Zenith Imp, 1972, DFL 492C

The Imp Site

Andy Dawson

Richardson, C.
Imp Revival ? / Clive Richardson; photos: Jasper Spencer Smith. - Cars & Car Conversions 1972, May. - p.100-101
Driving Andy Dawson's rally Imp DFL492C - Zenith/Solex carburettion.

 

CR drives Andy Dawson's rally machine, and wonders if we're in for an
Imp Revival?

SITTING IN ANDY DAWSON'S Rally Imp is a bit like being thrust into the fires of Hell, both from the banshee noise  - when all its available 10,000 rpm and 105 bhp are used in anger, and from the appearance of the interior, gutted to such an extent that it might have been fed through a furnace to dispose of all surplus weight. Externally too, this is very much a car of action rather than a showpiece, the shell showing battle scars from 4 years of hard usage, in spite of being camouflaged by numerous hand coats of Crown Polyurethane Gloss, regularly renewed with loving care by Herr Dawson's girl-friend Lesley.

Appearances can be, and are, deceptive, because this tired-looking machine is undoubtedly the quickest Imp in Rallying today, and its 25-year-old owner/ builder/ driver one of the most rapid of the up-and-coming breed of young Rally pilots, who seems to have taken over already from Colin Malkin as the fastest pedaller of an Imp in the land.

Rally results

Since putting his Imp into its present state of competitiveness well into last year, Andy Dawson has had a remarkable run of consistently high results, while still a comparative novice. First event in the present state of preparation was the Halewood, and 2nd overall, other notable successes since being 6th on the Manx, 8th on the Dukeries (his first serious stage Rally), 5th on the Tour of Dean, hopefully 3rd on the Snowman subject to the RAC tribunal, and on the Seven Dales -oops - 2nd to 13th in 10 yards when he off-roaded for 20 minutes not long before the end of the event.

Chrysler Competitions Department

Andy Dawson believes in Imps like some people believe in life after death: emphatically. As number two to Des O'Del1 at Chrysler Competitions Department, Coventry, it's obviously to his advantage to promote the competition image of the Imp, but it would be unfair to say that this is the reason for his love of this little rear-engined machine with which he's been so successful of late. No indeed, because DFL 492C began to dominate his life when he was at University, long before joining Chrysler.

Dawson Development

Nor is the Competitions Department responsible for this potential winning Imp, except indirectly. The car is Andy's own entirely, built in his own time in a barn just outside Coventry, and though naturally using a lot of lessons learnt on works Imps, the major part of the development has been pure Dawson.

     
 mmmm
 Zenith/Solex                                                                                                Air cleaner on roof
 Zenith Imp, 1972
  
 Zenith Imp, 1972, DFL 492C
  

Zenith Imp

A certain amount of sponsorship comes from Zenith, whose special twin 40DDH Solex twin-choke sidedraught carbs feed the mixture to the 998 unit. This variety of Solex is available on the continent, but not over here yet and Andy's is the only set fitted to a British car for competition, development once again being the reasoning behind it. Andy reckons them to be two stages of development beyond Webers and very easy to set up - a couple of runs up the road were sufficient to sort them out.
Anyhow, the outcome of all this is that the Dawson Imp isn't just any old Imp - it's officially known as the Zenith Imp, which should please Mr Dawson senior, Managing Director of Zenith UK.

Handling

Weight distribution,

Though the well-tuned and reliable engine counts a lot, Andy claims that he goes so quickly because of the work he has put into the handling. He's worked on the physics of the car, keeping the polar moment of inertia incredibly low compared with the wheelbase, so that the car will change direction very quickly, with the aid of the throttle. To do this he has taken as much weight off the front end as possible, so that the weight with 5 gall of fuel aboard is made up of 5 cwt on the front and 9.2 on the rear. Spare wheels, battery, tools, etc. all lie in the rear, only the Hartwell radiator (hence the grille in the front bonnet top), and the 10 gall Maurice Gomm alloy fuel tank lying up front. Ultimately the tank too will probably find its way to the back.

