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Thanks to Keith Potter in Thailand for this, his
second contribution to the OzBrick.
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There are many requests on the boards for assistance in removing the catalytic convertor from an 850, asking - what are the effects and improvement in performance? The author lives in Thailand, and bought his 850 turbo from a (non Volvo approved) dealer. The car was returned under warranty for several reasons, amongst them a lack of power. It was returned after several weeks (This Is Thailand) - with the power restored. But was completely undriveable. The noise inside the car was incredible. Outside the car, bad. Looking underneath to see what the hell was going on, I noticed the CAT had been removed. Not replaced. Removed ! A section of steel pipe had been welded in it's place! This is effectively the CAT BYPASS tube sold by many "tuning" companies. So only the stock rear silencer was in place. It is not good enough on it's own. Anyone contemplating CAT removal should understand that not only is it illegal in most countries (yes - even here in Thailand though few people are aware of any emission control regulations here) - but the performance of your car will NOT improve significantly. The noise it produces will "improve" - you are modifying a luxury sports saloon car and bringing it's performance in line with a 20 year old pickup truck. I make no apology for this statement. Let's be realistic. If you are an immature kid looking to get noticed, then this is the way to do it. But if you want a real performance increase, please think about what you are doing and why Volvo designed the vehicle the way it is. The CAT not only functions to reduce emissions, it is it's own right a very effective silencer, as it restricts the flow significantly. This is how the early, traditional silencers worked, by restricting the flow of exhaust gas. Remove it, and you increase the flow velocity of the exhaust gas. The engine ECU doesn't know anything of your modification ..... If you are lucky and your car was from one of those markets fitted with only one O2 sensor, then you will probably notice a performace drop at low rpm, maybe a small gain at full throttle of a few HP. On those cars fitted with two O2 sensors, the engine malfuction or O2 (Lambda) warning light will immediately come on to warn of the malfunctionig CAT. The car will run rich with full throttle, and will evenually set off the LAMBDA warning. If you are lucky, your engine will survive. Want to take the chance? Fitting a "High Flow" or "Race" CAT is similarly fraught with risk. The engine ECU was not programmed to run with a high flow CAT and it was not intended to compensate for one being fitted. Fitting a High Flow CAT will usually not meet emission standards in any case, and it will increase the noise level of the car. A properly reprogrammed ECU chip by a reputable company may be OK - read their literature and fit ONLY the exhaust components that they designed their program for. If you live in a country where removal of the CAT might be necessary because a replacement is prohibitively expensive - it is permissible by law - and you have no second O2 sensor problem - it is possible to restore the car's noise output to something near stock by fitting a silencer at the rear of the car, under the trunk. Noise level will be a little above stock. Addition of a second small silencer in place of the CAT will bring the nise back down to stock levels. The author was lucky enough to have access to a silence (muffler) shop with a large selection af silencers to play with. Believe it or not, it didn't make much significant difference WHAt type or make of silencer was fitted as suggested above - straight through, pancake, glasspack - whatever. With the stock large muffler still left in place, that is. Flying in the face of all popularly offered advice, try to find silencer which are IS restrictive. This will help to compensate for the tendancy to run rich after the CAT removal. BUT - you still have no guarantee that engine damage will not occur! Many aftermarket exhaust systems for the 850 are available, but few of them take the ECU program into consideration. They rely on Volvo's mapping of the system performance in the ECU to take care of the difference between their system and a stock one. Luckily for them, in order to take care of manufacturing tolerances, wear and tear, etc. the ECU program has been designed with some flexibility, and often does compensate adequately. But how do you KNOW it is doing so ? |
If you have any experiences, facts, hints comments or data that you think might be useful on the site, please
and I will post it, with an acknowledgement of your contribution (if you so wish).