Guest Martin F Posted March 7, 2003 Share Posted March 7, 2003 Can we just clarify that those pro's and cons are different for a J-spec car compared to a UK spec car. For example you are unlikely to get boost spikes on a full de-cat of a UK spec car due to the larger wastegate. Quote Link to comment Share on other sites More sharing options...
Nathan Posted March 7, 2003 Share Posted March 7, 2003 Originally posted by Martin F Can we just clarify that those pro's and cons are different for a J-spec car compared to a UK spec car. For example you are unlikely to get boost spikes on a full de-cat of a UK spec car due to the larger wastegate. Yes, sorry Martin. Many UK specs will still only hit 1 bar with a full decat so in reality you still need a boost controller anyway, which is probably why I didn't think of it. I'm sure there are a few UK specs out there that may just hit 1.2 bar with a full decat but it's the whole uncertainty of what you are going to get that I was trying to portray. Regards, Nathan TDI PLC Quote Link to comment Share on other sites More sharing options...
Mark Kindell Posted March 7, 2003 Share Posted March 7, 2003 Well put Nathan Quote Link to comment Share on other sites More sharing options...
Adam W Posted March 7, 2003 Share Posted March 7, 2003 How does a full decat car sound, compared to one with a single cat remaining? Quote Link to comment Share on other sites More sharing options...
Darren Posted March 7, 2003 Share Posted March 7, 2003 I think Supra pilot has a valid point that cars are generally running full decat for performance reasons. I tried leaving the first CAT in and running a boost controller but IMO the car runs better with the first CAT removed aswell and is more powerful. When looking at rolling road results the decatted cars were putting out more than single cat'd cars running 1.2bar via a boost controller. My J spec car is not suffering boost creep and has to be boosted via the controller for 1.2 bar heaven. As John said you do need to be careful with the throttle but if you have a rear wheel drive car with 400+ BHP surely you know that already? Just my two pennies worth. Darren Quote Link to comment Share on other sites More sharing options...
Supra Pilot Posted March 7, 2003 Share Posted March 7, 2003 Thank you Darren That is exactly my point.....95% of people on here are generally NOt technicialy minded(we do have many 'text book' mechanics/engineers)......and most here saw another did this and did that and got results etc, and want to do it too. ANyway the fact is the less restriction you have on any system(within reason), and especially a performance car the better. The basics of any engine is to get your juice in and out as quick and efficiently as possible.... it's called 'breathing' You take the catt's out for the engine to breathe better, she breathes better, the performance will get better.....simple and true(within reason and many other parameters). And most people that have done this, have noticed a difference! Including myself......... So basically it is benifical.... But then you are getting a down side with in the area of high exhaust temps etc.. this is very easily controlled or rectified. I won't say how, as there are many ways to do this! But the simple way I see it's been done on here is by the 'magic' restrictor ring...... Which as is proven is going back to square one again!!!!!! I wonder why those idiots in F1 or even in top fuel drag(fastest machines on the planet) don't use a Catt.... or even a silencer/baffle etc....just a raw manifold...... Quote Link to comment Share on other sites More sharing options...
Supra Pilot Posted March 7, 2003 Share Posted March 7, 2003 I suppose someone is going to want to try and explain another FAMOUS word ---- 'back-pressure' now........lol Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted March 7, 2003 Share Posted March 7, 2003 Originally posted by Supra Pilot Thank you Darren That is exactly my point.....95% of people on here are generally NOt technicialy minded(we do have many 'text book' mechanics/engineers)......and most here saw another did this and did that and got results etc, and want to do it too. ANyway the fact is the less restriction you have on any system(within reason), and especially a performance car the better. The basics of any engine is to get your juice in and out as quick and efficiently as possible.... it's called 'breathing' You take the catt's out for the engine to breathe better, she breathes better, the performance will get better.....simple and true(within reason and many other parameters). And most people that have done this, have noticed a difference! Including myself......... So basically it is benifical.... But then you are getting a down side with in the area of high exhaust temps etc.. this is very easily controlled or rectified. I won't say how, as there are many ways to do this! But the simple way I see it's been done on here is by the 'magic' restrictor ring...... Which as is proven is going back to square one again!!!!!! I wonder why those idiots in F1 or even in top fuel drag(fastest machines on the planet) don't use a Catt.... or even a silencer/baffle etc....just a raw manifold...... Don't follow... Are you saying removing the cats increases EGT's? Quote Link to comment Share on other sites More sharing options...
