If it helps the bonnet on my 410 is 165 cms down the long edge 107.5 cms across the top edge (nearest the windscreen) and 85 cms at the front.
Got me thinking as well and found these chaps
https://sportscarmetalworks.com/bonnet-louvres/
The links at the bottom of the page are interesting (well I thought so - from Jag forums - sorry).
I appreciate you weren't necessarily seeking advice but I'd try a mix of everyone else's suggestions before you break out the tin snips. So if it was me, phenolic block for carb (if none already), then if no difference remove sealing strip between bonnet and car to let air out (though increased risk of pongs in car).
As I suspect your issue maybe carb related and fixable you could try initiating the problem i.e. driving it around on a hot day then pull over and let it idle for ages this time with the bonnet open slightly and see if it cures your hot start problem.
A bit as per Kevin, I was recently stuck for an hour and a half on the motorway on a very hot day and was reluctant to turn the engine off in case it failed to restart. I'd let it idle for 45 minutes much to the understandable annoyance of other road users and in the end I gave in and turned it off and had no problems restarting. Mine's still on the cast iron manifolds and the only mods I've made are the phenolic spacer on the carb and it's got a new 500cfm Edelbrock on it.
That said some tasteful louvres could look cool and I like the idea of having a summer and winter bonnet!
Good luck
18-08-23, 11:02 AM
Threaded Mode