High performance manifold with stock cat?

[sam_a156]

Hi,

I am playing with the idea of trying the stock cat with my GTT manifold. I seem to remember that at least Paul had tried something similar with good results. There were also tons of posts about OBX mani + OEM cat at NAM.

Does anybody have comments on this, especially differences in terms of performance and sound? I presume there might be some hp/tq losses at the top end?

Especially with a rear seat delete the high performance mani+cat combo even with my (modded) JCW catback starts to be a bit on the loud side. So, this would be mostly to please my occasional passengers (less questions about my "exhaust being broken" ).

Summing up: I am looking for a little bit more subtle "sleeper" soundtrack, but would not like to sacrifice my hard earned power.

Cheers,
Sam

[GTT 280]

Urgh... if people started complaining about ANYTHING on my car, they'd be out the door doing a stunt roll !!!

Using a 600 cell CAT with a GTT manifold defeats the purpose to a large extent.

Cheers,
K.

[sam_a156]

That's what I thought as well...until I saw this:

MINI COOPER :: North American Motoring - OBX-Racing Header Dyno Results!

Surprising...and there seems to be a load of folks driving this combo in the US.

Edit:

Oh, and Paul's achievements with Janspeed mani + stock cat (here) were not too shabby either. As he stated there, even Roland made his famous 273hp with a OEM manifold with a pre-cat removed.

So, it seems indeed that the stock cat is not so restrictive in highly tuned applications.

[Ant FR]

one of the good ones have seen is the quicksilver one, it uses 400 cell cat but its twice the size of say the milltek one. My mate has it on his and it certainly sounds very different to mine thats for sure.

Thats why i stuck to the Milltek downpipe and exhaust combie as when i drive it normaly its not too loud, only when i go above 3-4000rpm does it go stupidly loud. i love it to bits

[Loui]

Quote: Originally Posted by sam_a156 (original)

That's what I thought as well...until I saw this:

MINI COOPER :: North American Motoring - OBX-Racing Header Dyno Results!

Surprising...and there seems to be a load of folks driving this combo in the US.

Edit:

Oh, and Paul's achievements with Janspeed mani + stock cat (here) were not too shabby either. As he stated there, even Roland made his famous 273hp with a OEM manifold with a pre-cat removed.

So, it seems indeed that the stock cat is not so restrictive in highly tuned applications.

Yeah Paul gained with a stock cat over a aftermarket one with an aftermarket manifold. I was going to have one made but with buying a house im a little skint

[Paul@1320]

With the std engine in 06 we made 185bhp without and 306bhp with nitrous with a stock ex manifold and one ball.

Don't forget Rolands stock manifold with the pre cat removed made 273 240 ft lb at 6-6300, whether this was a limitation of the manifold at this point and power was dropping I'.m ensure he will enlighten us.

We still have loads off testing to do with different combos, its just time and money

[sam_a156]

Quote: Originally Posted by Ant FR (original)

one of the good ones have seen is the quicksilver one, it uses 400 cell cat but its twice the size of say the milltek one. My mate has it on his and it certainly sounds very different to mine thats for sure.

Thats why i stuck to the Milltek downpipe and exhaust combie as when i drive it normaly its not too loud, only when i go above 3-4000rpm does it go stupidly loud. i love it to bits

Does "different" translate into "not so loud"? Do you know if this Quicksilver cat would fit as is the GTT mani?

Another question is: has anybody ever measured a difference between different cats (i.e. keeping the other exhaust bits unchanged)?

I do like the sound of the GTT + JCW combo normally...and it is still civilized at say 4000rpms or 150-160km/h (more than enough in most countries)...

...but I just did a 2000+km round trip on the German highways with long bits of the journey @ 180-200km/h (or @ 5000+ rpms). Something that sounds sporty and inspiring along the country roads can start to get a bit tiring after 9hrs. I am seriously thinking of taking noise canceling Bose headphones with me for the next trip

[GTT 280]

does anybody knowif the de-cat pipe is illegalon the road because of 1) noise, or 11) emissions? If it is quiet and does not generate emissions then can it be used?

Cheers,
K.

[Jaw_F430]

Quote: Originally Posted by GTT 270 (original)

does anybody knowif the de-cat pipe is illegalon the road because of 1) noise, or 11) emissions? If it is quiet and does not generate emissions then can it be used?

Cheers,
K.

I would say that the emissions is the problem hence not passing the MOT with decat


Regards

James

[Hyper Active]

Quote: Originally Posted by GTT 270 (original)

Does anybody know if the de-cat pipe is illegal on the road because of 1) noise, or 11) emissions?. If it is quiet and does not generate emissions then can it be used?

Cheers,
K.

You only need a Cat on to pass the emissions part of an MOT. You can then have a de-cat pipe put on to replace the cat, and run it until the next MOT quite legally. As the old motorsport saying goes, "the rules will bend before they break ".

It will be slightly louder, but not by too much though. But i haven't seen anything on here that proves you will gain any HP by removing the Cat .

[black20vt]

Not true.

If stopped and tested at the side of the road by the police you will be fined
http://www.roads.dtlr.gov.uk/consult...ons2001/07.htm

"It is an absolute offence under Section 42 of the Road Traffic Act 1988 to use (or cause or permit to be used) a vehicle on a road if it does not comply with the relevant provisions of the Road Vehicles (Construction and Use) Regulations 1986, as amended. The offence does not depend upon guilty knowledge and therefore it is not possible to mount a defence on the basis that a vehicle user did not know that the vehicle was in contravention of the Regulations at the time they were using it on a road."

"You (as named on the Notice itself) have been issued with the Notice because you were the user of the vehicle specified on the Notice when it was found, during a roadside enforcement check carried out by an Authorised Person, to exceed the maximum emission levels as laid down in Regulation 61 of the Road Vehicles (Construction and Use) Regulations 1986, as amended."

however...

"The Regulations permit the Fixed Penalty Notice to be waived completely in cases where you can show that the vehicle had passed an MOT emissions check within the preceding six months and the emissions performance of the vehicle is corrected within 14 days. To confirm this you must present both MOT test certificates (one dated before, but no more than six months before, the date of the offence; the other after, but no more than 14 days after) to the address shown on the Fixed Penalty Notice."

[MINI-Morgan]

I was thinking about this one today when I was refitting my stock manifold and I think I might have come up with an answer to it. As we all know if you put a high flow manifold and cat on a Cooper or One then you will loose power and torque. But no one ever expects it on the MCS since they automatically think forced induction so the exhaust can be as free flowing as possible. But like the Cooper it can still benefit from back pressure in the manifold. But how? Well this is where Daves theory comes in so feel free to comment and tell me how much ******** it is.

Take an MCS with a 17% pulley and a free flowing decat manifold. Inlet pressure should be around 18psi and the exhaust manifold at maybe 3psi.
Then take an MCS with a 17% pulley and a stock more restrictive dual cats. Inlet pressure may peak at 19psi and the exhaust at 5-6psi.
Now my thinking is as the cylinder still contains pressurised exhaust gases it causes the inlet pressure to go up slightly and so raises the effective compression ratio of the engine. So more torque and so more HP as the revs come up and pressure increases.

Total theory but hey it could just be right.... !