De Cat idea

[marmel31]

I have just got my car back from the local muffler shop and instead of removing the cat and welding in a straight piece of pipe he put the cat back in after removing all it's internals. The benefit for myself is that it looks like the local powers that be are going to pass laws requiring all Jap import cars to have a cat fitted to get a WOF. So it now looks like I have a Cat and it's not likely anyone is going to drill a hole in it to test it either. Just another option for us to consider.

[aaron68nz]

Isn't it possible to tell if the internals, ie catalyst materials, have been removed by tapping on the casing and hearing a relatively hollow noise? I think they do that here in Australia where there are tough anti cat. removal laws/fines.

[Trow]

I wouldn't dig out the internals, Cats are to expensive to replace if the need ever arises!

[marmel31]

Aparently all cars will have to have the cat replaced at 100,000km anyway, and at a cost of about $300 it won't be cheap. I'm pretty sure the local garage won't get too exited about banging on the cat to see if it's hollow or not, as long as it's there I reckon I will be OK. My car has just over 100,000km on it now anyway, so if the new laws are passed I will have to fork out for a new cat so I'm not too worried about ruining this one.

[Ollpen]

What sir??? The cat is empty????? :huh2:

Noooo, ohh the environment!! Im terribly sorry sir, i bought this exhaust system thinking it would be complete /duh :sick:

[ako]

The law on cat converters is still just an idea, and they can't police them being replaced (or not) at 100,000km anyway. They die after 60-80 thousand kays anyway, and its been proven on a few makes of car to offer absolutely no power gain whatsoever unless they're REALLY blocked up, just more noise.

Just do the whole exhaust in one go. Learn to weld and you can have a full 3", legal exhaust for under $300.

[dickytim]

the idea is actually to have the cars emission tested, the machine wont be fooled by that, have a decat pipe bolted in and keep your old cat JIC.

[jaimz]

I bashed the internals out of the cat on my old GTX Laser.
Aside from the possible side affects of inhaling all the noxious gasses which came fuming out of the thing, it made my car sound like a 1970s Datsun.

If you haven't noticed this on your car that's cool - the effect on the noise might be particular to each exhaust system.

Wouldn't recommend it as a mod though.

[ako]

I just went for the far easier option of replacing my whole exhaust with a big straight piece of pipe and a muffler on the end. Bit loud (ok, a lot loud) but its given the car a new lease on life.

[eeknz]

I just went for the far easier option of replacing my whole exhaust with a big straight piece of pipe and a muffler on the end. Bit loud (ok, a lot loud) but its given the car a new lease on life.

What did it do to fuel consumption? Magoo are hammering the adds on how a big ol pipe makes it leaner. It it true?

Eek

[bradc]

My car uses about 5% less fuel with a complete set of downpipes, and 3.5" exhaust the whole length of the car. It's still much better for fuel economy if you simply drive at 90kph instead of 110kph ;)

[ako]

Theory: Car has less restrictions, doesnt have top work as hard, gets better mileage in addition to having a bit more power when you ask for it.

Practise: The sound of a forced mitsi V6 at 7000RPM through a good exhaust means you'll use a lot more gas than before you had a loud exhaust on :evil2:

[marmel31]

I have noticed that the RPM is slightly lower at 100km per hour. Probably around 100rpm or so.

[ako]

Which makes no sense. An auto box should still lock up when it goes into overdrive.

[bradc]

my car does something a bit strange with it's rpm though, I can drive about 10km's from when the car is cold at about 100kph where the rpm is at 2500rpm, after 10km's it will drop down to about 2300rpm.

If I drive at 90kph it still runs at 2500rpm, but after 10km's it will drop down to about 2100rpm

[_simon_]

Maybe its the choke. Although 10K seems a long time. If I idle my car from cold takes about 1-2mins before the revs drop to normal.

[bradc]

yeah, if I idle mine then it does a similar thing, it sits at 1500rpm for a minute or two, then drops down to about 800rpm. But then on the motorway it still sits at 2500rpm at 90kph. The temp gauge is right in the middle of course, and it gets there in about 2 minutes.

I think it must be the choke that is doing it, but why?

[Kenneth]

um, surely it has to be the torque converter?

choke or no choke, the RPM that you are doing at a certian speed is relative to what gear you are in etc. the only way you are going to change that is with the amount of slip you are getting in your torque converter.

dont get that problem at all with my manual :D

although the choke does have some interesting side affects when changing gear...