Exhaust Opinions - ACT

[NuddyRap]

Six silencers, so far as I'm concerned, is a few too many. Six too many, to be precise .

That's what's on my Cerb at the moment, the ACT quiet system and although it's undeniably still a loud car it's quite sociable at ~motorway speeds and standing behind it I can still have a conversation easily. The first point I'm not too bothered about, and an inability to converse easily near it certainly has its advantages.

I do concede however that some silencing may be necessary in order to continue to meet the terms of my ongoing existence .

I have ordered the unsilenced decat pipes to replace my silenced decats, which will help a little. What I want in a nutshell is:
- More volume
- Distinctive edge
- As many pops, bangs and crackles as these things are capable of.

The real question is as follows, and I hope some of you have experience that I can benefit from since I can't really justify spending the money required for big bore + manifolds given that my existing exhaust works perfectly. Just to satisfy my inner hooligan I think that combination is a bit much, so it's one or the other:
- ACT performance equal length manifolds and remove some of the silencing from my present system (Tails are easiest according to Tim at ACT). I gather that the performance increase is debatable.
or
- Big bore from decats back, unsilenced (Maybe with silencer tails?).

Does anyone have some experience of either? If the equal length manifolds significantly increase the exhaust pulse effect and generate substantially more pops, bangs and crackles, that might swing it for me.

Thanks all.

Edited by NuddyRap on Monday 11th July 13:35

[Byker28i]

do you have a db meter?
How much do your silenced decat pipes reduce the noise currently?
Is yours the 2.5" system?

I have the ACT manifolds, 2.5" quiet system, with straight through decat pipes. Loudest with pops and bangs is 116db, 88db at idle, 106db at 4500 revs.

Adding the standard cats makes the car 8-10db quieter. Mine pops bangs, and flames sometimes.

Pops and bangs depends on your mapping and restrictions in your exhaust.

Having a loud exhaust is very overrated. I took the cats out because of the heat generated in the gearbox/cabin.

[NuddyRap]

My system is the 2.5 system and from what you say, it sounds like you have pretty much the setup I mentioned, only you've retained the silencers and silencer tails whereas I was looking at getting shot of at least one of those.

My idle at last measurement was 79db, which is 9db quieter than yours, so about the same as the standard cats. My highest at 4500 rpm was 98db, so it seems there's a fairly uniform reduction in noise compared to yours of 8db or so with the silenced decats.

I currently do get pops, bangs and flames, but I'm keen to remove as many restrictions and make the system as free flowing as possible so that once the car is properly set up and has been to Joolz for its remap, I'll be able to make the most of it. Jools advised me that the bends and pipes upstream are the most important aspects with regards to improving performance (Hence the equal length ACT performance ones), but I also need an owner's perspective to establish whether they have anything to offer on the noise front.

So assuming you have the mega £ performance manifolds, did you notice an appreciable difference in the frequency of the bangs and flames? Or was whoever did your mapping really able to release a few more horses or bangs than would normally be expected compared to a standard car as a result of fitting them?

[Shanksy87]

My configuration gives a good level of noise, pop and bangs, but perfectly good for cruising long distance.

Standard manifolds, unsilenced ACT decats, ACT big bore cat back (4 silencers - any less would probably put you in headache territory)

[NuddyRap]

What does the big bore do for the engine note compared to the standard exhaust?

It's interesting that you both find many silencers preferable. Does anyone live happily with a totally unsilenced exhaust?

Do either of you, or does anybody else with an ACT exhaust live in or frequently bring their Cerb to the midlands and if so, would you be willing to spare a few minutes for a comparison?

[Byker28i]

NuddyRap said:

My system is the 2.5 system and from what you say, it sounds like you have pretty much the setup I mentioned, only you've retained the silencers and silencer tails whereas I was looking at getting shot of at least one of those.

My idle at last measurement was 79db, which is 9db quieter than yours, so about the same as the standard cats. My highest at 4500 rpm was 98db, so it seems there's a fairly uniform reduction in noise compared to yours of 8db or so with the silenced decats.

I currently do get pops, bangs and flames, but I'm keen to remove as many restrictions and make the system as free flowing as possible so that once the car is properly set up and has been to Joolz for its remap, I'll be able to make the most of it. Jools advised me that the bends and pipes upstream are the most important aspects with regards to improving performance (Hence the equal length ACT performance ones), but I also need an owner's perspective to establish whether they have anything to offer on the noise front.

So assuming you have the mega £ performance manifolds, did you notice an appreciable difference in the frequency of the bangs and flames? Or was whoever did your mapping really able to release a few more horses or bangs than would normally be expected compared to a standard car as a result of fitting them?

Joolz mapped mine plus some inlet work, but the standard exhaust manifold was cracked So I had the ACT manifolds fitted.

So post Joolz work but with a cracked manifold I got 361.8bhp. No other change other than act manifolds gave me 380.7bhp



My exhaust system is this - before it was fitted


with silenced tail pipes



With the cats in I get about the same figures as you as the cats knock 10db off, so interesting to hear the silenced decats do the same. With cats in and trackday exhausts on I once was able to do a thruxton trackday - 88db limit.

[Byker28i]

I like this setup compared to the original/SP system as it's a lot lighter and a huge amount of road clearance.

I had an SP system but had huge issues with it, poorly fitted, build quality and it didn't make the claimed noise levels, was 10db louder so didn't meet trackday limits. Only after some time was it discovered their claims were with cats fitted, not without as it was advertised and claimed.

