Tuning baby cat bung, any good?

[Red Rocket CINQ]

On my seicento mpi I plan on fitting my 4 branch Mani with my stainless steel exhaust and need to know if any one has used a baby cat bung to avoid any eml or wrapping it up in foil like I done last time. This is the item

http://www.ebay.co.uk/itm/Top-Gear-...arts_Vehicles_CarParts_SM&hash=item484fcae6b8

Any help would be great. Thanks

 

[fingers99]

Daft idea, I think. Reasons:

1. You must run a Euro 4 car with a cat. Without you'll fail MOT, and if you get a VOSPA pull you'll probably have the car impounded. Oh, the joy!

2. It's easy enough to fit a cat. An SPI one is the obvious choice, a Rover V6 one should give better flow (and they're absurdly cheap). Use the lamda boss on the mani for the pre cat lambda, weld a second boss on after the cat for the post cat one. Extend the harness to the lambda connector if necessary, rather than the lambda harness itself.

Strictly speaking, this is a bit naughty (wrong type of cat), but you should get away with it.

 

[Red Rocket CINQ]

I know its not correct to run your car without a cat but you don't get the nice exhaust sounds with one. If it sounded the same i wouldn't think twice about keeping one on there.

 

[dave]

Get a spun sports cat and it will sound the same

 

[Red Rocket CINQ]

Different structure inside are they? How would it sound the same though, surely it would baffle the sound.

 

[dave]

hardly any restriction compared with a standard cat

a spun cat also has smooth walls to aid flow

 

[Red Rocket CINQ]

Anywhere supply them over here? On eBay they all seem to be from America. Thanks for the info aswell

 

[dave]

these guys on ebay http://www.ebay.co.uk/itm/2-5-63mm-...-Universal-High-Flow-Sports-Cat-/180970780952
the small one dont look so good though, they have a 3" that looks better

or where i got the pic http://www.classiccustomfabrications.co.uk/exhausts.htm

 

[Red Rocket CINQ]

OK, thanks for all the info guys.

 

[J.R Racing]

Failing that fit a straight decat pipe from four branch to centre section and swap the standard manifold back in every year for the MOT!

Amazing sound. Wrap second (post cat) lambda sensor in tin foil, cable tie out the way and connect pre cat sensor into manifold.

Not necessarily legal or politically correct but it works and sounds fantastic.

 

[fingers99]

hardly any restriction compared with a standard cat

a spun cat also has smooth walls to aid flow

It's an old, old idea -- detailed in at least one of the A Graham Bell books. Spinning is just the method of manufacture, most gains will be from the entry and exit angle of the exhaust. You could do much the same by hydroforming the can or simply welding up cones, much as folk were doing on 2 stroke exhausts in the 70s. (Did I say it was an old idea?)

The flow itself is, after all, through the core.

For the noise thing, being a little deaf (and with mild tinnititus) after doing marshalling without earplugs, standing too close to too many old Ducatis and angle grinders over the years, I can't say the sound of a slow reving 4 cylinder engine does much for me.

A Coventry Climax or an unsilenced 6 cylinder Maserati (through the streets of Bologna, FCS!) is something else.

Don't expect dramatic gains, powerwise or noisewise.

 

[dave]

if you used hydroforming you would have to cut it open to get the insides in

 

[fingers99]

You'll loose bugger all from the weld (even if you MIG it) And those ripples from the spinning must loose just as much if not more.

Essentially -- and the pressures involved in spinning stainless probably call for substantial tooling (can't imagine you can do it with just a big lathe, like folk do for annealede copper or aluminium) -- it's an easier, cheaper way of acheiving the same ends.

 

[dave]

welds always cause a week spot in stainless that rust

 

[fingers99]

Use the correct grade of stainless and rod and it's not going to rust. Ever. After all, it's what the innards of a nuclear power station (or a high test peroxide powered submarine) are made of.

Hydroforming also raises the possibility of doing it in titanium -- just try spinning that!

 

[dave]

the op isnt making he is buying, so grade of steel will be what ever it is, not a lot of choice with pre made exhaust parts

 

[ycming]

It's an old, old idea -- detailed in at least one of the A Graham Bell books. Spinning is just the method of manufacture, most gains will be from the entry and exit angle of the exhaust. You could do much the same by hydroforming the can or simply welding up cones, much as folk were doing on 2 stroke exhausts in the 70s. (Did I say it was an old idea?)

The flow itself is, after all, through the core.

For the noise thing, being a little deaf (and with mild tinnititus) after doing marshalling without earplugs, standing too close to too many old Ducatis and angle grinders over the years, I can't say the sound of a slow reving 4 cylinder engine does much for me.

A Coventry Climax or an unsilenced 6 cylinder Maserati (through the streets of Bologna, FCS!) is something else.

Don't expect dramatic gains, powerwise or noisewise.

"slow reving 4 cylinder engine does much for me. " - VTEC mate.

 

[fingers99]

the op isnt making he is buying, so grade of steel will be what ever it is, not a lot of choice with pre made exhaust parts

Sure. So I don't get the point -- either the material will be some sort of 304 rubbish or worse (easy and cheapo to manufacture) or something decent. If it's rubbish it'll start rusting and etc. as soon as it sees some salt and cat heat, regardless of whether it's welded or not.

Generally rust on SS exhausts is due to "specialist exhaust manufacturers" using mild steel wire to join otherwise adequate grades of stainless together. They should be lynched.

 

[fingers99]

"slow reving 4 cylinder engine does much for me. " - VTEC mate.

Ah, you've not lived yet................

 

[ycming]

Ah, you've not lived yet................

That's cause you not been VTEC yet.

Ming