Exhaust system help

[James93]

Can you believe my insurance goes down with exhaust modifications ?! Id defo pay more in insurance for the noise - basically I really want an exhaust mod but can someone clear up the myths and truths for me??

Some people say:

-rear exhaust mods dont make a difference to performance
- the computer doesnt like any changes
- any reduction in back pressure increases performance
-any exhaust mod ruins the performance



One thing is for sure - im not parting with any power or harmony between engine and exhaust.

What should i do? Because i really want more noise and even power if i can

Cheers,

James

 

[Smartbear]

Can you believe my insurance goes down with exhaust modifications ?! Id defo pay more in insurance for the noise - basically I really want an exhaust mod but can someone clear up the myths and truths for me??

Some people say:

-rear exhaust mods dont make a difference to performance
- the computer doesnt like any changes
- any reduction in back pressure increases performance
-any exhaust mod ruins the performance



One thing is for sure - im not parting with any power or harmony between engine and exhaust.

What should i do? Because i really want more noise and even power if i can

Cheers,

James

Hi, turbo cars go better with the least amount of back pressure possible but normally aspirated cars need a certain amount of back pressure to work efficiently, back in the day whenever my exhaust rusted off the performance definitely deteriorated
Rob

 

[James93]

Right okay so basically i cant do anything to the exhaust without feeling like an idiot for doing so? :thumbsdown:

 

[Silverstar]

Back in the day I had a Hartge sports back box on my E30 325i, can't say that it improved performance, neither did it make it any worse but the car sounded a hundred times better. Not sure about cars these days weather it affects their electronics, but I have not heard anything detrimental in this aspect. I will be looking to add some sort of sports back box to my 30i, once again purely for the improved sound!

 

[Mr Tidy]

Not sure if it helps, but a previous owner of my E86 had a custom cat-back exhaust fitted to mine and it sounds much better than standard.

But going by my previous E86 with a standard one it hasn't noticeably altered the performance for better or worse.

The only downside was that after it was fitted the same owner found he needed new Lambda censors, so major change can have some undesired results.

As it wasn't a performance system both the insurers I've used were happy to just note it as declared but there was no impact on premium.

I have heard one with a back-box delete which really had some volume, but was possibly a bit more than I would have wanted.

The only other options are probably to get a Sports system fitted, or there used to be someone on here who modified back-boxes by opening them up and removing some of the innards.

Ideally it might be best to see what a modified one sounds like before you commit - maybe go to a Z4 meet or post something to try to find someone on here local to you who has had theirs modified.

 

[CRE]

NA engines do not need back pressure. Back pressure is bad across the board. What they need is proper scavenging. I wish the whole "back pressure" thing would die already (It never will though). What scavenging is is maintaining a proper volume and flow to create what essentially amounts to suction to help evacuate exhaust gasses from the cylinders by tuning the exhaust for velocity, density and pulse width. By the time you get to the muffler on an otherwise stock system it's pretty much a moot point as the greatest interruptions, the headers and catalytic convertor have already passed. In an ideal setup you'll actually see vacuum in the exhaust path, hence why some high power, street legal builds are able to run the PCV to the exhaust instead of the intake manifold. The issue is that the dynamics required change constantly based on throttle position, load, temperature, valve profile and RPM. Headers coordinate the pulse overlap as exhaust charges leave the cylinder and enter the exhaust flow. A good NA header will create as smooth a flow as possible preventing said back pressure more effectively removing inert gasses and heat. A properly tuned exhaust is built for peak scavenging in the middle of the typical operating range... So, to make things even more complicated, it depends on how you drive too. If you're asking if you can delete your muffler with little change in performance, yes. If you're looking at headers and and all the way back, talk to a local tuner with experience with your specific engine.

 

[tomrdy]

I went initially with a supersprint powerloop backbox and Y pipe which made the car sound lovely, and minimal additional drone.

Performance would be placebo only but definitely no reduction.

