Pushrod Seven emphasis
Graham Nearn and his Caterham Cars concern are now creating their own traditions to keep the former Lotus Seven in production as the Caterham Seven. To judge from our readers’ reactions there are those who also mistake their traditional opening inside Motor Sport, a full page ad. as our editorial opening too. Graham tells us it is not unknown for letters to come to Caterham addressed to Motor Sport editorial and clearly referring to the previous monthly advertisement!
One of the Caterham traditions was the battle to get the Seven accepted for production sports car racing. They succeeded for the 1980 season, but it was by no means certain that they would be in for 1981 when this was written.
That acceptance for racing has thrown the emphasis in Caterham Seven racing and road production upon the pushrod 1600 models. Supplies of the Lotus Ford Twin Cam have virtually dried up — “those we can get hold of we send to Japan,” says Nearn. Thus the 1600 Kent crossflow unit has once more become the mainstay of production — and it is the only unit that Caterham are allowed to use for racing.
To introduce us first hand to the changes they have been making, Nearn arranged for us to race the Seven that has been campaigned by a number of people in British 1980 Prodsports Championship events, and to spend a day with the latest specification road cars. These have a number of useful improvements, including a new fascia and instrumentation, an unfortunately slightly wider ratio Escort Sport gearbox (supplies of the old 2000E casing are drying up too) and a Marina back axle, which saves both weight and money with consequent benefits to the ride. All this, and a lot more detail, is the result of a sensible development programme administered and carried out by former Triumph engineer Clive Roberts, who has also raced the car a couple of times as well, so there is no danger of the Seven “going soft.”
First the racing car, registered GPL 39V. It was built in November and December 1979 as a production 1600GT using the older Ford transmission components that have now been replaced in production. Sevens have been made with an infinite variety of axle ratios, mainly between 4:1 and 3.9:1. The cars started off on a production 3.5:1. but this was simply uncompetitive, so a numerically higher ratio was soon adopted (4:1).
The suspension came in for particular attention and had just been sharply improved by the co-operative efforts of Chris Meek and Caterham when I raced it. Basically it started the year with old production settings: Spax dampers allied to 75 lb rear springs and 105 lb fronts. Clive Roberts explained, “the improvement you had wasn’t really due to rate so much as to a change in supplier. Frankly, we had found the old springs sagging and so went for a change in supplier. When these came through they went up to Chris Meek, who was then working on the car for us in racing trim, and the benefit was obvious.” Meek told us the rates on the springs we raced on were 90 and 70 lb in rating. Current production figures are 100 lb front, 55 lb rear. Spax adjustable dampers are retained on the competition car, but the brake bias is altered to take off the front-end surplus of effort that Roberts says is necessary on the road cars to comply with current safety regulations. This is done most simply by fitting harder front pads.
Wheels and tyres ended up as a choice between 185 or 165 Kleber V12s (very nearly slicks when I drove, and very effective) on steel rims. The 165s have been proven the fastest combination and it is ironic to note that more Sevens are sold with alloy wheels (6″ rim GKN) than with the “production” steel wheels.
The engine was built by another man who sometimes races this Seven very effectively, Reg Price. As ever the regulations covering construction of a production engine are full of loopholes — we are told that, if you followed the RAC sheet the compression ratio would be 5:1! In fact entrants take their choice between 8.7:1 and 9.7:1. All the black arts of Formula Ford contribute something to the extra performance, including the carburation and camshaft, but nobody says exactly what has been done because the regulations are so ambiguous.
The result is a single twin choke engine that revs fiercely to 7,000 r.p.m. and is a joy to drive. Power output at the rear wheels corresponds to roughly 100 b.h.p. at the flywheel: a standard Ford unit is rated at 86 b.h.p.
The clutch was a standard Twin Cam one. We did have some trouble getting it into adjustment after the spigot shaft allowed excessive drag to develop just before the start. Road cars have a different, smaller plate unit now. Weight when we raced the car was some 550 kg/1,213 lbs, but current production 1600s are closer to 500 kg, over 15 kg of that saving brought by the substitution of a BL axle for the Ford Escort RS2000 unit.
The cockpit of a Seven is never going to qualify for the luxury limousine class, and that of a racing version must be back to the kind of spartan collection of aluminium spars and panels that originally delighted Colin Chapman.
Obvious racing changes include the Aley roll-over cage, not the same as that which is optionally available on road cars, a tiny leather-rim steering wheel; full harness and a fire extinguisher, somewhat precariously clipped and taped into the passenger footwell.
The choice of an early October two-day meeting at Silverstone was a fortunate one. In glorious weather a modest BRDC entry fee brought the chance to spend 25 minutes or so humming around the GP circuit on Saturday and for the 20 min. 9.5 sec. that it took us to complete the Sunday race.