Nathan Posted March 7, 2003 Share Posted March 7, 2003 Originally posted by Chris Wilson Don't follow... Are you saying removing the cats increases EGT's? Hi Chris, I think Dom is saying that as long as there is a restriction in the exhaust, your EGT's will be higher, which as we know is true. What may be causing confusion is whether you will have higher EGT's with both cats out and a restrictor ring at 1.2 bar or one cat and a boost controller at 1.2 bar. IMO I don't think there will be any real difference but then I haven't done any full de-cats on stock based turbos to compare. Either way, even cars that still have one cat on shouldn't be hitting dangerous EGT levels so it's immaterial really. Unless the fuel pump is sha**ed. Which is common these days. Regards, Nathan TDI PLC Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted March 7, 2003 Share Posted March 7, 2003 It looked to me as though he was saying the exact opposite... Quote Link to comment Share on other sites More sharing options...
Raoul H Posted March 7, 2003 Share Posted March 7, 2003 Been following this with interest, having gone full-decat.. I could be wrong, but I think, what is being suggested is that some fully-decatted j-specs can overboost (over 1.3 bar) and this in itself causes egt's to rise. This in turn necessitates putting a restriction back in the system (2nd cat/restrictor) which negates the 'performance' benefit of going fully-decat in the first place. Pre-decat, I used a bleeder and on v.cold days saw a max of 1.3bar on the gauge. Having gone full-decat I still see the same, in the conditions described, but the car is noticeably faster - especially mid-range oh, and much louder at wot. Rgds, Quote Link to comment Share on other sites More sharing options...
Supra Pilot Posted March 7, 2003 Share Posted March 7, 2003 Sorry guys, I may have gone off abit there....I do applogize. Basically what I am saying in simple terms is everyones wants a de-catt as it is one mod that 'is' required if you want to gain more power... Which it does....but in some cases it does this sooo well that it results in too high a boost pressure, with a resultant high eng/exhaust temp. Which high boost pressure is good if used correctly and controlled, but you don't want high temps.... You want more boost thats why you re move the catts to achieve this....but putting in the ring, you bring/limit the boost back........ there are many ways to keep the free boost safe and useable after the de catt to make the mod purposefull...... So thats basically the point I am getting at here....... Chris the ring is good and safe yes.....but whats the point of doing a FULL de catt if you are gonna put another 'restrictor' in! Appoligizes to all Quote Link to comment Share on other sites More sharing options...
Nathan Posted March 7, 2003 Share Posted March 7, 2003 Originally posted by Supra Pilot Chris the ring is good and safe yes.....but whats the point of doing a FULL de catt if you are gonna put another 'restrictor' in! Not trying to speak for Chris here but the 'point' is that it gets you in the 'zone' between running a single cat (which for example may give 1 bar) and a full decat (which may give 1.4). Granted, if you are putting a restrictor back in that takes the boost back down to single cat levels then yes, it would be a pointless exercise, but that isn't what they are used for. They are used to tryand get that 'inbetweeny' bit between 1 and 1.25 bar, which incidentally is the area that we use boost controllers for. Regards, Nathan TDI PLC Quote Link to comment Share on other sites More sharing options...
Darren Posted March 7, 2003 Share Posted March 7, 2003 IMO a single CAT would be more restrictive that running a 'ring' due to its honeycone nature etc...but I may be wrong just my opinion. Darren Quote Link to comment Share on other sites More sharing options...
