View Full Version : Cat Bypass Pipe - Ibiza 20VT
Mark@VAGWORX
05-08-2003, 16:45
Is anyone running a system with a cat bypass pipe on the Ibiza 20vt??
Wondered if there was anything adverse is taking the cat out, apart from the obvious MOT issue. Does the ECU not like it, throws codes? Car runs better/worse??
Got Supersprint cat-back at the mo, was thinking about the DP cat bypass section.
I think petrol cars have a lamba sensor on the cat. Besides that I dought you'll see much more in terms of HP. What you will get is the turbo spooling up faster.
Most exotic sport cats cost £££££ and only get you +3-4hp.
Mark@VAGWORX
05-08-2003, 17:04
Yeah they do have lambda's. I'm pretty sure that the sensors are inserted back into the new cat bypass section.
Surely having no cat has got to be slightly less restricted!?!
Yeah, that why I think you'll see quicker spool up. I still think you won't see more than 5-7hp tops (I sure someone will be posting otherwise soon;) ).
From what I have been told its more hassle than its worth due to the sensors.
Sensors before and after cat, from what ive been told.
Its only the oldish engines that would benefit from cat removal, like golf gti engines due to them being restricted more for emissions, where as modern engines the the 20vt are made from the ground up with emissions in mind
Mark@VAGWORX
05-08-2003, 18:40
true point
The cat is integrated with the downpipe. So you will either have to hack and weld your downpipe about to remove the cat, or just fit a new higher performance downpipe which will come with a sports style cat anyway. Which would be better, due to the above mentioned sensors.. With no cat, the ECU will throw a wobbly and ultimately will probably cause you to lose more power than you hoped to gain in the 1st place. Also, modern cats really are not as restrictive as people think these days.
If anyone wants CAT bypass for the new 20VT engines, he has to trick the ECU (second O2 sensor after CAT).
http://mkiv.com/techarticles/oxygen_sensor_simulator/
max_torque
06-08-2003, 08:13
few things to add to that article:
1) that actual shape of the waveform from the 2nd O2 sensor is not important, the ECU will just count the ratio of "switch counts" between the front and rear sensors( "switches" when the voltage crosses a threshold, typically 0.65 to 0.7V). the front sensor is before the catalyst, so it will switch rapidly at a couple of Hz as the ecu controls fuelling around lambda 1, the rear sensor is after the catalyst, and the oxygen storage capability of the cat will "dampen" these switches. therefore comparing the number of front switches with the number of rear switches, gives the ECU an indication of the health of your catalyst. now when you remove the cat, the rear sensor will switch as fast as the front and the ECU will detect this.
2) you can do exactly the same effect as that 555 chip box for about 50p by using a resistor and capacitor in parrallel with the rear sensor output to dampen it's signal, leaving it in the exhaust
3) leaving the rear sensor connected but "dangling" is not good, because it's heater will raise the tip temp to something over 250 degC, guarenteed to melt bits of your car / wiring off if it touches!
Originally posted by max_torque
2) you can do exactly the same effect as that 555 chip box for about 50p by using a resistor and capacitor in parrallel with the rear sensor output to dampen it's signal, leaving it in the exhaust
Are you sure???
I assumed this aswell but was told "this isn't an option" as the signal will not be corrected utilising the above:dunno:
Ive seen very good gains quoted from removing the cat and installing a larger diameter downpipe and was very interested in this at one stage,does this mean I should rekindle my interest in this?
Mark@VAGWORX
06-08-2003, 10:57
Everything's getting far too technical these days! :eek:
Bring back the days of high emissions, straight through side exits, wind-up actuators, whoosy Grp A dump valves and pants electronics................oops, slipped back into the 'tin foil pocket rocket' R5GTT days........:p ;) :D
Surfer_D
09-10-2003, 08:42
For those of you who are still wondering.
It works. I replaced the exhaust, including the knitted steel thingy right behind the turbo and yes I removed the cat.
