nope. none at all. if you have a map on your car you might want it tweaked to suit the new afr or at the very least disable the engine warning light. but in real terms, wont make a blind bit of difference (in a negative way that is).

 

Less back pressure can affect the turbo oil seals

 

I was always under the impression that a turbo engine wants as little (ideally none) back pressure as possible? Only N/A cars want some form of back pressure.

No?

Oh and the long term effects are being likely to be caught with a car that isn't road worthy or insured...

 

I was always under the impression that a turbo engine wants as little (ideally none) back pressure as possible? Only N/A cars want some form of back pressure.

No?

Oh and the long term effects are being likely to be caught with a car that isn't road worthy or insured...

You don't want any back pressure at all. The problem comes from going to a exhaust pipe that is to big and then the gas losses velocity.

Also the only downside to a de-cat is thats its illegal.

 

agreed with drifitingforlife. You really dont want any backpressure - not in the way "internet mechanics" believe. Another one of those misnomers. You want good flow and matched exhaust manifolds where "backpressure" kinda works. Its pretty technical what an engine really wants, and its all to do with valve design, shadowing, areas, etc etc thats just a little much to write on a quick post.

suffice to say with a turbo car, you want a good size pipe leaving the engine. As is, the exhaust cross sectional area on the mk7 is probably a little small for when it is mapped, but stock its fine. a de-cat wont have any effect on turbo seals (that really has absolutly nothing to do with turbo seals!) or have any detrimental effects whatsoever.

A good point is that it is non-MOT-able so is technically illegal.

 

the cross sectional area of the standard cat is actually very good, the same size as the standard cat on a Mk2 Focus ST225 5 cylinder, 3" entry, 2.5" exit, no need for a decat or sportscat a level 2, only when you up the turbo size, take a look at the mishimoto sportcat/de-cat development blog and also the attached dyno overlay of a decat vs standard cat on a level 2 car.

Courtesy of Collins Performance

 

generally most modern cats are actually not all that restrictive. Will have a good read over that blog post!

 

agreed with drifitingforlife. You really dont want any backpressure - not in the way "internet mechanics" believe. Another one of those misnomers. You want good flow and matched exhaust manifolds where "backpressure" kinda works. Its pretty technical what an engine really wants, and its all to do with valve design, shadowing, areas, etc etc thats just a little much to write on a quick post.

At last, people who know about the rubbish spouted about 'back pressure'

I can't helped reacting when I hear people going on about back pressure, it's completely misunderstood and the size of the piping is more to do with maintaining gas velocity.

A narrower pipe can aid faster flow and help certain engines whereas a wider bore would slow the gases and hinder the flow, but this is misunderstood by people as increasing 'back pressure'.

Like you say, it's a big topic to go into here, but worth people looking into to properly understand what the exhaust is actually trying to do.

 

Don't waste your money on a de-cat - simple