Noise wise it was nice, quietening down after a few miles use, but the build quality of the batch was very poor, with a tailpipe not correctly attached, out of shape and it burnt and crazed my rear valence through banging/too close. It also only left me with 75mm road clearance at the rear.



The system I have now is quieter, lighter and fits better.

[Shanksy87]

I found the exhaust note very similar, maybe a little deeper but no significant change in volume etc.

I'm based in Coventry, a little busy this month, but drop me a PM anyhow.

[NuddyRap]

Byker28i said:

So post Joolz work but with a cracked manifold I got 361.8bhp. No other change other than act manifolds gave me 380.7bhp


My exhaust system is this - before it was fitted

with silenced tail pipes


With the cats in I get about the same figures as you as the cats knock 10db off, so interesting to hear the silenced decats do the same. With cats in and trackday exhausts on I once was able to do a thruxton trackday - 88db limit.

Wow, thanks for the greatly detailed posts!

True independent verification of getting ~20bhp extra. This gives me food for thought and I think a trip to Joolz is in order to understand the state of my car at the moment. It seems noise and bangs probably won't swing it, but the combination of those with a potential RR rebuild and a remap should amount to quite a difference in the car's character.

Your system looks to be the same as mine assuming it's the 2.5" (Looks identical) apart from the unsilenced decats and I agree about the clearance and fit being great. Some other cerbs I looked at with other exhausts really were dragging very close to the ground.

I've now ordered the unsilenced decats, so step one is complete .

[Byker28i]

Biggest thing with a Joolz remap,
look at the before and after

Before - my car always showed 343 ish bhp - this one wasn't rev'd enough on the run, but shows the torque curve:


So if you compare the two you'll spot the torque I now have at lower revs, 2K upwards, so much more it makes it a really lazy engine to drive about town. So easy to drive, yet goes like stink when you want.

For me that was the biggest thing from the remap, the pure driveability, instead of it being really lumpy below 3K revs.

[gruffalo]

I have the silenced decat pipes along with the ACT balanced headers and big bore pipes feeding into an ACT quiet back box.

I did have the full sports system but went quiet because I was struggling with getting on track days.

The quiet back box released around 5bhp over the full sports system and my car in its current state of tune is delivering just over 400bhp at the wheels. The sound is a lovely deep rasp as an AJP should be and 100db track days are a doddle to get on, no noise issues at all.

[NuddyRap]

Byker28i said:

Biggest thing with a Joolz remap,
look at the before and after

Before - my car always showed 343 ish bhp - this one wasn't rev'd enough on the run, but shows the torque curve:

So if you compare the two you'll spot the torque I now have at lower revs, 2K upwards, so much more it makes it a really lazy engine to drive about town. So easy to drive, yet goes like stink when you want.

For me that was the biggest thing from the remap, the pure driveability, instead of it being really lumpy below 3K revs.

Those new curves are a very appealing sight since, as quick as it is and as wildly as it spins the wheels when provoked, I've always found lower in the rev range to be (relatively flat) and it's not as happy in a high gear at low revs as I always imagined a car with this much power and such little weight should be.

I'm looking forward to seeing my before and after!

[Hawkeye1922]

I'm following this with interest, as my original back box has just become noisier (possibly only a few miles before something catastrophic happening, like a tailpipe falling out...)

I really don't want it to get any louder - I currently run straight through decat pipes with everything alse original. It seems to me, then, that I want the "ACT quiet back box" and to think about getting the ACT silenced de-cats. Better get the cheque book out...

[purpleliability]

I recently changed from the ACT sports tails to the ACT back box.

I had the 6 silencer version with decat silencers (so decat silencer, mid pipe silencer as shown on the pic above, sports tails with silenced tails). Even with the track cans bolted on, I couldn't meet Bedfords Autodrome 101dB limit. I also have ACT 4.5 manifolds.

I've since fitted the ACT back box with the rest of the system and it is much quieter. Still sounds aggressive under throttle but so much easier to live with on a cruise and day to day. Also should squeak under any normal track limits although this is yet to be tested.

[NuddyRap]

Interesting reading the differences in individual cars and owner experiences here. Seems that the ACT manifolds might be a tad louder than the standard ones, but overall the improvement is in performance.

Although my car is undeniably a loud car (I never need to use a doorbell), by the standards indicated in a couple of these posts it is, for some reason, perhaps my current fuelling map and idle speed, a tad quieter naturally than some other cerbs.

Having called ACT, apparently Ken (Previous owner) was keen to keep everything as quiet as possible, so I don't understand why he opted for silenced sports tails rather than the large ACT back box since that is apparently much quieter. Perhaps he was already quite deafened and therefore thought the reduction was enough.

I've not yet tested my car at a race circuit, but I was considering some of those really ugly trackday cans with the slide in plates to enable me to get the noise down. That and refitting the silenced decats the day before a track day - after bulk buying a load of exhaust gaskets.

[Byker28i]

NuddyRap said:

Having called ACT, apparently Ken (Previous owner) was keen to keep everything as quiet as possible, so I don't understand why he opted for silenced sports tails rather than the large ACT back box since that is apparently much quieter. Perhaps he was already quite deafened and therefore thought the reduction was enough.

Probably wasn't available at the time? If it's like the SP or original box exhaust then there's a weight difference and adds a little bulk at the rear, reducing road clearance, usually discovered over ramps, especially if using the car on a trip with luggage or with rear passengers.

I have some ACT trackday silencers that just slot into the tail pipes that cut the noise by around 8db. I think the silencer decats are the next thing for me to try.