Guys,

 

Ive found a leak in the passenger side cat so i need to replace it. But i thought it may be the perfect opportunity to decat.....

 

Basically i need to find out if theres any cheaper alternative then paying £250 squid for decat pipes. Mind my ignorance but i think its kinda expensive for some exhuast pipes. (sorry, another thread!)

 

A place in East London do all sorts of motors, mate told me they're charge 30quid a cat.... but u jus cant trust any old person these days, and the 300 aint just 'any old motor'......

 

Has any1 had any luck getting decat pipes cheap, any advice would be great!

 

Cheers

jaz

cheap de-cat job?

Buy 30 quid cats

Smash out the internals

Job Done ;)

Gutting the cats leaves for alot of turbulence in the exhaust system, its better to just cut them out and replace them with two pieces of straight through pipe (thats costs around £30)

or get test pipes but like oyu say its not worth it.

I am not trying to call any one here but that is how engines blow. People want the extra power but are not prepared to pay to have it done correctly.

Its either a few hundred now or a few thousand later. :(

 

Stuart

Cool, Stu do u know wat the difference is between 30quid pipes

and the 250? ie like internals etc...... cos ur right, i dont wanna blow my eng... trust me i know! jus got my engine replaced!

Do you know what I dont know. I think with decatting its not that important, to me anyways, how you do it. But to be truthful I dont really know much of that side of the car. Warren confused me when he said just decatting causes turbulance. :confused: First time I head that but like I said I dont know much about it.

 

I think the £30 pipes are you cut out the cat section of the pipe and patch it with the £30 pipes. I think.

 

However its who you ask. I have heard from many people that gutting the cats is better than test pipes, again, I dont know why its just what I hear.

 

If it was me I would go for gutting the cats before cutting them and putting your own pipe on. MOT places check the cats just by looking at it and if there is a section of different pipe they know its been tampered with, while gutted cats look exactly the same. Not really a problem if you are legaly allowed to take them off but a problem if you are not.

 

Test pipes are just down pipes with no cat in there in the first place.

 

I think you will be OK with what you go for because its only decatting by any other mods dont skimp on money I think. That is why my car modding has come to a huge halt.

 

My choice would be in this order

 

Test pipes

Gutted cats

£30 pipe jobbie.

 

 

Stuart.

 

P.S.

I have had mine gutted, like you I didnt want to spend £200 on test pipes and replaceing a section of the pipe didnt sound that, how can I say this, clever. At the time I heard that gutting it was safer than test pipes.

Cheers Stu,

 

Been a great help matey!

 

jaz

sorry to barge in on your post but i have some de-cat pipes for sale ..........stainless...never fitted......open to offers....

cheers.

Jiz, def interested mate, could pm me ur number please! cheers

 

 

jaz

Jiz cant PM u mate, let me know how much u lookin for them....

 

:)

Does anyone KNOW what the best route is here? There is always such a lot of old wives tales with a topic like this. I have always thought that £300.00 was way too much for de-cat pipes, and gutting them, even if it does cause "turbulance" this is not always a bad thing, in fact it can be a very good thing, in the right place/time etc.

So, does anyone really know?

Hi jaz........email me tonight....

jiz300@aol.com...........ta

Originally posted by SRRAE

 

If it was me I would go for gutting the cats before cutting them and putting your own pipe on. MOT places check the cats just by looking at it and if there is a section of different pipe they know its been tampered with, while gutted cats look exactly the same. Not really a problem if you are legaly allowed to take them off but a problem if you are not.

 

 

 

at no point in the MOT do you actually check the physical presence of a cat!! if its a vehicle that falls into a cat test then as long as it passes the emissions test it passes.

 

zeds, however, are not in the database for a cat test - so should be tested as a non cat vehicle ;)

Gutting the cats basically leaves an expansion chanber in the exhaust section where the cat material was - this is what causes the turbulence Warren mentioned. This has been tried against proper decat pipes with proven power increase from the decats over the gutted cats. One extra factor everyone is overlooking, is that with decat pipes you get the chance to increase the pipe diameter - it is more likely that this is the cause of the increased power IMO rather than the turbulence. As you say Mark, turbulence CAN be good but I think that this is NOT the case here...

