Rantir

Hi guys,

ive got some plans and need your help about the whole project idea.

Well my 944.2 EU needs a new muffler, but i planing to go further as i like build something interesting.
Due to legal permissions iam not allowed to build a exhaust as free as i wish, thats why i want to build a sound controlled exhaust.

Let me explain what this mean:

The exhaust begins with a usual CAT unit but after this CAT unit, there is a Y connector with a electronical valve. While the car is between a certain speed range ( due to law ) the valve is closed and the whole gas needs to pass one pipe in order to muffle the sound down as much as the usual street muffler would do.
When the car is out of this speed range the valve is open and the overall sound has no legal limits by law.

To make some things clear in advance, this is no kind of trick the police or something like that, this is 100% legal in my country and is used my "modern" porsche/sport cars as well.
Secondary i dont want to unchain the hell when ever the valve is open.
My target is to get a nice deep sport sound.



There is a cable at the speedometer which can be used to get the current speed, which is usually used by some navigation units. This one is going to control the valve. Maybe i need to build a little microprocessor in order to convert the signal.

BUT my biggest question mark is the design of the exhaust and which mufflers/components to take.
I imagine 3 basic kinds of designs as one can see in the pictures.
The red block is the valve which is closed whenever the car operates within the speed ranges => common sound

The easiest one would probably be an usual Muffler and a parallel straight pipe, but iam not sure if a straight pipe will make a great sound and if there is enough gas pressure for the engine.

Another option would be to use 2 Muffler parallel.
The grey one needs to muffle the sound onto a common sound level while the blue one is only in use when the sound level has no limit. So the blue one needs to make the "good" sound.

The last option is to use 2 Muffler in a row when ever the valve is closed which need to result in an normal sound, while open the valve shall mainly bypass the orange Muffler and the grey muffler shall produce a nice sport sound.


So far ive got one other big problem, i dont know how to ensure the engine gets enough pressure from the exhaust system.
As far as i know a non turbo engine shall have some "pressure" from the exhaust system in order to ensure best result.


I hope someone got some experience and maybe have some suggestions about muffler options.




EDIT:

So there are basically two questions:

A: Which mufflers are recommend to have a great deep sound when there are to restrictions in dB ?


B: Which of these settings are recommend? ( Probably in cmbination with question A)

V2Rocket

Take a look at this existing product - perhaps it will work for what you want, or you could modify it as you see fit.

http://www.dynomax.com/mufflers/dynomax-vt-mufflers

Tiger03447

I think that option 1&2 are OK with an external valve. I don't fully understand option 3 and why you would want two mufflers except for extra quiet running. I think that JC Whitney makes an exhaust cut out valve which might be good...As far as the Dyno max, that looks really great until the spring loses pressure.from heat or breaks.With it being internal that would make it hard to work on in case it got all crudded up with exhaust carbon, etc..Hope that it all works out great for you..keep us posted!

thomasmryan

Beemers have been using an exhaust valve for a decade or so to light up the cat during warm up.....search 'golf tee mod' on most bmw forums. Some are set up just choking the 2nd tip on a dual exhaust which seems like what you are trying to accomplish.

Rantir

Thank you for your reply.


About Option aka the strait pipe option :
Iam pretty unsure if a strait pipe still delivers enough "back pressure" for the non turbo engine. ( An turbo engine whould like to have as less "back pressure" as possible.

About option 3:
The idear behind this is pretty similair to the 2. option.
the 2. Muffler is used to give the engine enough "back pressure" and a good sound.
while the 1. Muffler is added whenever the engine needs to be silent.

About the dynomax solution: iam not quite sure as this valve opens up with more and more pressure (speed/rpm?) I rather whould like to control the valve by a microchip, rather than pure mechanical, as iam not sure how much the valve opens in different ranges.

About the golf tee mod.
I did a quick search, as far as i understood they already got a valve controlled exhaust in there BMWs and they trick there valves, because the want to have "best sound" in very situation.

ramius665

Why not use an electric exhaust diverter valve tied to a switch, so you can open it up whenever you want?

V2Rocket

the Dynomax VT is "closed" at idle and low/part-throttle conditions.
When you push the pedal harder and more air is being consumed/pushed out by the engine it will overcome the weight/spring force of the valve in the muffler and open it.

What you could do for your project is simply modify the existing Dynomax valve to be opened/closed by an electric solenoid controlled by your microchip.

That way you only have to weld one muffler onto the existing exhaust system and still get sound control.

Rantir

Well that could be an option, but iam afraid that its not that easy to convert the valve to an elctonic control.

The point about the electronic part is pretty strait forward.
To fit the laws, there are serval areas where the sound must be below a certain limit and so on, its not just "above" x RPM or y km/h there is no limit.
And i feel like its way easier to adjust the valve exactly with a programmable micochip than by mechanical.

Did you use any Dynomax and found one with nice sound.
Or to ask a different question: is there any muffler which got a nice sound with no respect to sound restrictions?

Rantir

Ive edited the first post to make my questions more obvious.
Maybe someone can suggest me something

Humboldtgrin

Have you seen these mufflers?
https://www.maperformance.com/produc...Fc6Xfgodr0EGgg
https://www.ebay.com/itm/301071787349