Suspension

Suspension is all complementary to this weight distribution, being basically a Racing set-up, apart from damper rates and the lack of a front anti-roll bar. These differences create an unstable Racing set-up, which allows the car to be thrown into a bend.
Front springs are long, soft early Imp ones reset to Dawson ideas, with Armstrong adjustable dampers set soft (setting 2). Links are as available from Crysler Comps - seam-welded van ones, with extra bracing for the damper mountings. At the rear, springs are very hard, short ones to keep down the rear roll centre, developed from the works 'Monte' type, made to Dawson settings by the Park Spring Co., Sheffield.
Shockers are Konis reset to Dawson theories, and the links are the internally strengthened works ones with additional bracing on the rear hub bearing carriers for longevity.
Rear crossmember is the usual works type, with ideas being formulated for a new tubular braced one to combat breakage every four or five rallies, because of all the weight on the rear wheels. There's loads of negative camber on the back wheels and loads of positive on the front.

This complete set-up makes for a very (and deliberately) unstable car, which takes a lot of learning to drive on the limit. 'Don't try to follow these suspension ideas on a road car, because you might hurt yourself,' says Andy. 'The car has to be considered whole to make this work.'

Brakes

    Dawson Zenith Imp, 1972
Sparce interior and functional accessories denote single-minded contruction
  
 mm
Spare wheel, tools, battery all as far back as possible
  
 mm
The alloy fuel tank is a 10 gallon

On the braking side, front corners have Herald calipers, Viva discs and Imp stub axles, all modded to fit. DS 11 pads providing friction. Rearwards, brakes are standard Imp, even down to the linings to give a better handbrake - Andy using this item for putting the Zenith Imp sideways into all tight bends. Only difference from the norm is opened out rear cylinders, but no more details on that, because this is something which should not be undertaken without specialist knowledge and facilities. Master cylinder is a 0.7 in one to give better feel, helped out on the stop-job by a 1.8:1 Girling servo.

Wheels and Tyres

Still on the rolling gear side of things, wheel and tyre sizes are a critical factor with Imp handling. Normal wear on the Zenith Imp is 4½J Minilites shod with 1.55 Dunlop SP44 knobblies. On hard surfaces there's nothing to beat Racers on an Imp and Andy's 4.50 L12 Dunlops are mounted on 6J steel wheels.

Engine

Engine is the nearest thing in power output to Bill McGovern's Racing unit to be found in Rallying, the wet-linered 998 unit handing out 74 bhp to the rear wheels.
The only difference from the normally seen spec is a quarter-inch thick block-strengthening plate, which locates the main bearing caps by studs - a necessary safeguard in case of over-revving. Pistons are normal 998 with the crowns shaped to suit the combustion chambers of the full-Race head, with 1.4 in. inlets and 1.125 in. exhausts. It started off as an ordinary works head (carefully selected from the line by Andy!) and was subsequently very carefully and extensively self-modified.
Combustion chambers are shaped slightly differently from Racing practice to give more torque. Compression ratio is 11.3 : 1.

Camshaft

Cam is the semi-race R20 Chrysler Comps one, now pretty universally used in Rally Imps. Hotter ones have been tried but Andy has found they lose too much power low down.
A works distributor provides the sparks.

Oil pressure

At the bottom end, crank and rods are polished and the rods well lightened. Lightweight flywheel is a works part along with the rally clutch, the whole lot being balanced by Andy.
The Zenith Imp is probably the first competition Imp to use a bigger than standard oil pump, which pumps round Castrol R40 at 75psi instead of 50psi.

Air filter

As I've said, the carbs are the Solex by Zenith, mounted on works manifolding. As part and parcel of this set up is the trade mark of the Andy Dawson car - a Rapier H 120 air-filter mounted on the roof (the only place where clean air can be picked up on an Imp), connected to a cold air box on the carbs. Andy believes that this efficient system is the reason he has never had piston ring problems, while other rally Imp owners do.

