All Things Mk5 > Performance Modifications

Pre Cat removal

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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.


--- Quote --- 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.
--- End quote ---

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


--- Quote --- 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.
--- End quote ---



--- Quote ---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.
--- End quote ---


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, :happy2:

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.  :happy2:

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