Opus di Busso

Further to last week’s dissertation on the 1979 Alfa Six, we examine the contemporary reception to Giuseppe Busso’s Alfa Romeo 2.5 litre V6 unit, through the acerbic eye of LJK Setright.

The Busso V6 as fitted to the 1979 Alfa Six. (c) movitcars

Some engines arrive fully formed, others however, enter the world imperfect, but through a process of development and retrospective correction evolve to defy their early criticism.

A fundamental element of Alfa Romeo’s iconography was intrinsically linked to its engines, especially its pre-war thoroughbreds, those patrician in-line fours, sixes and eights which powered the carmaker into history books, not to mention the hearts and minds of all those with the blood of Portello coursing through their veins.

It was therefore an event of no little note on those rare occasions when Alfa Romeo introduced a new power unit, especially given that apart from the horizontally-opposed Alfa Sud unit, the storied Milanese carmaker had relied upon various derivations of twin-cam fours since the 1950s.

Of course what that statement conveniently ignores is the in-line six that powered various 2600 saloons, coupe’s (and a few convertibles) from 1962 to 1967, an engine which perhaps fell somewhat short of the high ideals, to say nothing of the expectations of the faithful.

The 1979 introduction of the Alfa Six was notable therefore, not simply because it represented the Biscione’s first attempt at an ‘ammiragila’ since the 2600’s demise, but more so because it also marked the debut of an entirely new, first-principles multi-cylinder power unit.

A six cylinder Alfa Romeo power unit seemed on paper at least to be a highly alluring prospect, so it was with some bemusement that the engine itself, designed under the supervision of Ing. Giuseppe Busso, was not only of a configuration not immediately associated with the marque, but contained within it, a number of technical solutions which, rather like the Jaguar V12 of 1971 departed noticeably from hitherto sacrosanct technical orthodoxies.

Alfa Romeo went to some lengths in 1979 to justify the adoption of a V6 layout for their new six, citing its connection to eminent engineer, Vittorio Jano, who was responsible for a number of legendary Alfa Romeo engines as technical director at Portello during the 1930s – although as LJK Setright somewhat waspishly pointed out in his June 1979 technical review for Car magazine, the engines Jano was associated with at Alfa Romeo were in-line units of six or eight cylinders.

Of course, following his dismissal from Portello in 1937, Jano went on to do what was arguably his definitive work at Lancia, and it was here that alongside Francesco di Virgilio, the first production V6 engine was developed for the Aurelia. Jano later went on to inspire the superb four-cam Ettore Zaccone Mina-designed V8 GP unit and latterly, the compact 65° Ferrari V6 which would (also) power Scuderia Ferrari to innumerable Grands Prix victories.

But if the connection between Alfa Romeo and the V6 configuration was, to say the least, tenuous, the engine itself was meritorious – albeit, this did not mean that some of its technical conclusions were viewed as being anything other than regressive, eliciting a theatrically raised eyebrow from Car’s resident engineering purist.

Arguably at least by the late 1970s, and certainly by the predetermined technical standards of Arese, the use of pushrod operated valvegear was not cutting edge technology, to say nothing of the employment of six individual carburettors, when fuel injection was already not only widely prevalent but preferable.

In his 1979 essay, Setright appeared at pains to debunk Alfa’s justification for their new engine, pointing out Alfa’s (correct) claims that their 60° unit was smoother running than rival units like the Douvrin 90° unit fitted to a variety of European rivals, but noting that while the Busso unit was narrower than a 90° configuration, it was also taller – albeit less so than an equivalent in-line engine.

However, (to paraphrase the late Jim Randle), despite the crankshaft not being the sort of thing one would ideally choose to have as a desk ornament, it was nevertheless a good deal shorter and torsionally stiff than that of a straight-six.

And if torsional stiffness might have aided the cause of smooth running, Car’s monocoled mutineer looked askance at the V6’s valvegear. Ingenere Busso either specificed or had imposed upon him the requirement to avoid unnecessary complication (perhaps bulk and certainly cost) and so the Alfa V6 employed single overhead camshafts operating at an included angle of 46 degrees 45 mins into part-spherical combustion chambers.

The larger inlet valves (41 mm in diameter) were directly actuated from the camshaft by piston-type tappets, while the smaller exhaust valves were actuated using short transverse pushrods and rockers – akin, LJKS suggested to pre-war BMW/ Bristol methodology.

