Exhaust Pops and Bangs for 35i and 35is

R.E92 · Post by **R.E92** » Fri Jun 17, 2016 1:32 pm

Just a heads-up for all the lovers of the pops, bangs and burbles that the 35i/s cars makes. There's now the ability to increase the magnitude and duration of these with MHD Flasher.

These noises are caused by fuel entering the cylinders and then exhaust when the engine is in overrun, i.e. when you take your foot completely off the pedal and coast.
The car will cut fuel injection to the cylinders after a certain period. In most N54 cars (335i) this is almost instantly. In our sporty models this is 1.25 seconds in normal mode, and 2.5 seconds in sport mode, hence why the exhaust sounds extra fruity in sport mode.

With MHD you can now increase this duration and even allow slightly more fuel to be injected for louder crackles.

Nictrix · Post by **Nictrix** » Fri Jun 17, 2016 2:13 pm

Downside I suppose would be increased MPG

R.E92 · Post by **R.E92** » Fri Jun 17, 2016 2:22 pm

Possibly. Although I imagine the amount of fuel injected during overrun is incredibly minimal, so minimal that the digital MPG readout wouldn't detect it. We're not talking full spray, the injector opening time is variable depending on the engine load.

A possible benefit is that injecting fuel cools the cylinder, which is why racecars make such a noise of decel.

I had leaking injectors for a couple of months and only noticed the MPG drop by 1. And that's with excessive fuel being injected at all times inside the engine.

On the flipside, you could also turn the feature off completely to save fuel and reduce exhaust noise if you are not a fan of pops and bangs.

jimbo1958 · Post by **jimbo1958** » Fri Jun 17, 2016 6:38 pm

Ok.....who"s gonna be first to try it?

R.E92 · Post by **R.E92** » Fri Jun 17, 2016 7:37 pm

I'll give it a go next week when I get back to my car.

Don't have any recording devices like a GoPro so don't expect video footage.

I'll probably keep it close to stock but the same in both sport and normal mode. I don't like how hard the suspension is in sport mode so I don't often switch it over.

jimbo1958 · Post by **jimbo1958** » Fri Jun 17, 2016 7:48 pm

R.E92 wrote:I'll give it a go next week when I get back to my car.

Don't have any recording devices like a GoPro so don't expect video footage.

I'll probably keep it close to stock but the same in both sport and normal mode. I don't like how hard the suspension is in sport mode so I don't often switch it over.

Look forward to that.....cheers.

stuartinzg · Post by **stuartinzg** » Sat Jun 18, 2016 9:18 am

What about damage to the cats?

Otherwise, I'm game, and I have MHD but I haven't used it yet

R.E92 · Post by **R.E92** » Sat Jun 18, 2016 12:44 pm

stuartinzg wrote:What about damage to the cats?

Otherwise, I'm game, and I have MHD but I haven't used it yet

That's a possibility. But our cars already do this in stock form. I haven't heard of any cats failing on 35i and 35is cars.

Maybe if you set the severity and duration to extreme numbers you could cause problems. I just plan on increasing the duration in normal mode so I don't have to use the sport mode any more.

techathy · Post by **techathy** » Sat Jun 18, 2016 8:12 pm

One question to ask is why did BMW set the time at that point?

R.E92 · Post by **R.E92** » Sun Jun 19, 2016 6:10 pm

techathy wrote:One question to ask is why did BMW set the time at that point?

There really is no set logic behind the duration other than what the engineers thought was the best balance to create some exhaust character without being too obnoxious.

It varies between models. The 35i/is are set to 1.25 in normal mode and 2.5 in sport mode. Most other cars are set next to 0.

In the 3 series the duration is increased when you buy the PPK flash from BMW. It's purely a gimmick in road cars and is used to make cars sound more sporty.

Pops and bangs are becoming much more common, cars like the F Type are setting the trend for eccentric exhausts. With people, myself included, going weak at the knees for the F Type's sound I thought this may be of interest. I understand it's not for everyone.

Z4_35i · Post by **Z4_35i** » Sun Jun 19, 2016 8:01 pm

Our 35i probably has the best OEM exhaust sound of any car we've owned. We've previously spent £1k+ on previous 911s and Jeep V8s on aftermarket exhaust systems, where the 35i is just right straight out of the box

techathy · Post by **techathy** » Sun Jun 19, 2016 9:53 pm

R.E92 wrote:There really is no set logic behind the duration other than what the engineers thought was the best balance to create some exhaust character without being too obnoxious.

I was wondering if there was an upper limit which was at this point you're likely to start overheating the cat. On my fiat there was this off-throttle balancing act, enough fuel so you could change gear smoothly but not too much that you'd burn/over-heat the cat (that I needed to get through the fast-idle emissions tests)

Z4_35i wrote:Our 35i probably has the best OEM exhaust sound of any car we've owned. We've previously spent £1k+ on previous 911s and Jeep V8s on aftermarket exhaust systems, where the 35i is just right straight out of the box

35i or iS?

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