nice work see no reason it should not work for air out.

when come in after a 1 hour ride, i have immediatly measured the engine head temps, usually around 180F,, now let car set for about 10-15 minutes temps read arounf 195/200F.

it is heat soak upward from the hot oil in sump that is usually hotter than engine coolant(a normal situation).

becomes a serious problem with the V12, like dropped valve seats.

especially after an hour or so on a hot Texas day,100F ambient.

seems most V12 seats loosen after the engine has been shut down, from this condition

TWR racing did not want to stop engine when in for tires etc.

caused some DNFs, or disqualify.

 

Air exiting under the car will cause a high pressure area under the car (unless a rear under tray is added) where the 2 air streams meet, reducing down force.

The best place to add vents is at the front of the bonnet, just behind the radiator, this is a low pressure area. Adding vents at the rear of the bonnet will not necessarily increase flow through the bay. Look at a picture of a Lancer rally car, it has the vent very close to the front and angled so the flow stays parallel to the bonnet.

 

At speed, say above 40 mph plus, a definite build up of high pressure starts under the XJS bonnet. The racing XJS, as confirmed by Allan Scott the TWR engine genius, in his recent book on the ETCC winning XJS. In the case of this car, TWR released the pressure and substantially aided under bonnet temps, under bonnet airflow, and therefore cooling effectiveness because of better airflow flow, by fixing the bonnet by pins which held the rear a couple of inches proud of the normal bulkhead shutline.


As Grant has also explained to us, airflow out of the bottom of the engine bay is poor, and in his vast experience the best non-bodywork mod you can do is to remove the foam rubber covering the gearbox. This allows far better airflow by allowing it out of the back of the engine bay.


The regulations of the ETCC prohibited bodywork changes, otherwise louvres would have solved the problem. The pressure build up at higher speeds was such that, even with the bonnet held open and secured by pins, on one occasion the pin fixings ripped out of their fixing points on the bulkhead!


The airflow out of the back of the bonnet is substantial. A few bits of wool taped along the bulkhead shutline (which is how Malcolm Sayer actually tested his shapes, on the back of a motorbike watching alongside the car as it was driven) will demonstrate that there IS substantial airflow out of the rear of the bonnet on the move when above 40 MPH. Fix the bonnet open a bit somehow and try it. On my car I have found that if I remove the rear bulkhead seal and switch on the electric rad fans (car stationary) a gale blows out of this shutline, bonnet properly closed. Replace the seal, nothing comes out. I deduce from this that there is a natural path for radiator air that it prefers to take from the rear of the bonnet.


There is a guy who runs UK firm called sportcar metalworks Bonnet Louvres | Sports Car Metal Works
I have spoken to him on the phone, not met him, and he will put louvres into the XJS for about 180 UKP. There is an XJS pic on his site. As soon as I think I can get this past the management, I am going for it. This is the only easy and definitely the most effective way to reduce underbonnet heat, in my honest opinion.
Greg

 

Hi Greg

I'm not sure what you mean by 'Rear Bulkhead Seal' where it is or what it looks like but are you suggesting that its a good idea to remove it?

 

Alan, It looks a bit like the bootlid shutting seal. It runs across the seam just in front of the wiper grille and the bonnet shuts against it and hides it when shut. I left the outer 6 inches each side, which the bonnet then shuts against, and cut off and removed the bit in between.
As BB said, if you have a leaky engine when you park and hot air can seep out into the wiper grille area, engine oil fumes may permeate the cabin - not on my car of course! If this happens to you, then before switching off the engine just turn off the aircon (RH knob to 6 o clock) and this will shut the blowers' air flaps into the grille well.
Greg

 

Right Greg

Got that, Thanks!

 

Hi Greg

That looks a bit of a 'Bargain!'

 

My work in progress, similar to Aston Martin. Black grill and water diverter box.

 

This is a surprise, I would have expected this would be a high pressure zone this close to the windscreen. I might try taping some telltails here once I get my car back on the road.

 

I will leave the scientific analysis of airflow to those way more qualified than myself but l remember years ago in my xj12 (not xjs granted but similar bonnet set up at rear) the Bonnet popped open at speed and the safety catch had a very hard time holding it down. Until then l had always assumed airflow at speed would close it due to the front hinge setup.
Just an observation.

 

Warren, bonnet shut, there might be. Bonnet on the safety catch (or pins as per TWR) as Baxtor mentions, plenty of air exiting above 40.
Greg

 

OB something like this, pic of mine, added chrome for visual effect!

it has about a 1/2" clearance between hood and chrome rail.

seems most effective in traffic and idling(tick over).

quite a bit of heat exits at gap,by feel, with electric fans on.

altho at hiway speed i dont notice any heat problems!

 

Cheers Ron

But its always hard to look at your Car, without me wanting to buy it.

Maybe if I win the Lottery on 'Roll over week' Lol.

 

OB its just an old junk XJS that was given to for nothing(no money or anything) other than to get it off the property!

buy it started to posses me an 30K later,the ghost of christmas's passed came to life again!

of course the learning experience was worth more than anything else, money is paper, knowledge is forever!

 

Cheers Ron

I better start Saving up then!

 

I installed Run Cool Louvers in my XJS and it worked out great. It releases a tremendous amount of heat from the motor and I love them. Similar to the E Type but a bit longer. and they fit perfect down the two lower channels on hood. It made a huge difference for me. I followed the instructions and went to work. After the hood was painted, I was happy. The hardest move was making the first scratch with cutting grinder on hood.

 

Being That Guy and resurrecting and old th@ronbros did you punch those louvers or were they grafted in? Any detail on your approach is appreciated-
Regards
Bob