Ralliarv Posted January 26, 2010 Share Posted January 26, 2010 Hi everyone! My name is Arvin and I'm in Canada. I have a 93 J-spec MKIV TT and I was looking at options to support my decat. I have all other supporting BPU mods. Problem is that ordering the pipes seem to be all from UK which is a bit of a problem and some of the places I have been looking at to order don't ship to Canada plus shipping is expensive as hell! So far temporarily a local performance exhaust shop has installed a 3" straight pipe from my 1st cat back to my HKS Hi-power cat back. At the moment the 1st cat is giving me enough restriction to hold at around just over 1 bar. Now I want to complete the exhaust by removing the first cat at the shop and was wondering if fitting in a 2" pipe in place of the 1st cat good enough to avoid overboosting? Or what can I do to simulate the restriction that the restrictor ring would provide? Thanks Quote Link to comment Share on other sites More sharing options...
heckler Posted January 26, 2010 Share Posted January 26, 2010 Hi everyone! My name is Arvin and I'm in Canada. I have a 93 J-spec MKIV TT and I was looking at options to support my decat. I have all other supporting BPU mods. Problem is that ordering the pipes seem to be all from UK which is a bit of a problem and some of the places I have been looking at to order don't ship to Canada plus shipping is expensive as hell! So far temporarily a local performance exhaust shop has installed a 3" straight pipe from my 1st cat back to my HKS Hi-power cat back. At the moment the 1st cat is giving me enough restriction to hold at around just over 1 bar. Now I want to complete the exhaust by removing the first cat at the shop and was wondering if fitting in a 2" pipe in place of the 1st cat good enough to avoid overboosting? Or what can I do to simulate the restriction that the restrictor ring would provide? Thanks Why not just get a restrictor ring? Quote Link to comment Share on other sites More sharing options...
Nic Posted January 26, 2010 Share Posted January 26, 2010 Impossible to say, it's not an exact science, it will depend on the car, how restrictive the exhaust is and intake temps. It has been done before, I use to have a full ARC exhaust fitted on my J-spec TT, this replaced the complete stock exhaust including both cats, the front section of the exhaust had a tapered/narrowed length of pipe roughly 2" diameter and 2" in length, this caused enough of a restriction to keep boost levels to around 1bar. I'm guessing it took ARC a LOT of trial and error though to get the design of the exhaust so it would give the required restriction. By far the simplest way would be to fit a restrictor ring and to adjust the hole size until you get the required boost level. Quote Link to comment Share on other sites More sharing options...
Rinus Posted January 26, 2010 Share Posted January 26, 2010 My Rring is 2", so if you place a 2 inch pipe instead of the 1st cat, I think that will be ok, cause its just a lllllong restrictorring Quote Link to comment Share on other sites More sharing options...
Ralliarv Posted January 27, 2010 Author Share Posted January 27, 2010 Thanks for the input guys! Actually I was considering a route like what Rinus was saying. I don't easy access to ordering the ring and it's very cheap and easy to try out the 2 inch pipe for now to see how that works. Or I guess something like what Nic said and start off big and taper down to 2" then meet up with my 3" mid pipe all the way out. I think I'll try that tomorrow if I have time and see how it works. I'll let you all know how it goes! Quote Link to comment Share on other sites More sharing options...
bodilx6 Posted January 27, 2010 Share Posted January 27, 2010 You can also just knock a hole through your 1st cat and then gradually widen it untill you hit the max boost you want. Working fine for me, and you will have the additional "safety" of being able to point police or who ever might visually inspect the car to the existing cat... Quote Link to comment Share on other sites More sharing options...
Rinus Posted January 27, 2010 Share Posted January 27, 2010 Before I had a first decat with Rring, I totally emptied the first cat (j-spec), and had 1 bar turbopressure, this is with 2nd decat and catback... Cause it took along time for my 1st decat to arive, I couldn't wait and started drilling 6mm holes in the side, and with 3x 6mm holes I was running 1,15-1,2bar boost... But then I had I leaky exhaust for a month or so Quote Link to comment Share on other sites More sharing options...
Ralliarv Posted February 1, 2010 Author Share Posted February 1, 2010 Update: I finally got my car to the shop to get some work done. We removed the 1st cat and fitted a 2.25" short downpipe to a 3" flex pipe that met with my 3" 2nd decat. Overall a very quick and simple job, just had to wait to get that flex pipe from another shop. I pulled the fuses for a quick reset for EFI 1 and 2 and gave it a good drive on the highway. I noticed right away first turbo spooled up nice and smooth and quite loud then when the second turbo went on it kicked my ass haha. I was seeing a high spike at around 17 almost 18 psi. It seems high but I think it is with our temps in my city. Right now we are at -34C. So when it warms up in a few months it should be quite fun. So far everything is running great and it's a lot of fun! I also have a Rush Racing Antilag unit from http://www.rushracingdev.com heading my way in the mail, I'll make a post when I get that in about it. Cheers! Quote Link to comment Share on other sites More sharing options...
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