In a petrol..... move the cats from under the bonnet to under the vehicle.... makes an enormous difference to the under bonnet radiated and convected heat.
Ceramic coating of the exhaust manifolds is also effective especially if your running headers ( i.e. not a 3.6 ).
Of course this is not a bolt on or simple DIY fix so not suitable for many. But stopping the heat buildup before it becomes an issue is far more effective that trying to reduce it afterwards IMO.
__________________
It seemed like a good idea at the time........
|