An Avenger gets the 'works' treatment

I remember once reading how a prototype Mini, using the 948-c.c. A40 engine, had put the wind up the old BMC management by virtue of its exceptional performance for those, and come to that, these days as well! At the time my only method of moving from Sussex to London and back every day was a very basic 850 Mini; the thought of the money needed to make this basic transport get up and go in the way that the ADO15 prototype had was enough to set a seal on my resolve to try a manufacturer’s development car one day to see if there were any snags to the levels of performance that had apparently been extracted from that particular small BMC saloon.

In fact the whole business of pre-production cars is a fascinating one, beginning with the period when alert readers or friends spot an unusual car on the road (or at a customs post, a favourite with Continental magazine photographers, or the traditional long lens test-track photograph which reproduces as a vague shadow in a blizzard!) to the period when a party of journalists first get to grips with the first 40 or so (assuming a mass-production firm are acting as hosts) “pre-production, production” cars, which will usually differ only slightly from the machines the public can buy at their friendly dealers.

Recently the Chrysler Competition Centre Manager, Desmond “Des” O’Dell, exasperated by our constant prodding, gave in to our request to try the Hillman Avenger which the department had modified with more than a passing eye as to the requirements of club rallying and potential customers for extra road-going horsepower. No prices were available at the time of our test, but a letter or ‘phone call to the Chrysler Centre’s Coventry base will probably produce additional information which should be known after these pages went to press. For potential Avenger owners who cannot wait to improve their Avengers there is a monograph later in the article which gives the names and addresses of other firms who tackle Avenger modifications, and whose cars the author has tested.

Although the green “works” Avenger that we tried had led a varied and exciting life as a mobile test bed, it was presented to us as a properly prepared road test vehicle with both interior and exterior smartly cleaned and polished. Originally the test Avenger was a 1250 model, so it lacks any extras of any sort save those needed for efficient performance such as the 1500 GT engine, and front disc brakes with servo assistance.

From this basic beginning the Competition centre staff have gradually built the car up to its present rorty specification. The exterior engine changes comprise completely new inlet and exhaust manifolding built up in steel, co-ordinated with a pair of sidedraught Weber 40DCOE twin-choke carburetters. To further improve the breathing a radically modified cylinder head was fitted with the standard 1.20-in. exhaust valves and 1.47-in. inlets: the standard 1500 has 1.42-in. inlet valves. Compression ratio was increased to 10.2 to 1 and both inlet and exhaust porting were modified to mate up accurately with the revised manifolding. The camshaft is profiled along well proven Cosworth lines, the profile originally being intended to act in conjunction with a Ford engine.

As we said earlier, this Avenger was strictly intended as a prototype and it was for this reason that the department naturally decided to explore the effect of some well-known profiles before looking at a completely fresh design of camshaft, or modification of an existing Chrysler one. The crankshaft, connecting-rods and pistons were left as standard, save for careful matching of weights and crankshaft balancing in conjunction with the production flywheel.

This modified Avenger’s most outstanding characteristic was to be the handling, despite which O’Dell intends to carry out even more work on the suspension in respect of front-wheel camber and castor angles. Softer rated rear springs than we had and harder bushes for the back axle location points to reduce compliance under competition conditions are also planned. The work that had been carried out included competition settings for the front MacPherson struts (adjustable units will also be available from Armstrong or Chrysler) plus much larger capacity Armstrong adjustable telescopics at the rear. Replacement springs all round reduced the car’s static ride height by approximately one inch, spring rates, with standard settings in brackets, being: Front, 100 lb. (80 lb.); back, 240 lb. (180 lb.). A set of 210-lb. rear springs will have been tried by the time you read this and it is expected that they will further help rear axle location over bumps.

To complete the handling story we must add a set of 7-in. rim Minilite wheels, as manufactured so capably by Tech Del in Acton, and four plump Dunlop SP Sport tyres of 195 section, 70% aspect ratio, suitable for 13-in. wheels.

If the engine was concealed under a frosted over bonnet, or was burning hot after a hard caning, the result after the fiddly ignition key had been turned was just the same—an instantaneous cough of life from the power unit. The only preparation needed to begin these exemplary starting manners was a brace of dabs on the accelerator pedal. After 30 seconds of holding the engine r.p.m. at 2,000, or thereabouts, the Avenger was ready to move off cleanly from a cold start without further ado.

