Established in 1938, the British Trial and Rally Drivers’ Association (BTRDA) is a major organiser of rallies in the UK and in 2019 – at the time of writing its last uninterrupted full season – it voted George Lepley as its Rally Man of the Year (writes Ian Bamsey). Lepley was the top two-wheel-drive (Silver Star) driver in its Forest Rally Championship, winning four of the five rounds he contested against all comers while claiming the Historic Cup with a clean sweep of class victories.
The Avenger BRM engine has proven competitive against the Cosworth BDA in the current UK classic rally scene
If there had been an award for Rally Car of the Year it would logically have gone to Lepley’s mount since it was a unique upstart in a world dominated by classic Ford Escorts. Lepley was driving the classic Hillman Avenger owned by Barry ‘Baz’ Jordan, for most events powered by a 2.0 litre naturally aspirated Avenger BRM I4 developed by Peter Jones’ Jondel Race Engines.
The owner of Jordan Road Surfacing, Jordan has over 30 years’ experience of national rally driving, mostly in Escorts. He has diversified into campaigning other makes though, and Jones recalls, “One year Baz decided to have a bit of fun with an Avenger, and we got that going well in its [stock] pushrod form. Then we thought about the BRM-designed and -developed twin overhead camshaft, four-valve-per-cylinder Avenger engine conversion.”
Introduced in 1970 and sold throughout that decade, the Avenger was Rootes’/Chrysler Europe’s answer to the Escort and Cortina mid-size family cars that Ford had developed for the UK market. The Avenger’s wheelbase was midway between that of the Escort and the Cortina, which was Ford’s next model up. All three cars had a longitudinally mounted front engine driving the rear wheels.
They also all had an engine that was a naturally aspirated iron block and head I4 with pushrod operation of two overhead valves per cylinder. Initially the Escort, which had been introduced in 1968, had 1.1 and 1.3 litre versions, the Avenger 1.25 and 1.5 litre versions.
In both cases the stock arrangement was of a single carburettor feeding all four cylinders, plus coil and distributor ignition. However, where the Escort’s Kent engine was a crossflow design, that was not the case with the engine specifically designed for the Avenger, which typically for its day had the intake and exhaust ports on the same side of its head.
The Avenger engine had a deep linerless block/crankcase that carried its crankshaft in five main bearings secured by two-bolt iron caps. Its single camshaft was chain driven from the front and was located high on the right-hand side of the block, keeping its pushrods short relative to those of the Kent engine.
Jones observes, “In many respects the Avenger engine was a better design than the Kent crossflow, having shorter pushrods and bigger valves.” The Avenger bore spacing was 99.6 mm (3.92 in), and dimensions of 86.1 x 64.3 mm provided 1497.5 cc, later enlarged to 87.3 × 66.7 mm for 1597 cc.
In addition to the UK, where it was designed and developed, the Avenger was marketed in Europe and North and South America under various names, including the Plymouth Cricket for the USA. There was a version unique to Brazil that had a 14 mm taller block facilitating a longer stroke for a displacement of 1800 cc.
Specifically for that country, the taller block was cast in Brazil, and it also featured larger diameter main bearing journals. However, with the exception of a Duplex rather than single chain drive for the camshaft, the 1800 cc Brazilian engine was otherwise to the same specification as the standard (UK) version, with the same bore spacing.
We saw in RET 130 (March/April 2021) how the Escort went rallying in the mid-1970s with an alloy block and 16-valve head; the BD series of engines designed and developed by Cosworth on behalf of Ford. There was no such factory-commissioned alloy block for the Avenger, but in 1974 Rootes did engage BRM to develop the aforementioned 16-valve, crossflow alloy head with competition in mind.
BRM only modified the top end plus the timing drive, as appropriate to the use of twin overhead camshafts. There are conflicting reports about how many of Avenger BRM engines were produced, and its rallying history is equally unclear; it was primarily used in UK national competition, and didn’t cover itself in glory. (In the late 1970s Chrysler Europe switched its attention to the Sunbeam model, which BRM’s arch-rival Lotus developed into a 1981 World Rally Championship-winning machine).
Jones says, “I believe the Avenger BRM engine was well-used in its day but it wasn’t successful owing to a lack of reliability.”
He adds, “Belt drives were rare in those days and – unlike Cosworth with the BDA – BRM went for a conventional chain drive. The stock camshaft was replaced by a jackshaft, having the existing front end chain drive. From that jackshaft, another single-row chain drove both overhead camshafts.
“I am told that on 100-hour endurance runs they found a problem with that chain, owing to an automatic tensioning mechanism that kept failing. It seems that was the engine’s Achilles Heel in its day.”
