Hi all

 

Im a fairly new Zed owner, i will post some pics of my blue beauty late tonight!

 

I have read through old posts and can see that the most effective way of increasing performance is via a EBC (in conjunction with a gauge of course!), after market air filter, de-catt/exhaust and a chip mapped for these mods.

 

My question is what if I missed out the de-catt exhaust, would that have a big negative effect on performance? the reason im a bit hesitant is due to MOT issues and because i have read on here that taking off the catts can sometimes prematurely blow the turbos due to getting rid of seals (or something like that!). My car drives nice, seems fine 100,000km recent jap import?

 

what do you guys think, i would prefer to take the catts off, as that would prob make it sound nicer as well but dont want to risk messing my car up! i like it too much

 

???

No need to remove Cats. Many (possibly most) dont. Decatting does improve spoolup and release a few more horses but the biggest increase is from the boost upgrade.

 

Although you dont need to worry about MOT with removing cats, and its not so much that they kill turbo seals but that but they unmask an already failing turbo seal.

Edited August 7, 200817 yr by Paul@SWZ

No need to remove Cats. Many (possibly most) dont. Decatting does improve spoolup and release a few more horses but the biggest increase is from the boost upgrade.

 

Although you dont need to worry about MOT with removing cats, and its not so much that they kill turbo seals but that but they unmask an already failing turbo seal.

 

 

 

thanks for the advice Paul, you know im after some de-cat pipes so you might be talking yourself out of a sale, but you'll be saving me mohoney"!:D

well i have de-catts just incase LOL

Hastings,

Removing the cats is effectively a boost upgrade. You will benefit by a 20% increase in power or 20% decrease in fuel consumption, you choose. There is no real reason for the turbo's to be in any way effected by the removel of this back pressure except that I suspect the seals will take a few thousand miles to re-profile themselves due to the reduced back pressure and may smoke for a time. This happened to mine but after 18 months there was little smoke and a further 18 months no smoke at all.

 

Due to the fact that your engine will able to produce more power and therefore be able to burn more fuel, the engine will be running hotter, especially around the turbo's. This will encourage oil residue burn off to occur throughout the exhaust system and may produce some oil smoke in itself.

 

All turbo's should be treated with care before engine shut off by simply allowing the engine to run at low boost for the last few miles. Allowing this to occur will help prevent hot to cold thermal damage across the seals extending engine life. Use the highest spec engine oil available, fully synthetic is expensive but will break down at a much higher temperature than cheaper oils. With oil you get what you pay for.

 

If I had little money and were able to make one modification to a 300 it would be to remove the cats.

GSY300

GSY300, although you show a lot of technical know-how, I have to disagree with your statement that decatting is effectively a boost upgrade - decatting as Paul says, reduces lag a little, as there's less bottleneck at the exhaust side. divorced/split downpipes off the back of the turbos also contribute to less lag. however maximum boost pressure stays the same and can only be increased by boost jets, or a manual/elecronic boost controller.

there have been many debates on this forum about whether to decat or not, and there were as many people who 'got away with it' as there were showing signs of seal failure and blue smoke on overrun/idle.

for a stock motor, the best and most cost-effective first mods are intake and zorst to let the car breathe better, then jets/EBC with mapped ECU.

Same here. Any obstruction has to be a bad thing unless you're a Greeny!

 

Also, without the horrible Cats you can expel more burnt gas on the exhaust stroke, and thus have extra room to sqeeze slightly more air into the cylinder on intake, giving a bigger bang for your buck. Plus you get a weight reduction and a better sound, and you no longer have a furnace under the car. And to top it all, you piss the Greenies off :)

Sorry SkylineDave but, with respect, you are incorrect. As Trevz quite correctly states, by removing the obstruction in any exhaust pipe, any engine will breathe more easily and therefore produce more power. In Guernsey, moped type bikes are sold to 14 year olds for road use and are restricted to 30mph by placing a washer in the exhaust at the manifold thereby reducing the airflow through the engine. Take the washer away and it will do 40mph. Simple.

 

A Catalyst works in an identical way. Remove the obstruction and maximum boost will increase by 2-3psi. On any non-turbo car, petrol or Diesel, performance will be improved without cats also, or if you drive sensibly, a fuel saving is to be had.

 

Other advantages are an improvement in torque, quicker spool-up of the turbo's and as mentioned by Trevz there is less likelihood of setting fire to the scenery when parking off-road. There will however be no noticeable increase in noise as the turbo's, in recycling all of that waste energy into usable power, makes the turbo motor an inherently quiet engine.

 

You mention 'boost jets, or a manual/electronic boost controller' as the only way to increase boost. Don't know what boost jets are as i'm old school, but I can assure you there are many ways to increase boost charge pressure including ram air, intercooling, NOX injection, tuned inlet and outlet manifolds, bigger turbo's, bigger valves, more valves and a host of other methods. However the cheapest and simplest single measure any engine can benefit from is an unrestricted exhaust, and by removing the cats, you have created a bigger hole for the exhaust gases to disappear through.

 

For the smoke issue re-read my post above. This is my experience and without meaning to offend I hope this helps readers.

 

GSY300

im not disputing that decatting doesnt help breathing at all - in fact ive had it done on my motor for that very same reason. i was challenging your claim that decatting is a boost upgrade. perhaps i misunderstand what you mean by boost upgrade as my understanding of it is 'to increase the maximum boost pressure, and/or reduce turbo lag', indeed most of the other mods you mention are horsepower upgrades, and will allow for more boost to be run, but aren't in themselves boost upgrades. perhaps we're picking over nothing, lol!

boost jets are mig welding tips that restrict flow to the wastegate actuator to ultimately force them to open later and so allow boost to build up above factory settings, although this results in spikes and should be used with care. i started off with jets, then moved to an EBC.

glad your smoke problems sorted themselves out, ive not heard of anyone decatting and then their smoking (should it happen) going away, but then again you did leave it for a long time whereas I went for a rebuild a couple of months later (I was having this done anyway not just because of my blue smoke)