Lotus Elan

Do I need an airbox?

PostPost by: urr333 » Thu Sep 07, 2006 11:00 am

Could someone advise on the pro?s and con?s of an airbox? I am presently restoring a 1970 S4 which has come with no airbox but with a pair of K&N filters. The K&N website suggests that these are not suitable (legal?) for road use but I wonder whether that relates to use in the US only.

Ted
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PostPost by: Emma-Knight » Thu Sep 07, 2006 1:18 pm

Uncleaned air increases damage to the cylinder walls via small, grinding particles resulting in less engine life. Imagine You are driving down a road in dry summer and a cloud of sand comes along...
Airboxes/long suction lines increase the torque of engines but make them a little more unwilling to rev. Some high class modern cars use switchable airboxes with long/short suction lines which operate via power demand from ECU. An air box can also influence the filling via resonance charging - air suction from one cylinder stops, pressure in airbox increases and next cylinder is filled with slightly compressed air. Also carburettors have to be set up for airbox type.

Anna :)
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PostPost by: tdafforn » Thu Sep 07, 2006 2:44 pm

Its also worth remembering that the airbox does a good job at separating fuel from sparks, an important thing to do in a plastic car!
Tim
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PostPost by: collins_dan » Thu Sep 07, 2006 5:11 pm

I am just in the process of converting from an airbox to a pipercross system with other lotuselan members have had good success with (Steveww). Ray Dent is actually running a close-out on them right now for $149; http://www.rdent.com/pages/specials.html They will accomodiate short velocity stacks, which I'm looking forward to seeing if they make a difference. Dan '70 S4 SE
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PostPost by: ppnelan » Thu Sep 07, 2006 6:31 pm

Using air filters bolted directly to the carburettors will make them suck in warm air from around the engine. The original layout was designed to suck cool air from the nose, to give 'better running' - see the chapter on 'Air Filtration & Silencing' in Miles Wilkins' Lotus Twin-Cam Engine book.
If the engine is standard, I say stick with what Lotus intended - they generally knew what they were doing.... :wink:

:arrow: Matthew
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PostPost by: stuartgb100 » Thu Sep 07, 2006 7:18 pm

I inherited pseudo K&N filters which I ditched ASAP, after sourcing an airbox.

I now run with the correct airbox (no filter) and a run of 4 inch diameter pipe down into the nose, connected there to a Pipercross filter.

I'm reasonably happy, but there's two things I wish to try:

1. adapt the airbox so that there's more space in front of no. 4 trumpet (and to a lesser degree, no. 3 trumpet).

2. then remove the nosecone Pipercross filter and replace (temporarily) with stockings/tights (eg), and give it a good blast.

The reason: I'm not at all sure that my Sprint is breathing optimally. It's free-revving fine, but the acceleration right up to the top end is not how I remember the twin-cam. That's the reason for the second test.

There could be other reasons, of course, for the seeming lack of blistering acceleration all the way up the top end (my memory, not the least), but I will follow this course for now.

Just to say that I also concur with Matthew, in that Webers need a cool supply of air.
Conversely, don't forget to dissipate the hot air from the exhaust manifold area.

Not yet having removed the head, I'm presuming an original configuration. When it does have to be removed, it will be breathed on a la Mr Vizard ........ should improve breathing no end.

Regards,
Stuart.
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PostPost by: twincamman » Thu Sep 07, 2006 9:35 pm

I put 4 motor cycle air cleaners ---one to each cylinder -----looks racy vroom vroom ---[and filters the rocks sticks and little old ladys out -- :lol: -ed
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PostPost by: collins_dan » Fri Sep 08, 2006 1:04 am

Here's a link from someone in the group that tested the theory of sucking in hotter air from the engine compartment vs the front grill and found no difference in temperature.

http://www.stig.uklinux.net/index.php?id=80

Dan
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PostPost by: type36lotus » Fri Sep 08, 2006 2:35 am

I had a pair of K&N pancake style filters on my Elan for a while. The induction noise was deafening! I early on switched to the standard air box with a K&N cone filter in the nose. Much quieter, I could actually listen to my CD when I was not enjoying the sound of the twink's exhaust.

My vote is for the cone filter. Also keeps the engine looking original. Yep, I'm one of those originality counts types. And from the number of first places my Elan has won I think many others think the same.
Mike Geiger
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PostPost by: hatman » Fri Sep 08, 2006 11:19 am

As Tim has already pointed out, the airbox is a useful (and designed?) barrier 'twixt petrol and sparks - on the twinc, any spitting back or fuel seepage will drop straight on to the handily-placed dizzy and leads which may well be, unbeknown to you, arcing quietly away to themselves! :shock:
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PostPost by: tdafforn » Fri Sep 08, 2006 3:21 pm

Sidedrafts also have a tendency to produce a "haze" of petrol vapour outside the trumpets (something to do with the pulses in the induction system I think)
My worry has always been that if this haze gets close to a spark... Booom!
Tim
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PostPost by: urr333 » Sun Sep 10, 2006 5:22 pm

Thank you all for your input. I will be changing the car back to the original spec.
Ted
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PostPost by: elansprint71 » Tue Sep 12, 2006 9:36 pm

This subject seems to crop up every couple of years, last time I asked if anyone on this forum had experience of a fire with non-standard air-cleaners. Zero response.
Bear in mind that K&N filters have a metal casing and have metal gauze, which flames cannot pass through (basic school physics), the standard airbox is one half metal, one half glass-fibre. Which is more likely to catch fire? :evil:

Cheers,
Pete (K&N with trumpets inside).
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PostPost by: elandoc » Wed Sep 13, 2006 2:01 am

Max bhp is achieved with large flared trumptes, curved (preferrably parabolically) all the way around to the sides, with no sharp edges. Unfortunately, this doesn't fit behind the standard airbox (No. 4 inlet is shrouded quite considerably already). I made a large airbox to fit an S4 backing plate. After much moaning and gnashing of teeth (and trimming of the top gaurd lip and bonnet support), I managed to get it to slip in and out over the trumpets. It has a 100mm snorkel to a large K&N filter in the nose and works quite well.
Another club member has made a more modest design to fit on an S123 backing plate without any trimming, but nicely cures any oiling up on No. 4 plug. I believe he sells them for a modest sum, if anyone is interested (let me know).
My system dyno's at 190bhp (1700cc), but any airbox system would perform better (bhp and filtration) than socks or individual filters IMHO.
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PostPost by: hatman » Wed Sep 13, 2006 7:36 am

Logic suggests, Elansprint71, that anyone who might have responded in the positive to your 'has your lack of airbox caused a fire?' survey wouldn't have done so because, having had their Elan destroyed by fire, wouldn't be using this forum anyway! :D
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