slick Posted February 5, 2005 Share Posted February 5, 2005 Hi everyone, bit of tech help needed please Long post alert! On the Thor dyno day back in November I ran my UK auto TT and it was stock apart from the boost controller (and required BCC/plugs ofcourse!) including the stock exhaust and both CATs still in place. I got the following graphs: http://www.boostman.plus.com/Thor/first%20session/BHP.Torque.jpg http://www.boostman.plus.com/Thor/first%20session/Torque.AFR.jpg Red line = controller off (less than stock boost) Green = 0.8 Pink = 1.1 ish Blue = 1.2 bar Which I was happy with to say it was only from a boost increase. Then the last month my Nur arrived and I ordered an Envy (2nd) decat pipe, it said it was for a UK model but didn't have the o2 sensor flange (I was told this prior to the order being confirmed so no complaints there) Now I'd heard different things about this, some said the second o2 sensor didn't matter, others said it did and that it would cause fueling issues by running rich. I thought that maybe this was people being a little on the cautious side so I went ahead with it to see. Took the Nur and the decat down to Thor who fitted it and did another dyno run to see the result. These are the graphs: http://www.boostman.plus.com/Thor/second%20session/bhp.torque.jpg http://www.boostman.plus.com/Thor/second%20session/Torque.AFR.jpg Red line = 0.8 Blue = 1.2 bar As you can see on the 1.2 bar run I lost on the peak bhp/torque but gained in other areas. On the stock boost run I gained everywhere really including peak. Now that was a bit disapointing ofcourse about the 1.2 bar run especially, not what I expected. Had a good chat with Pete about this and he was helpfull as always. As we knew the only thing to change was the O2 sensor was now hanging in mid (fresh) air, he suggested that this could be throwing the fueling out as it appeared to be running rich compared to the previous run. This would fit in with what I'd heard before, and seems to be the only explanation. If this is the case would you expect to see a more profound effect on the higher boost? I'm going to book it in to have the O2 sensor replaced/refitted at the same time as having the 1st CAT replaced, so should be sorted then I hope. It seems that with the UK model having the increased fueling this extra has tipped the balence too much, whereas I guess on a Jap spec it would be of benifit right? Anyone got any other ideas on the matter? Has anyone else had issues with leaving out there UK o2 sensor? Although unless you've seen your AFR's before and after you might not have realised. Thanks for any input Quote Link to comment Share on other sites More sharing options...
slick Posted February 5, 2005 Author Share Posted February 5, 2005 I must have posted in the wrong section, heres me thinking this was the technical section No one got any thoughts on this one, for or against the conclusion we came too? Friday night though, bet everyones on the like I should be lol Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted February 5, 2005 Share Posted February 5, 2005 You MUST have the second O2 sensor in the second de cat pipe on UK and US spec cars. it won't run right with it just tie wrapped up out of the way. Quote Link to comment Share on other sites More sharing options...
slick Posted February 5, 2005 Author Share Posted February 5, 2005 Cheers Chris, I take it you've seen these issues before then. Maybe I should have listened to my cautious side and looked into the issue more, and got one of your pipes by the looks of it as you do them with the flange ready fitted doh! Ain't hindsight wonderfull Not to worry, getting one fitted will sort it then and I should see the gains I was expecting. Oh well gives me an excuse to go back and get that 1st CAT out Might be worth while Envy guys if your read this to start having the flange fitted to your UK pipes like Chris's, to make it easier come fitting time. Quote Link to comment Share on other sites More sharing options...
Ian C Posted February 5, 2005 Share Posted February 5, 2005 The ECU is probably cranking it's closed loop setup all the way towards rich to compensate for the vast amounts of oxygen the second O2 sensor is picking up That'll bugger up your idle and your MOT results However, it all goes open loop on a dyno run so it shouldn't matter unless it was in some failsafe mode due to a fault code caused by the constant lean reading. Look at it this way, your power output has only changed by 13bhp, that's a 3% change, and the afrs are only a couple of points different *shrug*. I'd say that pretty much the graphs are the same. Put it down to environmental differences - air temp, density, mood the car was in, tyre pressures, christ knows. -Ian Quote Link to comment Share on other sites More sharing options...
slick Posted February 6, 2005 Author Share Posted February 6, 2005 Cheers Ian, but surely I should be expecting a GAIN from adding a Nur spec R and a second decat... maybe not loads but still defo not a 13bhp loss and even the same as before would still be disapointing. I thought the general idea was that exhausts gave good gains on the TT supra?? I think the missing sensor must have had an effect on the dyno run if this is the case. Besides it shows a small gain (20bhp peak and more torque over a better spread) on the stock boost run so there must be a difference in these circumstances between the fuelings effect from 0.8 bar to the run at 1.2 bar where it lost instead. Quote Link to comment Share on other sites More sharing options...