Setright lamented the engine’s good but not brilliant inlet valve area in relation to the pistons (21.7%), and appeared to infer that the Alfa’s complicated valvegear would lead to an unnecessarily noisy engine – a matter for which he may not have been in error – albeit, the quality of the noise is often of more significance than the disturbance itself, and one thing which can be said of the Busso V6 is that in any configuration, the noise it left in its wake was a pleasing one.

Ing. Busso’s engineers went to the trouble of providing a sound spectrum analysis, showing the noise reaching the driver’s ears at 120 km/h – a road speed which the carmaker stated would only require 80 bhp and 3725 revolutions per minute to propel the car – and which appeared to back up Setright’s assertion insofar as the “loudest apparent noises are at 12, 18, 24, and 36 vibrations per [crankshaft] revolution, which are clearly harmonics of the basic mechanical and combustion pulsations.

In addition to the complex valvegear, LJKS also pondered whether the source of engine harshness might have been related to the “instant and uniform” combustion Alfa Romeo made much of in their launch material, Arese claiming that at 415.3 cc each, the V6’s cylinders were ideally sized for thermal and volumetric efficiency – a matter which dear Leonard refuted as nonsense, citing SAE papers by Honda as proof. Indeed he asserted that were the engine to display the former trait for which Arese’s PR representatives claimed, the V6 would in fact blow itself to pieces.

But if Setright was perhaps a little uncharitable about aspects of the design (and the manner in which it was presented to the press), he was nothing if not prescient in his perceptions – no more more so than when he observed; “What is easier to accept is the idea that the V6 may one day sprout four valve heads, in which case this valve-operating mechanism may begin to make sense.

Possessing a lower stroke to bore ratio than its putative rivals, it was clear from the start that Arese had bigger plans for the unit – clearly then, cylinders of 500 cc each were better still…

The 24 valve Busso V6 as fitted to the 164. (c) : automotive database

Setright concluded in a more consiliatory tone, noting; “A pinch of salt should suffice. Much better to attend to the opinions expressed by those who have driven the car and are competent to judge it: they seem to like it, and that makes it likely that the 2500 is a good car.

What we now know is that whatever the merits of the Alfa Sei as a vehicle or indeed an Alfa Romeo, Ingenere Busso’s V6, much like Mr. Hassan and Mundy’s Coventry-bred V12, evolved into very fine engine indeed – arguably perhaps, one of the greatest.

Author: Eóin Doyle

Founder. Editor. Content Provider.

25 thoughts on “Opus di Busso”

  1. In a board meeting Giuseppe Busso once got accused that he was only able to design DOHC engines (what an accusation…). As a result he adopted the valve gear of an experimental engine designed for a joint development project with Bosch for his new V6 engine. This experimental engine had short horizontal pushrods for the exhaust valves and bucket tappets for the inlet side.
    This peculiar valve gear also allowed for an extraordinarily compact belt drive arrangement.
    Properly set up this valve gear is astonishingly quiet because the pushrods are very stiff due to their short length. The only problem can be premature wear because some batches of the engine were made with insufficiently hardened horizontal tappets and/or the design of these buckets doesn’t provide a proper oil reservoir for lubrication during engine start up and using the wrong oil (that doesn’t stick to the tappets) makes it run dry until full oil supply sets in after starting the engine.

    Ingegnere Busso insisted on using carbs on this new engine because it would deliver higher bmep than equipped with fuel injection – the torque curves of the carburettor vs. injection versions prove him right.
    The larger versions of this wonderful engine are mixed blessings and many Alfisti consider the 2.5 to be the best of the breed. The 3.0 and 3.2 are nowhere as smooth as the 2.5 and aren’t as willing to rev – everything is relative as there are few engines of this size as hungry to rev to and beyond 7,000 rpm. In the 3.2 there is very little material left between the bottom of the wet liners and the main bearing carriers so it’s close to the absolute maximum for a series production version of this engine.
    Early DOHC versions introduced in the 164 QV had a design fault in their cam drive making the belt jump a tooth or two every now and then resulting in expensive noises. This was only eliminated when the belt drive was comprehensively redesigned for use in the GTV 916.

  2. Now, why am I reminded of a Fulvia when I look at that pic of the camshaft?
    I still have a pair of cams and associated gubbins sitiing at the back of my garage.

