Decat silencer or high flow cat?

[ameano]

Hi guys

I've got the following exhaust system:
Apex flexi front pipe, Apex decat pipe and Apex catback exhaust

and an Apexi air filter for added induction roar

The loud noise was fun for a while, but is now getting extremely annoying, and I would like to silence it a bit Can't stand drowning in the constant boom and the harsh sound on the motorway, so have heard that a decat silencer is meant to get rid of these two problems. Having sat in a silent stage 2 car has definitely made me make up my mind.

I'm now stuck between these two:
1. decat silencer:
- advantages: cheaper option, free flowing and not much different to decat
- disadvantages: have to replace with cat for mot test
2. high flow cat:
- advantages: fit and forget, better for the environment
- disadvantages: slightly more expensive

This is as far as I know from what I've read around. Ideally I would like to go for the high flow/sports cat. Now my questions are:
how much different is a high flow cat to a decat in terms of horsepower?
and will an engine management chip, e.g. stage 2 work properly with it?

Any experiences and are you happy with either solution in terms of noise reduction?

Cheers

[Aj82]

High flow cats are coming down in price and companys like milltek etc are making some high flowing ones that dont affect power etc too much not enough to make you feel a difference.
Decat pipes are what most of us fit. Due to them being cheaper and offering alittle more flow than a hgh flow cats. Remember that if you get one of these dont worry too much about having to refit for your mot, your car may pass without one due to gas test or friendly mot man and even if you do have to fit it, its only four bolts man!! lol.

Good luck, i would go de-cat pipe and i have done with no mot probs mate.

Cheers Aj


Both of them will offer noise reduction, one more than the other, can you guess which? haha. And to be honest the difference will be minimal between the two and if you still find it to loud, find an exhaust specialist to fit a silencer in the system.

[SM]

Hi Flow cat wont quieten the exhaust that much, the decat silencer will.

[xR33]

Hey Amin. You can borrow my Sports Cat to try it .

[james_200sx]

Refitted my sports cat and it has made the exhaust much quiter. I bought mine off apex and it is not one of the high flow cats. It may flow slighty better then std.

[xR33]

Refitted my sports cat and it has made the exhaust much quiter. I bought mine off apex and it is not one of the high flow cats. It may flow slighty better then std.

I was under the impression that all Sports Cats were by definition 'high flow', and that the differences were between the cell density and wether they used a metalic or ceramic cell.

[ex-ctr]

I was under the impression that all Sports Cats were by definition 'high flow', and that the differences were between the cell density and wether they used a metalic or ceramic cell.

ceramic cats are really not worth using with our cars as there to fragile

[MikeyB]

I got the sports cat off Apex too, it's definatly high flow, as the piping is around twice the size of the stock pipe!
I had the same issue with the droning noise at motorway speeds, and as the MOT was nearing, thought I'd kill two birds with one stone and splash out on the cat.

Was worth it, I'm now fully legal, the noise is reduced a little on the motorways, and performance hasnt taken much of a hit either.

Take the sports cat option, if you want peace of legal mind, and save the hassle of taking it on and off every now and then.

[ameano]

Cheers for the input guys, still undecided though!
Hi Glynn, may very well take you up on that offer
MikeyB - you're saying the noise is reduced "a little" on the motorways?

So from the comments it seems that a decat silencer silences a lot better than a high flow cat?

[alexthegreat]

Good question. I've had a ebay dual exhaust for a few months. The noise has been not too bad. Until this weekend when fitted a apex elbow and downpipe. It feels as though its breathing a lot better but oh does it make more noise.

I was going to replace the standard cat with a highflow one but now I'm leaning more towards the silancer. Anyone have any experience?

Also can anyone recommend a quiet cat back exhaust? If I can't lower the noise then I might just replace the exhaust.

[ameano]

A good free flowing exhaust appears to be the HKS silent hi power, I've seen it on mates car, it has a bit of presence but not loud at all.

So if I understand this correctly, a high flow cat does only what it's supposed to do, i.e. it doesn't really act as a silencer?

And for mot legalness one should consider the cat and for superior silencing the decat silencer right?

Also does anyone know if engine management chips can work properly with a high flow cat?

[xR33]

I was running my Sports Cat with the DV blocked and it is still in one piece, so running it with a chip isn't going to cause any problems . When you want to collect it Amin? Also, does anyone know if the S14 and S13 cats are likely to be the same lenght? If so, I may be able to lend you the silencer from my car also .

[ameano]

Hi mate thanks for the offer, is there much point to putting on a sports cat though if its not really going to silence the car by much though?

Think I'm going to go ahead with decat silencer and come mot time I'll think of a way of sorting it out

[MikeyB]

ameano, with the Sports cat, I did notice a reduction in noise, but having never used a de-cat silencer, I cant comment on which is best, but its a fair assumption that the silencer is going to do a better job than the cat would.

I was going to get a silencer originally, but my hand was forced to the sports cat when the MOT came around, I cant be having the hassle of it failing and then having to buy a cat anyway. (And my MOT man is a little fussy, but the work they do there and prices are top notch)

I have the original DP & cat rusted (read welded) together but otherwise in working order if you wanted them for anything?

[ameano]

Thanks MikeyB - I still have the original cat, which I will be keeping for mot tests if necessary... I dont mind the changeover as its only about a 10-20 min job, gaskets cost money though!

[Drifter]

ameano, with the Sports cat, I did notice a reduction in noise, but having never used a de-cat silencer, I cant comment on which is best, but its a fair assumption that the silencer is going to do a better job than the cat would.

I went from a standard cat to a decat silencer. The exhaust loudness was similar, but the silencer made it alot deaper

[CamInHead]

I wonder if you could fit a little exhaust silencer where the cat should be and just tell the MOT peep it's a cat ? Not as if the tester can take it off and check.

[ameano]

I went from a standard cat to a decat silencer. The exhaust loudness was similar, but the silencer made it alot deaper

Funny you mention that as I recall my friend with the HKS silent hi power and decat silencer also mentioned about the deepness, so are you happy with the result of a decat silencer?

I wonder if you could fit a little exhaust silencer where the cat should be and just tell the MOT peep it's a cat ? Not as if the tester can take it off and check.

No he can't but he will be checking for exhaust emissions using an mot standard gas analyser so no way to fake that really.

[Drifter]

Funny you mention that as I recall my friend with the HKS silent hi power and decat silencer also mentioned about the deepness, so are you happy with the result of a decat silencer?

More than happy, dB's are well under 100 anyway

Certainly better than putting the bung in that came with the GT Spec. I tried it once, then promptly removed it a threw it in the hedge

[Mr G]

When peeps talk about decat silencers are you talking about a pipe that has little holes in the inside tube with baffles around it or are you talking about a hollow tube that has been "blown up" (if you know what I mean...)