Pre Cat removal

[zerolag]

To be realistic any improvements are going to be slight.  That said, I've found:

NOISE
I've noticed a deeper exhaust note, but not overly so.
I can hear the turbo more than before.

POWER/TORQUE
I think there is a slight improvement in the top end; the revs climb more freely than before, and I feel the turbo spins up a bit quicker; perhaps a little more torque in there also.

FUEL CONSUMPTION
Slightly worse when WOT'ing it... this leads me to believe that it's producing slightly more power.
Slightly better when cruising.

Overall, don't expect miracles, improvements are slight.
Cold starts: Fine (-3*C yesterday)
Downsides:  Can't think of any

[GrayMK5GTI]

Completely agree with the above ^^

Mine made about 5bhp extra on the dyno 

[the bruce]

So you've never seen the engine management light? Also no with these winter-temps?
So no downsides for this mod?
Have you also noticed a better fuel consumption?
What's the most noticeable? -> The quicker/better gas response? The sound? The fuel consumption? The bhp?

Never experienced any warning light and all my friends also didn't.  

On the orther hand I think pre cat removal is extremely overrated. I didn't feel any advantages.
Noticable engine response? No, don't get fooled by self-fulfilling believe. More power? Not what
you can ''feel' at all.
Yes, sound changes. It sounds more 'rough'. Personally it sounds louder, but less attractive, at
least with a stock pipe, not what I call a beautiful sound.
What's most noticable: When cold the car stinks. When I start in the morning and leave the car
to close my garage door it's stinking like an old car.

No question, on a new car I never would do this mod again.  

[zerolag]

So you've never seen the engine management light? Also no with these winter-temps?
So no downsides for this mod?
Have you also noticed a better fuel consumption?
What's the most noticeable? -> The quicker/better gas response? The sound? The fuel consumption? The bhp?

Never experienced any warning light and all my friends also didn't.  

On the orther hand I think pre cat removal is extremely overrated. I didn't feel any advantages.
Noticable engine response? No, don't get fooled by self-fulfilling believe. More power? Not what
you can ''feel' at all.
Yes, sound changes. It sounds more 'rough'. Personally it sounds louder, but less attractive, at
least with a stock pipe, not what I call a beautiful sound.
What's most noticable: When cold the car stinks. When I start in the morning and leave the car
to close my garage door it's stinking like an old car.

No question, on a new car I never would do this mod again.  

Out of interest, is your car mapped?

[Timvgti]

So you've never seen the engine management light? Also no with these winter-temps?
So no downsides for this mod?
Have you also noticed a better fuel consumption?
What's the most noticeable? -> The quicker/better gas response? The sound? The fuel consumption? The bhp?

Never experienced any warning light and all my friends also didn't.  

On the orther hand I think pre cat removal is extremely overrated. I didn't feel any advantages.
Noticable engine response? No, don't get fooled by self-fulfilling believe. More power? Not what
you can ''feel' at all.
Yes, sound changes. It sounds more 'rough'. Personally it sounds louder, but less attractive, at
least with a stock pipe, not what I call a beautiful sound.
What's most noticable: When cold the car stinks. When I start in the morning and leave the car
to close my garage door it's stinking like an old car.

No question, on a new car I never would do this mod again.  

Wow? That's something totally different compared to other reviews?! Others are 100% positive. Dyno's give around 5bhp extra, etc etc...

[the bruce]

Out of interest, is your car mapped?

Good point. No, it's not. On a remapped ED30 pre cat removal may be a different thing.
On a K03 GTI I guess not. Keep in mind the Cupra R, Mk.VI Golf R, Audi S3 and TT-S also
have the same pre cat and they are reliable with ~ 270 BHP.

Wow? That's something totally different compared to other reviews?! Others are 100% positive. Dyno's give around 5bhp extra, etc etc...

Yes, I know. For many years now I read the positive reviews on the web and these made
me to remove the pre cat. To be honest I think it's neccessary to tell the whole story.

