Decat original manifold
Discussion
Hey guys
Does anyone have a clip (or have you done) of a standard y piece with the cat removed?
I'm going to do mine this weekend, I'm leaving the precats in the manifolds but then rip out the main cat. Hopefully it won't sound as much like a tractor as ones i've heard with all the cats removed. I've got cherry bomb type silencers in the centre section already
Does anyone have a clip (or have you done) of a standard y piece with the cat removed?
I'm going to do mine this weekend, I'm leaving the precats in the manifolds but then rip out the main cat. Hopefully it won't sound as much like a tractor as ones i've heard with all the cats removed. I've got cherry bomb type silencers in the centre section already
Certainly removing the pre-cats will do you a huge favour in lowering under bonnet temperatures and raise the volume a little.
Are we safe in assuming you have a back-up Y piece for your MOT?
I've not heard of anyone passing a 'real' MOT without the main cat in place.
There is this thread on the subject; Advantages of main cat removal
Are we safe in assuming you have a back-up Y piece for your MOT?
I've not heard of anyone passing a 'real' MOT without the main cat in place.
There is this thread on the subject; Advantages of main cat removal
brett84 said:
Hey guys
Does anyone have a clip (or have you done) of a standard y piece with the cat removed?
I'm going to do mine this weekend, I'm leaving the precats in the manifolds but then rip out the main cat. Hopefully it won't sound as much like a tractor as ones i've heard with all the cats removed. I've got cherry bomb type silencers in the centre section already
Pre cats out ,standard Y piece and sports exhaust is the best combination . You can weld a cone inside the standard Y piece which stops that horrible tiny sound .Does anyone have a clip (or have you done) of a standard y piece with the cat removed?
I'm going to do mine this weekend, I'm leaving the precats in the manifolds but then rip out the main cat. Hopefully it won't sound as much like a tractor as ones i've heard with all the cats removed. I've got cherry bomb type silencers in the centre section already
For others reading this, my understanding is that the main cat is required for an MOT pass, not the precats.
It seems that if you remove precats, main cat and silencer box, the car will be VERY LOUD. Ie over 120 decibels.
Two out of three removed is more bearable.
I know that all the cats out, leave the main silencer in, gives you around 104-105 decibels.
All left in is about 95-97 decibels.
All measured using the standard method used at track days, ie at half a metre and 45 degrees up and out form the tail pipe.
Daz, do you know the noise level if you do as you suggest, taking the precats and silencer out, but leave the main cat in?
It seems that if you remove precats, main cat and silencer box, the car will be VERY LOUD. Ie over 120 decibels.
Two out of three removed is more bearable.
I know that all the cats out, leave the main silencer in, gives you around 104-105 decibels.
All left in is about 95-97 decibels.
All measured using the standard method used at track days, ie at half a metre and 45 degrees up and out form the tail pipe.
Daz, do you know the noise level if you do as you suggest, taking the precats and silencer out, but leave the main cat in?
QBee said:
For others reading this, my understanding is that the main cat is required for an MOT pass, not the precats.
It seems that if you remove precats, main cat and silencer box, the car will be VERY LOUD. Ie over 120 decibels.
Two out of three removed is more bearable.
I know that all the cats out, leave the main silencer in, gives you around 104-105 decibels.
All left in is about 95-97 decibels.
All measured using the standard method used at track days, ie at half a metre and 45 degrees up and out form the tail pipe.
Daz, do you know the noise level if you do as you suggest, taking the precats and silencer out, but leave the main cat in?
Agree with the above.It seems that if you remove precats, main cat and silencer box, the car will be VERY LOUD. Ie over 120 decibels.
Two out of three removed is more bearable.
I know that all the cats out, leave the main silencer in, gives you around 104-105 decibels.
All left in is about 95-97 decibels.
All measured using the standard method used at track days, ie at half a metre and 45 degrees up and out form the tail pipe.
Daz, do you know the noise level if you do as you suggest, taking the precats and silencer out, but leave the main cat in?
No idea about the actual noise level when "taking the precats and silencer out, but leave the main cat in", but I can tell you it is both lovely and bearable.
Just remove the pre-cats, no performance gain but will help a tiny bit with engine temp. The main cat removed fromt he OEM 'dustbin' sounds bloody terrible, more like a tractor than a performance car. Theres nice loud and theres horrid loud - your proposed mod falls into the latter IMHO. If you must go de-cat then change the Y-piece to ACTs narrower item.
I've only heard them with all the cats removed though and I agree they don't sound great, bit too agricultural for me.
Thats why I was thinking that leaving the precats in would give some silencing (along with the cherry bombs), but then removing the main cats would give the biggest performance gain? (doing it at the same time as Megasquirt, new intake, injectors etc etc)
I'm taking the manifolds off to blast them and paint, so I might just try it, if I don't like the sound then i'll have to take the plunge and get one of the ACT manifolds with the bolt pattern.
Thats why I was thinking that leaving the precats in would give some silencing (along with the cherry bombs), but then removing the main cats would give the biggest performance gain? (doing it at the same time as Megasquirt, new intake, injectors etc etc)
I'm taking the manifolds off to blast them and paint, so I might just try it, if I don't like the sound then i'll have to take the plunge and get one of the ACT manifolds with the bolt pattern.