There is no yellow light on yet, but even if it were the only thing is that the ECU is logging the error code. It doesn't effect engine.
My beeza is 2002 and it's AYP with two lambdas.
The gain is 30hp dyno measured and the car goes superb in high gears (4th and 5th). The oil is 10°C colder then before and the boost is higer.
The gain is felt just like when I got it chipped.
I recomend this to everyone. My whole exhause is totaly custom made with polished stainless steel material.
chriskaven
09-10-2003, 12:21
What did you do with the two sensors and wires then?? did you disable them or fit them in the new pipe?
chriskaven
09-10-2003, 13:17
Surfer D,
What modifications do you have? Did you have overboost problems when you added the cat removed exhaust? did you have to have a remap?
30hp sounds like alot. Was the Hp measured before and after on the same dyno bench?. I've seen big discrepencies between similar dynos.
Surfer_D
10-10-2003, 08:53
1. My modifications; Forge 007, new N75 "H" version, new larger turbo intake pipe and chip
2. I have this for about 2 days and I didn't notice any boost problems.
3. I will do remap in 2 weeks, but like I said I have no troubles with the new exhaust
4. Both lambdas are there as they used to be before, just in the new pipe. Today after two days I have a yellow light on the dash. There is absolutly no problems with the second lambda, because I doesn't do anything else than checking for the O2 values. Currently I should have an error logged about the exhaust because of the second lambda getting the wrong values. It doesn't affect the ecu or the engine.
I will make what EBC showed above to fool the ECU to get rid of the yellow light. This is recomended because if I would have some errors in the engine I wouldn't notice them, because the yellow light would be on because of the wrong O2 values.
5. HP were measured on the same dyno under the same conditions in compare to the stock exhaust. We measured it one day before the change so the results are very real. Oh and we used a totaly new MAF sensore when we measured - so it is real.
30hp gain is guaranted and I must say that they are well felt in higher gears (4th and 5th). This morning I flored it in 2nd and 3th - I thought I will fly away :) It's prety much the same difference as it was when I chipped the engine from stock.
What I change was totaly everything back from the turbo. The pipe is made from the stainless steel material which is polished all the way. I have a small first box (don't know the name) which is visually simulating cat, small centre box and back supersprint box which was modified (the pipe comes directly into the box, because the supersprints pipe in the front of the rear box was not good enough)
I'm very satisfied - all I need to do is to fool the second lambda to get rid of the yellow light. Like I said second lambda doesn't send any commands to the ecu on how to adjust the engine - this is the first one doing.
ibizacupra
10-10-2003, 18:53
30bhp from cat removal?????
Surfer_D
12-10-2003, 10:16
Originally posted by ibizacupra
30bhp from cat removal?????
and larger downpipe. Everything back from turbo is replaced with polished stainless steel material
ibizacupra
13-10-2003, 08:23
Originally posted by Surfer_D
and larger downpipe. Everything back from turbo is replaced with polished stainless steel material
Yea but 30bhp is............... well............. one hell of a number.
any dyno's to support this?
Bill
Surfer_D
13-10-2003, 09:36
Originally posted by ibizacupra
Yea but 30bhp is............... well............. one hell of a number.
any dyno's to support this?
Bill
yes I have - I just need to find a a scanner somewhere to get it scanned.
I'll post them still in this week.
30hp is in compare to the serial exhaust. We also measured what Forge 007p gives and the gain was 9 hp.
Forge tests were done after the exhaust was already changed.
Ohh, and guys not to mention how the tubro is whistling. You wouldn't belive it is a 1.8T engine.
max_torque
13-10-2003, 09:38
Originally posted by Surfer_D
Like I said second lambda doesn't send any commands to the ecu on how to adjust the engine - this is the first one doing.
The downstream lambda sensor does actually control engine fuelling, but only at part load (ie not wide open throttle) during steady speed cruising, where it measures the oxygen storage capacity of the catalyst and adjusts the fuelling to minimise exhaust emisions and maximise catalyst efficiency. But these are very small adjustments to the fuelling (typically 0.05 lambda either side of lamnda 1).