Ian C Posted February 6, 2005 Share Posted February 6, 2005 The big gains with this modification are found because the minimum boost level goes up from 0.8 to 1.2bar thanks to a more unrestricted exhaust system (hence the reputation of a decat being such a power-improving mod on the Supra). If you were forcing that level of boost with a boost controller anyway, you won't see any improvement! There will be better heat transfer away from the engine and slightly better VE, neither of which will show big changes on a dyno. -Ian Quote Link to comment Share on other sites More sharing options...
slick Posted February 6, 2005 Author Share Posted February 6, 2005 I see your point Ian but the stock exhaust looked restrictive enough and loosing a cat has gota be a good thing right? Also why the big increase on the stock boost run then after the exhaust/decat? (red line second graphs compared to green on first graphs). Especially the torque curve. Quote Link to comment Share on other sites More sharing options...
LeeT Posted February 6, 2005 Share Posted February 6, 2005 the double decat on my uk only raised the boost by 0.1 bar. my o2 sensor is tied up out the way too so when you have yours refitted let us know if it helps at all Quote Link to comment Share on other sites More sharing options...
slick Posted February 8, 2005 Author Share Posted February 8, 2005 the double decat on my uk only raised the boost by 0.1 bar. my o2 sensor is tied up out the way too so when you have yours refitted let us know if it helps at all Will do m8, it better help otherwise fitting a Nur and second decat looses you 'peak' power instead of giving any and I don't believe that for a second Quote Link to comment Share on other sites More sharing options...
Ian C Posted February 8, 2005 Share Posted February 8, 2005 I see your point Ian but the stock exhaust looked restrictive enough and loosing a cat has gota be a good thing right? Also why the big increase on the stock boost run then after the exhaust/decat? (red line second graphs compared to green on first graphs). Especially the torque curve. Yes, it's a good thing. There will be a power increase as the VE of the engine goes up due to a much less restrictive exhaust system, as well as the natural gain in power off the passive boost increase. I didn't realise you had a UK spec, my knowledge of how those respond to decats is limited - the boost increase is way more apparent on a J-spec, hence the unfortunate restrictor ring need. You gained about 20bhp on 0.8bar by decatting and putting in the wider pipe, there doesn't seem to be much of a gain at 1.2bar though, compared to the previous dyno, no idea why. -Ian Quote Link to comment Share on other sites More sharing options...
slick Posted March 12, 2005 Author Share Posted March 12, 2005 Just to update on this thread and finish the tale. Had the O2 sensor refitted today at Thor, new flange welded on etc. Result? Fueling was fine on the dyno and now putting out @ 1.2bar 349.7 (ok ok call it 350!) BHP and 358.3 lb/ft at the hubs with good curves Thats 18 bhp and 11 lb/ft more at peak and with stronger overall curves throughout the rev range than before... Now thats more like it, moral of the story is 'never underestimate the power of a single sensor!' Bit confused why it originally made 344bhp 354lb/ft with the standard exhaust/cat on still though, hardly gained anything with the Nur and 2nd decat compared to those initial figures I hit bang on 1.2 bar this time whereas last time it was 1.24, could the extra .4bar have given a few extra horses and lb/ft making the gains this time seem smaller? What ya reckon Quote Link to comment Share on other sites More sharing options...
LeeT Posted March 13, 2005 Share Posted March 13, 2005 thanks for the update, i'll have to put mine back in then and see if it helps my problem at all Quote Link to comment Share on other sites More sharing options...
Guest Synn Posted March 16, 2005 Share Posted March 16, 2005 Hi Guys Can I ask something relating to this topic... I have a UK TT Supra and was looking at getting a new exhaust system from the first cat back (so removing the 2nd cat). I don't know what to do with the sensor that's there. Should it just go back into the exhaust system without the 2nd cat, or does it need removing? Does the ECU need reprogramming to compensate or anything? Any help would be greatly appreciated Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted March 16, 2005 Share Posted March 16, 2005 If you buy my UK specific de cat pipe(s) (and I strongly recommend you remove BOTH cats for a worthwhile gain), then it comes with a flange welded in to allow the stock second O2 sensor to be bolted straight in. You MUST have this sensor in the 2nd cat pipe, it won't run properly with it in fresh air or removed. Quote Link to comment Share on other sites More sharing options...
Guest Synn Posted March 16, 2005 Share Posted March 16, 2005 Thanks for the info I don't want to remove both cats as I dont' want the hassle at MoT time Cheers though Quote Link to comment Share on other sites More sharing options...
LeeT Posted March 16, 2005 Share Posted March 16, 2005 If you buy my UK specific de cat pipe(s) (and I strongly recommend you remove BOTH cats for a worthwhile gain), then it comes with a flange welded in to allow the stock second O2 sensor to be bolted straight in. You MUST have this sensor in the 2nd cat pipe, it won't run properly with it in fresh air or removed. chris,my car is running extremely rich since removing my maf sensor and replacing with electronic gizmos. my sensor is tied up out the way at the moment. do you think putting it back in will help this at all. the us forums reckon the 2nd o2 sensor is not used on the obd1 ecu. what are your thoughts on this. have you actually done any testing to prove that this sensor actually does anything? Quote Link to comment Share on other sites More sharing options...
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