Incidentally, that dramatically bulged matt black bonnet caused more than one observer to enquire if the rumoured four-valve-per-cylinder engine was fitted. Our questioners seemed as disappointed to hear that a “conventional” engine was installed, as we were to hear that the four-valve unit has been officially shelved for some time. The car attracted an enormous amount of attention from enthusiasts during our week’s testing, the competition minded all asking: “Can you get a two-door?” Upon hearing that they could not, the next question was, “Well how much bigger can I make the engine, or will the factory be doing something larger soon?” Even faced with the negative reply to that enquiry most of our interrogators took the trouble to note the bulged wheel arches, investigate the under-bonnet layout and ask who the Chrysler Competition Centre were!

Although the Avenger would spin its wheels vigorously away from a standing start, the acceleration times were not particularly startling by today’s standards, the blame for this being attributable to the narrow range within which the camshaft was allowing the engine to give of its best. Nothing really happened, even in first gear, until over 3,000 r.p.m. were indicated and the power unit ran out of go above 6,500 r.p.m. Between 4,000 and 6,500 r.p.m. in top gear (70 to 102 m.p.h.!) the Chrysler engine really improves the most jaded motor noter’s pulse rate, the chief sound source being the angry rasp from the Webers’ open throats, finally settling into a harsh beat as the four-door bodyshell is hauled up to a maximum slightly over 105 m.p.h.

The magnificently graduated braking from the ordinary disc and drum system superbly complemented the remarkably roll-free cornering and exceptionally light steering. Really the padded steering wheel controlled the most exploitable handling I have ever enjoyed in a front-engine, live-rear-axle machine. The puniest seven-stone weakling could park the car using a fingertip grip, whilst at high speed the rack-and-pinion system gave exactly the responses that were needed. A perfectionist might ask for a little more castor and high-speed feedback, but for road and competition use the car seemed well provided for in the handling department.

Road adhesion was naturally pretty stunning with the amount of rubber provided, though a poor surface would have the back hanging out in easily retrievable fashion. Too many cars look the same nowadays, and feel the same as well on the road, but this Avenger had a character all of its own which allowed us to privately enjoy a great deal of rapid cornering, characterised by a little initial understeer and inevitably ending with the rear wheels sliding outwards as the car slipped flatly outwards to a respectable attitude before another curve. In public road use the standard seats offer enough location to allow a very detached, and undramatic, course to be chosen through any sort of cornering radius.

One point that puzzled us throughout the test was this Avenger’s quite extraordinarily stable path along exposed motorway tarmac. Normally we would expect a fair amount of tacking to be necessary on the draughtier sections of the M1, whether it was an Escort or an Avenger which we were conducting. However, Chrysler’s test bed wandered only slightly in really adverse conditions, such as passing between articulated lorries whilst emerging from a motorway cutting. On returning the car to Stoke we mentioned that their Avenger felt as if it had a front air dam attached, so stable was its progress, but the only possible explanation they could offer was that the reduced ride height, altered bonnet profile and replacement quarter bumpers (which were properly made, not sawn up!) had somehow combined to provide better aerodynamic downthrust at speed. Whatever the reason, this Avenger nearly provided front-wheel-drive standards of crosswind behaviour, taking much of the effort out of long-distance travel.

The original 1250 axle ratio, a 4.375 to 1, was retained, and this gearing choice is aimed at giving the best in acceleration. Legal limit cruising corresponds to 4,500 r.p.m. in 4th gear, but the engine gave no sign of distress when continuously operating at 6,000 crankshaft revolutions per minute, a speed of 94 miles an hour in top gear. At the r.p.m. limit we were asked to observe, 7,000 r.p.m., the intermediate gear speeds of 33, 53 and 81 m.p.h. were recorded. The gap between 2nd and 3rd is a bit too much for the absolute best in enthusiast terms and we were worried by the amount that the gear-lever jerked on the overrun. From sources outside the factory we have heard that there will be a Mk. 2 gearbox for the Avenger by the end of the year, and it should prevent any of the troubles that the really highly-tuned examples can run into with 2nd gear pulling out of engagement whilst decelerating.

