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4 Cylinder Air Filter Install

One of the first performance upgrades made to any car to improve performance is an Air Filter upgrade. Mainly because it's cheap and easy to do. This will increase air flow to the engine, and help it breathe easier. It;s a cheap and simple mod, that can be done in a few minutes (on a normal car), and goes great with an exhaust upgrade.

A few companies make performance Air filters for cars, and as we've used K&N filters in previous cars. we decided to purchase one of their filters for the Esprit. Not only do they increase performance (some say increases of 2-5bhp), but these filters will last the life of the car. Only needing a re-oiling every 100,000 miles or so. So it's an upgrade you'd be stupid not to do.

We'll take you through the simple process of changing an Air filter on a 4 cylinder Esprit.


You will need the following parts:

New Air filter (I used a K&N)

You will need the following tools:

11mm spanner or socket

Removal & Fitting

(click here for Giugiaro fitting guide)


The Air filter is located on the right-hand side of the engine ( when looking from the rear of the car) and is underneath the trim that was removed for the Ram-Air conversion. The Air filter box is secured by two clamps, held by 11mm bolts. You'll see all sorts of pipes attached to the box (see above left). These do not need to be disconnected to get at the Air filter.


Undo the nearest bold and clamp. You could loosen it, but I just took mine straight off. Then undo the other side. The box will now only be held in place by the pipes.


Pull back the box carefully and you'll see the Air filter. Remove the old filter from the box. You can see from the picture on the right that there's plenty of space without troubling any of the pipes.


Once the filters out of the car, you'll need to remove the rubber seal from it to use on the new filter. This isn't glued and should come off really easily. Replace the rubber surround on the new Air filter. Then you can put the new filter back into the box.


Then replace each clamp and tighten the bolts to hold the box in place. This whole process shouldn't take more than 20 minutes, and will a filter only around £40-50, it's worth the effort.

Remember to place the sticker supplied on your air box. This will stop it being thrown away for a new standard one at a service interval.

LEW's Verdict

LEW's verdict on this install, is do it. We changed the exhaust and cat pipe first, which isn't the right way around to do it. So the Air filter doesn't make any noticeable difference. Anybody who knows anything about performance mods, will tell you that one of the first things to do is to change the Air filter. Our advice is every Esprit should have a filter and exhaust change. And considering the filter will last 100,000 miles, you won't ever have to replace it (you may need to clean it). Then if you keep your Esprit long enough, you'll save on the price of new filters over those years. A performance upgrade that will save you money!

Due to legal problems with the metal frame on the K&N we've used above, they are no longer available (note, these are now available from Esprit Engineering May 2011). What is available is a K&N one without the metal frame, which isn't easy to fit, or a Green Cotton Filter, which fits. Alan Paterson has worked out a way of fitting the K&N filter to an Esprit.

This mod was performed by LEW on their 1992 Esprit SE.

If you have any comments, feel free to e-mail us at admin@lotusespritworld.com

Carbon Fibre Airbox

This carbon fibre Airbox for the 4-cylinder Steven's Esprit is a top quality product from CarbonCerbie. The Airbox is prepreg made in an auto clave so the material costs are higher than wet lay-up but the finish is far superior.

Fitted to your engine bay, you'll see a great improvement in visually and also a 0.5kg weight saving. A Beautiful piece of kit. See LEW's guide here

Prices: £176.25
+ p&p (starting from £6 for UK orders)




Fitting Currently Available K&N Filters
by Alan Paterson

I’d heard a lot about the performance increase (4-5 BHP) claimed for the K&N air filter, but I put this down to hype and little boy racer talk. All the same, I’ve wanted the chance to see if it made any difference to the Esprit and was given the opportunity by Les Twigg at the Stoneleigh Team Esprit meet. Other people have fitted a K& N filter at the same time as doing other performance upgrades, so the effect (or otherwise) of the part could not be gauged effectively.

The original filter in the Esprit came off a Triumph Stag and others from the same era – and is of a paper element construction suspended in a rigid metal frame around which a rubber seal is fitted.

The K& N is of a cotton element type with a fine metal gauze. There have been some copyright issues with the metal framed K&N filter for the 4 cylinder cars and this is currently unavailable, so the one I fitted has a flexible plastic frame – which led to a problem when trying to fit the rubber seal as you will see, but it’s not an insurmountable problem with just a bit of lateral thinking.


Follow the steps above for removing the old filter. Remove the original air filter. The original air filter has a rubber seal fitted to its metal frame. This just pulls off. This was when the fun started. Fitting the old rubber seal to the edge of the K&N filter is not easy. I’d be so bold as to say impossible but I’m sure someone will manage it . I thought that if only Ian Rawlings was here, he’d have enjoyed the challenge. The flexible plastic frame is so wibbly wobbly that the seal keeps coming off. Eventually I tried using Dunlop 1358 carpet adhesive to stick it on. This glue, which sticks to anything, would not adhere to the plastic. I tried gaffer tape, masking tape, trim fix tape, gaffer clamps ( I used to be in the film biz) but nothing would hold it in place. I tried fitting it within the air box – nothing worked.

I discarded the rubbers seal and reached for my tube of Halfords black silicone sealant. I ran a thick bead all round the contact face of the inner surface of the air filter box, then fitted the filter in place. I then looked for any gaps and filled them too. I let it set for 15 minutes then refitted the filter box and jammed it up nice and tight without bursting the bolt threads. I used silicone on the edge of the air filter box to stop any leaks.

Testing, conclusions & recommendations

After waiting a couple of hours for the silicone to set properly, I gave it a test. I was using SuperUnleaded but had already become accustomed to the effect of that fuel. The only change was the air filter. I reminded myself of the placebo effect and tried to rule out any subjectivity in my thoughts.

On the road I noticed that I could hear the air being sucked in behind me more than before. The car seemed not to be straining as before and more relaxed. It was getting there and breathing more easily. Maybe just changing the air filter for a new original paper element one would have achieved the same result.

On flooring the pedal, I noticed the turbo boost was much more smooth with no lumpiness or jerkiness at all. I could hear the air being sucked in to the carbs more clearly, like a whistling kettle. The car definitely was more responsive and perky

( definitely not pinky) than before. It was as close to flying as I’ve been in a long time. The turbo wastegate fluttered like the wings of a dove on lift off and the engine just sounded, well, nicer. There’s a bit of subjectivity for those who have been waiting for it. The car does feel better to drive, but how do you measure 4-5 horsepower?

Without going to the expense of a rolling road test, I know within myself that the K&N air filter has made enough of a difference to be noticeable and justified itself as a very worthwhile upgrade. Anyone who does not notice a difference is on Valium and should not be driving a car.

Treat yourselves and your car. It’ll thank you for it. Save money by getting it from Les Twigg. He’s doing the best price.

This mod was performed & supplied by Alan Paterson on his 1988 MY Stephens Esprit Turbo.

itg Air Filters now available

Lotus Performance now have itg Air Filters for the both 4 cyl. and V8 Esprits. This gives an alternative to the K&N's and Green Cotton Filters. Call Les Twigg on 01629 650800 for more information.


If you do this conversion. Feel free to e-mail LEW with your opinion on it and we can add it to this page. admin@lotusespritworld.com.

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