Air filter housing

[nigel jarrett]

I was wondering if anyone has a diagram of the internals of the Javelin air filter housing .When I purchased my car most of the filter had rotted and disappeared from years of storage and strip down ,so I made up one to a rough pattern but no idea of the internals .later years I acquired an oil Bath and now would like to fit this .Any help would be appreciated

[Keith Clements]

There must be many available with much less trouble than making one. Try JCS, if not I will look in my pile.

[David Morris]

Hi Nigel,

If Keith doesn't have one, please let me know, I am pretty sure we should have one. I think we kept the bonnet from a sadly scrapped Javelin last year. They are things that don't really go wrong and the oil should keep them relatively free from rust. As they are a part of the bonnet, they tend to stay together.

All the best,

David

[Chris Spencer]

Nigel - And if all else fails I reckon that I have a few in decent order

[nigel jarrett]

Sorry for delay in replies ,.i was on auto login and the system logged me out then I couldn't find my password.
JCS are looking to see if they have any filter boxes left ,they have sold some over the years .Thank you for your replies

[Srenner]

My air box has been off the car since the rebuild in 1988. I recently decided to re-install it, but it is in sad shape and as another unit is not on the horizon on my continent, a rebuild seemed reasonable.

I was surprised when disassembled to see the design. Keeping in mind Mr. Clement's tale of a better running motor when his bonnet popped open, I measured the orifices.

Using the calculated area of the intake opening of the carbs as the minimum amount of square inches needed, the intake slot becomes pretty marginal, but is not the big problem.

The area above the oil bath is a plenum walled off from the back part of the air box and has a transfer tube that passes from the front plenum to the back one. That tube is very restrictive, at just over 1/2 of the area of the two carbs. A bit like running a marathon and breathing through a straw.

In the US at high speed ovals, NASCAR uses a restrictor plate under the carb to reduce flow and thus limit horsepower. The plate is simply a smaller orifice than the carb above it. To my thinking, this transfer tube functions much the same. There may be a large volume of air in the box, but it can only fill as quickly as the smallest restriction allows.

I'm fairly certain the boys at Jowett never considered carb pulses, shock wave or sonic tuning or any advanced concept when they made this. Anyone have any idea why they used such a small tube?

[Keith Clements]

The bonnet popping open was when I had replaced the oil bath with a pair of modern paper filters. These worked fine with the Delorto carbs but the Zeniths were upset at 70 mph. Not only that there was a very load induction noise with these paper filters which went completely away when the oil bath was put back. I do not really know if the top speed has been affected, but that could easily be tested with a popping bonnet, but I would fit a pair of strong restraints. I had the bonnet pop on the Autobahn at 80 mph in the Jav and the hinge only just held!

I do think Jowetts did know about standing waves and not only designed the exhaust crossover but also the induction system to make use of the unusual firing order.

Would be interesting to feed some parameters into a CAD system.

[Srenner]

I am currently reassembling the box and have left the center bulkhead out in case I decide to enlarge the passage before completing the rebuild.

I'm not so sure about Jowett being on top of pulse tuning. Both the Jav and Jup exhaust systems are hideous, with the Jup's "Y" behind #3 a bit of an improvement. Was that part of Weslake's input?

The box is a series of 4 plenums, starting with the oil bath and ending with the distribution plenum inside the rear plenum. And none of the openings are the same size as the others, capped by the transfer tube at 1/2 the carb flow area. So the air twists and turns, speeds and slows before reaching the two holes in the floor of the filter box.

Two stoke motors use expansion chambers to monkey with the gas flows and fill the bore without scavenging the entire fresh charge. I have my sincere doubts Jowett did that inside this box!

[PJGD]

Scott,
I doubt that the Jupiter exhaust layout was due to Weslake; I never heard that Harry Weslake was involved with anything other than the combustion chamber design, and that work was done in 1947, well before the Jupiter was under development. My guess is that the exhaust layout was an "idea" tried out in the experimental department and it appeared to work so it moved into production. The "idea" may have been due to any number of people including Horace Grimley, Charles Grandfield or Roy Lunn, but it is too late to know now. I note that the original Jupiter chassis (probably one of the ERA batch) as drawn by Max Millar in 1949 had a Javelin exhaust layout.

Photos of a disassembled Javelin air cleaner would be good to document for the future.

Philip

[Srenner]

Here's a couple of shots of the insides.



The oil bath sits underneath the floor of the box at the front under the large open area. The top of the box is compressed paper as used for the door cards. The transfer tube passes through the center bulkhead and is riveted to the distribution plenum. There is a gap of about 1/8" around the tube as it is not sealed to the bulkhead. The floor under the distribution plenum has one hole at both ends and the floor that seals on two rubber ferrules when the bonnet is closed.

Fairly complex, but the need for the center wall and tube seems a planned restriction, as does the rear stamped steel part. I have loads of questions and hope others can add to the conversation.

[PJGD]

Scott,
Those pictures are helpful. I assume that the oil bath is located below the first plenum that you show? I can't remember how the air gets into the oil bath area. I also imaging that the tube between the plenums must help to attenuate the induction sound, which as we know from the Jupiter can be quite staccato.

As for the flow area issue, of course only one cylinder is breathing at a time (well, there is a small overlap between cylinders, but it is when the valves are barely open and the piston speed is low), and the maximum flow area at the inlet port is 1.22"^2 [792 mm^2] minus the valve stem diameter gives 1.15"^2 [742.5 mm^2] for an equivalent diameter of 30.7 mm. So long as the flow area through the air cleaner is at least say 750 square mm, then we should be OK. What would help though is if the entry to the inter-plenum tube were bell-mouthed, then that would be much better than the sharp-edged design it now has.