Gearbox

All this power is put through a latest production type gearbox rally ratios i.e. uprated 1st, lower 3rd and top. 2nd is strengthened.
Only other alterations to the transaxle are a polished diff cage and works bolts holding the crownwheel onto the cage. The works themselves now have available complete transaxle assemblies better than this one, with the same gear ratios, but better synchro and works type diff. These ratios give 10 mph/ 1000 in 3rd and 14.2/ 1000 in top.
Normal level road speed is about 100 mph in top. But Andy will forever recall pulling 8400 rpm in top down Tholt-y-Will on the Manx, with Nigel Raeburn screaming his head off. Work that speed out for yourselves!

Braking technique

Andy's driving technique of using clutch and gears to brake, then dropping the clutch in viciously to get the tail out, is light on driveshaft couplings, the present ones having done five national and one international event. Robin Eyre-Maunsell, using the gears to brake and put the car sideways, gets through a set per event - and he uses GT6 couplings.

Body panels

The well-used body-shell features gutted steel doors, glassfibre bonnet and boot, perspex windows, a skid underneath the front links braced into the bodywork, 1/8 in. dural under the floor and over the tunnel, a lightened and strengthened steel works sumpguard, a strengthening tube bracing the front link mounting and strengthening plates on the rear end. A nine-row oil cooler sits in the engine compartment, fed air by a duct from the rear panel, and another air duct in the n.s. rear window cools the transaxle by 20 degrees.

Interior

Coming back to where I began inside the car, there literally isn't any trimming apart from black paint. Only instruments are a rev counter,temp gauge and 70 mph speedo, plus Halda and clocks.
Full roll cage is a John Aley one in aircraft alloy; seats are the bare minimum of buckets with full harnesses and the navvy has a foot bracing bar.
Steering wheel is a 14 in. one with the spokes set so that he can grip them with his right hand. 'Don't use a small wheel for a road car unless the car's set up properly.'

Driving experience

I'd never driven a full-sorted Imp before, and have no love for standard Imps, but this one was something different. Using gentle revs to start with to get the Castrol R circulating and properly warm there were no protests from this high rev potential mill, which would potter along quite happily on low throttle openings. With well-spaced ratios it was easy enough to keep the revs strategically placed, way up in the higher scales.

Handling was simply incredible and no-wonder Dawson likes his Imp. As far removed from Escort or similar handling as Harry Worth from Sir John Gielgud and even more fun. Getting the tail out on open bends was simply a matter of lifting off the throttle to get the tail out to the right degree on opposite lock, then booting it and following through - a method useable safely on rough and tarmac. Very long fast bends were best accomplished in a series of lurches to flick the tail out, keeping the foot down all the time. All very dramatic to watch and be driven like, yet surprisingly easy to pick up for oneself. Though almost constantly sideways for maximum progression, with the wheels never in a straight line, astoundingly safe and controllable. 'I think I'd have preferred an even smaller steering wheel to raise the ratio slightly. Traction of any Imp, of course, is fantastic, and not a lot of acceleration's lost by loose surfaces, a fact that was witnessed by a tarmac 0-60 time of 9.2 sec, slowed to only 10 sec on the rough.

The art of not losing this Zenith Imp was to set it up sideways before the bend and power it round. The way to lose it would be to lift off once sideways in the bend! Driven incorrectly the car remained an understeerer - it was essential to set it sideways by tweaking and throttle to gain the right stance. The handbrake was always a help in emergencies.

So much for the quickest rally Imp around, then. But it won't be for long; Andy is about to build a new shell with an 1160cc unit and there's every chance that it could be unbeatable.

 

oo - 00 - OO - 00 - oo

 

 



 

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© Franka
Version of: 3 May 2014
File started: 26 Apr. 2014