Cobalt Exhaust - Internal Diameter / Bungs

[J-Tuner]

Hi All

does anyone happen to know the internal diameter of the cobalt exhaust tip? Reason being i am looking for a bung to bolt in just in case i have noise issues at a track day i am going to.

Likewise has anyone got a bung they know fits the cobalt well and can recommend ?

Cheers

Steve

[MX-5 Lazza]

What other mods do you have to your car? It takes quite a lot of fail the noise test in an MX5.

[J-Tuner]

Hello mate

The car is supercharged running about 7.5psi via crank overlay and smaller nose pulley with a JR 4-2-1 manifold cat and cobalt cat back system.

To my ears it makes a racket at both ends when gunning it. Just want to have the bases covered in case they get funny at the noise test

Edited by J-Tuner on Wednesday 4th June 18:53

[CaptiV8ted]

J,

I've just measured my Cobalt for you. It is 73.5mm internal. (measured with digital vernier).
Also, be aware that the internal dimension starts to taper inwards after 110mm of depth.


Can I ask you to pm me if you find a suitable insert? I'm in the same boat as you, there's a day at Thruxton coming up and their limit is 90dB - 90! - silly low. I don't think my car is loud at all, but I don't particularly want to drive 170 miles each way and part with £189 to be told to go home!

Cheers,
Nick

[J-Tuner]

Cheers nick! Much appreciated.

Sure thing will let you know how I get on either way

[MX-5 Lazza]

Mine is supercharged (MP62 at around 8psi - 240bhp) with standard manifold (better flowing than Mk1/2), Larini Sport cat & midpipe (both 2.25") and Racing Beat Power Pulse Dual backbox. It's pretty noisy but still easily passes noise tests at every track & airfield I've been to.

[J-Tuner]

MX-5 Lazza said:

Mine is supercharged (MP62 at around 8psi - 240bhp) with standard manifold (better flowing than Mk1/2), Larini Sport cat & midpipe (both 2.25") and Racing Beat Power Pulse Dual backbox. It's pretty noisy but still easily passes noise tests at every track & airfield I've been to.

Ok well that's promising then for the sake of 17 quid I have ordered a 3 inch universal bung to see if it fits. If I don't use it that's fine but at least I have an option should I have an issue. Just don't want to miss out the day

[Cardo]

Hi Steve,

The Cobalt exhaust and de cat on my car flies through the MSA noise test easily.......I think it's in the mid 80dba. region if I remember rightly.The stewards usually comment on how quiet the MX5's are.

Cheers

Rich

[J-Tuner]

Cheers Rich - always good to get other peoples real world experiences with the same gear!

Steve

[J-Tuner]

For nick and anyone else that's interested : got a 3" universal exhaust db killer off eBay and the fit is very tight which is what you want but it looks like it will work with some slight manipulation on the outer edge which is flared out so it fits cleanly when cold. Fits fine in terms of depth.

Since there is the outer heat shield I think the only way to secure it decently is to get a longer bolt that goes through the heat shield and the exhaust itself and into the bung.

Otherwise I think it should be good to go. No idea what it will sound like though and his long it would last bit its a basic device not much to go wrong!