Looking at the car and taking it through scrutineering I had been in querulous mood about the preparation. The steel wheels were rusty, there was evidence of tape holding important ancillaries like the fire extinguisher in place, and I complied with the mirror rules by applying two stick-on jobs to the screen. By comparison the privateers’ Sevens looked immaculate. I seriously wondered about racing the car at all but if the scrutineers were happy, who was I to worry?
In fact, I did about three corners behind Chris Meek’s class-leading Panther Lima 2.3 and all doubts vanished.
The Seven felt absolutely brilliant. Sitting out in the open air — you do not race a Seven with the hood up owing to a gentleman’s agreement about what constitutes “doors” — was a new experience for me in competition. The exhilaration was akin to the first time you step into a racing car. Which is saying a lot in my case, as that was 13 years ago.
As one would expect the Seven leapt to the limit of third gear, 85/90 m.p.h., very quickly. Thereafter it ran into the usual Seven aerodynamic brick wall, lapping in 1 min. 59.31 sec. (fractionally over 86 m.p.h. average) for its best of the session. From a driving viewpoint it was very straightforward, third gear just needed at the Becketts hairpin and chicane, unless race traffic was encountered.
The most important priority became finding any other competitor to pull one down Hangar straight, or under the bridge and into the chicane. On the latter section a good tow would increase the maximum shown from 115 m.p.h. unassisted to 126 m.p.h. This also meant a full blooded 7,000 r.p.m. plus instead of the usual 6,500 to 6,800 r.p.m. employed in the gears.
Brakes were not a priority on the GP circuit: as with some of the formula cars tested, there was a tendency to over-brake the Seven. Long fourth gear corners like Club, Stowe and Abbey, which are taken in the 95-105 m.p.h. region, set up a gentle weave in the chassis, and the bump in Abbey might occasionally flick the car momentarily off-line at speed. The alert chassis reaction to the slightest twitch of the steering took care of these problems the instant they developed.
The race was an anti-climax. The clutch reached the limit of its adjustment just before the off. A last-minute adjustment saw the Seven able to take the lights without creeping, but not able to show the true worth of its acceleration abilities into the first corner. A few weeks later Price reached that first corner second overall, right in amongst the Morgan 3 1/2-litre V8s and TVR 3-litre V6s that dominate this category. Owing to the authorities, the Seven 1.6-litre pushrod is forced to race in the same class as cars of twice the capacity.
During the first lap I had to recover a position or so from that poor start, settling in behind Chris Meek and the Panther Lima: this made a big difference to my early lap times as the Lima pulled the Seven along to a 1 min. 58.51 sec. lap (approximately 89 m.p.h. average). Then the engine started overheating, having consumed much more of its water than it was entitled to, and I gradually fell back from the Lima 2.3 (which is in a lower class!) to a lonely sixth overall: headed by a 3-litre TVR (of subsequent Champion Colin Blower), a trio of Morgan V8s and the Panther. Behind were Alison Davies and her fleet 1.0-litre Ginetta G15, a 2-litre TR7, an assortment of 1.5 Sprites and the smarter looking Sevens.
I tried driving the car home with pleasure, but the rock hard ride and occasional spasms of overheating rather spoilt the trip. Terrific memories remained of the Seven roaring round the track, wing-tips fluttering in the breeze, the human inside astounded at how easy it was to drive it to a reasonable sixth overall in one’s first open air race.
The 10-lapper I did was a round of the DB Motors Championship, but the Seven completed 23 events in 1980 collecting only two non-finishes. In fields that usually boasted 20 or more entries (“ours” had 19 and we started from the third row, sixth fastest) the Seven racked up two fourth places, a fifth, and six sixth positions. There were only two failures to finish, both caused by racing fracas rather than mechanical unreliability.
The Caterham Seven could be made a lot more competitive. Chris Meek enthusiastically said of the car we drove that it “only needs £100 or so to tidy it up,” but after the long struggle Caterham had to get the car into the category, one gets the feeling they do not want to be doing any winning for some time. However that should not stop the works car looking as tidy as those of the privateers!
Generally speaking the aerodynamics work against the car at a track him Silverstone, but the Seven still enjoyed one of its best results around the fast Northampton circuit. The driver could not stop grinning for several days after the outing, which is what Caterham/Lotus Seven motoring has always been all about.
The latest road cars
As Clive Roberts wryly commented Caterham had a few years to catch up on the development front, some changes forced by supply shortages in obsolete components and others by the desire to simply make the car a better buy. On the latter subject we were interested to hear that Nearn finds there is practically no interchange between the Morgan customer and that for the Caterham product. Certainly the waiting times are a lot less at Caterham, though they were embarrassed at quoting nine months for the Twin Cam model before the present engine shortages, and delivery times for the 1600 model is a good three months in most cases, a delay that can be reduced by supplying your own engine and gearbox. As ever, Sevens are delivered in Britain in kit form, but there are a lot more completely assembled than used to be the case.
