CAT Join Modification

[Blue Mez]

I have noticed that many people on here have had the cat modified to fit a 2.5inch bore aftermarket exhaust.

My question is; does the modification actually do anything at all? I just cant see it doing much to help the airflow, but please correct me if im wrong.


I'm having a straight through section fitted on saturday as the baffles have gone in the resonator (MILLTEK), and if it will benefit me, i'll have the modification done at the same time, but it'll obviously cost extra.


Cheers,
Mez

 

[Blue Mez]

Hello?

 

[Fred@BTM]

its not going to set the world on fire

 

[Blue Mez]

Lol but would you say it's worth it? Bearing in mind the extra cost, plus messing around if I ever sell on?

 

[Fred@BTM]

no

 

[Blue Mez]

Ok mate, just always wondered why people do it if there's no difference

 

[Fred@BTM]

one person did it and said it was good, half of CS followed, same thing with turini's

i'm going to give BTM £10 and tell everyone its a great idea, see if everyone follows

 

[jack_kemp]

one person did it and said it was good, half of CS followed, same thing with turini's

i'm going to give BTM £10 and tell everyone its a great idea, see if everyone follows

Lol.

The trusty old bandwagon.

 

[franx]

matching inlets , this was a good bandwagon to jump on

 

[Gray]

i'm going to give BTM £10 and tell everyone its a great idea, see if everyone follows

WOW... Does this work for the Megane's aswell? what are the expected gains?!!!!?!?!

 

[Blue Mez]

one person did it and said it was good, half of CS followed, same thing with turini's

i'm going to give BTM £10 and tell everyone its a great idea, see if everyone follows

what exactly was good though?

 

[vecbtb]

Mark Fish swears by it, BTB do it a lot. It removes the restriction on the outlet (from 2 inch to 2.5inch roughly). It isn't going do do any harm that's for sure, but whether it's worth the money is between your wallet and you!

 

[Fred@BTM]

there's an argument for having that "so called restriction" in place as without getting too technical it can actually help the gas flow, its been a while since i did my enginering milarky but if my memory serves me correctly and you're really bored this may be relevant (i maybe talking complete crap also, sleeping in lectures FTW! )

http://en.wikipedia.org/wiki/Bernoulli's_principle

 

[aucky]

http://en.wikipedia.org/wiki/Bernoulli's_principle

I <3 Fluid dynamics

 

[DaveW_cup]

Is this to make a stock cat fit a "slide" in 2.5" bore system?

If so how do you go about it?
The reducer sleeve with flange for my KTEC System sucks.

 

[vecbtb]

Is this to make a stock cat fit a "slide" in 2.5" bore system?

If so how do you go about it?
The reducer sleeve with flange for my KTEC System sucks.

We're mainly talking about the 182 and the bore difference between either side of it's sports cat.

A couple of pictures from BTB to illustrate...

BTB replace the normal join with a tightly clamping joint which is a bonus.

 

[Fred@BTM]

I <3 Fluid dynamics

its all spanish to me, hence why i slept through those lectures LOL!

 

[Blue Mez]

there's an argument for having that "so called restriction" in place as without getting too technical it can actually help the gas flow, its been a while since i did my enginering milarky but if my memory serves me correctly and you're really bored this may be relevant (i maybe talking complete crap also, sleeping in lectures FTW! )

http://en.wikipedia.org/wiki/Bernoulli's_principle

Ok, so my head actually hurts pretty bad now after reading Bernoulli's_principle. It seems to refer alot more to liquid, i know it mentions gas flow but only once or twice, so im assuming the principle stands the same for both liquid flow and gas flow?

Can anyone who understands the context of Bernoulli's_principle, care to put it in english please?

 

[Fred@BTM]

in simple terms, leave it LOL

its all to do with velocitys, venturis yada yada

its a road car, at the end of the day you won't change the earth's orbit

 

[Kam.]

basically the diameter of the pipe changes the velocity of the gas/liquid flowing through it.
applying it to the exhaust, a thinner pipe usually helps low down power as gas speed is kept high, but if the engine produces more than will flow easily then you create a bottleneck at high rpm.
A bigger bore may loose torque at low revs but be more optimised for high revs. (thats why the decat pushes the power band higher as flow is improved)
but then theres plenty of curve balls along the way so its usually easier to just test a few sizes out and see what happens on the rolling road

 

[Fred@BTM]

^but with this "restriction" it can actually help increase the flow by increasing the gas velocity after the "restriction" ie in other words this pipe reduction helps cause the gas to be "sucked" out the cat

pulse tuning yada yada, its all complicated stuff

 

[Meek_racing]

Just put a decat in

Doesn't the centre section box also have something to do with the gas flow and back pressure? So having a straight through complicate the matter further? I'm no car tech so will go back to my sewing...

 

[vecbtb]

Just put a decat in

Doesn't the centre section box also have something to do with the gas flow and back pressure? So having a straight through complicate the matter further? I'm no car tech so will go back to my sewing...

... and there begins another story as the de-cat changes the velocity of exhaust gases as well!

 

[vecbtb]

My head hurts. I'm going to try and work out something easy, like the universe.

 

[ash_s3]

Mine's booked in a week on saturday at BTB for the 182 cat modification.

Will be reporting back with the results!

 

[Dean.]

^but with this "restriction" it can actually help increase the flow by increasing the gas velocity after the "restriction" ie in other words this pipe reduction helps cause the gas to be "sucked" out the cat

pulse tuning yada yada, its all complicated stuff

what about decats then as most of them dont have the 'restriction'?

 

[Blue Mez]

in simple terms, leave it LOL

its all to do with velocitys, venturis yada yada

its a road car, at the end of the day you won't change the earth's orbit

basically the diameter of the pipe changes the velocity of the gas/liquid flowing through it.
applying it to the exhaust, a thinner pipe usually helps low down power as gas speed is kept high, but if the engine produces more than will flow easily then you create a bottleneck at high rpm.
A bigger bore may loose torque at low revs but be more optimised for high revs. (thats why the decat pushes the power band higher as flow is improved)
but then theres plenty of curve balls along the way so its usually easier to just test a few sizes out and see what happens on the rolling road

^but with this "restriction" it can actually help increase the flow by increasing the gas velocity after the "restriction" ie in other words this pipe reduction helps cause the gas to be "sucked" out the cat

pulse tuning yada yada, its all complicated stuff

Not only have you two confirmed my doubts as to whether it increases performance at all, but explained it could actualy be benificial to keep the bottle neck there.

Cheers Lads.

Just put a decat in

Doesn't the centre section box also have something to do with the gas flow and back pressure? So having a straight through complicate the matter further? I'm no car tech so will go back to my sewing...

The Cat creates back pressure not the resonator, I know some cars rely on back pressure. Not sure if the clio is one of them.

My head hurts. I'm going to try and work out something easy, like the universe.

My head hurts more, I'm going to try and work out something easy, like women.

 

[Fred@BTM]

what about decats then as most of them dont have the 'restriction'?

ours does!