Drew Posted July 7, 2009 Report Share Posted July 7, 2009 Hi,ok ive got a raceland mani which is gonna be fitted to my car soon.I'm getting a custom cat back system made up, but i cant decide what to go for cat wise.I had a sports cat on my last car and im not sure if it made that much of a difference. The guy who i was speaking to said tbh a sport cat will give you 3-4% increase is this right?He said an option was to do a bolt on de-cat so it can be removed for MOT time, but how do GTI's run with de-cats?The other option is just have my mani, orignal cat then the cat back system.What have you people got out there and which do you think is the best option? from yuor experience?Cheers Quote Link to comment Share on other sites More sharing options...
Drew Posted July 9, 2009 Author Report Share Posted July 9, 2009 Anybody running any of the above? within there system? I know Casper is but ayone else? Quote Link to comment Share on other sites More sharing options...
crash Posted July 9, 2009 Report Share Posted July 9, 2009 Anybody running any of the above? within there system? I know Casper is but ayone else?I have a 200cell sports cat and have had it remapped...think it was more torquey with the sports cat and since the remap it seems much better alltogether! I have heard bad reports when it comes to decats...personally I would rather have a sports cat but opinions differ! Quote Link to comment Share on other sites More sharing options...
Tarrier Posted July 9, 2009 Report Share Posted July 9, 2009 i knew a guy running raceland mani and straight through pipe quite loud but proper quick Quote Link to comment Share on other sites More sharing options...
Defcon5 Posted July 9, 2009 Report Share Posted July 9, 2009 I would expect it to be quicker with a sports cat, a decat will give you zero backpressure which is bad. On FI cars you want the least resistance possible, but not on an NA Quote Link to comment Share on other sites More sharing options...
Drew Posted July 9, 2009 Author Report Share Posted July 9, 2009 Yeah i've heard that you'll lose back pressure with a de-cat and obviously dont want that!, i also cant be chewed with switching it for MOT.Is a sports cat a sports cat? if you get my drift? I saw a 200 cell sports cat on ebay last month for 99p but then see some for £150 does it matter aslong as the exhaust place can make up the pipes either end for it? Quote Link to comment Share on other sites More sharing options...
nfbr Posted July 9, 2009 Report Share Posted July 9, 2009 That's the pre-cat Ben. Quote Link to comment Share on other sites More sharing options...
Defcon5 Posted July 9, 2009 Report Share Posted July 9, 2009 Yeah, i think the '200 cell' is something to do with the surface area inside it. I think cats are pretty much all the same, so as you say its just a case of making it fit with the existing pipework. Quote Link to comment Share on other sites More sharing options...
vr6turbo Posted July 10, 2009 Report Share Posted July 10, 2009 why not a race 100cell cat? cells are calulated cells per square inch Quote Link to comment Share on other sites More sharing options...
SamGTi Posted July 11, 2009 Report Share Posted July 11, 2009 All this talk about back pressure.... im sure I spoke to a guy that rebuilds race engines told me that its not the back pressure which will cause issues, its Pulse Timing?... or i might be getting confused with something else¬!! lol Quote Link to comment Share on other sites More sharing options...
SamGTi Posted July 11, 2009 Report Share Posted July 11, 2009 Oh, BTW.I have a raceland mani and de-cat, its very revvy, seems to have lost a slight ammount of torque IMO. Feels quicker, but my engine management light has just come on yesterday with the emmissions. Going to have a normal cat put on, with a cat-back system Quote Link to comment Share on other sites More sharing options...
AwesomeAl Posted July 11, 2009 Report Share Posted July 11, 2009 why not a race 100cell cat? cells are calulated cells per square inchMost cars that run 100cell Race Cats fail MOT emission tests. Quote Link to comment Share on other sites More sharing options...
sam bignell Posted July 11, 2009 Report Share Posted July 11, 2009 Most cars that run 100cell Race Cats fail MOT emission tests.Does anyone how whether a GTI would fail though?I'm quite interested in this and can't find much information regarding this type of thing for the Lupo GTi . . . .new region it would seem.Sam Quote Link to comment Share on other sites More sharing options...
DJ TROOPA Posted July 12, 2009 Report Share Posted July 12, 2009 I'm looking to get a 100 cell race cat when i get the whole exhaust system done in good time. My bro's Scooby STI has a 100 cell race cat and passed MOT first time. Quote Link to comment Share on other sites More sharing options...
CasperGTI Posted July 14, 2009 Report Share Posted July 14, 2009 (edited) Back pressure is needed in NA cars for efficient burning of exhaust gasses.On the exhaust stroke of the engine, fuel rich gasses are pushed in to the manifold due to valve overlap and unburnt gasses from the previous compression stroke. These gasses can be burnt, which in theory gives you torque provided you can get them back in the engine.Back pressure in the exhaust system aids the fuel rich gasses to be pushed back towards the engine to be effectivly burnt, loosing them, looses effective power or torque of the engine.Forced induction is different as there is little or no need for back pressure hence the scooby having a small cat and a big exhaust system. Infact the sti engine apparenly can nearly pass an emissions test withough a cat all together, every engine is different, personally i think a 100cell is too small for a road going NA car.A 200cell High flow cat is what you would want for road use, 100cell's are a bit to small, and may well give you emissions issues. I have a 200cell on mine and it passed no problems.Cat's now-a-days arent that restrictive anyway.IMO the best sort of system for the GTi would be a raceland mani or custom mani, 200cell high flow cat with a matching manifold-back system, at the same pipe bore size as the original. Edited July 14, 2009 by CasperGTI Quote Link to comment Share on other sites More sharing options...
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