Nathan GT
  The Nathan GT cornering at Bottom Bend. Its sleek body line contributed to a 155 mph maximum speed with Le Mans gearing.
  Nathan GT - tubular subframe
  The Imp power unit slots neatly into this tubular subframe at the rear. An experimental limited slip diff was installed for the test.
  Nathan GT - ply monocoque centre section
  Front end of the ply monocoque centre section showing suspension mounts and ancillary subframe.
  Nathan GT - cockpit
  The Nathan's cockpit is very well trimmed and the car is amply instrumented.

The Imp Site

Nathan GT

Nathan GT / by John Blunsden. - Motor Racing 1966, September.
- p.378-379. - [Motor Racing Track Test ; No. 64]

SOME 15 months ago we had the privilege of being the first (apart from Roger Nathan himself) to drive the Costin-Nathan sports-racing car, the track test report of which appeared in the May 1966, issue of MOTOR RACING. Now Roger has allowed us to get up-to-date with the latest developments by doing a few laps in the works Nathan GT version of the same car.

Comparatively little has been seen of it this year because it was held back for Le Mans (where it was eliminated by an obscure electrical fault the cause of which even now remains a mystery). The pale blue GT, however, is likely to be a much more familiar sight on British circuits during the second half of the season.

Compared with the sports car, the GT is some 220 pounds heavier, but a considerable proportion of this weight was added purposely as part of the Le Mans preparations  - steel tanks, extra cladding, quick-release filler, and so on, to obviate the need for ballast. As it turned out, the weight build-up was overdone because the car tipped the Le Mans scales at 1,220 pounds, or nearly 100 pounds over the minimum limit. Steps are being taken to eliminate the excess weight on future production models (which cost £2,15O in complete component form), and so far three GTs and five sports cars have been built. A road car is to appear soon powered by a Stage 3 Nathan Imp engine.

Mechanically, the GT is almost identical to the open cars, although both have been refined in detail during the past year. Suspension material has gone up from 20 gauge to 18 gauge, the top front wishbones have been beefed-up, a more sophisticated brake-balance arrangement has been fitted, and the GT has a centre gearshift.

The original body has been 'GT-ed' very neatly. A glass-fibre cockpit top section, incorporating a stuck-in screen and its own recessed rain channels above the waistline is strapped and bolted to the centre section of the hull in the front corners of the cockpit, and secured at the rear to the wood hoop which provides the main rollover protection. 'Ears' in the body sides let air into the cockpit, and swivelling intakes are also built into the dash area, the air being extracted through openings in the door windows.

As the car appeared at Olympia, the engine was covered by an open-ended hood, also in glass-fibre, but this caused a vacuum around the leading Weber 40IDF carburettor, resulting in poor fuel-air mixing. Intakes cut into the sides of the hood increased the airflow and the vacuum, but the problem was solved by sealing off the rear of the hood, and allowing the air to swirl around the intakes, the surplus being extracted into the engine bay around them.

Spring rates are up on the sports car, and the GT runs with a 9/16th inch front anti-roll bar and a 7/16th inch adjustable rear bar. Our test laps coincided with the experimental fitting of a 70 per cent limited-slip differential to try to cure rear-wheel spin on tight corners, but the modification was not a success. After the test it was found that the cw and p were not meshing properly (indeed, a tooth had been broken off) and this in itself must have caused some power loss. The GT did not appear to handle as consistently through the corners, and would tend to flick into an oversteer through all the right-handers, whereas fundamentally the Costin-Nathan is an understeering car. The result was some rather untidy and inconsistent cornering, usually terminating in excessive understeer which was scrubbing off speed just when it was most needed.

Despite slightly improved gearing since Nathan's previous visit to Brands Hatch (when he lapped the GT in 57.2 seconds), the best both of us saw at the braking point for Paddock was 8,500 rpm in top, or 110 mph, whereas without the diff Roger had found another 4 mph, through exiting from Clearways more quickly. Le Mans gearing, incidentally, gave a top speed of about 155 mph!

This apart, the GT felt a very pleasant car to drive, even though I found the cockpit room restricted, particularly around the pedals. The interior is fully trimmed and well padded, and there is a profusion of dials and switches including fuel pressure, ammeter, gearbox oil pressure, water temperature, engine oil pressure and temperature gauges and a tachometer.

You sit slightly legs-left with the small leather-covered steering wheel also angled inwards. The gearshift has very short, quick movements, neutral into second being so short in fact that you cannot feel any engagement. A second gear stick on the left of the centre tunnel was a reverse selector for when the five-speed box was fitted for Le Mans. With the four-speed box (ratios 13.5, 9.3, 6.55 and 5.53 to 1) third sufficed for most of the Brands Hatch club circuit, top being used along both straights, and second for the hairpin.

The clutch had quite a light pedal, the accelerator action was not too comfortable (this is being altered), and the brakes required a very heavy foot, although they worked extremely well when pushed hard. The Stage 4 'plus' Nathan Imp engine, which produces 102 bhp, has been used up to 9,000 rpm in a race, although we restrained ourselves to 8,000 rpm. It is a very 'torquey' engine, allowing ample overlap between the gears, and feels really great above 7,000 rpm.

Roger Nathan considers a sub-57 second lap well within the GT's capabilities, and remember he has already been timed at 57.2, while at Snetterton his best so far is 1m 46.3s. Remember, too, that this one is a Le Mans 'heavy-weight', and that future GTs will be 100 pounds lighter. Then they should really go!

 


See the steering wheel - the CN in the middle remains, but the Costin name over the logo has disappeared, below the logo it reads 'Nathan'.

 



On YouTube there is a bit of footage uploaded by 'jackwdh' (UK) called 'Costin Nathan GT Onboard' which show his dash. - It's different from the dash above. It's at Oulton Park Gold Cup Meeting. Jackwdh is not too informative...
jackwdh: Costin Nathan GT Onboard

 



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