SEVENS

Last Updated 07/09/00

Options

The Caterham seven has a huge multitude of possible options and extras, I'll describe, explain and give the upgrade cost for a few of them below. Pictures are still waiting for a few of them - hence the dead pix.jpg links. Some of the items are shown for identification purpose only.

6 Speed gearbox
LSD
Big Front Brakes
Apollo Tank
Supersport conversion
6 Point Harnesses
S type Leather Seats
Tonneau
FIA rollbar
K&N Air filter
Wings: Cycle/Swept
Heater
Screen or not
Engine
Widetrack front suspension

Caterham 6 speed gearbox - Ł1500

This is perhaps the best option of all, although for the price it should be. The picture above is from a Japanese magazine advert which is I think for some sort of modification to the box. The 6 speeder is a bespoke close ratio gearbox designed by BGH. It has a very fast change with a short throw and the following close ratios:

This gives about 17 mph per 1000 rpm in top gear with my 3.92 rear diff: the ratios are VERY close :) It suits the revvy nature of the K series and especially the Supersport and VHPD derivatives very well - it's not for those who like a relaxed torquey car!

The very early gearboxes (1994ish) were manufactured by a company that soon went bust. The replacement firm were not capable of producing sufficiently high quality units and many failures were reported. A third company has been used every since and the 6 speed has proven to be reliable providing it is kept topped up with oil as it can leak a little around the speedo drive seal.

BGH gearboxes also manufacture alternative ratios to fit into normal Ford 5 speed boxes which otherwise suffer from a 1st gear that is far to low. This is a cheaper route to a similar result (although with 1 gear less).

Limited Slip Diff - LSD - Ł600

An LSD is designed increase traction out of slow corners or other occasions when grip is at a premium. The way it works it to ensure that both wheels receive some torque at all times as opposed to a conventional diff which will divert all the torque to a wheel if it loses grip by lifting into air.

For example: Accelerating whilst turning hard left with a traditional open diff will result in the airborne inside wheel to spin away all the power as it lifts, the outside wheel therefore gets no drive and the car slows until the inside wheel touches the tarmac generating some resistance so the outside wheel gets some power. In practice lots of wheelspin and reduced forward motion.

With an LSD the inside wheel gets some torque even if it has very little traction and the rest goes to the outside, thus the car moves forward more rapidly.

The disadvantage is that when you try to turn into a corner the LSD will give more power to the inside wheel and thus generate a bit of resistance to turning the corner. This effect is outweighed by the advantages especially in the wet or with very powerful cars.

The LSD is also an important safety device, if you nail the throttle on a wet surface an open diff will allow the wheels to spin at vastly different speeds as grip changes, the back of the car will wobble unstably around and a spin is likely. With an LSD both wheels turn at a similar speed, if the car starts moving sideways the effect mentioned above works to pull the car straight. Thus a negative feedback effect keeps you in a straight line.

There are various methods of making an LSD. A viscous diff effectively has a plate mounted on the end of each half-shaft, a thick oil surrounds these plates so if one turns the viscous fluid drags the other around with it. This can also be done with each plate coated in a friction material rather like a clutch. An alternative method is the patented Torsen (TORque SENsing) diff shown above. This uses the property of worm gears that they can drive power one way but cannot be driven backwards to allow torque to be split in a ratio of up to 75:25 in either direction compared to 50:50 when in a straight line.

These fancy feats of engineering will usually placed in a standard cases and so look normal from the outside. An LSD can be tested for by jacking up the rear and turning a wheel, an open diff will cause the other wheel to turn backwards. With an LSD the other will turn with it.

Big Front Brakes - Ł600

The standard Caterham brakes allow fairly rapid retardation, however, being standard road car items them lack feel and can fade after a few track laps. The AP "big brake kit" gives you 4 pot race callipers that will not fade and look far sexier. They also possess sufficient feel that it is possible to hold the car right on the limit of braking with the front tyres just slipping slightly for maximum retardation. Their greater power also shifts the brake bias further forward to decrease overall braking distances.

Apollo - Anti-Cavitation Tank - Ł200

As a car corners the oil in the sump moves to one side of the engine, in extreme cases (e.g. a seven on reasonable tyres) the oil pickup is uncovered and starts sucking air as well as oil from the sump. The ideal solution is a dry sump which continually pumps oil out of the sunk into an oil tank where it is held under pressure, from there oil can be distributed to the engine. However, this is a Ł1000 option and the Apollo tank does almost as good a job for one fifth of the price.

The Apollo tank resembles a large (18" tall) washing up liquid bottle that sits just in front of the engine. Oil is taken from the sump and pumped tangentially into the top of it. The oil then swirls around the edge of the tank and settles in the bottom, the bubbles are therefore driven out and so the oil can do its job properly. The system increases the oil capacity to about 9 litres rendering oil changes almost twice the price. The tank has provision for a temperature sender allowing a gauge to be fitted, this reveals just how long oil temperature takes to reach operating temperature - 3 times as long as the water!