Later I deleted the secondary cats with supersprint front pipes and the sound now is raucous (quite raspy) and very droney - ive gotten used to it + it got milder + added sound proofing, but not a subtle option. It also pops and cracks on lift which... I'm a child about :evil:

The secondary cat delete and everything together gave a noticeable performance increase. I wouldn't dare claim any numbers but the increase is noticeable.

*I had a lot of fitment and QA issues with Supersprint so I personally don't recommend them. Other members have SS systems and been fine though so I was unlucky I guess.

 

[Davz]

NA engines do not need back pressure. Back pressure is bad across the board. What they need is proper scavenging

Absolutely spot on! The rear silencer is just that a silencer, changing this will have no effect on performance, having fewer baffles will just change the tone.
If you want more performance then you'll need to get rid of the mid silencer and resonator but this will affect scavenging and not always for the better so you could end up with less performance.
Adding a crossover is a tried and tested method of scavenging, this can be in the form of an H-pipe or X-pipe. The H tends to be better for low to midrange with the X better at higher rpm. Working out the distance from the headers where to weld it in place is a helluva mathematical problem, the position will affect the scavenging.
The nice thing about having a crossover is it stops the pops and bangs and gives a proper straight six sound, personally I hate all the pops and bangs and it just means that scavenging is not working well that well.

This youtube link shows a crossover system that to my ears sounds spot on for a straight six.
https://www.youtube.com/watch?v=n33IdLSiIsQ

Avoid the cheap ebay exhaust system as that has a large centre box which then is reduced down to a single pipe, not good for pressure and will reduce perofrmance in comparison to what can be achieved with a proper dual system, but if you just want sound then it will provide that.

Later this year I will be having a custom made system, once the missus has forgotten about the B4's, eibachs and whiteline arbs I have just fitted. I have already sourced the stainless crossover and silencers and will be getting these fitted, the parts are very reasonably priced, just need a quote for fitting and custom pipe bending. If you want the links for the parts pm me.

 

[CRE]

An excellent example of a fairly well thought out system. Calculating the position of the crossover is a big factor if you're looking for peak performance. In the setup in that youtube a helmholtz resonator (NOT to be confused with the mini-muffler "resonators" that are commonly used on production vehicles) on each pipe would help even more. It reduces the fluctuations or "bubbles" by providing air to fill in the gaps in the pulsating exhaust discharges from each of the cylinders and trimming high pressure pulses... Think of it as shock absorbers for your exhaust... just like the resonator that most ignorant people remove from their intake. That's right, they silence the intake for more than one reason. Looking underneath really high performance vehicles you'll see these as small canisters connected to the exhaust. These can be skipped with a VERY well mapped header and collector setup, but you're not going to find an aftermarket solution with the required level of engineering. These setups, as Davz mentioned, are tuned for a very specific range of operation.

I'm still trying to decide on the optimum setup for my car. Adding a supercharger and meth injection has changed things quite a bit. I'm considering using a couple magnehelic gauges to map out the high and low pressure points of my exhaust to determine the best dynamics possible. It's still rather amateur but not hardcore ghetto. I'm just not sure if it's worth all the effort.

 

[Zedtastic]

I wish the whole "back pressure" thing would die already (It never will though).

Me too. I'm surprised this myth still exists.

 

[Oh4show]

Get a scorpian custom made exhaust not cheap to be fair but I can tell my engine breaths alot better , no drone and defos more power with a great raspy noice especially with the sport button on as I do all the time as this helps with steering issues as it comes more alive and direct ,If you want to hear how it sounds let me know il post a video .

 

[Hillbilly]

I bought and fitted the £289 full stainless system from eBay. It fitted perfectly and sounds utterly fantastic! I would recommend it to anyone. Gives it a lovely retro straight six sound, reminds me of a TR6.

 

[G600]

Get a scorpian custom made exhaust not cheap to be fair but I can tell my engine breaths alot better , no drone and defos more power with a great raspy noice especially with the sport button on as I do all the time

How does the sport button make a difference to the noise?