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I was at rsport recently. the system they experimented with was a very large bore exhaust system straight from the manifold. basically no cat, no mid silencer. Obviously noise was ear-splitting, but apparently power gains were huge.
Rsport reckon a decat pipe can be used, but they dont have a twin lambda decat, i.e something that will allow the lambda after the cat to remain ok. I assume that after a while this would show up a fault on the engine mgt. Various companies in France including technomap use a resistor connected to the second lambda sensor to trick the system , but they too are not 100% happy with the setup.
rsport have removed that exhaust system from their car and gone back to std including cat and silencer. They will be at donnington on sep 4 if anybody wants to have a chat
phill you seem to know what your on about is there a de cat pipe or not available from r,sport and what is tim on about????? or is he just telling porkys because seems to me he doesnt know much about where he got this de cat pipe that takes the two sensors and doesnt put the warning lights on
Tim is absolutely not telling porkies. Basically rsport have experimented with a wider bore cat-less and silencer-less exhaust and say they had 200+bhp results just doing that and a grpN ECU (latter simply increases torque mid range). As I said above, I am not aware of any company rsport or any other that has come up with a decat pipe that allows the second lambda sensor not to report a fault. Frankly I dont see how such a pipe could exist as the second lambda sensor cannot sense any difference from the first one if a proper cat is replaced with a bit of pipe. So the choices are:
1 dont remove the cat
2 remove the cat, get some benefits - maybe 3-4 bhp - and wait for you second lambda sensor to put a fault warning on the dash and on the diagnostic system. that will be easily spotted by renault next time you service it
3 same as 2, but if you dont care, you might as well go to the extreme of fitting a large bore straight through exhaust decat, no silencer etc. problem is you will look like a right moron, get earbleeds and you will never be allowed anywhere near a track because of the noise..
4 remove the cat and attempt to trick the second lambda sensor into thinking everything is aok. A simple resistor circuit can be used, but to my best knowledge this will only r****d the inevitable fault/diagnostic warning.
5 replace the std cat with a less restrictive cat. Sounds expensive for 3-4bhp?
If anybody knows better /different about decating a mk2 172, please let us know.
oh one comment on Tims original post, Rsport said they only change one of the cams to a grpn spec, that is the exhaust cam only, so Tims only typo is to refer to grp n cam"s", as opposed to cam - no big deal to me either way!
Personally Im not too sure how changing just the exhaust cam will do much good - typically inlet/exhaust are worked together, but Ill leave that to the experts
WHy doesnt somebody test the 1st lambda and second lambda for values at idle and mid rpm. Simply because it only runs closed loop part of the time.
THen check if the differing values between lambdas are linear...if they are, run the 2nd lambda wires spliced off the 1st lambda which you keep working and put a resistor of the right amount in there....if indeed its linear or even reading a lower voltage.
if it aint, well.........nevermind, just off the top of my head.
I think thats what technomap did in France Ben, used a resistor, but the owner told me that eventually they got a diagnostic fault. Anyway as you say only way to find out is to test. Surely this would be worth the effort by somebody like k-tec as I imagine many people would fit decats if there was a reliable fix to the sensors, and if k-tec came up with a pricing scheme for a yearly fee to put the cat back on for MOTs..
the job of the second sensor is to relay emissions info to the ECU. THe MK2 has to comply with EURO 3 spec emission laws which state no warmup period, so it needs to know when the cat has warmed up and doing its job then it can move away from the startup map that many complain about as rough startup".
The computer will soon detect that the second lambda has inconsistencies.
this cack thread still going then.
Ben why bother mate?
After all this lot acheive miracles with resistors that cycle and everything! Its a b*****d miracle! NASA will be at their door wanting their advice.
If any of you actually knew about EFI and how related sensors work you might actually realise what sh*te you spout.
