[Davidlindsey]

is it not worth just knocking out the o.e downpipe cats, you would get most of the gain of after market d.p's, it will pass an m.o.t because you still have the main cat and even with a full visual inspection you wouldn't be able to tell.

they should fit properly too....rflmao.

[ashmostro]

I think most people don't do this bc it's a dirty pain in the ass to do it. And you don't want to breathe in those particles as you knock them out.

SHould be essentially the same flow as DPs. I've seen someone on here cut the cat in half and weld in a straight pipe to eliminate the possibility of turbulence in the "expansion chamber" that you end up with.

Also, I've heard the ports on the factory pipes are a bit smaller and "stepped" compared to aftermarket DPs. FWIW.

[Davidlindsey]

so basically if you can be bothered its not a bad plan, its easy knocking a cat out , wear a good dust mask no problemo.....its just taking them off then thats a pain.

[ashmostro]

Post pics!

[windymissile]

The standard dp's are quite restrictive due to the narrower diameter compared to vsrf/ ap items.
Have you seen the price of oem dp's.?! If you have no intention of ever refitting them, then swap them for cattless aftermarket ones and sell the oem to cover the costs. Just had my vsrf installed and it has made a huge difference.
WM

[old grey steve]

Originally Posted by windymissile

The standard dp's are quite restrictive due to the narrower diameter compared to vsrf/ ap items.
Have you seen the price of oem dp's.?! If you have no intention of ever refitting them, then swap them for cattless aftermarket ones and sell the oem to cover the costs. Just had my vsrf installed and it has made a huge difference.
WM

Second the above comment made by windymissile, I've had my VRSF's installed for about 2 weeks, pick up is better, makes a nice sound too, only downside was a small amount of resonance when turning left which turned out to be a small amount of chaffing on one of the heatshields which was easily sorted. The only other issue you may encounter from time to time is the odd EML blip, mines always returned as 29F4 & 29F5 for cat conversion, which can be cleared but is or will be on be standard map an annoyance.

Remapping will allow this issue to be dealt with but the other thing I've noticed which hadn't crossed my mind or has been mentioned is a slight benefit in fuel economy proving the de-restriction qualities of removing the restrictive cats

[doughboy]

Originally Posted by Davidlindsey

is it not worth just knocking out the o.e downpipe cats, you would get most of the gain of after market d.p's, it will pass an m.o.t because you still have the main cat and even with a full visual inspection you wouldn't be able to tell.

they should fit properly too....rflmao.

OE down pipes are narrow and turbulent with the ribbed flex sections.

You will still pass an MOT with DPs on as the MOT guy will see the bigger secondary CATs and all is well.

If it passes the emissions (which it will) the MOT guy won't give a hoot.

I told my MOT man that the DPs were catted, he can't see to check, he said they must be catted or else the emissions warnings would be on

[Mitch.]

Originally Posted by doughboy

OE down pipes are narrow and turbulent with the ribbed flex sections.

You will still pass an MOT with DPs on as the MOT guy will see the bigger secondary CATs and all is well.

If it passes the emissions (which it will) the MOT guy won't give a hoot.

I told my MOT man that the DPs were catted, he can't see to check, he said they must be catted or else the emissions warnings would be on

If going through a MOT with de-catted downpipes and a JB4, does the JB4 need to be put on map 0 (pass through) to pass emissions test?

Are there any other things to do, to get through MOT with downpipes and JB4?

[doughboy]

No, if you put the JB4 on Map 0 then the emissions warning will come on due to the primary CATs missing which is not good.

The auto code clear doesn't work in map 0 so leave it on any Map you like as long as its not 0.

MOT test in the UK does not involve them plugging anything into the OBD port.

Best when the exhaust is warm (hot) give it a good thrash on the way to a time booked or while-u-wait MOT, avoid leaving it all day to go cold.


Before your MOT is due, visit some small local MOT garages, go and talk to the mechanic, tell him the car is mapped (quite legal) and ask him if they can just run the emissions test for a tenner / few pints.

This will a) help find a good garage and b) check your car is OK before the MOT runs out.

[windymissile]

Originally Posted by Mitch.

If going through a MOT with de-catted downpipes and a JB4, does the JB4 need to be put on map 0 (pass through) to pass emissions test?

Are there any other things to do, to get through MOT with downpipes and JB4?

No. Just make sure its up to running temp before going on the gas tester.
Just to put the official word in here.
"Any removal of standard emissions control equipment will result in a fail"
This is regardless of the outcome of the gas test.
You would have to be really unlucky to have a tester that wants to search for your front cats! If he does, you need to be in another garage.

WM

[doughboy]

I told them my DPs had CATs in them, he doesn't know, and that is perfectly legal.

It quite legal to fit aftermarket replacement parts as long as they have the same function. The car passing the emissions test would prove the 'emissions control equipment' was all working.

If your CATs failed you don't have to re-fit BMW CATs, any will do.

Forcing you to fit BMW parts would be against all sense and EU regs.

[windymissile]

Originally Posted by doughboy

No, if you put the JB4 on Map 0 then the emissions warning will come on due to the primary CATs missing which is not good.

The auto code clear doesn't work in map 0 so leave it on any Map you like as long as its not 0.
.

A very good point.
WM

[Davidlindsey]

what are the "real" gains from de cat d.p's ?........10 bhp maybe and better cooling ?

[doughboy]

More like 30bhp with a map JB4.

Lots more torque, less lag, less stress on turbo system....

and they sound great

Not sure about cooling, but at a given boost pressure the exhaust and turbine will run cooler due to lower gas overall pressures

[windymissile]

Yeah. Maybe 20bhp top end. But its the spool up lower down where you will feel it the most. Its like the powerband is widened and brought in earlier. It's a must have mod in my opinion.
WM

[phil200tdi]

Dp's are a base requirement for more boost. They alone may net you 20-30hp with the correct tuning.

But if you take things further by running Meth or even Bigger turbos, they become more of a necessity.

I wouldnt recommend going over 14psi with stock DPs.