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Replacement air filters !

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Eurocarb has them:

clicky to Eurocarb

I believe the correct ones are part# 56-9265

or try ebay or K&N direct.

I have them on my S1. I like them because you can see and access the engine components a lot easier because the airbox is no longer covering everything up. They are also a lot louder than the standard airbox. I haven't really noticed a power loss, but then again I don't drive my S1 that hard. I respect the elderly too much. Each to their own I guess.

Edited by GavinT
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I just checked what I paid for mine direct from K&N, 46.50 USD each. They were out of stock of one and ordered it from the UK. Try K&N direct in the UK, you may find the price is a bit better than Eurocarb's.

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Besides being quieter and delivering much cooler air, the air box prevents carb backfire fires (however rare). IMHO a free flowing filter within the box is the best of both worlds.

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This has come up a few times over the years, and the general advice is not to remove the air box as the inlet ait temps will go through the roof.

I'll have a look for the post I wrote a while back as it explains whats going on, ah, here it is.....

Everyone knows stuff expands when you heat it up, well the same goes for air.

Cool air is more dense and hence contains more oxygen.

As cool air has more oxygen in it than warm you can add more fuel and get a bigger bang out of it for the same volume.

A VERY basic rule of thumb is that for every 1°C rise in air temperature you loose 1/2 BHP (ish).

With the air box and piping you will be sucking air in from the atmosphere at around 25°c in summer (depending where you are) and much less in winter. By the time it has gone through the pipework and air box and into the engine it may have risen to 30°C in this example.

Say you now junk all that air box nonsense and just stick some small bike filters on, where is the engine going to get it's air from ????

The answer is from inside the engine bay, and the one on the Lotus is effectivley an upside down bath tub. Hot air from the engine rises and collects under the cover waiting to now be sucked in by the engine.

The engine is running at 80°C so lets say the air in the engine bay is at 70°C just to make the numbers easy.

So now the air going into the engine is 40°C hotter than with the air box so roughly that is 20BHP (40°C x 0.5 BHP) less!!!!

In the real world it is probably even worse.

The reason you would want to loose the air box and piping is to reduce restrictions, but any small gains you may get are instantly wiped out (and more besides) by the power lost due to the massive rise in inlet charge temperature.

Also, warm air is more prone to detonation so you can't run as much ignition advance either so it is a double hit.

This is why on turbo cars you really need an intercooler or charge cooler because the act of compressing the air generates heat as well as passing through a hot turbo increase the charge temperature.

So don't mess with the inlet system, unless you like the look of the bike filters and can't handle to power :police:

As for the electric fan superchargers, done even go there.........


1981 S3 4.2 V8 6 speed (The Mutant)

Mutant V8 Conversion Thread

Knowledge is power .................... apparently.


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As Hilly says, Cold air induction is the way to go, no point dragging in hot air.

Amateurs built the Ark

Professionals built the Titanic

"I haven't ridden in cars pulled by cows before" "Bullocks, Mr.Belcher" "No, I haven't, honestly"

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  • 4 months later...

I actually asked about this "upgraded air filter" a while back for my '87 Turbo and my airbox does more than just hold the air filter. It has some other hoses and "functions" which would be screwed up with a different air filter system. Id love to ditch that airbox - Its in the way and its a pain to get the filter out of, but I have no choice. I'll just keep servicing the K&N thats in there, I guess. Meh.

Edited by s2mikey
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