Fabricated Air Box

[jemgee]

After reading quite a few threads about getting better air supply to the engine I wonder if anyone has gone the whole hog and used a large fabricated air box (possibly in conjunction with the metal rad cowl mentioned elsewhere to get the ram effect). I have seen this done on track cars presumably to improve the performance across the rev range. Do you really need an air filter if the car is in normal operating conditions - would a few flies into the engine be likely to cause a problem?

[Guest Yellowdog]

Mike,

 

I think I saw a ram type air box on Revington's website but did not find it on a quick visit just now.  There is a guy on our side that makes a pretty nice one out of aluminum.  www.goodparts.com  There has got to be someone over ther doing the same.

 

As for running without an air filter, would you walk into a burning building without a respirator?  Not a good thing for your engine.  Go to K&N filters website, (knfilters.com) they have all the pieces and parts to run a 4 or 5 inch duct into a homemade air box.  Just an idea . . . .

 

Don

[Tom Fremont]

 There is a guy on our side that makes a pretty nice one out of aluminum.  www.goodparts.com  

This must be the box for the triple Stromberg setup he sells - a good arrangement as far as the airbox is concerned and he also offers the duct and air filter box too - I think it's larger than the factory P.I. duct.

 

For triple carb setups, whether Weber or Stromberg/S.U., the wheel arch of the early cars ( don't know the cutoff year, but it's after 1969 ) will interfere. In fact, I don't think the above airbox will work for these cars, and designing one that will work for Webers is no picnic. My current project has the wheel arch notch moved a bit forward to facilitate one which I hope to create. I've seen a couple of offerings which were not inspiring...

 

My motive is to civilize the sound and appearance rather than ram air - but this is only because over 120 mph I would probably not enjoy the experience much :laugh:

[Bob Stubbs]

Jemgee

 

I fabricated one for my PI system a couple of years ago.  I took an old plenum chamber, opened it up at the seam and added a strip (probably around 3") to take the finished diameter right out to about 4.75". It still takes air in from the original flexi-hose and air filter with a K+N filter in it.  I also have a tight fitting Racetorations radiator cover that fits neatly over the rad and air filter and effectively rams the air into the right places.  Since fitting this set up, I've had no issues with uneven burn at the plugs.

[stephen cooper]

The Idea of opening up the plenum chamber is mentioned in Roger Williams' guide to improving TR4-6. If I remember rightly Mike your car has a k&n on the end on the plenum chamber currently? Or is it totally standard? I'd recommend getting a 6 branch manifold to go with increased air going in.

[Andy Moltu]

The PI system doesn't like air being forced into it (can't adjust for atmospheric pressure changes.

It's a matter of welding in a piece of plate to take it to 4" diameter - you can get tubing & air filters to this diameter - it is better to have the filter in front so it sucks cool air rather than the hotter, less dense stuff from the engine bay.

[jemgee]

Stephen is nearly correct - I still have the flex hose to the original plenum but managed to clip the long cone type K&N filter on the end and then cable tie it to the support bar so it picked up the air through the front grille. I do not want to butcher the original plenum so I thought I would have a crack at fabricating a simple rectangular box made up from sheet aluminium (so as I could just replace the plenum and hose) and self tap screw it to the metal rad cowl.

[lee]

Out of interest I recently spoke to Malcolm of Prestige injection regarding fitting the 3 individual K&Ns. He reckons that contrary to belief the hot air from the manifolds makes little difference to the running (I would tend to disagree but I'm no expert)

 

I was keen to fit the K&Ns because I just love the induction roar but they interfered with the new linkage. I had an engineering firm make up 6, 4 inch ally tubes to extend the filters further out onto the inner wing moving them further away from the manifold.

 

Sound wonderfull on full throttle.

[JohnC]

Mike,

The outlets from the original plenum look like six ram pipes; how are you sourcing those for your fabricated one? If you have a source I'd appreciate the contact details.

Cheers,

John

[Andy Moltu]

Mike,

The outlets from the original plenum look like six ram pipes; how are you sourcing those for your fabricated one? If you have a source I'd appreciate the contact details.

Cheers,

John

The ram pipes built into the existing chamber are said to be quite important. That's why it's easier to extend an original plenum than to fabricate a complete new one.

[Red 6]

Re performance and warm air,

 

I can confirm that feeding hot air from the engine bay has a noticable effect on performance.

 

I contributed to another thread recently and explained that i have twin su's with k+n's on my 250. The engine pulls strongly

up to the point when the engine bay heats up when the power fades away.

 

To overcome the problem i installed a cool air zone within the engine bay allowing the carbs to breath fresh cold air which solved the problem but as it was an experiment it looked messy and has been removed (problem has returned).

 

I am now fabricating a plenum chamber which will connect by a flexipipe to a large k+n sited as per a tr5/6 in the cool air in front of the rad and in front of a rad cover, all in aluminum of course, and polished dto boot!

 

I did this on my race car and it worked a treat.

 

I do not know of a commercially available "box" in the UK. Good parts do one but it is expensive and as far as i can see is not optimised for injector manifolds but provides a good idea of what such a chamber would look like.

