[Source: Lotus via Paul Tan]
We won't argue that it'll be at least slightly more difficult to open up the exhaust ports in search of every ounce of power, and it will likely turn out to be a lot more difficult. That said, the Integrated Exhaust Manifold is really aimed at OEMs and Lotus Engineering likely doesn't give a flip about enthusiasts. It will take a little while for this to trickle down to everyday cars, let alone into the grease-stained mitts of performance junkies. As unexciting as it seems, there's performance gains to be realized.
First, and most in keeping with the Colin Chapman legacy, the IEM will reduce weight. Lotus has developed their IEM technology to be manufactured out of aluminum, so it's off to the slag heap for those old cast iron beasties. Reducing weight is like free horsepower; or you could think of it as free gasoline. Less mass is just plain good. Another performance gain comes from the reduction of underhood temperatures. Engine compartments these days are hot environments, but the IEM can significantly reduce the heat level. Like marine engines, which pump raw water through their exhaust manifolds to keep engine room temperatures managed, the cooling system is integrated into the IEM. By capturing the heat in the exhaust, engine warm-ups are faster, meaning passengers have heat more quickly, a comfort and safety improvement. The catalytic converter can basically be mounted where the old manifold and downpipe used to be, which reduces thermal losses before the cat, and speeds light-off. Faster light-off means reduced emissions. Keeping the engine bay cooler reduces the temperature of air in the intake ducting, as well as helping the HVAC do it's thing more efficiently. As usual, efficiency equals both eco-friendliness and performance.
"Siamesed" exhaust ports that combine in the head or block are nothing new - the Ford Flathead V8 had a single port for the two center cylinders in each bank; and the exhaust ports all went through the water jacket. That's not to say the IEM is a copy of the old V8-60, it's way more high tech. The Lotus IEM will offer fewer underhood failure points, which bodes well for reliability. The technology will also yield a cost reduction, which will equal money that can be spent elsewhere. Some packaging efficiency gains are also envisioned. We think the real news here is the faster catalyst lightoff; Lotus claims it's up to 20%. The faster you can get those emissions systems scrubbing, the easier we can all breathe.