Chris and Alana Posted December 9, 2006 Share Posted December 9, 2006 Im going to get a cat back exhausts (hopefully a Miami GT) after christmas and a second decat (keeping the first cat). I would like to know what the boost level will increase to with these mods. there must be lots of you guys nd girls out there with the first cat still in. Iv searched for an answer but give up and thought I would ask instead. The only thing I found was 'You might as well take the first out aswell'. (not to helpfull) I found that someone said his boost went upto 1.1bar and another comment that said it wont increase the boost much. Its a bit varied. Quote Link to comment Share on other sites More sharing options...
Wez Posted December 9, 2006 Share Posted December 9, 2006 Depends on the condition of the cat. Would be better to take it out and get a restrictor ring if you are J-Spec, then use a boost controller to bring it upto 1.2bar. Quote Link to comment Share on other sites More sharing options...
Steviekid Posted December 9, 2006 Share Posted December 9, 2006 I would like to know what the boost level will increase to with these mods. there must be lots of you guys nd girls out there with the first cat still in. If you're just taking one out, remove the first as it's far more restrictive. About 1.0 bar is your limit, above that the remaining cat will start to melt and you'll hit fuel cut. You can use an EBC or manual boost controller to reach this. Some cars suffer from boost spike with one cat still in though. If you remove both you'll need a FCD to get over 1.0 bar along with a restrictor ring. Quote Link to comment Share on other sites More sharing options...
R Black Posted December 9, 2006 Share Posted December 9, 2006 Sorry for the hijack, but if you take out both cats at the same time, when its time for an MOT can you put them both in, still attached together? Also does anyone know if the HKS Front Down pipe is any good and can it mate to the original exhaust? or is it 3 inches needing a reducer? Quote Link to comment Share on other sites More sharing options...
Steviekid Posted December 9, 2006 Share Posted December 9, 2006 Sorry for the hijack, but if you take out both cats at the same time, when its time for an MOT can you put them both in, still attached together? The front cat is a bastard to remove and replace. You should pass the mot ok with just the rear one in. Quote Link to comment Share on other sites More sharing options...
Chris and Alana Posted December 9, 2006 Author Share Posted December 9, 2006 If you're just taking one out, remove the first as it's far more restrictive. About 1.0 bar is your limit, above that the remaining cat will start to melt and you'll hit fuel cut. You can use an EBC or manual boost controller to reach this. Some cars suffer from boost spike with one cat still in though. If you remove both you'll need a FCD to get over 1.0 bar along with a restrictor ring. So even with the first cat in turbos can still overboost. I was under the impression that leaving the first cat in would allow the tubbies to produce 1.0 bar but I dont know if that is true. I also thought thought the first cat would leave enough back pressure to stop over boosting. If they over boost anyway with thje first cat left in I might as well do a full decat and use a restictor ring but I was only wanting to produce about 1.0 bar boost? Quote Link to comment Share on other sites More sharing options...
Chris and Alana Posted December 9, 2006 Author Share Posted December 9, 2006 Also can you get restrictor rings to hold the boost at 1.1 bar? Quote Link to comment Share on other sites More sharing options...
Steviekid Posted December 9, 2006 Share Posted December 9, 2006 So even with the first cat in turbos can still overboost? Not generally. A very few cars every now and then can spike, but I know of at least one person on here that had boost spikes when all they'd changed was the cat back section (still had both cats in!). Chris Wilson can make restrictor rings to suit different boost levels. I've had one sitting in my garage for six months that's supposed to hold the car at 0.9-1.0 bar. Quote Link to comment Share on other sites More sharing options...
Chris and Alana Posted December 9, 2006 Author Share Posted December 9, 2006 I may be tempted to go full BPU Iv already got a HKS SSQV and apexi power intake. I checked out my SMIC and all the fins are still there so my intercooler should be up for it. I take it I should get a walbro fuel pump first then buy an exhaust and decat. What do you think. Am I missing anything? I wont need a EBC on a J-spec to reach BPU with the correct restrictor ring will I. (I know I will need to change the plugs, I will do after exhaust) Thanks guys for all the info. Quote Link to comment Share on other sites More sharing options...
