I’ve heard that wrapping said manifold and the connecting pipe with thermal bandages can work wonders for performance.
The hotter the exhaust gas stays the faster it travels, the more inlet charge it pulls into the cylinder. On a well tuned car with a well tuned exhaust, it’s well worth doing. On a standard car with an off the shelf (i.e. not in any way tuned) manifold and system, I reckon the trouble would not be worth any gain. The bandages deteriorate and need replacing regularly. Ceramic coatings have now largely replaced thermal bandages.
Don’t ever go by rolling roads claims. I can get 20bhp on any car just by replacing the washer fluid.
Use 1/4 mile terminals speeds, very repeatable and reliable, there is a calculator out there somewhere.
^This. I used to run it on my racers, because every little helps. It does keep engine bay temperatures lower too. We also used to have the engines out all the time, so it was never a hassle to replace it. Get yourself some lockwire pliers.