Hollow Cat

Dr_Jones · Post by **Dr_Jones** » Sat Apr 10, 2004 7:16 pm

Was speaking to my brother the other night and I was talking about exhausts etc and he said that the cat on his car is hollow inside so it's just a shell basically so it looks like it's there still. Obviously this is not legal but has anyone done this on the fto and achieved any decent gains?

Also how would I get this done?

payaya · Post by **payaya** » Sun Apr 11, 2004 12:43 am

the power increase would be tiny, the fine huge.

Dr_Jones · Post by **Dr_Jones** » Sun Apr 11, 2004 1:19 am

That's good advice that's enough for me not to do it.

ruchi · Post by **ruchi** » Sun Apr 11, 2004 1:23 am

This could actually lead to a performance decrease due to changes in exhaust back pressure and oxygen sensor readings. It will also probably make the car a bit stinkier

A car is a "system" and as such should be altered / tuned as a whole. Making a dramatic change to a single part, such as this, can often have adverse effects as the rest of the components that make up this "system" will not be in tune.

TimmyD · Post by **TimmyD** » Sun Apr 11, 2004 2:44 am

ruchi wrote:This could actually lead to a performance decrease due to changes in exhaust back pressure and oxygen sensor readings. It will also probably make the car a bit stinkier

A car is a "system" and as such should be altered / tuned as a whole. Making a dramatic change to a single part, such as this, can often have adverse effects as the rest of the components that make up this "system" will not be in tune.

, you know too much ruchi..

but you no what they say... u can never know enough.. hehe

ruchi · Post by **ruchi** » Sun Apr 11, 2004 3:00 am

Thanks for the compliment, but in all honesty I really don't know that much about cars!

There's many people on this forum who have much more knowledge than I do! e.g. Scracy, Dannyboyau, Eric (MADFTO)

I'm just a very logical person who looks for the underlying principles of how and why things work / happen. I often drive people nuts because I am so logical and methodical

While they just want to use it, I want to pull it apart and find out how it works

I'm much more of a technical nut than I am a mechanical buff (there's a greater chance I can fix your computer than fix your car

).

D-TRAIN · Post by **D-TRAIN** » Sun Apr 11, 2004 2:53 pm

Dr_Jones wrote:That's good advice that's enough for me not to do it.

Alternatively, you can get a hi-flow catalytic converter instead.

MADFTO · Post by **MADFTO** » Sun Apr 11, 2004 3:38 pm

I honestly don't know too much detail about cars either =) I'm just a very curious tinker =) Ask me about engine timing and what effects changing one variable has, and I'll have to hit the books =)

And I could try to guess the alignment of the cam gears for our friend before but I didn't want to spout out guesses.

Oh, and my guess would of been get the first cylinder at TDC for each bank, then change to the angle require for opening the inlet valve, then line up the inlet cam so it just starts touch the valve stem. Then repeat for the exhaust cam with the engine cranked at TDC 180 degrees earlier/540 degress later. I'm guessing Inlet opening will be before TDC and exhaust opening after TDC. It's probably be easier to do the exhaust cam first then the inlet cam *shrugs* doesn't really matter, just have to make sure you're cranking the engine the right way =)

Wouldn't want your exhaust to be your inlet =)

Mind you, I'd be cranking that engine with my hands for a few rotations afterward and checking the angles just to double check eveything =)

With machines so expensive, you should be methodical about things, you wouldn't want to blow that motor which is worth a few thousand =)

Eh, sorry for the long winded post guys =) Enough rambling from me =)

Breza · Post by **Breza** » Fri Apr 16, 2004 2:24 pm

D-TRAIN wrote:
Dr_Jones wrote:That's good advice that's enough for me not to do it.
Alternatively, you can get a hi-flow catalytic converter instead.

Or one of Brockies famed "Energy Polarisers"...................

GPXXX · Post by **GPXXX** » Fri Apr 16, 2004 2:58 pm

from several friend's experience removing the cat and/or replacing it with a high flow job made very minimal difference to performance whatsoever...

it's just not worth the risk, because it will cost you more in the end, and i mean MUCH MORE (if you get busted)

Post by **smorison** » Fri Apr 16, 2004 3:39 pm

punching out a cat (check the robb drawings in the gallery btw) would lead to a reduction in back pressure however the turbulance created would probably result in reduced performance.

its hard to say, basically i'd say it depends on NA or Turbo and how restrictive the stock CAT is.