As others (and the OP) have said; removing the main cat is likely to sound terrible.
I recently followed a full decat + sleeved exhaust Chimaera for a few miles, no offence intended to the owner and he admitted the same, but it was horrible at lower revs. Very tractor like, and then utterly deafening at 3000+rpms.
It seems that it is the massive reverberation in the empty main cat dust bin that is a culprit.
In the other post I referenced Clive says "to start with removing precats will give on average an extra 5-10bhp, with decrease in under bonnet temperatures, then removing the main cat will give another 10bhp minimum, and again further decrease in under bonnet temps."
Doing a very simplistic calculation;
Remove precats +5 hp
Then remove main cat +10hp
+- 5 hp, and IMO it's safe to assume I think that; as Clive is suggesting that a further 10+ comes from removing the main cat after the precats are removed, then it is unlikely to achieve the same level of increase with the precats left in.
That logically ends up with a +5 OR a +10 in your example of leaving one or the other in.
And as beautiful music is a substantial part of your intended goal, I think precats out, main cat in, unless you can acquire an equivalent to the Clive 'Y' piece.
I recently followed a full decat + sleeved exhaust Chimaera for a few miles, no offence intended to the owner and he admitted the same, but it was horrible at lower revs. Very tractor like, and then utterly deafening at 3000+rpms.
It seems that it is the massive reverberation in the empty main cat dust bin that is a culprit.
In the other post I referenced Clive says "to start with removing precats will give on average an extra 5-10bhp, with decrease in under bonnet temperatures, then removing the main cat will give another 10bhp minimum, and again further decrease in under bonnet temps."
Doing a very simplistic calculation;
Remove precats +5 hp
Then remove main cat +10hp
+- 5 hp, and IMO it's safe to assume I think that; as Clive is suggesting that a further 10+ comes from removing the main cat after the precats are removed, then it is unlikely to achieve the same level of increase with the precats left in.
That logically ends up with a +5 OR a +10 in your example of leaving one or the other in.
And as beautiful music is a substantial part of your intended goal, I think precats out, main cat in, unless you can acquire an equivalent to the Clive 'Y' piece.
if you want to hear a chim 400 at full chat with standard exhaust, clive y piece and pre-cats still in then go here
http://www.youtube.com/watch?v=X-MCerRS_QE
fast forward to 1:20
http://www.youtube.com/watch?v=X-MCerRS_QE
fast forward to 1:20
Phazed run a stock main cat section on the green 4.6 car but gutted out with a bit of thermal wrap and a stock exhaust and that sounded as sweet as the same exhaust with a pukka de-cat pipe 
what does sound bloody awful is a full decat and sleeved silencer the noise makes me wince 
all noise no action 
what does sound bloody awful is a full decat and sleeved silencer the noise makes me wince all noise no action Thanks all
Hmmm, I might just bite the bullet and get one of the ACT 8 bolt Y pieces, I've not heard anything bad about these and they do look amazing.
I suppose it's all personal preference as well, it's just a bit late once it's been hacked about to change my mind. But then again, i don't suppose an old 8 bolt manifold is actually worth much if anything at all? I suppose i could try it and see, if it sounds like a tractor then i'll have to give ACT a call.
Hmmm, I might just bite the bullet and get one of the ACT 8 bolt Y pieces, I've not heard anything bad about these and they do look amazing.
I suppose it's all personal preference as well, it's just a bit late once it's been hacked about to change my mind. But then again, i don't suppose an old 8 bolt manifold is actually worth much if anything at all? I suppose i could try it and see, if it sounds like a tractor then i'll have to give ACT a call.
It won't sound like a tractor with the Pre cats removed. Just a little louder and more intentional. Do that first.
If you then want to try more, get an ACT Y piece and swap it in. Nothing lost, as there's bound to be someone who will buy it off you if you don't like it, in which case you can swap your original Y piece back in. It will just sound a bit louder again and a bit more intentional/brutal. not like a tractor. The tractor sound can come from removing the cat from the standard Y piece.
If you want a lot louder, then remove the silencing from the exhaust pipes.
Doing it one stage at a time lets you decide when to stop.
PS, what year is your car? Is there any chance it has no cats anyway?
If you then want to try more, get an ACT Y piece and swap it in. Nothing lost, as there's bound to be someone who will buy it off you if you don't like it, in which case you can swap your original Y piece back in. It will just sound a bit louder again and a bit more intentional/brutal. not like a tractor. The tractor sound can come from removing the cat from the standard Y piece.
If you want a lot louder, then remove the silencing from the exhaust pipes.
Doing it one stage at a time lets you decide when to stop.
PS, what year is your car? Is there any chance it has no cats anyway?
brett84 said:
It's a 1993, everything is wrapped at the minute, been like it since I got it.
Any way to tell from the outside?
No way to tell without looking inside. 1/8/92 was C-Day, after which all petrol cars first registered here had to have catalytic converters. So K reg onwards. However, yours may already have been partly or totally decatted.Any way to tell from the outside?
The Y piece is, I think, bigger if there is a cat inside? Can someone please confirm?
The precats you can see/feel if you take the Y piece off and lookup the manifold. Grey honeycomb.
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