Exhaust booming?

[Stu_b7]

Hi all so I have maybe made a massive mistake and had a 200cel sports cat fitted but now under hard acceleration when I hit about 5000 rpm I get a very loud booming kind of noise which I take it is from my exhaust but not 100% sure.
Anyone heard of or had a similar experience would be greatly appreciated.

 

[Charlie Farley]

When I had the 034 HFC it used to make a loud raspy note when giving it some welly, but not what I'd describe as a booming tone.
What exhaust is fitted to the HFC?
Did you have a remap aswell?

 

[Stu_b7]

So I have the old cat that has been gutted then a miltek 3 inch down pipe and the sports cat cut and welded into the bottom of that then off to a 2.5 inch stainless exhaust that was custom made no resonator and only two small boxes on

 

[Charlie Farley]

First off I think you may have created an issue by keeping the oem cat albeit gutted, when you say gutted , is that all the innards so you just have a large cavity now?
You have lost that smooth free flow as the large void in the old cat will create more gas turbulence which can create issues before it exits into the 3" downpipe and into the sports cat.
Non-res systems can be a bit boomy and you are not the first to notice it, it tend to be higher up the rpm range too and can be irritating on motorways too.

In a way you created a small bottleneck by keeeping the oem cat shell in place with a 3" down pipe as the oem cat inlet and outlet are smaller diameter, would have been better to have had a 3" pipe from the turbo and remove the old OEM cat , just using the sports cat .
Its all about flow with these things.

 

[Stu_b7]

First off I think you may have created an issue by keeping the oem cat albeit gutted, when you say gutted , is that all the innards so you just have a large cavity now?
You have lost that smooth free flow as the large void in the old cat will create more gas turbulence which can create issues before it exits into the 3" downpipe and into the sports cat.
Non-res systems can be a bit boomy and you are not the first to notice it, it tend to be higher up the rpm range too and can be irritating on motorways too.

In a way you created a small bottleneck by keeeping the oem cat shell in place with a 3" down pipe as the oem cat inlet and outlet are smaller diameter, would have been better to have had a 3" pipe from the turbo and remove the old OEM cat , just using the sports cat .
Its all about flow with these things.

Hmmm that’s a very good point! the cat was completely gutted out but it does reduce a lot before going back up to 3 inch Downpipe Maybe I should get a decat straight 3 inch pipe to replace the old cat and see how that goes

 

[Charlie Farley]

You have nothing to loose by replacing that oem shell cat now, it is doing you no favours, just wack in a 3" decat pipe it will be a good move.

 

[Stu_b7]

Yeah I definitely will do! Problem is I did it all the wrong way round really I had a custom exhaust done from the Downpipe back then had a 3 inch miltek Downpipe fitted then had the sports cat cut in and the OEM cat gutted out, now I look at it the OEM cat does restrict down alot at the end of it which must be causing the noise it’s almost like a load rattle/bang noise over 5000 rpm.
Any suggestions on a decent decat the ones I’ve seen are mostly eBay ones or 2.5 inches

 

[Stu_b7]

You have nothing to loose by replacing that oem shell cat now, it is doing you no favours, just wack in a 3" decat pipe it will be a good move.

Do you know where I can get a decent 3” decat pipe I’m struggling to find any?

 

[Charlie Farley]

They are a bit short on the ground , but can Be found, I’ll have a look too.
I did have one a while back but no one on the forum was interested so sold it in fb market.

 

[Stu_b7]

one on the forum was interested so sold it in fb market.https://www.ebay.co.uk/itm/165338984925?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=i4ITrLQ6QTq&sssrc=4429486&ssuid=Buwwb0ofT5-&var=&widget_ver=artemis&media=COPY

 

[Charlie Farley]

cant see that page .

 

[Charlie Farley]

I can now, and they have gone up in price
I should have sold mine for way more.

have you looked on FB too.

 

[Stu_b7]

I can now, and they have gone up in price
I should have sold mine for way more.

have you looked on FB too.

Nope I haven’t also I’m confused took the car out today and this is the noise it makes mostly under hard acceleration but sometimes stationary but very rare sounds like a vibration but nothing is knocking or touching under the car?
Not the best recording

 

[Stu_b7]

How do I add videos

 

[Stu_b7]

iCloud

Sign in to iCloud to access your photos, videos, documents, notes, contacts, and more. Use your Apple ID or create a new account to start using Apple services.

share.icloud.com

 

[Stu_b7]

I have also added the clip to my story on my Instagram stu_b7