Why Have A LargeBore Pownpipe and De-Cat?

[GTI-Ross]

Hey guys,

My knowledge on exhaust systems is limited, up until now ive only had middle section and back box done on my other cars, now having a GTI....

Can someone explain why having the DP and Pre-Cat added / removed makes such a difference and where on the list of mods it should come. ie

1.)Remap
2.) .........
3.)Intake
4.) suspension & Brakes................etc

Any help would be great. Mainly to do with the DP and Pre-Cat

Thanks Guys

[Baz300]

If you are planning on a remap and exhaust and intake you would be best to get the exhaust and intake done first then get the car mapped to make full use of the added hard wear, rather then get a map now and have to get another map once fitted

It's totally up to you whether to do the performance mods or handling and breaking mods

But if you get the handling and braking sorted first then you can make better use of the extra power later on

[Nodz]

I wouldn't go decat as the car wont pass an MOT on the emissions test.

Basically depending in the down pipe depends on how restricted the flow of gasses are. On the standard exhaust it is a smaller diameter, has a cat and a pre cat so the flow gets restricted. Then on after market you get decat, 100cel or 200cel sport cats. I think the 100cel is an MOT failure but te 200 is fine.

If you want to change the DP you will be looking at a turbo back exhaust but if you don't you'll be looking at a cat back exhaust

[Baz300]

Sports cat is a better option

I have a decat fitted but I'm hoping to get a sports cat system in the next few weeks from a member on here

[MC71]

I'd get the map first and enjoy it for a while then add an intake and TBE, then get a stage 2 map put on. I really wouldn't bother with a decat, it's a personal choice but for me it's about "fit and forget so a 200 cel sports cat is the way to go IMHO.

As for suspension and brakes, as and when you can although a BBK will be needed with all those extra ponies!

 

[GTI-Ross]

Sports cat is a better option

I have a decat fitted but I'm hoping to get a sports cat system in the next few weeks from a member on here

Yeah so thats what im really trying to find out, how much difference does a Sports cat (200 Cell) make compared to standard.

And (if im Correct) Cat-back is just for sound improvement and a turbo back is for performance, what kind of gains would you expect with a remap and intake?

Thanks

[four!]

By having an exhaust system which flows better you can run more ignition advance.

There are lots of other things which come in to it but basically more ignition advance will usually mean more power.



Depending on how close the mapper has pushed it, running on a map properly adjusted for de-cat and then sticking the cat back on could potentially cause problems.

Your tuner will be able to advise you further  

[MC71]

have you done a "Search" on here? Covered to death this.

As you say, a Cat back is for sound and TBE for performance. I take it you have a standard GTI with a K03 Turbo with 197bhp? Stage 1 alone, you might expect to see around 230bhp, with a Cat back and intake you may see around 250bhp (ish) and with a full TBE and you may then need a HPFP (high pressure fuel pump) and a bigger intercooler you may get about  280bhp.

 

[RedRobin]

have you done a "Search" on here? Covered to death this.

As you say, a Cat back is for sound and TBE for performance. I take it you have a standard GTI with a K03 Turbo with 197bhp? Stage 1 alone, you might expect to see around 230bhp, with a Cat back and intake you may see around 250bhp (ish) and with a full TBE and you may then need a HPFP (high pressure fuel pump) and a bigger intercooler you may get about  280bhp.

 

....I'm advised by JKM that you don't need a bigger intercooler unless you go to Stage 2+. I doubt if you'll see 250 bhp (on a K03) with a Cat-back and not a Turbo-back exhaust.

[Shabba168]

have you done a "Search" on here? Covered to death this.

As you say, a Cat back is for sound and TBE for performance. I take it you have a standard GTI with a K03 Turbo with 197bhp? Stage 1 alone, you might expect to see around 230bhp, with a Cat back and intake you may see around 250bhp (ish) and with a full TBE and you may then need a HPFP (high pressure fuel pump) and a bigger intercooler you may get about  280bhp.

 

....I'm advised by JKM that you don't need a bigger intercooler unless you go to Stage 2+. I doubt if you'll see 250 bhp (on a K03) with a Cat-back and not a Turbo-back exhaust.

I only have cat back at the moment
With 265 on JKM rollers

[RedRobin]

have you done a "Search" on here? Covered to death this.

As you say, a Cat back is for sound and TBE for performance. I take it you have a standard GTI with a K03 Turbo with 197bhp? Stage 1 alone, you might expect to see around 230bhp, with a Cat back and intake you may see around 250bhp (ish) and with a full TBE and you may then need a HPFP (high pressure fuel pump) and a bigger intercooler you may get about  280bhp.

 

....I'm advised by JKM that you don't need a bigger intercooler unless you go to Stage 2+. I doubt if you'll see 250 bhp (on a K03) with a Cat-back and not a Turbo-back exhaust.

I only have cat back at the moment
With 265 on JKM rollers

....Then I'm either wrong  or you have your Revo settings somewhat max'd up. So, you have OEM fuel pump internals and OEM air intake? - If so, I am surprised. Your 265 on JKM rollers was the same day as mine too.

[Powervalve Nige]

Large bore downpipe and 100 cell motor sport cat (Make sure manufacturer guarantees it's MOT friendly  ) - make sure the cat is 125mm dia for maximum benefits (essentially = to a de cat in terms of surface area when calculating flow velocity. Turbo pressure decreases improving life expectancy especially when re mapped and spool up time improves (when stock oem system in place). Believe it or not energy is required to drive gasses through the exhaust system so the implementation of the 76mm down pipe reduces the kinetic energy lost in this process - where is this transferred to (law of the conservation of energy) - the crank - where do we feel it ? in our neck (Torque increase )...simplulls
Cheers
Nige

[GrayMK5GTI]

have you done a "Search" on here? Covered to death this.

As you say, a Cat back is for sound and TBE for performance. I take it you have a standard GTI with a K03 Turbo with 197bhp? Stage 1 alone, you might expect to see around 230bhp, with a Cat back and intake you may see around 250bhp (ish) and with a full TBE and you may then need a HPFP (high pressure fuel pump) and a bigger intercooler you may get about  280bhp.

 

....I'm advised by JKM that you don't need a bigger intercooler unless you go to Stage 2+. I doubt if you'll see 250 bhp (on a K03) with a Cat-back and not a Turbo-back exhaust.

I only have cat back at the moment
With 265 on JKM rollers

....Then I'm either wrong  or you have your Revo settings somewhat max'd up. So, you have OEM fuel pump internals and OEM air intake? - If so, I am surprised. Your 265 on JKM rollers was the same day as mine too.

Surely Shabba's is an edition 30??? 

[RedRobin]

Surely Shabba's is an edition 30??? 

....No, I know him personally (he PDI'd my car way back in 2005) and his GTI is a K03 car. 

[GrayMK5GTI]

Surely Shabba's is an edition 30??? 

....No, I know him personally (he PDI'd my car way back in 2005) and his GTI is a K03 car. 

265bhp on a k03 without a downpipe is witchcraft  a decent intake and HPFP must be fitted though?