[GRSmotorsport]

Just interested to know how many of you guys are running De-cat pipes on the road

[Bhozar]

At the moment, I am.

I blew a bit of a hole in my cat, and crushed some of the cells.

I'm looking at getting a new manifold and cat at some point.

Some reports have shown that without a cat you loose performance.

[batou]

1320 Paul said from what they'd seen the decat loses power!

[BigShow300]

I think it lost 2bhp on mine, it defo didn't gain.

[MINIMANIAUK]

A cat must form a restriction to flow ,by virtue of it having a cross sectional area and being in the pipe!! probably a low restriction 1-2 psi drop but a restriction - they will also absorb some heat ,cooling very slightly the pipe/air temps after the cat .
This will release 2 or 3 bhp if removed -PROVIDED that the cat shape and size canister remains-sustituting a straight pipe in place will alter the airflow/pulses in the whole system and hence could actually lose a couple of bhp ,
The cat does however break up sound waves and cars are very loud with out the cat.
Any rich running cars or overfuelling or slow starting that allows fuel down the manifold and into the cat will ruin the cat quick smart , this could lead to a MOT fail and manifolds/cats are not cheap.
The "green" issue is not that clear ,as usual , it is overlooked that the cats themselves contain undesireable metals
A bit like the leaded/ unleaded fuel thing where for years we were told the lead is killing our kids- then we stop using leaded -and presto ......its now thought it was lead in paint that was the problem and it uses more oil to produce unleaded against leaded

[slider]

Quote: Originally Posted by MINIMANIAUK (original)

A cat must form a restriction to flow ,by virtue of it having a cross sectional area and being in the pipe!! probably a low restriction 1-2 psi drop but a restriction - they will also absorb some heat ,cooling very slightly the pipe/air temps after the cat .
This will release 2 or 3 bhp if removed -PROVIDED that the cat shape and size canister remains-sustituting a straight pipe in place will alter the airflow/pulses in the whole system and hence could actually lose a couple of bhp ,
The cat does however break up sound waves and cars are very loud with out the cat.
Any rich running cars or overfuelling or slow starting that allows fuel down the manifold and into the cat will ruin the cat quick smart , this could lead to a MOT fail and manifolds/cats are not cheap.
The "green" issue is not that clear ,as usual , it is overlooked that the cats themselves contain undesireable metals
A bit like the leaded/ unleaded fuel thing where for years we were told the lead is killing our kids- then we stop using leaded -and presto ......its now thought it was lead in paint that was the problem and it uses more oil to produce unleaded against leaded

i have the mini maina manifold fitted along with the de-cat, i have never fitted the sports cat as it sounds so good. i plan on fitting the cat when the next mot is due. Oh & boy does it pop & crackle !!!!

[Lucky Dave]

Mine runs better with the cat in.

[MINIMANIAUK]

"Mine runs better with the cat in."


This is very likely ,the cat has to be substituted with an expansion chamber of similar dimensions.
The position of the cat is important also ,they should be a multiple of the distance of the primary pipe length or the same as preferably , this is far more critical in a 4-2-1 manifold than the 4-1 .
But even the 4-1 is likely to lose power with a straight replacement pipe .
The 4-1 manifolds have longer primary pipes and the cat should be as far back as those ,but the position of the cat sensor wires is fixed which limits this and the the cat cannot go too far back as it has to get up to temp quickly to operate correctly
Even with compromises aftermarket manifolds are still better than stock

[slider]

Quote: Originally Posted by MINIMANIAUK (original)

"Mine runs better with the cat in."


This is very likely ,the cat has to be substituted with an expansion chamber of similar dimensions.
The position of the cat is important also ,they should be a multiple of the distance of the primary pipe length or the same as preferably , this is far more critical in a 4-2-1 manifold than the 4-1 .
But even the 4-1 is likely to lose power with a straight replacement pipe .
The 4-1 manifolds have longer primary pipes and the cat should be as far back as those ,but the position of the cat sensor wires is fixed which limits this and the the cat cannot go too far back as it has to get up to temp quickly to operate correctly
Even with compromises aftermarket manifolds are still better than stock

do you belive that your manifold with your de-cat pipe runs better that your manifold with your high flow cat.
I ask because i have one of your manifolds with the de-cat in place at the moment..

[MINIMANIAUK]

the gain is very little 1-2bhp , but it allows the cat to be replaced easily and refitted easily ,prolonging the cat life ---the noise however increased !!!
How is the torque on your car post manifold?

[slider]

Quote: Originally Posted by MINIMANIAUK (original)

the gain is very little 1-2bhp , but it allows the cat to be replaced easily and refitted easily ,prolonging the cat life ---the noise however increased !!!
How is the torque on your car post manifold?

the torque is much improved , the noise is not extreme untill you get high up the rev range.
What is the typical bhp increase you have seen with your manifold as i have not had it dyno'ed yet. Also if i decide to fit the cat & it fails how much is a replacement cat from yourself.

[MINIMANIAUK]

Torque and bhp increase between 10-14% , a replacement cat is £99