By highly-tuned the author means 90 b.h.p. or more; it is impossible to be specific about the mileage at which this might occur, because in the cases we know of one Avenger did a regular commuting run twixt Scotland and London plus all the usual magazines (except this one) for road test, before succumbing, whilst others have given trouble earlier on. However, it should be emphasised that all these machines have been involved in performance figure sessions, and there’s no finer way of wrecking an otherwise perfectly acceptable transmission!

The Competition Centre have built up an excellent base for a Clubman’s or International rally car which could also do well when Group 1 saloon-car racing comes to the UK next year. Now we just hope that the parent company will be able to support the loyal staff they have in Stoke for a defence of their London-Sydney Marathon win.

***
At Standard House we have now tried three other Avengers apart from the one featured here. A mildly and inexpensively converted version was reviewed in Motor Sport of October 1970, the work being carried out by Davenport Vernon at High Wycombe. Team Hartwell at Holdenhurst Road in Bournemouth, and Janspeed Ltd. of Southampton Road, Salisbury, Wiltshire, have also lent the writer examples of their craft, which have not appeared in Motor Sport’s pages before.

The Hartwell Avenger was a genuine 100-m.p.h. machine which had covered umpteen thousand miles as a hire car. Mechanically this Avenger was perfect and the 1500GT-based engine, with all new manifolding but using the GT’s 1 1/2-in. choke Stromberg carburetters, gave acceleration to 60 m.p.h. in under 12 seconds and as punchy performance as an Escort Mexico throughout the r.p.m. range. Shortened coil-springs and 5 1/2J Ford steel wheels gave a worthwhile improvement in road-holding and handling, the whole package being reasonably priced by today’s standards: probably the work is within the scope of a Do-It-Yourself fiend as well.

The Janspeed car was far more briefly tried, the author borrowing the car despite warnings of how much it had suffered in other hands. On this car 2nd gear could be used just for acceleration, but that did not stop us enjoying a run of 25 miles or so. Including a £40 labour charge the completely rebuilt Avenger unit would cost £217, independent tests showing 0-60 m.p.h. times comfortably under 10 seconds, allied to a top speed of just over 105 m.p.h.; a cheaper kit, similar to Hartwell’s in concept, is also offered by the same company. The car we tried also had 6-in. wide GT alloy wheels (manufactured by the Mill Accessory Group, commonly known as MAG) with 185 section Goodyear GP radials, plus an experimental lowering job which took roughly 1 1/2 in. off at the rear and an even inch at the front. Unlike the “works” Avenger, Janspeed’s car did not spin its wheels whilst getting away, but it certainly had a lot of power, delivering the same sort of performance as one would expect from a production Escort TC—if one could lay hands on such a device. Above 85 m.p.h. or so the Avenger would lag behind an Escort Twin Cam, but up to that point there seems little difference in road use.

The handling of Janspeed’s car was similar to an Escort as well, the axle following road ripples and sliding outwards, albeit in a very foreseeable fashion. Third gear would pull on a light throttle from under 2,000 r.p.m. and 4th from 3,000 under a heavy application of accelerator. Overall fuel consumption was said to be 25 m.p.g., but I think that the sort of driving that almost inevitably is meted out to such a car would bring it down into the sub-20 m.p.g. range recorded by the low (high, numerically) geared Chrysler converted car.

Summing up, the Avenger customer is well served by the conversion specialists at present, so that almost any stage of performance can be specified by the client with comparatively cheap suspension and braking modifications equally freely available.—J. W.

Performance figures
Acceleration:
0-30 m.p.h. – 3.6 sec.
0-40 m.p.h. – 5.8 sec.
0-50 m.p.h. – 7.9 sec.
0-60 m.p.h. – 11.1 sec.
0-70 m.p.h. – 16.2 sec.
0-80 m.p.h. – 22.0 sec.
0-90 m.p.h. – 35.8 sec.

Gear speeds (first three at 7,000 r.p.m.):
1st – 33 m.p.h.
2nd – 53 m.p.h.
3rd – 81 m.p.h.
4th – 105.6 m.p.h. (best), 101.0 m.p.h. (average)

Overall fuel consumption: 18.8 m.p.g.

Converters and prices: contact Andrew Dawson, Chrysler Competition Centre, PO Box 25, Coventry.