Jondel’s contemporary recreation of the Avenger BRM uses a Duplex chain drive to the jackshaft (later stock UK Avengers had that) plus a conventional manual tensioning system for the single race-spec chain to the camshafts. Jones says, “The bottom chain with its traditional tensioner has never been a problem of the Avenger and we have never used the automatic tensioning mechanism for the top chain. Our BRM timing drive has proven fully dependable.”
However, Jones recalls that this Avenger BRM project, which is a partnership with Barry Jordan, threw up a problem of combustion chamber cracking that had to be overcome. He notes that in its day the BRM head was only ever seen in its original guise; it wasn’t around long enough to have been developed into a further iteration. It has subsequently fallen into obscurity.
BRM’s twin overhead camshaft cylinder head for the Avenger I4 is chain driven
“When we decided on this project it seemed that nobody knew of the whereabouts of a 16-valve BRM head anymore, but eventually we managed to track one down and Baz bought that as a complete 1600 cc engine,” Jones recalls. “We rebuilt it and successfully campaigned it, but when we made a 2.0 litre version we ran into the problem with the head cracking inside the combustion chambers.
“I remember a rally down at Minehead [in south-west England] on which the car was absolutely flying – until it got halfway up Porlock Hill [the steepest A-road gradient in the country] when suddenly there was water everywhere. That was the moment we decided we definitely had to do our own BRM head!
“At that time I was working on a historic BRM Formula One engine project, and the customer told me he had seen the patterns for the Avenger BRM head at Hall & Hall [the racecar restoration specialist]. They are based in the former BRM factory at Bourne [in the east of England]. It turned out they also had all the drawings there – some 220 massive old-fashioned blueprints – so we bought all that from Hall & Hall. That is how our remanufactured head came about.”
Digitising the blueprints and using that data to create CAD models and refurbishing the patterns permitted the BRM head to be cast (by an undisclosed foundry) in LM25 rather than the original LM9 alloy. A prototype casting was destructively tested and found to be sound. “The first casting we had all sectioned up, and it was perfect – so we had cut it up for nothing!” Jones recalls. “So we went ahead and had another five cast. All have been CNC machined but so far we have used only one of them.”
The remanufactured BRM head has always been used on a 2.0 litre engine. It has proven fully dependable, the best part of 50 years of improvement in casting materials and techniques having overcome the cracking issue.
This was the engine used by Lepley in 2019. “It never missed a beat over a dozen events,” Jones recalls. He explains that this 2.0 litre engine exploits the taller Brazilian block, and notes, “We bought a Brazilian Avenger. It was known as the Dodge Polara. They made 96,000 of that 1800 cc model and I believe we have the only such car in the UK!”
Aside from the timing drive, the Brazilian block-based wet-sump bottom end is unchanged from production, aside from normal competition upgrades such as bespoke crankshaft, rods and pistons, and enhanced oiling. The wet sump is fully baffled, and the oil pump is uprated. In view of its wet sump the engine is equipped with lightweight alloy forged pistons having three rings.
The BRM head for the Avenger is a crossflow design, unlike the stock engine
Jones reports that the BRM blueprints reveal a design was made to accommodate Lucas mechanical fuel injection, whereas so far Jondel has retained carburettors, using a pair of 48 DCO/SP model Webers. Those twin-barrel carburettors are jointly fed charge air via a single ITG filter and provide an individual 48 mm venturi ahead of each cylinder’s runner.
Jondel has found it necessary to enlarge those runners, which are formed in an aluminium manifold that in the process becomes very thin walled. “There weren’t many original intake manifolds available so we had to have new ones made, and we have given those a bit more thickness,” Jones notes.
The inlet manifold attaches to a head that is faithful to the original BRM geometry, albeit with the porting enlarged. Jones reports, “We have only modified the head within the context of the original design, such as developing the porting and fitting valve springs and camshafts exploiting modern technology – in the same way as the BDA, which we also prepare, has been developed for classic rallying nowadays.”
The Avenger’s linerless block, the cylinders of which are uncoated, gives scope for a 90 mm bore. Jones feels that is a reliability risk, saying, “We don’t want cylinder porosity problems.” Jondel consequently works with an 88 mm bore, which is allied to an 82 mm stroke for 1994.9 cc.
As developed by Jondel, the porting is not designed to exploit tumble. Valve lift is 11.43 mm (450 thou) intake and exhaust. The BRM head provides an included valve angle of 30 degrees and its pent-roof chamber is used in conjunction with a piston crown that is flat, aside from valve clearance notches, with the compression ratio being 12:1.
The engine is designed to run on ‘super unleaded’ 99 RON octane roadside pump petrol. “These engines run just short of detonation,” reports Jones. “We aren’t allowed to run knock sensors in competition but we use them on the dyno for engine set-up.”
Ignition is by a traditional-type Lumenition system using a distributor that Jondel builds itself. Ignition timing is “32º at full advance, as per the BDA”. The ignition and jetting are fixed on the dyno, and in normal circumstances need no adjustment in the field. The single central spark plug is 10 mm, as is likewise used in the BDA these days rather than the 14 mm original, since that is the size that currently provides what Jones considers to be the best quality product.
