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Tuning with a Sports Cat

General Tuning Discussion

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Hi all, my first post on the forum.

I am looking to install a sports catalytic converter to a car mapped with a decat system.

Are there any particular changes you would expect to need to make, some do's and dont's specific to running with a catted system?

Engine is a Subaru Impreza with circa 500BHP, run on pump fuel. ECU is Syvecs.



It's possible that the catalytic convertor may add additional back pressure which will affect the VE of the engine. This may result in the engine running slightly richer under high boost. You may also find the engine is more prone to knock under high load. It really comes down to the relative back pressure.

It's probably also worth mentioning that without setting up the ECU to dither the lambda back and forth across stoich the cat won't actually work to reduce emissions.

Thanks Andre,

The owner is looking to use this mainly for emissions legality checks, so will probably have a bespoke map for that testing.

Is there any issues with killing the cat if the engine normally runs with relatively rich Lambda targets? 0.75 is the full power target.

the cat is expected to be a high flow motorsport spec unit, (current WRC spec), i don't yet know the flow limit of this, just trying to get some info together at this stage.

To get it to cycle across stoich, how would you do that whilst using a wideband with a normal closed loop lambda target?

You shouldn't have any issue with cat life at that sort of WOT lambda target, particularly as you'll be cycling the lambda target based on load.

To make the cat work you'll need the make the air fuel ratio cycle back and forth across the stoich point. The Syvecs ECU should be able to do this but I haven't had the need so far so can't advise further sorry.

Thanks Andre, i'll do a bit of digging on the syvecs settings required.