Hi

I was just wondering whether a standard cat bypass on a cat back exhaust system is street legal as it seem to me to be a grey area. Also most 'street'suppliers have a tendancy of selling you back boxes etc. that don't conform as legal on the road??

P.S Cheers for your comments an advice

If you drive a diesel, you don't need a cat as the MOT only measures particulates and not emissions.

Chris

Yes you better off getting a custom exhaust made with just 1 stright pipe(Or as straight as it can be)

I brought a Miltek with race cat for my Ibiza PD and ended up chopping it off and fitting a £70 piece of pipe

So, no cats are needed at all? cool never knew that! guess what i'm going to be looking into lol lol lol

So, no cats are needed at all? cool never knew that! guess what i'm going to be looking into lol lol lol

Be very careful if your mapped and have the standard turbo.

Pm me for details

I run quite a bit of power. My exhaust is made up simply of a custom big bore downpipe and a 2.25" bore stainless pipe right out the back. Cost me very little compared to "branded" exhausts, and is ultra-efficient.

PM sent lol

so enlarging the bore will help NOT to do any damage?

No, thats not how it works.

If you decrease the back pressure (As the exhaust creates it, widening it removing the cat will reduce the resistance) then you are giving the turbo a little bit less to work against meaning it can spin up quicker and easier. Decrease it too much and the turbo goes outside it's tolerances and fails early (There are several ways in which this can happen and none of them are good).

Jason runs a larger turbo and a custom map meaning his system is setup to make the most of that exaust. Just bolting a 2 1/2" pipe onto the manifold is not going to have the effect you think you will get on a car with standard turbo etc. You will need to work within the tolerances of the turbo and get it mapped accordingly.

Removing the cat will give you a reasonable amount of pressure relief and will aid the turbo to spin up quicker and there could even be modest power gains if mapped accordingly, the great bit about this is it can be done with little expense. It does however still carry a small risk of the above mentioned issues.