[rdhayward]

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[flash]

this is a long debated subject - long ago, before the development of today's cats. removal made sense and resulted in a freer flowing system - today however, it is not always a good thing - many cars actually run worse, and tuning is often required now to get the mixture right after opening it up with cat removal - without the cat, the car runs rich, costing power



i removed the factory cat as a part of the header installation, and my car has never been quite "right" since - i have tried 6 different cats now, and am finally getting closer to a solution - of the aftermarket units i have tried, i have found that the the more restrictive the better performance



further, with the mobile test units now out on the road, i'm not willing to risk having my car impounded because i drove by and was too dirty



i had a member send me an oem cat with about 18k on it - i am trying to figure out a retrofit for that unit - however, i am not sure it is going to work - if not, i will either be returning it to him, or making it available to somebody - i will know for sure in a couple of days

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[Kim]

Against what was thought originally to be my better judgement, I had mine welded in exactly the same place that you describe. It was worked perfectly since. Although it won't last forever it has lasted so far (about 25,000 km). For $80 it was worth it.

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[clivehuggins]

For what its worth, my 968 tip coupe has had the cat removed (by a former owner a few years ago) and replaced with a muffler which looks identical to the standard one further towards the tailpipe. Hence I now have two mufflers. NZ emissions are less stringent for a 92 car than in the states so this is how it has got away with it. My report would be this, the exhaust note is purposeful especially between 2k and 3.5k rpm, but not too loud, fuel consumption (in relation to possible running rich) is excellent on long runs (close to 28mpg driving hard) using 95-98 octane. I can't comment on any loss of torque as its all I've know and haven't had the pleasure of another 968 to compare, but my gut feel is that it should feel stronger in the low rpm range. I will be bringing the subject up with my mechanic next time she goes in to find out why and what was done during the cat removal and will report back.

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[flash]

it's not just that the exhaust was well tuned, that the intake is a big factor on the exhaust (pulse timing),and that changes in flow have less that predictable effects - the problem is that mixture tuning will need to be done once you do find the magic flow rate - been there, done that



yes, the cat holds heat - that is exactly the issue - without that heat, it runs rich - i am going through this now - i need to hold MORE heat - the header lets too much out, and the O2 sensor doesn't do its job right - same thing with high flow cats and "test pipes" - might be ok on open loop runs, but the rest is a mess



i am wrapping the header today



but as i said, this is a long standing and long debated subject - i would be very careful about making any permanent changes in the exhaust without testing - i have gone through over a dozen systems now, and left them all clamped - glad i did - all but this one i have now LOST power

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[tkacki]

Cat delete should be done together with the switch to M150 option. This disables lambda and DME is using fixed maps. To switch the DME You should put 1k resistor in 3 pin sockect near DME plug. There is also a need to put 10k potentiometer to lambda socket to staticaly adjust mixture/CO at idle. Refer to the wiring diagram.



This solves the problem refered by Flash.

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[PorscheDude]

M150 option? Is this like the 1177 modification?

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[flash]

it's a real option code "Emissions Systems removed for countries without unleaded fuel"

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[94SilverCab]

[quote name='tkacki' post='58224' date='Aug 22 2008, 04:40 AM']Cat delete should be done together with the switch to M150 option. This disables lambda and DME is using fixed maps. To switch the DME You should put 1k resistor in 3 pin sockect near DME plug. There is also a need to put 10k potentiometer to lambda socket to staticaly adjust mixture/CO at idle. Refer to the wiring diagram.



This solves the problem refered by Flash.[/quote]





tkacki,



Holy smokes ! I have no idea what your post means, but I get the impression that you really know your stuff. Tell us about your car...any tricks up your sleeve?



Welcome !



Jay

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[flash]

i'd like to hear more about this too - would this resolve the rolling dyno issues at 2500 rpm, which is where i have the problem

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[unknown4u]

Should the engine have more power with the m0150 option? of maybe more torque?

I'm interested in the dynoresults Flash.

Let us know.

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[xrad]

tkacki...interesting stuff!



How accurate are the fixed maps?



have you done any dyno/real life stoich readings?