Super Sports Conversion - SS - Ł1000

Not much to see on the out side except for the red plug lead cover on top of the engine and the longer exhaust primaries. However, 1000 quid for an extra 20 horse power and a guaranteed resale value is a bargain. The engine becomes more revvy (especially on the 1.6) and suits the 6 speed box brilliantly. You also get a shift light at about 7500 rpm - great fun! The power delivery is pretty much linear up 7500 resulting in a feeling that the acceleration just keeps building, more powerful VVC models feel like they're really tailing off in comparison. The exhaust note is also amazing, Autosport claimed only the McLaren F1 sounds better, that may be hyperbole but tunnels or narrow streets sound great. :)

On the down side the SS conversion is, apart from the exhaust, an upgrade dead-end. The kit swaps the non programmable Rover MEMS ECU for another non-programmable one with different settings. The cams are higher revving than standard but aren't that wild either. If you want to be on the road to ultimate power then leave the engine standard and but a programmable ECU that will see you all the way to the heady heights of 240bhp and beyond. For more info go to Dave Andrews's site.

6 Point Harnesses

Vital on the track for safety and the way they hold you so firmly. 6 pts are only a 15 quid upgrade over 4 points and prevent submarining. Submarining is when you slide under seat belts in a frontal impact - not good!

They're a bit of a pain on the road as they take a while to do up - especially in the dark! You can always leave the bottom undone and use them as four points. If you must you can have conventional 3 point belts fitted as well as they have different mounting points.

S-Type Leather Seats - Ł150

Supremely comfortable, wipe clean, hold you perfectly on the road and reasonably on the track. You sit only a inch off the ground so the only advantage of race seats is the better support on the track.

Tonneau - Ł100

The first upgrade I bought for my car (most of options were fitted when I bought it) and definitely the best value money. Without it you have to put the hood up whenever you stop, this is a pain and takes 5 minutes when its warm and is nearly impossible in the cold as the vinyl doesn't stretch. Also great when driving alone, cover the passenger side to keep the draughts out.

FIA rollbar - Ł150

The FIA rollbar weighs 10kg instead of about 2kg. Even a very simple analysis suggests that it is 5 times stronger. It is also higher (many people find that their helmeted head is above the standard bar) and cross braced. I refer you to the above picture if you think that a seven won't ever roll or that a small rollbar is sufficient. Luckily the driver in the above car has nearly recovered use of his arm after 6 months.

On the lighter side an FIA bar makes a Caterham look FAR more purposeful and it is a requirement for L7oGB track days.

K&N Air Filter

Requires cleaning with special K&N fluid and then re-oilling with special oil - see the separate page for instructions.

Wings: Cycle or Swept

There are two types of front wing available - cycle or swept. The former are much larger and continue back as far as the driver - they are attatched to the side of the car. They reduce the amount of muck thrown up but create a bigger draught resulting in a higher drag coefficient (0.67) and perhaps a little lift. Cycle wings are attatched to the front upright (so the move and turn with the wheels - very kiddy) and have less drag (0.62).

Heater - Ł100

It weighs a few kg so is not considered by the truly macho who say that engine heat will do the job if you wait long enough. Stuff that though I've got one and its lovely and toasty :)

Screen and Wipers - Ł400

The main chassis performance advantage of the superlight models is the lack of a screen amd therefore wipers, wiper motor, screenwash etc. This makes the car much lighter and substantially reduces drag but a helmet is recommended. There is also much less vortex effect giving a less turbulent cockpit - provided that you're short enough to get under the small plastic wind deflector that replaces the screen :) A windscreen also has the disadvantage of getting wet on the inside greatly reducing vision in wet conditions.

Engines - Rover K / Vauxhall 16V

Vauxhall 16v cars are no longer available as new cars but many second hand examples exist. Itcomes down to a simple choice between torque (VX) or lightness (K). The VX is around 40kg heavier which slightly blunts the handling of the car but it has 170 bhp that can *easily* be tuned to 210 bhp and 280 is possible with enough money. see SBD for more information. In contrast the lighter K series gives about 115 bhp (depending on size), 135 with a supersports kit, 180 is possible with throttle bodies, cams and some head porting (needs new ECU), and the ultimate version (so far) is around 240 bhp. Dave Andrews is the man to talk to for information on this route.

Widetrack front suspension - Ł300

This widens the front track to make it the same as the rear. It gives more stability under whilst braking and stiffens the front end considerably. However, the ride quality suffers and stability improvement is said to be 'just about noticeable on the track with back to back comparisons'.