Hence it wn't effect the performance of the car at wide open throttle (where even the upstream lambda will not be operating at WOT)
The light on the dash will be a P0420 code or similar, indicating that the catalyst efficiency is below the 1.5x the legal threshold.
On typical turbocharged engines i have tested when utilising active and agressive knock control (ie BOSCH Me7 a-la 1.8T) the sensitivity to post turbine exhaust back pressure is between 1.2 and 1.6 bhp per kPA, ie a 1 kPa reduction adds between 1.2 and 1.6bhp. So assuming that the 1.8T cat losses approximately 15kPa (typical value at max airflow / exhaust flow, although higher on chipped cars running more boost and hence more air / exhaust flow) you should gain something like 18 to 24 bhp.
A std road exhaust system with catalyst and silencer boxes will have approximately 50kPa pressure loss (VW development target), and good aftermarket system with catalsyt removed and only 1 straight through box may be able to drop the pressure loss to 25kPa, which is worth 30 to 40 bhp)
Surfer_D
13-10-2003, 15:09
max_torque: Thanks for the info. You seem to know a lot about this things. Do you know for any aftermarket "second lambda" for 1.8T which would lie and always show the right values.
I hate the yellow light on the dash.
Shock_Xe
13-10-2003, 17:12
Originally posted by Surfer_D
I hate the yellow light on the dash.
Take the bulb out :p :D
I've built one of the circuits at lunch... not tested it yet...
Max - will the 555 solution be an acceptable one to 'fool' the ecu with out it having a detriment on performance (or causing fueling problems)?
Originally posted by Surfer_D
[B]We also measured what Forge 007p gives and the gain was 9 hp.
Someones playing with the rolling road 'calibration settings'
A DV giving 9hp :confused:
Surfer_D
14-10-2003, 07:42
Originally posted by smithrc
Someones playing with the rolling road 'calibration settings'
A DV giving 9hp :confused:
yes you read this right - but DV was measured on my friend's leon cupra 1.8T (180hp) - chipped, new n75, larger turbo intake pipe, turbo back exhaust without cat - like mine. It's the one I bought from Bill - Forge 007p. It holds the boost longer and steadyer.
Surfer_D
14-10-2003, 07:43
Originally posted by smithrc
I've built one of the circuits at lunch... not tested it yet...
Max - will the 555 solution be an acceptable one to 'fool' the ecu with out it having a detriment on performance (or causing fueling problems)?
isn't this 555 solution for Toyota Supra
it is indeed - but with a bit of playing and VAG-COM logging i've moddified the circuit slightly to give a signal that is better matched to the O2 sensor logs I've got.
OBDII sets the standards that everyone trys to conform to so they should be interchangable.
max_torque
14-10-2003, 13:02
Originally posted by smithrc
I've built one of the circuits at lunch... not tested it yet...
Max - will the 555 solution be an acceptable one to 'fool' the ecu with out it having a detriment on performance (or causing fueling problems)?
It should be acceptable, but might need a bit of playing as you suggest to get the right "number of switches". Because if you have too few switches the ecu will diagnose a duff rear sensor, and too many a duff catalyst.
I have only played with the resistor / capactior bodge to prevent false catalyst failure diagnosis. on this a ratio of about 10% rear switches to front switches seemed ideal.
ibizacupra
14-10-2003, 14:23
Originally posted by smithrc
Someones playing with the rolling road 'calibration settings'
A DV giving 9hp :confused:
A DV cannot give power.... does'nt work like that.
Maybe a leaking one looses power (boost) but thats about it.
Surfer_D
14-10-2003, 14:38
Originally posted by ibizacupra
A DV cannot give power.... does'nt work like that.
Maybe a leaking one looses power (boost) but thats about it.
you got a point here, but if you have a chip all serial are leaking. We used two serial one on leon and in both cases the same result. By the way Leon has a different one then beeza. The one on Leon looks smaller.