Pre Cat removal

[markc]

Hi guys,

I've seen the pic on another post of one smashed out with a hammer, is it worth for doing for power gains, or driveability ?  Are there any possible negatives to this,......... MOT failiure, error lights/codes etc

[Janner_Sy]

this is a quote from my tuner with reference to me smashing out mine.

Removoin the pre-cat helps quite a bit, it significantly lowers the exhaust back pressure, so it helps to keep the EGT's at reasonable levels. My philosophy is safety first, I try to keep EGT's below 1000C and keep knock protection in stock levels.

and this is about the reason a precat is used and with future MOTs

Correct, pre-cat helps cold start emissions. A three-way catalytic converter found on the modern engines require a certain temperature before it actually becomes a catalyst. "pre-cat" as close to the combustion chamber as possible warms up quicker, which helps to burn unburnt hydrocarbons after start.

MOT emissions test isnt a problem after you remove the precat.

When a new car is type certificated, you're required to run an emissions cycle to prove the car is acceptable within EURO3/4/5 or whatever.

On this cycle, the car is run in a dyno with a "plastic bag" in the exhaust pipe. You run the car to a certain norm, and then open the bag and smell whats in there...

That test includes a cold start (which is actually the most important part on the test, because most of the "bags" fill up during this part), some city runs and accelerations to highway speeds.
From this test we get the data known as combined/city/highway mileage and the CO2 emissions. Thats why manufacturers try to cheat as much as possible on these tests. For example, regulations dont specify brakes on these tests other than brake calibers, discs and pads. Thats why some manufacturers use springs to keep pads off the discs during these tests. In the industry, this practice is called "cycle beating"  Also they use the smallest allowed wheels/tires on this test (for example, Volvo has specified smaller tires than you can actually buy)

So, thats why we have a pre-cat on these cars. The main cat is enough for MOT pass when its hot enough (normal operating temp). Two cats only help in post-start treatment.

im expecting to get a good increase from this, just by looking at the pictures of it, you can see that the exhaust gases leave te turbo and hit a wall of catalyst material straightaway.  if you remove that you speed up the flow of exhaust gases and you will defionately get gains, more so if you get a map tweak to utilise the extra flow

[markc]

Thanks Sy,

I take it there is no seal to be replaced or anything when fitting back together, just bolt back up ?

I am mapped yes, I cant adjust it though.  I will have to have a word with my tuner.

[Janner_Sy]

the exhaust it self doesnt get taken apart.  you just take it off the car hit the CAT material with a hammer so it shattersm make sure there are no bits left in the downpipe nd put it back on.  i think the ecu will adapt enough to make this worthwhile

[acespizee]

Get rid of that pre-cat. 

[Bogwoppit]

I removed my precat at the weekend on my (BWA) engine) Octavia vRS TFSI running the original map. The EPC light came on today, oh joy!!
Anybody else had this problem? I am getting the fault code read tomorrow.
If the fault code is caused by the precat removal can a remap remove this problem?

It could just be a coincidence but I doubt it.

[Bogwoppit]

I have now been running without a pre-cat for 2 weeks (on the standard map) and the car runs fine without any engine lights. The EPC light I mentioned above was for something else and was totally unrelated to the pre-cat removal.

It's difficult for me to say if I have noticed any difference in performance due to the pre-cat as I fitted a Neuspeed intake, SFS Intercooler hoses and a rev d diverter valve at the same time as removing the pre-cat.

The car definitely feels perkier and sounds better after carrying out those mods though 

[JMP]

Bringing up this old thread..  What tools did you use in clearing out the cat and did you have any issues in doing this? Did you replace the exhaust seal to turbo?

And has anyone else done this, any more experiences with the power gains and how the exhaust note changes? Im thinking about doing the same for my BWA golf as I want to keep the stock appearance.

[vRS_Pagey]

Since this original thread I am aware of a few members on Briskoda removing the pre-cat on their vRS's, mine will be coming out when the car is next serviced.  I have a couple of spare exhaust/turbo seals but tbh as they are metal they probably won't need replacing (they're only a few quid anyway), to remove the cat material you only need a hammer and chisel, the DP will need to be off the car to make sure you remove all the material, if you plan on doing it yourself this may help in the removal of the DP -

http://briskoda.net/forums/topic/124442-tfsi-downpipe-fitting-guide/page__p__1561519__fromsearch__1&#entry1561519

I was going to complete the job myself, but I figured for the minimal cost to pay my mechanic and the likely hood the bolts being seized I would prefer that he had the headache! 

Regarding power gains, I think reports show that the turbo spools significantly quicker which should convert to a few extra torques, apparently the exhaust note will deepen under accelaration but beyond that no real difference.

HTH, Lee.

[JMP]

Thanks for the info! I also found the other thread on this forum that had pictures of the smashed cat. Im going to be doing this myself and there are quite good DIYs available for this, heres one done on Golf: 

http://www.golfmkv.net/blog/archives/20#

[the bruce]

The advantages are well known. Worthwile mod for remapped engines.

The disadvantages:

- ''smell'' when engine is cold
- louder noise, (very little) drone
- one hour of work (+ risk of braking bolts)
- illegal


I placed the DP upside down to prevent dirt polluting the (main) cat.
Then I used hammer and chissel and at least a steel brush. 

TAKE CARE NOT TO DAMAGE THE OXYGEN SENSOR (or remove it) !!

I used new seal and nuts.

[Weston]

How would this compare to a full decat?

[JMP]

The advantages are well known. Worthwile mod for remapped engines.

The disadvantages:

- ''smell'' when engine is cold
- louder noise, (very little) drone
- one hour of work (+ risk of braking bolts)
- illegal

Has anyone actually broken bolts (or nuts) when taking the downpipe off? I picked up a couple of rust penetrating sprays yesterday to ease those.

[vRS_Pagey]

The advantages are well known. Worthwile mod for remapped engines.

The disadvantages:

- ''smell'' when engine is cold
- louder noise, (very little) drone
- one hour of work (+ risk of braking bolts)
- illegal

I placed the DP upside down to prevent dirt polluting the (main) cat.
Then I used hammer and chissel and at least a steel brush.  
TAKE CARE NOT TO DAMAGE THE OXYGEN SENSOR (or remove it) !!

I used new seal and nuts.

Is it?  Cold start emissions testing is not currently part of the UK MOT test......

@JMP - Also have a look here -  http://briskoda.net/forums/topic/197778-pre-cat-removed/

[Tfsi_Mike]

I have now been running without a pre-cat for 2 weeks (on the standard map) and the car runs fine without any engine lights. The EPC light I mentioned above was for something else and was totally unrelated to the pre-cat removal.

It's difficult for me to say if I have noticed any difference in performance due to the pre-cat as I fitted a Neuspeed intake, SFS Intercooler hoses and a rev d diverter valve at the same time as removing the pre-cat.

The car definitely feels perkier and sounds better after carrying out those mods though 

Made the mistake I do every time.  Want to feel the difference of a specific mod but do them in bulk every time as it's usually more cost effective

Would certainly imagine removing the pre cat played a part in the improvement felt.  Car's not ussually MOTd at cold start anyway