Exhaust Options......again! Suggestions please.

[KatoKid]

Hi all.

 

I'm at a place with my project where I need to make a decision on exhaust design and am seeking some guidance.

 

I'm using the factory headers which are a paired 3 into 1, each finishing with 2" collectors. In the E36 M3 application and in fact most performance BMW applications they use 2" full length dual pipe systems and all the aftermarket systems are also full length dual pipe systems so I figure there is a good reason they do this given the weight penalties. To replicate this I would like to go with a full length dual pipe system but wont tolerate a low hanging exhaust and unless anyone tells me different I doubt I could fit a 2" dual pipe system that tucks up high enough and provides the room for resonators mid way in the tunnel and still uses the original single muffler location etc? Anyone got any pics of a dual pipe system like this?

 

So I reckon I'm stuck with merging the 2 x 2" collectors into a single system but don't want this to be too restrictive or terrible to live with (must also meet noise limits for engineering and rego). From a common sense stand point I thought it would be worth comparing total cross sectional area of the various options:

Factroy 2 x 2" is 6.28 square inches.

Single 3" is 7.06 square inches

Single 2.5" is 4.9 square inches

Single 2.25" is 3.97 square inches

 

In my mind single 3" is overkill and will hang too low and be obnoxious to live with anyway. 2 1/4" is too small so looks like 2.5" is the best option. I know Adam (Brown Hornet) has done a lot of research and is going this way but Ive also seen comments from OP on booming and resonance issues they couldn't solve, mind you this was with L series engines.

 

Feel free to chime in with suggestions.

 

Thanks

[peter mc]

hi kato

the 3'' system is not over kill and can be done right. i run them in all my big setups as it has large Gaines over 2.5 .but it must have a reducer after the merge collector .on l28 s race motors  the system i had at the engine day for people to take picks off is Worth 15kw over a 2.5 system they make the same sort of power as the bmw

[NZeder]

Well I am going for a dual 2" setup on my install aka Z432 style the centre muffler looks like this.....internet surf'n for a pic of the setup I have (mine is at home under the bench = hard to get a pic while at work  ).....ok got pic attached now

 

you can see it is not that high at all - nice and low

[Zedman240®]

I've fitted a twin 2" system on mine very much identical to the SA Safar rally cars. Trick is to find a 2 in, 2 out resonator for the center where it fits neatly almost under the gearbox. I have plenty of ground clearance and it's not loud at all. When I get home I have some pics on my home PC if you want to see.

[KatoKid]

Thanks guys.

 

Yes please pics Dimitri.

 

 

[Zedman240®]

Pic from my Tamiya 1/12 Safari rally car instructions showing what I have under my car but with the best view.

[Scoota G]

Here's some pictures of the System Peter Mac had at the engine building day.

[zed240au]

I ran twin 2" system on my old v8 no worries fitted in easily Im currently running twin 2.5" system with hi flow cats did run hotdog resonators in middle but have since removed them .

Biggest issue i have found with twin system is choice of rear muffler that has twin inlets and single outlet that will fit in space avilable on my twin 2" system i had custom made muffler On my current system have berklee 2.5" twin in and single out but its pretty much a straight through muffler

My worry for u would be keeping that bmw 6 quiet and drone free will be real challenge have done some custom systems on mercedes and bmw 6 cylinders and they can really be a pain to get sounding right

 

mick

[Wayne G]

The twin system is very good for mid range torque, helps keep the vehicle muffled, and keeps the BMW sound. 

 

I have fitted 3" to BMW. Slight better top end, not as nice midrange and sounds like any other falcadore with 3" and hard to keep quiet! Berkley do a good range of mufflers although I am not familiar with their stainless range.

 

Single 2.5" would work for street but there is no challenge to that and clearly, you love a challenge!

[jamo240]

Hi Kato

 

While I was at Holden, I saw some remarkable results achieved regarding attenuating exhaust booms (aka droning) by pinching the cross section of the pipe down where it enters the rear muffler (such as a Z is configured...main muffler at the rear of the car). The N&V engineers told me at the time that the attenuation is related to the ratio between the pipe area to the expansion area (inside the muffler). Muffler volume comes into it as well. The added benefit is that you are reducing the area the farthest from the engine where the exhaust gas is cooler and of less volume and hence the restriction to flow is lowest. This minimises power losses compared with attenuating closer to the engine.

 

In my case, I custom made a rear muffler to maximise the volume available in the cavity beside the fuel tank. I run a 3"single all the way, and the rear muffler is configured as a tri-flow...the gas goes thru to the back, then internally forward to the front chamber, then out to the ambient air. The center chamber is only used to expand the gas into, and there are a series of holes in the muffler internal transfer tubes that facilitate this process. It does a pretty fair job of keeping the engine quiet for a relatively large diameter pipe...I expect this would work even better with a 2.5 of 2.75" system. The starting point for exhaust attenuation is muffler volume however, and this is problematic in early Z cars when modified for relatively high horsepower engines....there just aren't any places where a big muffler can reside unless you relocate the fuel tank!

 

Cheers

 

Jamo

[KatoKid]

OK, dredging this one up again because I'm at a stage where I need to actually start building the exhaust.

 

Ive done lots of research and with help from members here I'm pretty well decided on which way I'm going, key factors which are driving my decisions:

• Car must meet 94DB for engineers and rego
  
• Needs to be dual system right to the back, all advice says that its the only way to get the "BMW" sound they are renowned for
  
• Must have good ground clearance
  

 

There are off the shelf systems from Fujitsubo and Rein Hard that look really good but  Fujitsubo quote 105DB, Rein Hard don't quote DB but its a sure bet theirs is similar and at the quoted price of $2,300 its stupid money.

 

So my preferred option is to build something myself. Key to getting the system to work, sound good and be quiet enough is going to be the resonator and rear muffler size and design. I haven't found an off the shelf resonator that will fit the bill so its going to have to be a custom jobie, pretty much like the tamiya model the Dimitri posted that runs the full length of the tunnel under the tail shaft.

 

As far as choices Ive really only found http://www.dpe.net.au/ and http://www.surefloexhaust.com.au/frame1024x768.htm does anyone have experience with or know of customer muffler builders?

 

Thanks.

 

 

[NZeder]

Not much help bit the fabricator I use here in NZ makes his own stainless stuff when required.

[jamo240]

Hey Dave

 

Definitely agree on the twin 2" configuration. While my 3.5" (necking to 3") is certainly quiet, it is boomy and that is part and parcel of large diameter systems.

 

As for muffler building, that Motorsport place opposite purple pig in the bayswater area builds mufflers for very reasonable prices. Give them a call.

 

Cheers

[zed240au]

havent got my car here to measure but would suggest a magnaflow 11385 or 14385 muffler for middle of your car dual 2.25 pipes in and out 14" long body with 4" x 9" body for rear if your happy to go with stacked tail pipes like my car could run same muffler on rear magnaflow is a good brand

cant say ive tried these mufflers on a zed so dont know what sound level will be

Better still ship car over to tassie and ill make u a sweet system

 

Mick