Hey All... Been a while since I've had to open the hood of the XJS,,, feels strange - haha

I'm not big headed enough to assume that this is a novel idea or that I'm the frst one to think of it, but I'm wondering what folks think of this...

I have the old school quad headlights on my 1990. I lovvve them, the look and the authenticity they bring to the front of my XJS convertible.

But I been thinking. Ususlly where the problems start...lol

What if the two inner most headlights were essentially removed, space hollowed out and in their place a wire mesh cover followed by a smooooooth set of ducts run to the trumpets....? Trumpets cut back a bit to the area of their widest diameter, towards the breathers... I mean, cool, fresh forced air, run thru smooth tubes right into the breathers, at speed, almost being forced into the intakes... I like the idea. I havent looked superclose at the obsticles under the hood. Would it work?

I would love to hear what yall think!

I found these but there are a lot (I was surprised) of options.

 

Would need something to keep all the bugs out but would restrict air flow.
What about high and low beams.

 

The outers have H4 bulbs which work on low and high. If you converted the inners to air intakes, then the high beam intensity would be reduced as the outers would not be there; he low beam performance would be unchanged. You would have reasonable high beam lighting, even so. The so-called "euro" one-piece headlights have only a single H4 bulb; but a bigger reflector, of course.

 

Thanks Greg... Are you saying the low beams are double filament? Just wondering. That when the highs are clicked on,,, the lows get a boost? Or have a second filament...?

I was also thinking about a good fog lights or,,,,
I do find myself using the highs often. And need something there.

I'm no electrician by any stretch of the imagination BUT I was thinking if I could find a dual high beam low beam light of the same size and shape I might be able to wire the high beams in the duals by splicing in the left over wiring from the removed high beams...

I hear ya about bugs but I would only worry if it was literally a FLOCK of bugs...

Later, after the post, what I really started thinking and worrrrrrying about, is water and rainy days. Water literally being blasted into the air stream and intake. Seems to rule this idea out. I drove on the highway in the rain this morning.

 

I was thinking exactly the same,,,, and later about rain water.

 

Isn't this a solution on the higher end Challenger? Seems like someone discussed using these headlights.

 

Hey Man... If ya don't mind, could ya elaborate a bit...?

 

Someone on the old jag-lovers.org list I believe actually did that modification. You could search the archives there, or it might have been mentioned in Kirby's tome.

FYI, Roger Bywater wrote that even though Jaguar went to cold air intake late in the XJS production, he thought the existing set up was the better engineering compromise. Basically he stated that cold air is good for horsepower at the upper end, while hot air is good for fuel economy, and that the existing trumpets get the best of both, Hot air in the conditions that fuel economy boast is most beneficial, and that at high speed there is plenty of cold air being forced into the engine bay.

 

I'll look... Thanks for the lead! Really!

I wonder about the fuel economy, and it makeing such a difference. I mean, when I went in this direction (v12) I have to admit I never even considered fuel costs, and kinda still don't.

 

JJJ
The H4 bulb in the outers is a double filament build, which switches filaments as the low/high is selected.

 

Here is what I did to mine a loooong time ago.

There was much HOO-HA about the 50mm ducting I used at the time. My care factor for that, LESS than zero.

I used the Donaldson Air Filter Application chart I had at the time.

Using 3ltr per side, NA Induction, and 7000rpm max revs. 45mm was all that was required, which is an impossible size to find, so 50mm became the call of the day.

I wrote this in 2015ish from memory.

Along with the big throttle discs, etc etc, this little exercise transformed that car, and more so at highway speed, when pulling out to overtake, there was a distinct "kick in the pants" from that engine when the fresh air charged down those tubes.

Bugs were not an issue. One trip across the Hay Plains, ??speed, a small bird did not fly fast enough and got sucked into the LH tube, and that upset Her Majesty something serious. Took an hour on the side of the road, 45C out there, to get it out. It only went in about a foot, but that was enough.

Always had the thought of a screen of some sort, never did do it, no more birds etc, so it got forgotten quickly.

 

Grant, do you have a write-up on the throttle discs that I've missed all these years?

If not, can you elaborate?

I've been meaning to ask for some time

Cheers
DD

 

I second that ^^^^^

So I was just out during a "break" from work poking my head under the car,,,, oh! But first - Grant! Thank you for the write up. Amazing. I do have a quick question about where the open ends end up,,, exactly. Maybe I missed that in the write up BUT are they,,, yeah, where does the open out of engine bay end up and what does that look like, if ya can...?

Back to head poked under hood...
Basically, with a re-location of the cigarette pack, the rears of the headlight frame out look like they were made for the piping. I think Grants use of a fiber (rather than plastic) tubing makes great sense when thinking about rain water. Also, to solve the rain problem, maybe a down bend in the pipe (which is crappy for air flow) with a little drain?

I think rain water is the only thing that's going to STOP this from being the right idea.

Then,,, for beams and headlights, maybe there is a round light replacement for our sealed lights that accept a duel filament bulb that could be wired to the high beam switch simply using the old/OE wiring... I guess I'm in the hunt...!

 

This is what you need JJJ.
https://www.bowerspartsonline.co.uk/...ion-with-pilot
they are available in the USA I am sure.
Straight swap into the headlight bracket hardware, plus an Osram nightbreaker H4 bulb, x 2 units.
They willl be far better than the candle power sealed beams you have now. If your existing outers have single filament bulbs, just wire the dip and the high beam loom feeds to the respective terminals of the H 4 bulb, or buy a dedicated terminal and wire that.

 

Damn Greg...! I think I should just send you my bank account information... Here in NYC, we have a lotta what we call "professional shoppers"!!!

Great. And I swear I would order these things right now IF...

I'm waiting for someone to school me on the rain water issue. I mean,,, will driving 70mph on a rainy day leave me with a gallon of water in my intakes and engine? All the silence on this issue is leading me to believe that y'all are waiting for me to go on ahead and test the waters,,,, no pun intended, 😆

 

Forget the rainwater idea. It will be fine.

 

doug i use 3" diameter brass TB discs! bought them from a magzine article(order by telephone no internet yet) 26 yrs ago, cant remember from who).
set the TB up in a lathe and bored them to size, works fine!
they were originally made for a roots blower fuel injection TB! but they are well shaped and never had any sticking!
ron

 

pic of my HI beam LED lights, sealed from water, mounted in the Euro housing , also my OLD projector low beams can be seen( they are lousy lights small bulbs).
could be up graded to much new LED projectors!
ron

 

I have a vague recollection of some guys using XJ40 throttle bodies. Bigger than the standard 5.3 units and virtually bolt-on?

Cheers
DD

 

There is no need for larger throttle bodies on an unmodified engine. TWR did an evaluation of the V12 in 1985 to see what improvements they could do the engine and market it as a higher performance version. They found that the standard throttle plates could handle a 35% increase in power, and then when they went to 70mm throttle plates instead of standard 63mm the difference (with 35% more power than standard) was only an increase in power above 5500 RPM. For a road car and a standard engine, there is no point in going to bigger throttle plates.

They actually discovered that the intake manifolds are too big, there was a torque increase and a faster 0-60 time when the inlet runners were made 3-4mm smaller than stock. The standard manifolds, throttle plates and valves actually work better on a bigger engine, when they increased the displacement by 15%; they recorded a 27% increase in power.