 

HTH

 

CheerZ,

 

Andy

Originally posted by SRRAE

I am not trying to call any one here but that is how engines blow. People want the extra power but are not prepared to pay to have it done correctly.

Its either a few hundred now or a few thousand later. :(

 

Stuart

 

Im sorry but how on Gods green Earth can there be a difference in having precut pipes (aka test pipes) and having your cats removed and just two straight through pipes put in there places?

Its the exact same thing, except one costs about a 10th of the other one.?

Please forgive me if i ask a stupid question

 

I have a NA. 1990

 

Is it ok for me to gut the cats? and how do i do that anyway?

 

My mate just said smash them but that sounded abit to harsh for me!

 

If the decate pipes are not sold how much do you want?

 

Thanks

Gutting the cats on an NA will probably have an adverse effect on performance! Back pressure is good for an NA engine (and to a certain extent a turbo engine) and if you remove the cats you may well find yourself left with a very 'flat' powerband.

 

HTH

 

CheerZ,

 

Andy

according David Vizard, a very well respected engine tuner.

 

i remember many years ago reading a book by him & various articles in magazines, and in one article he actually stated that any exhaust manufacturer that stated that back pressure is good is either lying or doesnt know what the're talking about!!!

 

shock wave tuning is actually more important, allowing the inertia of the gasses to keep flowing & actually "pull" the gasses exiting the combustion chamber.

 

if you can find any articles by him, he makes very interesting reading.

As far as I was concerned it was always N/A as much back pressure as poss and TURBO less as poss, (but retaining some!)

Why would you want more back pressure, the object of an exhaust is to remove the products of the combustion process.

The situation with 2 strokes may be a little different because they can rely on back pressure in certain places in order to create the standing pulses and scavenging effect that can help to move gas from one place in an exhaust to another.

 

There was a guy called John Robinson who wrote a number of books on motorcycle design, but he also covered both 2-stroke and 4-stroke engine theory. Always interesting reading ...

 

 

Originally posted by james300

As far as I was concerned it was always N/A as much back pressure as poss and TURBO less as poss, (but retaining some!)

With a turbo motor go large at the front because the gases are hottest and will flow very quickly and as they cool down, they begin to slow down and you can then decrease the pipe size down to the back to help speed up the flow where it will be cooler and slower.

 

So go 3"-3.5" off the turbo's and decrease it to 2.5" after the downpipes to the rear.

 

Worked very well on my 200sx with massive gains but lookout for your turbo seals as when you remove some of the backpressure the seals cannot do their job as well (unless you have hybrids with uprated or staggered gap seals) and you start to see smoke appearing !

 

The cats are by far the most restricting part of the exhaust and eliminating them will make a huge difference.

paul c i am with you...the less back pressure the better..........you dont see many drag cars with a nice silencer on do you.......?.....or F1 cars..........

the pipes are still for sale...mail me and i will return you mail.......

ta

When I said as much back pressure as poss for an N/A engine, I didn't mean anything extra to increase it, just certainly not any measures to decrease it!

Sorry guys just need to change the subject slightly, but the decat pipes that GPS, johnny is selling for 250, r they the same as the ones on lukes site for 180?

 

If so y such a fluctuation in £££, i would have thought getting the cats chopped off & replacing them with straight pipes would be logical, cheaper and more sensible.....cos i agree with 300z on this one. I know alot of people choose the cheaper option, try to save money etc but then run into a lot of trouble cos of that. In this instance i think this senario is not justified and not comparable, if u look at it logically.....

 

well that my opinion, wat do u guys think?

 

jaz

Some good sense here, and like I said some OLD WIVES TALES. Thanks for answering my question though.

Hi Guy's

Something else to think on, if you decat the pipes on a N/A, it's gonna be well loud. And i mean LOUD!!

My Z still has the cats fitted with a Powerflow Stainless system and it's LOUD, God knows how loud it would be if i took the cats out as well???.

Don't get me wrong i love some noise and alot of people couldn't live with how noisy:D my car is now.

Take the cats away, don't think so!!!!:eek:

Cheers Dave.