I don't doubt the 5 bhp increase on the dyno. But you won't feel this difference when
sitting in the car. So there are some very slight performance advantages. On the other
hand there are some downsides which I don't like: one hour of labour, a stinking car and
(to my ears) a less beautiful sound (slightly more drone).

[GrayMK5GTI]

Turbo spool is noticeably improved, reduced EGT's are also a benefit. The pre-cat is seriously restrictive so I'm surprised you can't notice a difference. The gains are especially noticeable on a remapped car

You get a little more "spooling" noise from the turbo too. Fantastic mod that you can do at home. 5bhp is 5bhp, it's not going to be a huge kick in the back when you accelerate so im not sure if you were expecting more feel when you did it?

I got no drone whatsoever, no horrible smell (the cat takes the nasty smells out) - Milltek downpipes etc don't have a pre-cat and I've not heard anyone else mention a change in smell from them?

Its basically a great bang for buck mod  

[zerolag]

imho, I think the K03's are in need of a pre-cat delete more than a K04.

For the K03 to run anywhere near 270bhp, it's going to need stage2/2+ software and a full TBE which doesn't have the pre-cat, as the K04 doesn't need to run as high a boost level to produce the 270bhp it can cope easily with the pre-cat -- less boost, less heat, lower EGT's, less need for pre-cat removal.

[Janner_Sy]

I don't doubt the 5 bhp increase on the dyno. But you won't feel this difference when
sitting in the car. So there are some very slight performance advantages. On the other
hand there are some downsides which I don't like: one hour of labour, a stinking car and
(to my ears) a less beautiful sound (slightly more drone).

I agree the 5hp isnt a huge amount and isnt going to create a massive improvement on the bum dyno, however with the precat in place at stage 1 levels of tune it can cause the EGTs to rise which leans the map will richen the AFR to cool it down hence lose power.  I'll try and see if i can find my old logs which showed this.  Kind of the same effect as heatsoak with the standard intercooler, except EGTs are alot more important to keep within limits.

If your going stage 2 then its probably a waste of time to do, however if your going to stay stage 1 at the most then i think its a great little mod that will aid longevity.

[the bruce]

I got no drone whatsoever, no horrible smell (the cat takes the nasty smells out) - Milltek downpipes etc don't have a pre-cat and I've not heard anyone else mention a change in smell from them?

Metallic cats do have much less mass than the stock ceramic one, that's why
metallic cats do heat up much quicker.
Nonetheless from what I know Milltek do also make a street legal DP with two
cats like many other makers do. This is the only way to run a Euro 4/5 car fully
street legal - at least what most exhaust makers claim.

BTW, the coming Mk.VII GTI will have only ONE cat, which is close to the turbo.

[Janner_Sy]

BTW, the coming Mk.VII GTI will have only ONE cat, which is close to the turbo.

Thats exactly what it is like on the 1.4TSI.  The cat is within a few inches of the turbo.

[Timvgti]

Ok, so besides 'the bruce' I only read positive experiences with the precat removed.
In my situation I have a stage 1 (Abt) mk5 gti, with stock exhaust except the middle resonator (I replaced it with a Simons sport resonator and sound is excellent!) and I have no plans for stage 2.
Guess the removed precat will be a good and noticeable mod for me?!

[Janner_Sy]

Guess the removed precat will be a good and noticeable mod for me?!

I would say so.  I see no downside to it.

Less back pressure, lower exhaust gas temperatures, more longevity, free of charge, small power gain, quicker spool

[Dan.b]

Ok, so besides 'the bruce' I only read positive experiences with the precat removed.
In my situation I have a stage 1 (Abt) mk5 gti, with stock exhaust except the middle resonator (I replaced it with a Simons sport resonator and sound is excellent!) and I have no plans for stage 2.
Guess the removed precat will be a good and noticeable mod for me?!

What's the deal with a Simons sport resonator?

[zerolag]

BTW, the coming Mk.VII GTI will have only ONE cat, which is close to the turbo.

Thats exactly what it is like on the 1.4TSI.  The cat is within a few inches of the turbo.

Cost cutting measure then?