Smaltze
Senior Member
W/S210 E320 2002
I deleted my primary cat a week or two ago inspired by Alexanderfoti's guide, i could definitely feel the effects. Unfortunately i could also feel the negative effects in that i had a noticeable reduction in low end torque and throttle response. It was barely any but enough to bug me.
I do enjoy trying to find solutions to problems, so i set to work
I knew that the reduction in torque etc was because i had left myself with a massive chamber right behind the turbo, which meant horrible exhaust airflow velocity. It just meant my power band had been raised in the revs to where the pipe size wasn't such a factor..
Anyway i wasn't such a fan of this since i think lower end torque is definitely more fun since G's off the line is where i get most of my kicks!
The aim - Mod the cat somehow to increase the flow velocity.
Solution - Stick a straight pipe in there that directed the air! (as much as i could)
I intend to go all in, cut open the cat and weld/shape things into a secure sealed pipe or something in future but for now this was just an experiment.
(I figured id need to keep the cat body intact for MOT, please someone tell me i can loose it though ha)
Heres what i did.
The Cat exit hole to the chamber is a very akwardly positioned at about 70 degrees and too the side. I was thinking of making a tube with a bend but i wouldnt be able fit it through the top whole of the cat. I just wanted something to test. Heres the design i used:
Making up the correct size pipe (ended up being about 65mm diameter)
Complete tube
Cutting a cylidrical shape out of the edge on the exit end. (refer to next picture)
This is roughly how the end pipe was positioned, except it fitted much much better for real.
Thats the profile of the Cat, and the dotted line is the pipe position.
A better depiction of the shape pipe i used. (forgot to take a picture)
This is the tube almost in place in the cat, it ended up fitting extremely well, it was almost sealed against the back wall of the cat, the slanted rear wall of the cat pushed the pipe downwards closer to the exit tube. the cylinder cutout actually ended up nicely above the exit tube there was frankly minimal excess space for the air to escape in other directions.
The tube wedged in perfectly into the cat and actually sealed itself all along (loosly), when it was in its final place the edges of the pipe didn't overlap like in the picture and it was plentifully air tight. I opted not to tack weld the tube closed so that is had some flexibility (weird idea i know but it worked).
Now lets remember this was a test, i was simply going for as directional and air tight of a tube as i could get without butchering the cat and welding things. I planned to do it properly if it had worked...
And it DID! A test drive quickly concluded that it worked, and worked well!
The car resumed alot of its low end torque, perhaps not as much as i had hoped, but it also certainly felt faster in general. perhaps i had found a better middle ground, a good combination of strong air flow!
I now plan to redo this, ill cut open the cat so i can make a proper shaped pipe and seal it all for maximum air flow.
A big question i must ask though, does anyone know if i even need my primary cat in place to pass MOT? i have my two secondary cats untouched. It would be ideal if so because i could weld the two end fittings onto a straight pipe instead of worrying about the stupid cat chamber looking intact for MOT!
I know some people may not approve of my cowboyish modding antics, but i just thought i would share anyway! im having fun and learning alot
Cheers!
I deleted my primary cat a week or two ago inspired by Alexanderfoti's guide, i could definitely feel the effects. Unfortunately i could also feel the negative effects in that i had a noticeable reduction in low end torque and throttle response. It was barely any but enough to bug me.
I do enjoy trying to find solutions to problems, so i set to work
I knew that the reduction in torque etc was because i had left myself with a massive chamber right behind the turbo, which meant horrible exhaust airflow velocity. It just meant my power band had been raised in the revs to where the pipe size wasn't such a factor..
Anyway i wasn't such a fan of this since i think lower end torque is definitely more fun since G's off the line is where i get most of my kicks!
The aim - Mod the cat somehow to increase the flow velocity.
Solution - Stick a straight pipe in there that directed the air! (as much as i could)
I intend to go all in, cut open the cat and weld/shape things into a secure sealed pipe or something in future but for now this was just an experiment.
(I figured id need to keep the cat body intact for MOT, please someone tell me i can loose it though ha
)Heres what i did.
The Cat exit hole to the chamber is a very akwardly positioned at about 70 degrees and too the side. I was thinking of making a tube with a bend but i wouldnt be able fit it through the top whole of the cat. I just wanted something to test. Heres the design i used:
Making up the correct size pipe (ended up being about 65mm diameter)
Complete tube
Cutting a cylidrical shape out of the edge on the exit end. (refer to next picture)
This is roughly how the end pipe was positioned, except it fitted much much better for real.
Thats the profile of the Cat, and the dotted line is the pipe position.
A better depiction of the shape pipe i used. (forgot to take a picture
)
This is the tube almost in place in the cat, it ended up fitting extremely well, it was almost sealed against the back wall of the cat, the slanted rear wall of the cat pushed the pipe downwards closer to the exit tube. the cylinder cutout actually ended up nicely above the exit tube there was frankly minimal excess space for the air to escape in other directions.
The tube wedged in perfectly into the cat and actually sealed itself all along (loosly), when it was in its final place the edges of the pipe didn't overlap like in the picture and it was plentifully air tight. I opted not to tack weld the tube closed so that is had some flexibility (weird idea i know but it worked).
Now lets remember this was a test, i was simply going for as directional and air tight of a tube as i could get without butchering the cat and welding things. I planned to do it properly if it had worked...
And it DID! A test drive quickly concluded that it worked, and worked well!
The car resumed alot of its low end torque, perhaps not as much as i had hoped, but it also certainly felt faster in general. perhaps i had found a better middle ground, a good combination of strong air flow!
I now plan to redo this, ill cut open the cat so i can make a proper shaped pipe and seal it all for maximum air flow.
A big question i must ask though, does anyone know if i even need my primary cat in place to pass MOT? i have my two secondary cats untouched. It would be ideal if so because i could weld the two end fittings onto a straight pipe instead of worrying about the stupid cat chamber looking intact for MOT!
I know some people may not approve of my cowboyish modding antics, but i just thought i would share anyway! im having fun and learning alot
Cheers!
