To decat or not to decat

[S18 RSG 429]

Hey. So I'm in a bit of a situation here, wondered if some of you could help point me in the right direction. I'm trying to decide on a manifold (and yes, I've read a million other topics discussing this very thing) but struggling to come to a decision.

Currently, I have an overpipe-back system, with secondary decat. It's fairly loud already, but following the remap at Abbey, the car became so much better to drive, that all I can think about is how the torque dip is the only thing keeping this car from being truly great to drive, as most daily driving takes place right in the middle of that torque dip. I want to rectify that now.

I originally wanted a catted UEL manifold from JDL in the states, but crunching the numbers yesterday, it ends up at around £900 after shipping and taxes (even after they knocked off around $300 of shipping costs), which is just a little excessive for a ~£500 manifold. The 1320performance UEL seems to get great feedback, and it's less than £500 landed in the UK, but it's decatted. My question is, to those of you with a similar setup, did you find it TOO loud? If so, and you fixed it, what did you do to quieten it?

I was thinking I could replace the secondary decat pipe with a resonated one, which I could swap out with the CAT come MOT time. Or is it possible to run with the original CAT back in place to reduce the noise, or would that have too much of an impact on performance?

Help please 

[Andrew Smith 156]

At the moment I am running the standard system and after a conversation with Mike at Tuning Developments have decided to go for his decat manifold and overpipe  leaving the rest of the system stock. This to me seems like the right way to go as it would give the best gains whilst keeping the noise down for track days and also giving a fair chance of a pass come mot time (not a certainty though)

I will let you know how I get on with that at the end of the month when it and a few other bits and bobs are done.

[Church 209]

Catless header no doubt will make exhaust louder. Seen cases of switching to stock or quieter catbacks when catless header was bought/installed after aftermarket catback due resulting loudness becoming unbearable. Among quietest alongside stock i often see mentioned Invidia Q300. But then again there are owners, to whom even straight mufflerless race pipe setup isn't too loud, so it might be subjective thing. Of course, one of louder times is during coldstarts, when ecu tries via valve/ignition timings to throw unburnt fuel in exhaust for cats to heat up sooner to get to working temperatures. Tuning out coldstarts by competent tuner will eliminate at least this, one of most annoying to neighbours, noise issue out.

NA power gains are expensive. If it's for car, you intend to use for longer time, imho one just has to bite the bullet and accept spendings, instead of getting something subpar and regretting that later on.

My own choice would be going for best possible catless header and leaving stock 2ndary cat in front pipe for easier passing smog checks. Currently i'm thinking of Ace type A/350 (and IIRC with clearance issues for RHD, so @UK CS400 might be better choice, especially if low/mid rpm performance matters a lot), but it costs way more then even catted header you mentioned, so very probably will not be among your choices. On overseas forum i heard Gruppe S header often brought up as budget choice. If you are willing to use OFT instead of Ecutek, then OFH+OFT is good price/performance package.

[Varelco 211]

You haven't told us what catback you are running as this will have an influential factor (An Invidia Q300 will be a lot quieter than a Tomei 60S for example) How many resonators do you have in the current set up? Whenever I've seen a video with a catless manifold and front pipe its been LOUD.

[S18 RSG 429]

17 minutes ago, Varelco said:

You haven't told us what catback you are running as this will have an influential factor (An Invidia Q300 will be a lot quieter than a Tomei 60S for example) How many resonators do you have in the current set up? Whenever I've seen a video with a catless manifold and front pipe its been LOUD.

My exhaust was custom made by a place called Prospeed Exhausts in south Wales. It's resonated, but the secondary decat means it is fairly loud. In terms of volume, it was around the same as @Lauren's, and I believe she has a resonated Milltek system. It's not over the top loud, but it's certainly not quiet.

Cold start isn't an issue, because it was mapped out by Mark when I had the remap. My biggest concern is the fact that I occasionally work early, and because I live in a small, fairly enclosed street, I wouldn't want to annoy my neighbours even more than I already do. Of course a decat manifold won't help with that, but if slotting the original CAT back in place is an option to reduce noise and not affect performance too much, then it may be the best option.