Supra Pilot Posted March 7, 2003 Share Posted March 7, 2003 Again I have to say.... I understand all that what you are saying.......but the point I am making is 99% of people on here that put a ring in was because of 'boost creep/high temp'! THAT IS A FACT...... They use(d) a ring to cure that....... Stability yes, but the MAIn reason was to stop the above! It is all in past threads............. Whats the first thing that is said when people do a de catt, (besides saying boost pressure is unstable).. Typical thread on here.... 1/ Question : what next do I need to do? Answer : 'An EGT gauge' (on this forum) 2/ Ques : Why? Ans : to moniter and make sure you don't run hight tempts (with your new half done mods.) 3/ Ques : Ok thats done, I am getting quite high temps and boost raising to 1.4 etc.. Ans : wooooo, thats dangerous......you now need a ring to stop that 4/ Ques : Good ring fitted, boost now more stable, temps not so high 5/ Ques : Now car is fine, but boost limited and brought back down because of this..... 6/ Ques : Seems I have not gained much here really... MY Answer : because you have done half a mod(as I keep saying). and should of gotten a proper solultion from question 3/. 'Right this is a typical thread on here'..all the time....... Someone asks that first question and thats the immediate answer he gets swamped with! It's the wrong answer, thats the alternative answer...... Look I am not trying to be difficult guys,,, I may have said this all in a confusing type of way.....trying to type this at work here, in between my job... But as I said, there is no way you can say a ring is a benifit to power gain.....it is a cheap cure for a problem created by an incomplete mod...... End of the day, everyone does mods and spends loads of hard earned dosh doing this to achieve more power/speed (thats a FACT)....... Like to hear the big power supras on here say if they have a 'restrictor', sorry a ring...or have any of your big power machines you guys 'Nathan' built have one of these in them.... Quote Link to comment Share on other sites More sharing options...
Raoul H Posted March 7, 2003 Share Posted March 7, 2003 Valid points made dude. Certainly don't think you are being difficult here. One thing to bear in mind in this discussion is that the boost-creep problem was *mainly* seen by those who have 3" diameter decat pipes. Those that used the CW 2.5" pipes *typically* had no issues w.r.t boost creep/hight egt's etc. The restrictor ring is, I believe for the 3"pipework. In general the figures I see for the configs (on stock turbos) appear to be: a) 3" decat - 1.2 - 1.6bar (depending on car) b) 3" decat + ring - 1.1 - 1.2bar c) 2.5" decat - 1.1 - 1.2bar d) 2nd cat in place - 1.0 - 1.1bar With a) yielding the highest risk of high egts. Again, all the above is with respect to J-SPEC supras. Rgds, Quote Link to comment Share on other sites More sharing options...
Supra Pilot Posted March 7, 2003 Share Posted March 7, 2003 Originally posted by Raoul Haynes Valid points made dude. Certainly don't think you are being difficult here. One thing to bear in mind in this discussion is that the boost-creep problem was *mainly* seen by those who have 3" diameter decat pipes. Those that used the CW 2.5" pipes *typically* had no issues w.r.t boost creep/hight egt's etc. The restrictor ring is, I believe for the 3"pipework. Cheers Raoul, but I know for a fact of 2 people on here had those problems with even the 2.5" pipe. Anyway these issues/debates are good for everyone as hopefully we all learn and benefit from them. Thanks to all the inputs Actually just so Chris doesn't take it the wrong way, I think he knows better with me as I know he is a guru in his own rights and have megga respect for him, and I must say I have called on him many a times for opinions/advise on different issues. Rgds D. Quote Link to comment Share on other sites More sharing options...
Thorin Posted March 8, 2003 Share Posted March 8, 2003 Originally posted by Supra Pilot 4/ Ques : Good ring fitted, boost now more stable, temps not so high 5/ Ques : Now car is fine, but boost limited and brought back down because of this..... 6/ Ques : Seems I have not gained much here really... err, well not gained anything other than the turbo's now spooling faster, running at 1.2bar instead of 0.8, and the EGT's being lower, and it not costing me anywhere near as much as a boost controller. I kinda understood what you were trying to say but don't really know where you are going with that post, but then what do I know, it's nearly 4am. Quote Link to comment Share on other sites More sharing options...
Supra Pilot Posted March 8, 2003 Share Posted March 8, 2003 Originally posted by Thorin but then what do I know, . My point exactly..... Quote Link to comment Share on other sites More sharing options...
