All Things Mk5 > Performance Modifications
Pre Cat removal
the bruce:
--- Quote from: zerolag on January 14, 2013, 04:49:50 pm ---Out of interest, is your car mapped?
--- End quote ---
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.
--- Quote from: Timvgti on January 14, 2013, 04:50:23 pm ---Wow? That's something totally different compared to other reviews?! Others are 100% positive. Dyno's give around 5bhp extra, etc etc...
--- End quote ---
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 :smiley:
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:
--- Quote from: the bruce on January 14, 2013, 05:11:20 pm ---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).
--- End quote ---
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:
--- Quote from: GrayMK5GTI on January 14, 2013, 06:58:25 pm ---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?
--- End quote ---
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.
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