[Lauren 2259]

Mine's a non-resonated Milltek, Ross with with a secondary de-cat and over pipe. It really is perfectly liveable. I drove Kev/Debbie's and it was much louder, which I would expect make road driving on long trips a bit wearing. Mine doesn't drone at all at cruising speeds. 

[Foulsmell 120]

Cheapest way is to drive around the dip. It doesn't take much effort. Or changing the final drive will give you more torque to play with and it will still pass an MOT.

[Rich 378]

I have a 1320 performance header and overpipe, stock front pipe and Milltek cat back. It's fairly loud but not crazy.

I don't have any torque dip really, since having it remapped.

[Ade 517]

I have a 1320 performance header and overpipe, stock front pipe and Milltek cat back. It's fairly loud but not crazy.

I don't have any torque dip really, since having it remapped.

Have you had it checked for sound level?

[S18 RSG 429]

11 hours ago, Rich said:

I have a 1320 performance header and overpipe, stock front pipe and Milltek cat back. It's fairly loud but not crazy.

I don't have any torque dip really, since having it remapped.

How was the ordering process with 1320? 

I added the manifold and overpipe to my basket on the site, and shipping came up as $19.52, which seemed a bit cheap to me. I didn't order it as I wanted to get a human response from them first of all to check everything was ok with the order, but I've had no response.

If you ordered straight from the website, did you have any issues? And how long was delivery?

[smudge 1020]

Decat 

Stop being a pussy

[Rich 378]

7 hours ago, S18 RSG said:

How was the ordering process with 1320? 

I added the manifold and overpipe to my basket on the site, and shipping came up as $19.52, which seemed a bit cheap to me. I didn't order it as I wanted to get a human response from them first of all to check everything was ok with the order, but I've had no response.

If you ordered straight from the website, did you have any issues? And how long was delivery?

I emailed them first to confirm. Their cart software doesn't do international shipping, so Jeff raised a separate paypal invoice for the difference between standard shipping and international.

Delivery was a couple of weeks, including a week sat in customs.

[Ztox 230]

Just go for it, noise will be fine 

A few people (myself included) like the Tomei UEL, just to throw another one in the hat that hasn't been mentioned

[Varelco 211]

You could always get a catted front pipe and use it was a catless manifold. It will be quieter than ditching both cats and can get you through an MOT.

 

I have a Berk HFC front pipe for sale...

 

***shameless plug***

[S18 RSG 429]

49 minutes ago, Varelco said:

You could always get a catted front pipe and use it was a catless manifold. It will be quieter than ditching both cats and can get you through an MOT.

 

I have a Berk HFC front pipe for sale...

 

***shameless plug***

I was always under the impression that the Berk HFC would fail MOT with a catless manifold?

[smudge 1020]

1 hour ago, S18 RSG said:

I was always under the impression that the Berk HFC would fail MOT with a catless manifold?

Some have passed and some have failed with the Berk HFC 

[Varelco 211]

I've only read issues with the Cobra HFC, not the Berk.

[Deacon 1357]

9 minutes ago, Varelco said:

I've only read issues with the Cobra HFC, not the Berk.

There have been issues with the Berk too. Seems like a lottery to be honest with all of the HFC's.

[Rich 378]

On 4/12/2016 at 9:36 PM, Ade said:

Have you had it checked for sound level?

I reckon it's about 95 dB using an ebay special meter. The acid test will be at Snetterton.

[Ade 517]

Just now, Rich said:

I reckon it's about 95 dB using an ebay special meter. The acid test will be at Snetterton.

I'm starting to think my cat back is loud. Measured 95.5dB at Bedford. The SC makes it about 3-4dB louder apparently.

I really fancy a header but it too liud for my taste even now.

Will look forward to hearing it

[Ade 517]

A correction to above. At Snetterton my exhaust was measured at 92dB which is what Cosworth said it should be which the sc fitted.

[Rich 378]

To add some more info. At Snetterton mine was measured at 97 dB @ 6000 rpm, which is probably about right. I wouldn't want to go louder than that personally.

I have the option of fitting a resonator in the mid-pipe, which I will probably do if I ever go S/C.

[Test Drives Unlimited 278]

Mine only measured 85db

Sent from my Archos 53 Platinum using Tapatalk

[S18 RSG 429]

Well I finally gave in. I'm sure most of you can make an educated guess on what I went for: