Anyone gone 'backwards' cat-wise?

[T40ORA]

Has anyone on here decided to bolt cats back on, and found that they have more power/torque or a more usable delivery?

[Liquid Tuna]

M4cruiser said:

T40ORA said:

Has anyone on here decided to bolt cats back on, and found that they have more power/torque or a more usable delivery?

What on earth do you mean? Sorry I don't even understand the question!

He means putting the catalytic converter back on to a car that's had it removed and replaced with a straight through bit of pipe (de-catted).

A system will be set up to run with a cat from factory. If it's removed, I suppose it's possible that the car would run worse (change in back pressure etc) unless it's been setup correctly.

[vtecyo]

No.

[VBRJ]

OP - better to ask on the TVR forum.

I don't think you will get the answers you want from the Saxo gang in GG.

Peace.

[Daston]

On a Speed Six I can't see there being too much of an impact in removing the cats. On a turbo charged engine however it can make a massive difference.

[trashbat]

I've been looking at what I can do to a dull NA 4 pot and a few people were disappointed when they did major work including a de-cat, claiming to have lost low down torque. I'm not sure that tells you all that much as it may have been a failure to properly map for the new system. Me, I'm replacing manifold backwards but it will include a sports cat.

Edit: e.g. http://www.alfaowner.com/Forum/alfa-147-156-and-gt...

Edited by trashbat on Tuesday 3rd June 22:46

[T40ORA]

VBRJ said:

OP - better to ask on the TVR forum.

I don't think you will get the answers you want from the Saxo gang in GG.

Peace.

I'm at least getting MORE answers from Saxo drivers. And it would be a general issue; I've done a little Googling (well, the wife is away - what is a man to do?) and in general there is a 'six of one, half a dozen of the other' view.

What I'm after is any car that has before and after graphs.

Mind you; most TVR owners love their graphs and numbers

[Raize]

If I lost back-pressure I'd put a restrictor in the exhaust before putting a cat back in. They're too useless and expensive to bother with having.

[JackP1]

I went for a sport cat (200 cell opposed to 400 cell standard ) on my milltek, i was running the highest torque compared to some de-catted cars at a RR day.

It is a crappy fiesta though so not exactly ferrari power.

[P I Staker]

Since removal I get pops, bangs and flames out of my...



Saxo.




Not even joking.

Once you de-CAT you never go back.

[T40ORA]

P I Staker said:

Once you de-CAT you never go back.

Yeah. But with 111.1dB I can't get on track!

[T40ORA]

JackP1 said:

I went for a sport cat (200 cell opposed to 400 cell standard ) on my milltek, i was running the highest torque compared to some de-catted cars at a RR day.

It is a crappy fiesta though so not exactly ferrari power.

This is the issue. I have real de-cat pipes, but there is a school of thought that with free flow sports cats there is a better balance of no restrictions and adequate back-pressure.

[T40ORA]

trashbat said:

I've been looking at what I can do to a dull NA 4 pot and a few people were disappointed when they did major work including a de-cat, claiming to have lost low down torque. I'm not sure that tells you all that much as it may have been a failure to properly map for the new system. Me, I'm replacing manifold backwards but it will include a sports cat.

Edit: e.g. http://www.alfaowner.com/Forum/alfa-147-156-and-gt...

Edited by trashbat on Tuesday 3rd June 22:46

From your thread;

"As naturaly aspirated engines need some back-pressure in the exhaust piping. If you make the exhaust with almost no resistance (straight pipe) you will loose torque in low revs = you will loose some driveability."

This is my concern/question. I have equal length manifolds at the top and a sports box at the back end, and the cats have been replaced with properly made de-cat pipes. But I seem to be suffering the loss of low down torque.

Looks like it is suck it and see. Buy and fit sports cats, get it mapped and dyno'd in comparison to the existing set up. Simples.

Apart from the bloody cost involved.

[Checkmate]

Gahh! Back-pressure is wholly undesirable.
What you are looking for is exhaust gas velocity suited to give the biggest area under the curve for your particular engine, putting it terribly simplistically. Clearly not going to be achieved by having a restriction in the exhaust. Such as a cat.
Though why you feel you have lost driveability by removing one is anyone's guess.

[DanielSan]

Only thing I've ever found with a De-cat pipe on an N/A car is more noise. Certainly not a hugely noticeable difference in response. At.best a very slight improvement. But more than likely a placebo effect of the extra noise

[T40ORA]

Checkmate said:

Gahh! Back-pressure is wholly undesirable.
What you are looking for is exhaust gas velocity suited to give the biggest area under the curve for your particular engine, putting it terribly simplistically. Clearly not going to be achieved by having a restriction in the exhaust. Such as a cat.
Though why you feel you have lost driveability by removing one is anyone's guess.

Not sure it is that simple.

http://www.pistonheads.com/gassing/topic.asp?h=0&a...