Bonnet louvres:
They might let some hot air out when the car is standing still.
But
They are almost always in the wrong place to extract air at speed.
They let in water to cause problems with the ignition system.
They reduce the stiffness of the bonnet panel.
To me, they don't have any positive aesthetic value on a Jaguar saloon.

If it's necessary to cut slots in the visible, external panels, do it on the vertical part of the wing fender, where the modern Jaguars have a slot. It will require some ducting to connect to the under hood space.

 

Coombs Bonnet Vents

 

I agree, for a daily drive I would not use hood (bonnet) louvers. In fact my car came with a louvered hood, which I sold as I want the car to look more stock. The ram air intake I created to scoop the air into the engine bay is funneling the air into the engine bay and ideally the exit points should be more at the same level which is why those ports at the lower portion of the inner fender well work great. These cars even stock had a problem of trapping the hot air into the engine bay and acting like an oven; when I put a much more powerful engine that created more heat the problem was exacerbated. Nobody is going to see the lower ports so the engine bay can finally breath well ad that solves the design flaw in a much better way than cutting holes in your hood. Plus with an opening up high I do not think it would be as good in my opinion regardless of looks. Remember I did everything possible for heat prior to the ram air scoop at the bottom and all those things just kept the engine cool but that was never the problem. The engine always was cool, the problem was the Jaguar engine bay acts like an oven so without a better way to get air to flow in and out the things around the engine have issues. I probably could have done none of the other heat treatments other than radiator and the front valance and everything would be the same with no issues.

 

You did a darn good job considering what you have to cool!

 

Not sure I like louvers in a Jaguar bonnet and although they do let hot air out they can also let water in. I had louvers in the bonnet of my Lotus Seven and the water was getting in and sitting in the spark plug holes. (Twin cam engine like the XK, Plugs in the top) I had to make a panel under the louvers to direct any water to the side of the engine so it would not foul the plugs. Only happened when the car was stationary in the rain but a bummer trying to start the car after a rain storm. Had to carry a screw driver around with me to remove the plug cover and paper towels to dry up the water until I made the panel.

 

E Types have louvers in the bonnet from the factory, and I never had any problem with water on the engine on my car. E Types generally don't have problems with water from the louvers.

 

E Type Bonnet/Hood louvres are somewhat differently positioned to Coombs.

Coombs:




E Type:

 

I think they work on the E-Type because one focuses on the centre bulge.
The length of the bonnet helps matters too.
The scale of the bonnet makes them less noticeable over-all.

The Mk II's hood is too small to allow the louvres to look correct.

 

Thanks Glyn. I think the cars look nicer without the louvers and I do not like the idea of water getting all over the electronics, etc. Why create more potential issues, especially when I drive my Jag daily and rain does not stop me?

Also how many E-types really drive in the rain? and do they drive it in stop and go? Even if it does not cause the engine to faulter, it will make the engine and everything around it dirtier....

 

The only point I was wanting to make was E Types had louvers from the factory and any potential water ingress didn't cause problems.

When the cars were new, many were driven in rain. I knew several people who had an E Type as their only car and drove them year round - and not in sunny California either. One fellow I know bought his car used in 1972 and still owns it. He now has over 600,000 km on the car and it finally needed an engine rebuild in 2014 at 500,000km. He competitively slalomed the car too, he didn't baby it. When maintained, the XK engine lasts a long time

 

If you look at Glyn's photos in post 27, it's clear that the E type louvres are set further apart than where they are typically placed on a Mk2. They are well clear of the valley in the cylinder head. I think they are placed to allow air out at low speeds and do little at higher speeds.

 

I think the other reason the louvers work on the E Type is how widely they are positioned in relation to the centre line. Any water entering the louvers tends to fall down the sides of the engine. On my Lotus Seven the louvers were closer to the centre line and any water entering fell straight on to the top of the engine and into the Plug valley. Something to consider if you did decide to go down the route of louvers on a Mk2 bonnet.
Most of the under bonnet heat must come from the exhaust so as Primaz has done, louvers on the inner wing or just cut a chunk out of it right by the exhaust and a lot of heat will go that way. I think I would go the route of ceramic coating on the exhaust manifolds. Radically reduces the temp of the exhaust manifolds and sends the heat down the pipe and out the back. On my Lotus Seven I wrapped the manifolds in a heat wrap tape. Did not look pretty but reduced the under bonnet heat.

 

I simply don't like louvres on an S Type or Mk2 bonnet/hood. I think an E Type would look odd without them

Primaz under nose scoop/s, for want of a better word, and triangular cutaways (IIRC) at the rear sides of the engine compartment obviously work very well with the mileage he has put on that car.

 

As standard, our cars have nothing in the way of a chin spoiler to prevent air going under the bumper into the engine bay, raising the air pressure under the bonnet and under the car and blocking air flow through the radiator. This increases the tendency for the nose to lift and makes the heat removal problem worse at higher speeds. Reduce the flow under the bumper and you will both lower under hood temperature at speed and improve engine cooling. I'd prefer scoops to direct air to the front of the radiator. When the car isn't moving or is going uphill at low speed, we are relying on the fan. That will certainly be helped by slots in the inner wings.

The primary parameter controlling the effectiveness of a chin spoiler is the clearance from the ground. Shape and precise position are secondary and can be driven by other design requirements (parking nose to kerb) and aesthetics. The spoiler will also lower the Cd. With a scoop from the spoiler to the radiator, it would be possible to close the top of the standard air intake and improve the aerodynamics even further. With a bit of effort, the nose of the Mk2 can be as aerodynamic as it looks.