It would seem that fixed maps come in all DME units as a back-up in case the O2 fails, so do we need the M option to do this?



Thanks!

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[tkacki]

M150 is no cat option. PET says: M150 - operates with leeded gas. It is: no cat, no lambda, fixed maps. Every ecu has fixed maps.



To convert You need 10k potentiometer and 1k configuration resistor.



You can also convert Your 968 to "original factory" M150 using folowing parts:



1. Confuguration adapter / plug 944 612 492 00 - which is simple 1k resistor as mentioned, to be inserted near DME.

2. CO potentiometer 944 606 212 00. Originally it is located near ignition coil.

3. Cable / harness (between pot and lambda socket) 944 607 175 00.

4. Support 944 606 053 01 - to mount potentiometer.

5. Screw / cap 900 219 015 00 - to fill the hole afer lambda removal.

6. some minor hw (bolts, washers).



Cost here in Poland about 150 USD.



Have fun.

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[flash]

i'm curious about the potentiometer - what is it that you are adjusting with it?



where does the resistor insert?



any pics on any of this?



i'm sure that it would fail the visual tests, but it would be interesting to see the outcome

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[PorscheDude]

very interesting information.

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[jlm968]

flash, two questions:



First, how well do the OEM manifolds withstand being wrapped?



Second, are you certain your issue with the O2 sensor is mechanical (heat-related) rather than an electronic issue? I would think an 11:1 compression ratio, and exhaust spewing from an aluminum head, would generate plenty of heat for an O2 sensor. My car will have the O2 sensor downstream of the turbocharger (no catalytic converter, no resonator/muffler), where much of the heat energy has already been used by the turbo. Exhaust temp will be considerably less than what you have. I don't anticipate any problems. Lots and lots of race cars out there with no catalytic converter. Check your electronics.



It's interesting to hear from someone in another market - Poland? - about an option code that deletes the O2 from the system, or at least fools the DME into thinking things are fine from the O2 input. MAF systems can run without an O2 (or knock sensors) but might lack some flexibility. I'd want to change my oil and plugs more often but otherwise wouldn't sweat it.

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[flash]

yes, i am certain that it is heat related - i even changed the O2 sensor to be sure that it wasn't just old and tired



remember, this is not a running condition problem - this is strictly an emissions problem



there are a number of factors contributing to the problem - the biggest is that the aftermarket ceramic cat is not up to the job - the oem cat does a MUCH better job - to get anywhere near clean enough, the O2 sensor and the cat need to be EXTREMELY hot - whether it is the chicken or the egg, the problem is "resolved" by heating it up



the real solution is to put the oem cat back in there - aftermarket ceramic cats are not enough - i have tried 5 different ones now, ranging in sizes and cell counts - NONE even got close - the small ones actually made power losses in addition to running dirty

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[jlm968]

Bummer. I just recycled a perfectly good OEM cat. Would've been happy to ship it to you.

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[tkacki]

In M150 mode potentiometer adjusts the CO at idle. If DME is switched in M150 mode and potentiometer is missing or failed, the DME will store specific error code. The 1k configuration resistor should be inserted in the socked near DME plug. You can find the drawings of all mentioned elements in factory repair manual. The configuration resistor is also enclosed in wiring diagram in manual - just check near DME wiring diagram.



There is a one great advantage of this mode. You heve a total contorl of the engine when modifiyng fuel and ignition maps stored in DME's memory - result is not fuzzied by lambda regulation loop. In addition, the DME's memory stores in fact 3 sets of maps. 1st - standard lambda loop (norhing pluged), 2nd - M150 (1k resisror pluged), 3rd - lamdba for low octane fuel (specific countries) - jumper pluged (siple wire). You can mount a switch on that plug and switch the mode on the fly (switching ignition off is not required). It takes about 2 seconds for DME to switch between the map sets during driving, so You can use the switch to select maps (f.e standard and agressive setup).

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[flash]

i think there must be some very real differences in your DME - it takes a lot longer on DMEs here to clear maps - this was verified on dyno tests when we were doing the chip testing



what page of the manual is the diagram with the resistor mod on? those diagrams are pretty hard to search



again, i don't think it will solve my particular problem, but this is interesting stuff

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