Steviekid Posted December 9, 2006 Share Posted December 9, 2006 Am I missing anything? Just a fuel cut defender. You don't need an EBC. Changing the fuel pump is a good idea. Quote Link to comment Share on other sites More sharing options...
Chris and Alana Posted December 9, 2006 Author Share Posted December 9, 2006 thanks steviekid Quote Link to comment Share on other sites More sharing options...
Supradan Posted December 10, 2006 Share Posted December 10, 2006 I still have both cats in but have an Hks ti 4" cat back system and on a cold day i have seen nearly 1Bar boost on the guage.As others have said best to get rid of both cats rather than one at atime as the cats can melt. Try to find a friendly mot station as they can pass it with both cats out,mine just said "well its not life threatening haveing ni cats in is it"lol:d Quote Link to comment Share on other sites More sharing options...
Steviekid Posted December 10, 2006 Share Posted December 10, 2006 As others have said best to get rid of both cats rather than one at atime as the cats can melt. The cats shouldn't be damaged as long as you don't go over 1.0 bar. There's nothing stopping you sticking a restrictor ring in even though a cat is still there if there's a problem with boost spiking. Quote Link to comment Share on other sites More sharing options...
Guest sindrejl Posted December 10, 2006 Share Posted December 10, 2006 weird, my car has one cat in, but it doesnt boost spike at all. and No restrictor ring. Kinda not smart of me to go over 1.0bar with the cat in then? Quote Link to comment Share on other sites More sharing options...
ivan Posted December 10, 2006 Share Posted December 10, 2006 I've got 1st decat and a Miami-GT exhaust with the supplied restrictor ring. That and the K&N panel filter give me almost exactly 1 bar maximum boost. Quote Link to comment Share on other sites More sharing options...
Steviekid Posted December 10, 2006 Share Posted December 10, 2006 weird, my car has one cat in, but it doesnt boost spike at all. Not many do, I'm just pointing out it is possible. Kinda not smart of me to go over 1.0bar with the cat in then? No. Quote Link to comment Share on other sites More sharing options...
Chris and Alana Posted December 10, 2006 Author Share Posted December 10, 2006 Thanks guys. I was thinking of a second decat and a miami gt exhaust and was hoping to get about 1bar. If I do take both cats out can I still run on the standard fuel pump for a lttle while? Quote Link to comment Share on other sites More sharing options...
Steviekid Posted December 10, 2006 Share Posted December 10, 2006 If I do take both cats out can I still run on the standard fuel pump for a lttle while? Yes. The j-spec fuel pump when new should be capable of supplying fuel up to 1.2 bar, it's more of a precaution to change it. You'll be fine at 1.0 bar. Quote Link to comment Share on other sites More sharing options...
Chris and Alana Posted December 10, 2006 Author Share Posted December 10, 2006 I've got 1st decat and a Miami-GT exhaust with the supplied restrictor ring. That and the K&N panel filter give me almost exactly 1 bar maximum boost. What boost does the supplied restrictor ring restrict the boost to? Quote Link to comment Share on other sites More sharing options...
psymon Posted December 10, 2006 Share Posted December 10, 2006 As someone as already stated, by just removing the 2nd cat you can sometimes get fuel cut. I had it when I took out 2nd cat. Spiked at 1.1 bar, scared the shit out of me as I was doing triple leptons. In general though you should be ok.. Quote Link to comment Share on other sites More sharing options...
ivan Posted December 11, 2006 Share Posted December 11, 2006 What boost does the supplied restrictor ring restrict the boost to?Presumably 1 bar? I must admit, I didn't try the mods without the ring fitted. Quote Link to comment Share on other sites More sharing options...
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