The BRM head has a detachable aluminium cam carrier with the camshafts running in five shell-type bearings retained by individual aluminium two-bolt caps. With the BRM engine purchase Jordan acquired a number of original cam carriers and (aluminium) cam covers, so Jondel has not had to remanufacture those items.
However, it has been necessary to remanufacture the front cover. Jones says, “The front cover is a complex LM25 casting, and that was challenging for our machine shop. But we were determined not to switch to billet; we were determined to keep to a casting using the original patterns for authenticity.”
The BRM design retains the production 10- bolt head attachment, Jondel acquiring original size – 7/16 in – bespoke studs and nuts from ARP. For head-to-block sealing Jones notes that in view of the 12:1 compression ratio a multi-layer steel gasket would be ideal, but that is a very expensive solution for such a short production run, hence good old-fashioned Coopers rings are used instead.
A feature originally of the Cosworth DFV, those are compressible steel rings that fit into a groove that is counterbored into the deck around each cylinder. There is then a surrounding gasket of organic material to seal the water passages. The head retains the stock water inlet and outlet passage locations.
The remanufactured BRM head is fitted with iron valve seats and bronze guides. All the valves, which are supplied by Race Engine Components, are solid stainless steel and uncoated. A pair of straight-wall steel coil springs close each of them, those running without an interference fit. Jones reports that the BRM uses very similar springs to BDA engines he prepares, although the valves are smaller because of the 2 mm smaller bore.
Steel spring platforms protect the alloy head, while the conventional spring retainers are likewise steel. The valves are opened by steel inverted bucket tappets with steel adjustment shims underneath. The working surface of the bucket is DLC-coated and operates against a superfinished billet steel camshaft. DLC is typically thus used in classic rally engines as a wear-reducing, cost-saving measure.
The bespoke steel exhaust is four into two into one, as befits the quest for a wide power band as appropriate to rallying. The firing order is 1-3-4-2 while the oil pressure is 70 psi – close to standard, even though the oil pump is modified – and the water temperature is around 80 C – similar to stock. The Avenger BRM is located in the chassis using standard production engine mounts.
Jones admits that on his dyno the BRM in its current, not yet fully performance-optimised guise has about a 5% top-end power deficit compared with the BDA. Of course, the BDA has been consistently honed over half a century. “The BDA has had a lot of development, whereas we are the only people to have developed the BRM engine,” Jones reminds us.
The valve angle is narrower than that of the BDA, to the benefit of combustion chamber form, while as measured by Jondel the BRM head flows better. On the other hand, the BDA benefits from its 90 mm bore in terms of valve provision.
At the end of the day, rallying is as much about driveability as top-end power. Jones remarks, “We don’t develop different engine specs for gravel and tarmac rallies. At Jondel we pride ourselves on producing very driveable engines with a wide power band; torquey engines that will pull from almost nothing. We have done that partly by redesigning a lot of parts in our carburettors to help make the engine pull well from low revs.”
The BRM engine pulls from 3000 rpm to its nominal 9250 rpm redline – which, Jones reports, Jordan and Lepley have often exceeded without harm to the engine. “Baz and George have both regularly run to 10,000 rpm without issue,” he says.
Peak power is made at 8600 rpm and is “in the region of 250 bhp”. Jones adds, “I liken it to the Holbay Warrior [the 16-valve derivative of the Ford Pinto I4] – we have built quite a few of those. On our dyno we don’t see quite as much power as a BDA but the drivers seem to think they drive better.
“We haven’t done the Avenger BRM justice yet by pushing the development as far as it can go, but it produced the goods from the outset. I look at the project as having discovered a lovely, unfinished painting that we have now almost completed!”
When it comes to Escort versus Avenger, there is also the whole car package to consider. Although the BDA’s alloy block makes for a lighter engine package, the Avenger scores overall weight-wise, being slightly lighter as a complete rally car. Moreover, Jones reports that for inherent chassis reasons beyond the scope of this article, “the Avenger handles better – partly due to its rear suspension design, it turns in much better.”
Thus the Avenger BRM is certainly a match for the Escort BDA these days, irrespective of any top-end power deficit. Lepley’s success is evidence of that.
JONDEL AVENGER-BRM
2.0 litre Classic Rallying
I4
88 x 82 mm = 1994.9 cc
Naturally aspirated
99 octane pump petrol
Iron block and aluminium head
Linerless
Five main bearings, plain
Steel crankshaft, four pins
Steel con rods
Light alloy pistons; three rings
Chain-driven double overhead camshafts
Four valves/cylinder, one plug
30º included valve angle
Valve sizes undisclosed
Analogue electronic ignition
Twin carburettors
12:1 compression ratio
Maximum rpm, 9250