What's the bottleneck in my engine?

[BevanWright]

I dont have an SPF, it is a NZ made replica by Almac Cars. It does have a flat bottom now which I made out aluminium, but I was running at the 185 - 190 mark without it, and it just started getting light at that speed. That is when I decided to make the flat bottom, and intend on making an air-damn as well. The intention was to go over 200, but I was young, single and without kids at that stage - maybe I would think twice now?

I dont know why my car is so stable at speed, it is low, it has an aluminium tonneau cover and a small aeroscreen, so i guess that allows significantly faster air flow over the top of the car. Also the bonnet has lots of louvres to let air out, and the flow of air out the side louvres is pretty open from the engine bay.

I have been surprised by the comments of the 140-150 mph being the tops for most Cobras, but then I havnt driven a Cobra with a full windscreen etc over 100mph.