 

I doubt whether fitting a big plenum chamber to a std engine would do anything for performance, a k+n and a flowed manifold would, but it would look kind of "interesting" when the bonnett was opened.

 

Let us know how things go with your quest.

[jemgee]

I accept that getting a square box fabricated is the relatively easy bit and hooking up to the 6 inlet pipes would be the challenge - I had assumed (probably wrongly!) that the box would have 6 holes in the side with a rubber grommet in each to allow a push fit over the inlets ie doing away with the black connectors to the tubular manifold. The 'design' was only in sketch form in my brain (or what little is left of it). It would be the classic have a fiddle and see if it works solution, but it seems clearly easier to acquire a spare tubular manifold and widen it out

[Red 6]

Mike,

 

There is a plan "B".

 

I remember talking to Tony Lindsay-Dean of Kingston sportscars who showed me some long injector manifold ram pipes he had manufactured.

 

These can be inserted into the injector manifold at one end and onto a shaped plenum at the other. Thus making redundant the existing plenum chamber.

 

I have used a similar set up and it works.

 

I am sure the solution will be reassuringly expensive!!

[jean]

Here is another beautyfull but probably expensive box from Lumenition, I think in the picture is a 4 cyl box, but it would look nice in a TR6.

http://www.lumenition.com/airbox.pdf

 

I think Andy is right when mentioning the ram pipes. This pipes are quite important for a TR6 engine. The way they are designed they are supposed to create the necessary swirl to assure a good fuel/air mixture. As the injectors are very close to the inlet valve the risk is present that a proper fuel/air mixture does not take place before the mixture enters the cylinder. The negative aspect of laminar inlet flow is that it produces higher pressure boundary conditions what will choke off airflow.

Some might remember the little tabs on aircraft wings close to the trailling edge, called vortex indicators, their purpose is to destroy the laminar flow, reduce boundary pressure, and so accelerate the airflow over the wing.

I was told that long manifolds, like TWM, should have a rough surface on the inner side for the same reason.

Jean

[jemgee]

Jean

 

As ever your knowledge shines through - that is a seriously expensive looking airbox! I guess I am going to have to chat with my son who is studying engineering at uni to see if he would like to do a project with hands on experience and potential long term benefits ie he gets the TR when I shuffle off!  

[jean]

No Mike, no shining of knowledge, unfortunately, just trying to learn my lessons and inform myself the best I can    And, being retired, I have now plenty of time to do that.

My best regards to Pauline

Jean

[john.r.davies]

Jean,

I'm sure you're right about intake manifolds. However I thought that roughness was not to do with promoting non-laminar flow, but because a finely polished surface is just a marketing tool.   It does no good and slight roughness helps to vapourise fuel that has dropped out of the airflow.

 

But I'm not sure about the vortex generators.   I thought that they are not intended to  destroy laminar flow, but to induce tiny vortices that inject flow into the boundary layer, delaying flow separation and the onset of turbulent flow.  On a wing that means a stall, and on a car means loss of downforce or increased drag.

 

And it's that rounded edge to the opening to the inlet tube that is important.   A straight ended tube has more resistance to flow, so opening out the original plenum is a useful way to slow the flow in the chamber (fast flow=less pressure), reduce resistance from the relatively small radius and keep the advantage of the original inlet.

 

John

[jean]

Yes John that's exactly what I mean, but probably could not write down the way you do. To prevent the airflow to be disturbed over the wing the tabs are fitted close to the trailling edge. As far as I learned , but it's a long time ago, the task is, in certain flight configurations, to accelerate the airflow on top of the wing by creating a vortex at the rear part of it.

These tabs are the most effective at high speed with low angle of attack and they are supposed to keep the centre of lift at the right place, or am I wrong  

Jean

[Roger H]

To make a set of inexpensive (but very effective) ram tubes, carefully butcher an old airbox, cutting out the 6 flared 'tube ends' in pairs. Braze/solder each of them (in pairs) to a tube that fits snugly into the inlet manifold. The inside face of the trumpet should fit flush with the inside of the extension tube and can be finished with a seamless join.

 

The old airbox forms a web around each pair of trumpets which can then have holes drilled in to allow threaded rods to clamp each pair to each manifold.

 

Fun in cool weather and at speed - terrible in heat and/or traffic!

[Tom Fremont]

What about a box with a front cover, and placing trumpets such as available for S.U.s or Webers inside? This is the route I'm planning for a triple Weber box. Currently I have short trumpets inside 2" K&Ns. If I can I'd like to use longer ones inside a deeper box... ::

 

When Kastner was experimenting with the P.I. system he found very long inlet trumpets beneficial; he never perfected them but toyed with some which doubled back over the head.

[jean]

You are right Tom, I have the same short trumpets, about 2 inch long on my EFI injected 6 with Piper Cross filters.

 

According to my EFI manual long trumpets improve low/middle range torque. They are seen often on V8' s used for hillclimb

and races where no high RPMs are achieved.

 

Unfortunately as you say, and you probably use TWM manifolds on Weber's, not much room is left in the engine bay, even with a recess in the inner wing, like on my 6.

 

Unfortunately the PI TR6 throttle bodies/manifolds do not allow for a bolt on system in an easy way as the original box is pushed on design, held in place by hose clips.

Jean