Nathan Posted March 8, 2003 Share Posted March 8, 2003 Originally posted by Supra Pilot But as I said, there is no way you can say a ring is a benifit to power gain.....it is a cheap cure for a problem created by an incomplete mod...... Dom, I hear what you are saying but I'm not sure where it is going! Both CW and I have both said that a ring is indeed a crutch..., but it works for some. I don't like them, and prefer to have more control over boost ie use a controller, but going the full decat route with or without a ring is still a viable option for some. because you have done half a mod(as I keep saying). and should of gotten a proper solultion from question 3/. OK, the 'proper' solution, as Chris said, is if you want to do away with both cats and have controllable boost, is to have replacement turbos fitted with larger wastegates. I'm sure we don't need to state how much this would cost....? Like to hear the big power supras on here say if they have a 'restrictor', sorry a ring...or have any of your big power machines you guys 'Nathan' built have one of these in them.... No, I've never put a car out of these doors with a ring, or indeed a full decat on stock based turbos, let alone big single or twin cars. I'm still missing your point. Or was your mail directed more at CW? A little confused Nathan TDI PLC Quote Link to comment Share on other sites More sharing options...
Supra Pilot Posted March 8, 2003 Share Posted March 8, 2003 It was directed at no one in particular........maybe thats the problem...... Anyway m8, I have said enough on this, what I want to say anyone can discuss this with me in person anytime and I will set you/them straight. Because I can't see what you or anyone else cannot understand. ANyway you answered my last question..... I'm done.... Quote Link to comment Share on other sites More sharing options...
matt Posted March 8, 2003 Share Posted March 8, 2003 I have run on on the front Cat with HKS 2nd cat replacement and Dual dragger for a couple of years now. Max boost was a little over stock and any increase was by way of a boost controller. I recently acquired a CW 1st cat replacement pipe and stuck it on whilst I had the turbos off recently. Result very slight increase in boost..... now runs about one bar stock and stable. It rose to about 1.1 on a really cold night.. Now I had read that boost spikes can be uncontrollable on some j'specs and that others don't have a problem. I guess I was fortunate.. If the boost had become uncontrollable I would have tried a restrictor ring. The restriction would only be doing the same job as a stock cat and a little further away from the manifold.....which is a good thing IMO My point is that you won't know if your j'spec has runaway boost with both cats removed, until you try it. If it does, and a restriction is needed, you then have the option to refit a cat or use a restrictor ring. I would personally use a ring at this point (If I had fitted both pipes and had boost issues) for a number of reasons .... Its a lot easier to fit a ring than it is to refit the first cat! The restriction is further away from the manifold and will generate less heat than the Cat.. Hell, its even considerably lighter ! It seems that a full decat is a bit of a gamble, when it comes to j'specs.......... but theres plenty of gamblers out there! I'm a little confused as why you seem so passionate about this Dom............. it aint gonna be a problem on the NA:moo: Quote Link to comment Share on other sites More sharing options...
FaithStalker Posted June 9, 2003 Share Posted June 9, 2003 I know that this is an old thread and i've only just read it, but some of the posts in here should not be lost and i think some of the info should be put into a FAQ's asap as its top notch stuff I for one have been considering the pros/cons of decat and its certainly helped me, i'm sure we'll get a lot of newbies asking this question over and over again (like i did :-) ) Nice one to ChrisR for linking this thread off his sig ! Quote Link to comment Share on other sites More sharing options...
MONKEYmark Posted June 9, 2003 Share Posted June 9, 2003 i have had various de-cat pipes hks 3" with 1st cat and nur spec exhaust all in one de-cat pipe replacing both cats (hit up to 1.5bar) now got both cw de-cat pipes in and was hitting up to 1.4bar and hit a high of 1050degree at dragstrip on EGT gauge since fitting fmic my high is 1.3bar with mainly 1.2bar and EGT of just over 900 degrees. the car is running slightly less boost than before but feels a lot faster to me. would it not be a case of fittine some better cooling mods like bigger intercooler and maybe water injection. my car is j-spec and used to get real hot under the bonnet before. also no boost controller fitted. could not see the point if car is hitting highs of up to 1.3bar Quote Link to comment Share on other sites More sharing options...
Thorin Posted June 9, 2003 Share Posted June 9, 2003 Yep, real men don't have any CAT's at all. I've tried telling monkey this but he got rid of both cats anyway Quote Link to comment Share on other sites More sharing options...
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