The venerable Vauxhall C20XE, or the ‘Redtop’ to its friends, has been a cornerstone of the European tuning scene for decades now, and this despite it having long ago been supplanted by more powerful and more technically advanced twin cams. Not only has the ‘Redtop’ powered pretty much any car you can think of (seriously, at this point it would probably be easier to list the cars that haven’t had an XE transplanted into them), it has proven its ability to make impressive power time after time.

Of course the reason for the XE’s brilliance, certainly its ability to accept an impressive array of tuning hardware and punch spectacularly above its weight, are its Cosworth origins. Originally signed off by General Motors in the mid ‘80s, the engine was produced with one eye on motorsport success and the other on the burgeoning hot hatch sector. The design of the new, fuel injected DOHC was duly entrusted to the eponymous Northamptonshire tuning legend, whereupon it was given the codename ‘Cosworth KBA.’

Our very first ‘complete’ project car, an Ascona 400 replica, boasted a C20XE

While it would be fair to say that Cosworth is a name more readily associated with fast Ford than ballistic Vauxhalls, the pairing had worked together previously, most notably on the Manta 400’s engine. The relationship would go onto give us (well, a select band of elite DTM drivers) the Cosworth KF, the manic, high-revving 2.5 V6 found in the Calibra touring car, but we digress. The pair’s success in the recent past meant there was only ever one firm GM was going to entrust the development of its new hot hatch power plant to, and by 1986 the wheels were already in motion.

More specifically, Cosworth was entrusted to devise a suitably performance focussed head for GM’s ‘Family 2’ series of blocks. This was over 30 years ago, remember, and a time when forced induction was still the preserve of competition machinery or ultra exclusive, high performance supercars. A mass produced, turbocharged hot hatch would therefore have to wait, so until then the best means of extracting big power figures from an engine was old school, honest-to-goodness tuning (and capacity), and in the mid ’80s that meant one thing – a beautifully engineered head.

An XE powered Mini makes for quite the unruly beast, trust us!

Herein lies the secret to the XE’s success, its ability to remain relevant in the modern world, and why we’ve opted to utilise it at the heart of some of our most important builds. Cosworth’s expertise lead to a square engine with sensational characteristics, brilliant response…and the small matter of 156bhp. That might not sound all that impressive now that Mercedes will sell you a four-wheel drive ‘hyper hatch’ with near enough 400bhp, but in 1988 it really was worth shouting about.

Perhaps unsurprisingly given the capabilities and track record of its maker (pun very much intended), the real secret to the ‘Redtop’s’ performance potential can be found within the structure of the head itself. Big, hungry ports and open throats were a standard feature, as were decidedly restrictive inlet and exhausts. This means that simply swapping these for free-flowing aftermarket equivalents clears the way to 170bhp or so at a stroke, as generations of would-be racers and Nova tuners will attest.

Another Retropower built Ascona B powered by a ‘Redtop’, albeit a supercharged example this time around

It is of course impossible to talk about the ‘Redtop’ and its maker without also discussing the legendary ‘Coscast’ head, those cast by Cosworth up until mid 1992. Chances are that if you know one thing about this engine and its (limited) list of foibles, it’s the predilection of those heads produced by GM to suffer from issues related to porosity. The fault is often left at GM’s door, specifically the firm’s desire to save money on the production of its potent Astra propulsion device.

Whatever the cause, the diagnosis of a porous XE head is almost always the same, the main oil way running across the head. The lack of ‘meat’ between this and the centre head bolt has been proven to be the cause of untold mayo-related, head gasket failure-misdiagnosis over the decades, with the reduction in metal quality brought about by GM’s desire to pinch pennies the cause. Which is why it pays to hunt out a Coscast head for any ‘big power’ XE build.

The ‘Redtop,’ so good even the Ford boys want one

Not that this has ever put us off utilising the ‘Redtop’ in such applications, particularly as the nature of our work means that we invariably rebuild and uprate any XE destined for a Retropower build. And herein lies another of the engine’s biggest strengths, its ability to, Supermarine Spitfire-like, accept seemingly endless power boosting upgrades in order to remain a viable proposition for tuners and club motorsport devotees. There’s a ‘Redtop’ for any car and any state of tune, basically.

We’ve used the C20XE in more projects than any other engine, which is about as good a recommendation as you’ll get considering. The iconic, ‘hockey stick’ shaped plug cover has graced the Chevette HSR, Mk2 Escort track car, 4-door Ascona, a trio of Ascona 400 replicas, an Opel GT and even a Mini. So yes, the Vauxhall Redtop – it’s not just OK in our book, it’s a fully paid up Retropower hero!

It takes a fair bit of work to squeeze a ‘Redtop’ into the diminutive nose of the Opel GT, but we managed it.

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