Hello if recently brought a mk1 octavia vrs 1.8t, it's had stage1 map a few pipes, dumpvalve and power flow backbox, the map was done on a rolling road so it's set up for everything on it, so I brought the car and the rear mount had gone on the engine and this caused the flexy on the exhaust to split near the turbo so I went and had a 3inch straight pipe fitted and custom made as I was going to boost the car a little, since this exhaust has been fitted the car won't go over 4k when revving and when driving it will half boost to 4k then Lagg its way past it, it almost feels like I'm tapping the break as I'm driving, any ideas? Maybe new map to set up the new exhaust? I have no idea I'm lost

If you’ve had a custom dyno and since changed the hardware, it’s recommend you go back and have it redone to match. Having a 3”straight through is a little much in my opinion. 
 

Is it a decat or do you have a sportscat installed?
 

Also, are you actually running a ‘dump valve’? As these are not designed for our engines, and you should be running a ’Diverter Valve’.

 

Take it back to your mapper and let him work his magic.

Yeah it's 3inch straight through no cat, and I'm sure it's a dump valve it's sat at the back right side corner connected to the 3 pipes, il contact the mapper see what he says, thank you

18 minutes ago, mk1vrs2005 said:

Yeah it's 3inch straight through no cat, and I'm sure it's a dump valve it's sat at the back right side corner connected to the 3 pipes, il contact the mapper see what he says, thank you

If he knows his stuff, he’ll advise somewhat similar to what I’ve said. As my advise is gathered from here over the years and my own remapping.

 

Also, don’t get caught by the plod as they’d have a field day with no back box or cat.

as above, you need a diverter valve not a dump valve. forge 007p(iirc) with the right spring seems to work very well. 

 

and it would need reconfiguring of the map, its going to be looking for exhaust pressure readings that arent there with a straight through exhaust. (and hope you dont sniffed out or heard by your local LEA... )

Lool all these comments about the decat your going to make me a nervous wreck ahah and honestly it might be a diverter valve, if never messed with dumpvalves or anything I just guessed it was

3 hours ago, mk1vrs2005 said:

Lool all these comments about the decat your going to make me a nervous wreck

The likelihood of passing an MOT with a decat is very low, and removing the cat on a car certified to need one (which a Mk1 Octavia is) then using it on the road is AFAIK a moving traffic offence which is why plod would be 'interested'.

 

We're not trying to make you a nervous wreck, just making sure you understand the legal niceties of deleting the cat on a road car.

Edited 18 May, 20233 yr by PetrolDave

I think I'm going to opt for a sports cat il calk the garage Monday 

1 hour ago, mk1vrs2005 said:

I think I'm going to opt for a sports cat il calk the garage Monday 

That would be wise.

We're here to help and not offer daft advice as seen on Facebook.

 

1 hour ago, PetrolDave said:

The likelihood of passing an MOT with a decat is very low, and removing the cat on a car certified to need one (which a Mk1 Octavia is) then using it on the road is AFAIK a moving traffic offence which is why plod would be 'interested'.

And, as Dave said they'd use the 'Construction & Use" act, would cover any car that left the factory, alterations then make it illegal. i.e. removing a back box which is there from the factory. Of course, there is common sense and not all officers are out to get you. But, if you happen to come across a joint operation of Police/DVLA, and they find something like a decat, they prohibit the car from the road, and you'd require a new MOT.

GCM on Youtube did a great series covering a lot of this with a Police officer.

 

Edited 18 May, 20233 yr by DeanVRS20VT

It's like any modification on a car then really ain't it, like a induction kit, uprated turbos, intercooler ect

21 minutes ago, mk1vrs2005 said:

It's like any modification on a car then really ain't it, like a induction kit, uprated turbos, intercooler ect

No, some mods don't affect certification but others like removing the cat do.

1 hour ago, mk1vrs2005 said:

It's like any modification on a car then really ain't it, like a induction kit, uprated turbos, intercooler ect

As above, those are covered by insurance and don't come up MOT regulations, where the others do.

It's not really clear unless you delve into the Act and laws of all this, and it gets all too confusing.

But, I hope we've helped.