Clattery when cold
Join Date: Feb 2012
Location: United Kingdom
County: Greater London
The thing is that swirl flaps only do anything useful because of the exhaust gas being fed through the EGR valve. The whole point of introducing exhaust gas is to spoil the fuel burning efficiency at lower revs, which reduces combustion temperatures and produces less NOx. But a side effect of that is that the deliberately poor combustion increases hydrocarbon emissions from unburnt fuel.
The swirl flaps operate to create turbulence, to better mix air and exhaust gas to try and reduce that happening. When operating, they close one of the two inlets to each cylinder so the gas enters from one side of the combustion chamber and 'swirls' to mix air with exhaust gas.
Basically they are a kludge to get around the inefficient combustion caused by using EGR to reduce NOx at low revs.
At larger throttle openings, above ~2000 rpm, the EGR closes, the swirl flaps open, and the engine runs on air alone.
Unfortunately the swirl flaps are poorly engineered and will eventually detach from their spindles.
If you only remove the swirl flaps, you will notice some loss of low-down torque from the degraded combustion. But if you also blank off the EGR, your prevent exhaust gas reaching the cylinders and the swirl flaps then serve no useful purpose. The engine is inhaling clean air alone, not soot, CO and CO2 from the exhaust.
I ran my car like that for a couple of hundred miles and it was fine, except I had a MCSF light because of the blanked EGR. Eventually I took it to Autolusso who mapped the EGR out. But that isn't, I am sure, just disabling the MCSF fault. I'm guessing AL are slightly increasing the fuel supply to match the increased amount of oxygen available once there's no exhaust gas being inhaled - in other words restoring fuel efficiency to what it should be. It made an immediately noticeable improvement to drivability at low revs. The engine pulls well from tickover without using the clutch (cruel to the DMF, but it does it, even in 2nd).
If you were to measure NOx at <2k rpm, I expect it would be somewhat worse, but that's the only downside. The upside is eliminating a whole heap of stuff that causes problems - the periodic choking-up of the EGR valve, the build-up of restrictive carbon goo on the inside of the inlet, and the hefty engine damage that will happen when one or more flaps detach and enters the combustion space. It's relatively simple to remove the inlet manifold and delete the swirl flaps on the CF4, replacing the head is a much bigger, costlier job.