Exhaust note - how to tune it?

WorldClassAccident · #1 22nd February 2015, 17:38

Thinking of replacing the twin side pipes that Chris put in for me with something coming out the back.

The side pipes get a bit wearing when I am using the car for 2-3 hour commutes but also the tone isn't great.

They attract attention and are okay on maximum attack but between 2-4000 rpm they are a bit droning. I think this is as much the engine as the pipes as there are few interesting sounding BMW 2.8 engines that I have found on u tube.

Anyone know the maths, science or hammer methodology for tuning an exhaust to reduce the drone?

Tribute Automotive · #2 22nd February 2015, 17:51

Have a read of the FAQ's on here:

http://www.supertrapp.com/

Ian A had a similar home brewed system on his Z3 when we did his Z300S conversion.

WorldClassAccident · #3 22nd February 2015, 17:59

Cheers Chris - if I provide gas and wire, can i borrow one of your welding sets for a while?

Supertrapp are US based - do you know if they have UK distributor?

Was Ian's car a good sound?

Similar to my Merc?

Tribute Automotive · #4 22nd February 2015, 18:57

http://www.demon-tweeks.co.uk/motors...p-on-silencers

Top Gear is just about to start.........

Scottie22 · #5 22nd February 2015, 19:54

I usually make my own WCA, and they mostly turn out right, sometimes they are too noisy, so changing the main box will sort it out. Also, I only use straight-though pipes for power and nice noise.
What ever you choose, go for stainless steel, as it resonates and beats mild steel for sound every time. And of course does not rust.

Good luck with it.

Mister Towed · #6 23rd February 2015, 06:11

Quote:

Originally Posted by Tribute Automotive

http://www.demon-tweeks.co.uk/motors...p-on-silencers

Top Gear is just about to start.........

Hmm, Top Gear last night. Anybody else find the feature slagging off Peugeot a bit tiresome?

It's not often I find the show misses the mark, but I thought that part of the programme wasn't up to their usual standard and found it a bit of a yawn fest.

Oh, and I like the sound of the traditional, mild steel Cherry Bomb for the crackle it adds to the overrun. The e-type tail pipes Phil J uses also sound awesome on a straight six.

froggyman · #7 23rd February 2015, 08:06

Yes Towed I agree, 'Top Gear' is going off the boil for me too. The Peugeot scene just proved how silly and childish they can be. Some factual content there, I don't think!

Grey V8 Pete · #8 23rd February 2015, 08:21

Quote:

Originally Posted by WorldClassAccident

Thinking of replacing the twin side pipes that Chris put in for me with something coming out the back.
..................................................

Anyone know the maths, science or hammer methodology for tuning an exhaust to reduce the drone?

A long box will absorb low frequencies and a short box will absorb the higher (crackle) frequencies.

I had a factory fitted 24" box in each tail pipe on my Marlin Hunter (Rover V8 3.9i) and found it a bit harsh. I had the local Powerflow stockist fit me an extra 14" box at the back and it now sounds much more mellow for general driving. Still sounds good though when you turn the taps on full!

WorldClassAccident · #9 23rd February 2015, 17:08

I put the car up on my home made ramps so I could more easily look underneath and see what options I had with the exhaust.

With the better visibility I worked out how to almost completely solve the nasty exhaust note problem

I replaced the one loose bolt holding the back of the pipe to the catalytic converter with two tight ones. This had the effect of lifting the exhaust pipe slightly where it was sagging at the joint and closing the hole in the join between the pipes.

Now my exhaust is a much straighter piece of pipe with the axhaust coming out of the ends and sounds a lot nicer.

Tribute Automotive · #10 23rd February 2015, 19:15

Quote:

Originally Posted by Mister Towed

Hmm, Top Gear last night. Anybody else find the feature slagging off Peugeot a bit tiresome?

As a Peugeot 104 owner I felt compelled to watch the repeat showing of last nights Top Gear on BBC2 tonight. I can confirm that I found it HILARIOUS on both occasions. It reminded me of my late Fathers driving style in his Peugeot

. More un-PC behavior from Mr Clarkson gets my vote.

BTW Glad you got your exhaust sorted Nick.

IanA · #11 23rd February 2015, 20:48

Quote:

Originally Posted by Tribute Automotive

...Ian A had a similar home brewed system on his Z3 when we did his Z300S conversion.

During the conversion i had a very short 90deg pipe on the back of the centre silencer.
Now- per the pics in my build thread I have a longer pipe that exits in front of the rear wheel. In order to tame it for commuting I have a set of four perforated baffles on a piece of 10mm studding clamped inside the pipe.
It sounds great and has a nice burble on the overrun. The only problem is that when I boot it, there is a hissing noise as if there is an exhaust leak. It gets very hot so the bracket that clamps it to the pipe is very rusty- the pipe itself and the baffles are stainless. Happy to dismantle at Stoneleigh so you can see it. You'd need two of course if your clamp tightening hasn't worked well enough.

fatbloke · #12 24th February 2015, 11:25

If any of you fancy a drive opp north I can recommend CSK Fabrications in Pocklington for custom exhausts. Charlie is a one man band but is a master of fabrication. Just take a look at the images of the exhaust manifold he made for a turbo charged Suzuki drag bike.

https://www.facebook.com/CskFabricat...ref=ts&fref=ts

IanA · #13 26th February 2015, 20:42

Having removed the rear silencer and pipe from just behind the centre silencer - I measured the pipe length required and checked the angle and had the pipe supplied and bent by:

Seller:
Pipewerx Cars Ltd
info@pipewerx.com

Note to seller:
Hi Jeff, As discussed previously, this is for a 60 degree bend close to one end in a 63.5mm OD pipe but with an extra 250mm length on the other end. Many thanks. Ian

Qty: 1
Unit Price: 14.99 GBP
Total: 14.99 GBP

Postage and packaging: 8.00 GBP

Total: 22.99 GBP

Then I cut the pipe to length in front of the rear wheel.
Find him on eBay.

WorldClassAccident · #14 26th February 2015, 21:14

Having just driven southampton to stevenage and back I can confirm that fixing the bolts tightly has cured the problem and that the Hatfield tunnel sounded great

IanA · #15 27th February 2015, 17:02

Quote:

Originally Posted by WorldClassAccident

... the Hatfield tunnel sounded great

Ah - tunnels...
Once got caught in a confiture (sorry - bouchon) on the A13 towards Rouen/Le Havre just off the Peripherique in my Escort Cabrio with a stainless beancan on the back- easing the throttle up the torque curve in second sounded better than a Fezza with a Tubi.