gordy.r Posted June 15, 2016 Share Posted June 15, 2016 Ok, so I'm running a 3" NUR Spec R cat back exhaust with 1st and 2nd 3" decats on my jspec BPU TT auto. I've been looking at getting a full titanium 4" cat back system for some time now (as much as I love the NUR Spec) but I was wondering if there will be any adverse or negative performance effects whilst on stock twins (i.e. back pressure wise or anything?). Also, will I need to upgrade to 4" decat pipes as well, and will these connect to a stock manifold? Also....what would I do for a 4" restrictor ring (pointless I know but planning on going single in the not so distant future so it would just be to safeguard the stock twins just now). Other option is to keep my 3" decats with restrictor ring and have a 4"-3" adapter for the new cat back system until I progress my build. Lots of questions and beard stroking going on here Quote Link to comment Share on other sites More sharing options...
Glanza_Mike Posted June 15, 2016 Share Posted June 15, 2016 Hi mate, i went from a 3" to a 4" boostlogic though it sounds like my exhaust is different to the one you are considering as i needed a 4" v-band to 3" 2-bolt adapter to fit mine to the second decat, therefor i could still use my 3" restrictor ring. I think you will be able to as well though? Most or all 4" systems i've seen can either use this adapter or size down themselves at the 1st/2nd decat end. Quote Link to comment Share on other sites More sharing options...
Littler Posted June 15, 2016 Share Posted June 15, 2016 I went from a nur spec R to a 4" HKS Ti on stock twins with a 2.5" 1st decat and 3" 2nd decat. I fitted the HKS 4"-3" adapter which led to the exhaust coming further out at the rear bumper by about an inch, I was quite happy with this as it wasn't noticeable. Performance wise I definitely didn't feel any difference (although it wasn't dyno'd compared), a freer flowing exhaust on a turbo setup should allow more power but at stock or BPU power levels I'd imagine the difference is minimal as a 3" exhaust can flow perfectly for up to small singles. Don't think you will have a problem Quote Link to comment Share on other sites More sharing options...
Burna Posted June 15, 2016 Share Posted June 15, 2016 Isn't the diameter of the exhaust a mute point as you're having to run a 2" restrictor anyway? Or am I missing something? Quote Link to comment Share on other sites More sharing options...
Mike2JZ Posted June 15, 2016 Share Posted June 15, 2016 Isn't the diameter of the exhaust a mute point as you're having to run a 2" restrictor anyway? Or am I missing something? Not to mention the stock downpipe size Quote Link to comment Share on other sites More sharing options...
gordy.r Posted June 15, 2016 Author Share Posted June 15, 2016 It's only until I decide which single set up. I've got a good shout at a decent discount from ETS just now in the States and I've always fancied one of their 5" intercoolers and titanium exhausts. I'm getting a Tial BOV to go with the set up which ETS offer a flange for on the intercooler kit with the big single configuration so it won't be getting fitted straight away. Was just wondering if it would be worthwhile fitting the exhaust or wait until I complete the rest of the build (Syvecs, Turbo, Intake etc). Quote Link to comment Share on other sites More sharing options...
Mk4Gaz Posted June 15, 2016 Share Posted June 15, 2016 Isn't the diameter of the exhaust a mute point as you're having to run a 2" restrictor anyway? Or am I missing something? My thinking exactly Quote Link to comment Share on other sites More sharing options...
Burna Posted June 15, 2016 Share Posted June 15, 2016 My thinking exactly /QUOTE] Or you could just go buy a UK spec which comes with a larger diameter down pipe as standard, and also then run no restrictor ring I'm just pulling your leg Quote Link to comment Share on other sites More sharing options...
gordy.r Posted June 15, 2016 Author Share Posted June 15, 2016 Or you could just go buy a UK spec which comes with a larger diameter down pipe as standard, and also then run no restrictor ring I'm just pulling your leg Funny you should say that.... I've got my eyes on one [emoji6] One owner, low mileage, totally stock, hasn't been driven in 10 years, immaculate condition.... Would make a great stripped out track car... Quote Link to comment Share on other sites More sharing options...
