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I was just wondering if anyone has done testing to determine if Lean Cruise results in hotter or cooler exhaust and engine temps? I have done some google searches and can find examples of people saying exhaust temps go down and some that say they go up? Has anyone seen for themselves what happens to temps during lean cruise? I am using a CXWK VT memcal which is a hsv L67 memcal on a L36 with an aftermarket supercharger. This tune allows lean cruise to go a little higher than 18:1 and am wondering if this has any negative effects on my engine? Also would the L36 be able to cope with such lean AFR's?

if you go too lean you get hotter temps, and if you get too much heat you can do damage ... the other thing though is if its at light throttle its not so bad ... 18 is getting pretty lean, i've seen my ecotec 16-17 but thats about it. aslong as you can't feel it its "suitable" but i've seen heads with bad valve seat recession (ecotec heads) so im not sure if that is from excess heat from lean or just normal .... most i've seen have pretty much none normally.

Actually the hottest temp is stoich, either side it gets cooler. NOx emissions get high on the lean side of stoich but otherwise exactly what holden202 said - so long as you cant feel lean cruise at light throttle its ok.

A direct injection engine can appear to have really lean burn (ie > 25:1 AFR) when measuring the oxygen content of the exhaust stream, but due to injecting fuel next to the plug and finely atomising it can actually ignite the mixture.

Ive tried lean cruise at various speeds cutin and out, also different afr's for different loads and different amounts of air mg/s per cyl, i havn't really noticed any great improvement or loss in fuel economy and coolant temps have remained the same, that's not to say exhaust temps are cooler or hotter, i havn't tried over the 17.2:1 that stock goes upto but i dont think there would be any further savings.

The best improvements ive found is lowering the cut in time after idle, then if your keen play with the lean cruise afr vs mg/s cyl table to get your afr's better suited to the conditions you want to lean it out at lower load while cruising, the stock table still leans out to much when using more throttle you loose power and end up using more fuel than your trying to save.

Ive ended up with maybe half a litre per 100km saving.