideal air/fuel mixture.
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