safcdixon Posted June 16, 2016 Share Posted June 16, 2016 Mines had no adverse effects the 4" exhaust only good tbh, Mine is the whifbitz 4" (hks copy iirc) , my RR is 2.5" though not 2" as said above so that helps i suppose , my bpu made 431.1 bhp Only thing Id say is if your sup is low! low! Then ground clearance is quite abit lower, the big vband on the 2bolt convertor tends to catch on things more than the normal exhaust would Quote Link to comment Share on other sites More sharing options...
gordy.r Posted June 16, 2016 Author Share Posted June 16, 2016 Mines had no adverse effects the 4" exhaust only good tbh, Mine is the whifbitz 4" (hks copy iirc) , my RR is 2.5" though not 2" as said above so that helps i suppose , my bpu made 431.1 bhp Only thing Id say is if your sup is low! low! Then ground clearance is quite abit lower, the big vband on the 2bolt convertor tends to catch on things more than the normal exhaust would Thanks for the reply, exactly what I was after! Wasn't sure if I could just remove my restrictor ring and have the boost controller sort out the boost or is that wishful thinking? I'm not massively low as it stands due to my ridiculous offset on my alloys and my NUR Spec hangs low anyways so hopefully it will be ok. Cheers again Quote Link to comment Share on other sites More sharing options...
Burna Posted June 16, 2016 Share Posted June 16, 2016 Thanks for the reply, exactly what I was after! Wasn't sure if I could just remove my restrictor ring and have the boost controller sort out the boost or is that wishful thinking? I'm not massively low as it stands due to my ridiculous offset on my alloys and my NUR Spec hangs low anyways so hopefully it will be ok. Cheers again An electronic boost controller can only raise boost, not lower it, so you will still need your restrictor ring. I would say fit now what ever exhaust you want to end up with when you go single. Quote Link to comment Share on other sites More sharing options...
gordy.r Posted June 16, 2016 Author Share Posted June 16, 2016 An electronic boost controller can only raise boost, not lower it, so you will still need your restrictor ring. I would say fit now what ever exhaust you want to end up with when you go single. I thought that might be the case, what I've noticed with my Turbosmart system, it brings any turbo spikes down from say 1.26 or 1.3bar etc down to the tolerance that's been set (1.2 bar) when accelerating hard (is there any other way to accelerate?). I should just have bought a UK spec to begin with shouldn't I lol Quote Link to comment Share on other sites More sharing options...
Burna Posted June 16, 2016 Share Posted June 16, 2016 I thought that might be the case, what I've noticed with my Turbosmart system, it brings any turbo spikes down from say 1.26 or 1.3bar etc down to the tolerance that's been set (1.2 bar) when accelerating hard (is there any other way to accelerate?). I should just have bought a UK spec to begin with shouldn't I lol Well that's what an EBC is designed to do, keep a stable boost pressure that you set it to, but it won't ever bring the boost down below the baseline level of the system. Without a restrictor ring you have no baseline boost level, it will just overboost and kill your turbos :/ Quote Link to comment Share on other sites More sharing options...
gordy.r Posted June 16, 2016 Author Share Posted June 16, 2016 Well that's what an EBC is designed to do, keep a stable boost pressure that you set it to, but it won't ever bring the boost down below the baseline level of the system. Without a restrictor ring you have no baseline boost level, it will just overboost and kill your turbos :/ Ah yeah, well...you know what happens when the turbos die.... Quote Link to comment Share on other sites More sharing options...
Nic Posted June 16, 2016 Share Posted June 16, 2016 Only thing Id say is if your sup is low! low! Then ground clearance is quite abit lower, the big vband on the 2bolt convertor tends to catch on things more than the normal exhaust would Just to add, titanium exhausts use very thin walled tubing, if you do ground the exhaust then the tubing/welds can easily crack. An exhaust that follows the route of the stock exhaust will have better ground clearance than one that follows a straight path from 2nd cat to tail pipe. Quote Link to comment Share on other sites More sharing options...
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