Alfa 147 Pre cats Modification

Has anyone cut open the pre cats on an alfa 147 and emptied them? Was just thinking it may be cheaper than buying a supersprint manifold and downpipe.

Cheers

I got rid of them, but I had custom manifold installed.

I don’t know how will empty pre-cats behave performance wise. I guess it is not a good idea as the gases will quickly expand too soon behind the engine = will cool down, get thicker and loose their speed. Just my guess.

What can I confirm from experience, getting rid of pre-cats will not cause any problems with lambdas or ECU. No error codes, and emission test is fine as well. Main cat can deal with it once it warms up. Emisions will be higher only till the engine is cold.

BTW: even though you drop the manifold, it will not be easy to break the cats internals out. When you put the 4-2 pipes down, you have just 2holes much narrower than cat interior and 2 small lambda holes..... You will have to cut them and weld back.... you can weld straight pipes in their places as well with the same effort....
http://kgb.alfaromeo-bg.com/gotcha/E...nifold/007.jpg
http://kgb.alfaromeo-bg.com/gotcha/E...nifold/008.jpg
http://kgb.alfaromeo-bg.com/gotcha/E...nifold/005.jpg
http://kgb.alfaromeo-bg.com/gotcha/E...nifold/004.jpg

I agree with gotcha. Your choices are:

1. Remove secondaries, cut away precat housings and replace them with plain curved pipes.
2. Replace whole exhaust manifold (both primaries and secondaries) with one from an early 156 2.0TS Euro II. You'll need some work to be done to the exhaust midsection because the 156 manifold is longer but the gain will be significant. And while you're at it fit a 200cpsi metallic main cat.
3. Same as 2 with a good aftermarket manifold like SS or a custom-made one. More expensive but (slightly) more effective I believe.

In solutions #1 nd #2 you will have to make inserts for the lambda sensors on the secondaries at approximately the same spot they were on the stock precat housings.

I have tried solutions #1 and #2. Solution #1 may cut the stock ceramic main cat's life short. Mine lasted for 40,000kms after removing the precats. After that I went to #2 along with a full cat-back exhaust. Gave me an extra 6HP dynoed at the wheels (147 1.6TS).

Originally Posted by kav

Has anyone cut open the pre cats on an alfa 147 and emptied them? Was just thinking it may be cheaper than buying a supersprint manifold and downpipe.

Cheers

Hi chap
have a look at my post. i used an old manifold and down pipe.works great.

http://www.alfaowner.com/Forum/tunin...-decating.html (GTV ts exhaust mod plus decating)

regards john