There are two 1600 models that will form the basis of the Caterham production now: a 1600 GT at £5,046.33 and a Sprint version with an uprated twin carburetter engine, but otherwise similar specification: we concentrated upon the Sprint in these impressions.
These prices do not include commonly specified extras like alloy wheels and 185 GP Goodyears (“we’ve yet to find a better tyre for our purposes,” they say) at £109.25, or a number of basics like seat belts (£21.16), heater kit (£55.77) and £28.17 roll over bar.
Fundamental changes for current production centre on the gearbox and back axle. Herewith a comparison of the Escort Sport Ratios now current and the old 2000E:—
Roberts happily reports a weight saving of a good 30 lb. with the Leyland axle and a look under the back confirms that the A-bracket location to the differential is also history, though the vertical coil spring damping the axle location arms remain. The benefit to unsprung weight is considerable in that the total axle avoirdupois saving is in the order of 25% plus, allowing damping and springs less of a mass to control over bumps.
The clutch is now a cable-operated 7 1/2″ diameter plate instead of the previous 8″ plate: the smaller unit has been tested thoroughly by hitching it up to a turbocharged Seven power unit that they have run for over a year with a Garrett unit boosting output to 140-150 b.h.p. Needless to say they encountered no problems, though in racing the story was different with the old plate.
The Mk 4 Spitfire front suspension is now complemented by BL wheel centres too.
For our money the smart and rigid stainless steel exhaust manifolding comes as a high priority bonus on the later Sevens: its note proved attractive to the driver and not quite as head-turning in hard use as the previous unit. Around town it is very mellow indeed.
The cooling could get out of hand on the old models, mainly because the electric fan had not been switched on. Now that operation is automatic and the fan itself has been repositioned for maximum effectiveness.
There are a few safety-conscious touches too, though many tend to frown on them: one importer from a country that demands rear lamps actually risks the wrath of the law by taking them off. A true traditionalist, perhaps?
Amongst the safety changes comes extra bracket location for the steering column and brake failure warning light.
It is the electrics that have been changed most of all. A new wiring loom incorporates many of the features that are routine on today’s saloons, but brand new to the Seven. Illuminated rocker switches (no less!) are now featured in a brushed aluminium dashboard. It carried current Smiths instrumentation. From left to right it covers: fuel tank contents, water temperature (just above 90°C on the Sprint in November), oil pressure (resolutely just under 50 lb indicated), a 7,000 r.p.m. tachometer, redlined at 6,500, and a 120 m.p.h. speedometer with trip reset facility. To the right of the dash are longer levers to control the whooping air horns and headlamp flashing.
On the road
Snuggling into the open cockpit of a hybrid demonstrator — it still had the old transmission components — sent an anticipatory tingle of satisfaction round the writer’s system. You either love ’em or . . .
A 28 amp alternator and pre-engaged starter are part of the Ford 1600 motor today, but the Sprint package definitely is not.
You get what amounts to the Old Holbay Clubman level of tune that Lotus used to offer before the Twin Cam. The crankshaft, flywheel and clutch assembly are balanced locally. A Newman equivalent to the Cosworth A2 camshaft profile is introduced. The Holbay manifold of sandcast alloy is installed to mount double Weber 45 DCDE sidedraught carburetters and smart air cleaner. The stainless steel exhaust system for 1980 is retained and the cylinder head, still along Heron principles. The cylinder head is machined to a 9:1 cr, the inlet and exhaust porting smoothed out. A chrome rocker cover identified the job, but sandcast aluminium version is the more likely for production.
The result is a crackling 110 b.h.p. at 6,000 r.p.m. and 97 lb ft torque when 4,500 revs are attained.
The handbrake seems more effective in action and more easily released from its cumbersome under-fascia perch, but to drive the Seven feels much as memory indicated. However, there is one very important difference. The car feels a lot more solid and absorbent over country roads. This is the result of detail chassis modifications to the space frame over the years, and the policy of using a stiff spring with softer, adjustable, damping. The front wings still flap like those of a trapped butterfly over any road irregularity, but with a nice sturdy new steering whee4l to twiddle, and the thought that the BL axle should make life a little less twitchy over mid-corner bumps, it did not seem to matter.
The Sprint engine is generally excellent. I would defy 95% of drivers to tell the difference between it and what used to be the production Twin Cam in pre-Big Valve head days.
At one point there is a big change in behaviour though. Between 2,000-3,000 r.p.m. the jetting shows its compromising nature and the engine stumbles a bit until 3,500 r.p.m. brings a new surge of interest to swing the r.p.m. counter deftly to 6,500 with minimal delay.
Altogether 18 months development intelligently spent on one of the author’s personal favourites. A car that can put a smile on most enthusiasts faces, even in today’s traffic, where its nimble agility remains astounding to bystanders and driver alike. On a practical note you can also expect to get slightly over 25 m.p.g. from a Sprint model capable of 110 m.p.h. (90 is the instant top speed) and 0-60 m.p.h. in less than 7 seconds.