  3. Speaking of the Jaguar V12, outside of the reputedly underpowered experimental prototype (developed prior to the AJ6) could a Jaguar V12-based 2.5/2.7-3.0-litre+ V6 have ever been a credible rival to the Alfa Romeo V6? And if not what would have been the best approach to take to make a V12-based Jaguar V6 viable?

    Know Jaguar had their reasons to dismiss DOHCs for the V12 (e.g. complex, large, heavy, noisy), with one opinion suggesting the V12 could have been improved by benefiting from a Honda style SOHC with rockers arrangement (allowing scope for a 48-valve version) though not sure how that would have been relevant for a hypothetical Jaguar V6.

    It seems Autodelta and others did managed to further enlarge the Alfa Romeo V6 to around 3.5-3.7-litres (with a few even stretching to 3.8-litres) and putting out around 300-328 hp.

    It is also interesting to note that Alfa Romeo did look at a 900cc version of the Twin-Cam engine for the Alfa Romeo Tipo 103 prototype as well as 750cc 2-cylinder version of the Twin-Cam engine in Project 13-61 (at a time when the Giulietta was still in the development phase) which preceded the Tipo 103 project.

    1. Jaguar intended to build an inline 6 from the V12. I’ve seen some old company advertising from the 1970s, although I’m not sure it ever made it to production.

      If you you were ever going to build a 6 cylinder from a V12, I don’t know why you would ever bother with a V6. Especially for Jaguar in the 1970s and 80s, where their cars were designed for inline 6s.

    2. Jaguar investigated a number of options before settling for a Slant-6 that eventually became the AJ6, a V6 being the most logical (despite the experimental prototype being underpowered) because it is basically an extension of the stillborn 60-degree V8 that was planned with the Jaguar V12 (and intended to both replace the XK6 as well as move Jaguar further upmarket), one which could have been put into production at very little cost in capital or development time.

      Could have potentially worked out well had the V12 been better developed and soon filtered down to a related 60-degree V6 capable of rivaling the Alfa Romeo V6, however as the V12 was such a V6 would have probably been more suited for an XJ Junior model as opposed to a worthy XK6 replacement.

    3. We have been around the houses at least twice on this one, I seem to recall.

      Jaguar did build an experimental 48-valve version of their V12 – as far as I can gather it was handed to TWR, who built a series for their joint Group C racing programme. One of these engines resides in the prototype XJ220, itself a permanent resident of Jaguar’s Heritage collection. In addition, a number of twin-cam V12 units were made during the mid-60s – ostensibly for the XJ13 programme, but a couple found their way into experimental Mark 10 saloons, which provided rather vivid performance.

      The slant six derived from the V12 was adjudged to be okay, but it lacked swept volume and given the type of cars Jaguar was making, would have proven inadequate. The lack of performance derived from the 2.9-litre AJ6 is ample testament to that. A V6 derived from the V12 ought to have been relatively easy to achieve and could, I would assume, have been capable of being made on the same transfer line as the larger unit. However, it would have suffered the same issue – even with a 3-litre capacity, requiring expensive solutions to provide a competitive power output.

      Why did they not consider a V6? Engineering orthodoxy I assume, not to mention BL politics, which were no small matter at the time AJ6 was conceived. However, Jim Randle did suggest that a V6 layout would have been preferable for AJ6 in retrospect when we spoke in 2016. Of course another rationale was that they genuinely believed they could alleviate the inherent imbalances of the 60 degree V8. This was achieved, ( I’m reliably informed) but much, much too late.

      However, As I also pointed out in the past, a 2.7 – 3.0 litre Jaguar-developed V6 would have been a very useful power unit for the group as a whole and could have supplanted the Rover/ Buick V8 in SD1, and perhaps obviated the requirement for Honda’s V6 unit for the 800 Series.

      But surely we aren’t simply going to discuss Jaguar engines in the (virtual) presence of Ing. Busso? Where are our manners?

    4. Potential uncouthness aside, the Alfa Romeo V6 eventually the benchmark from which other (existing or hypothetical) V6 engines are judged, whether it could have been doubled up for a truly flagship Alfa Romeo (and GT coupe – fuel crisis notwithstanding) in the same way the Jaguar V12 could have been halved is another subject.

  4. LJKS must have had a fit with the 2.5 litre Honda C Series engine that appeared in the Legend in 1986. I know I did when I got to inspect a cutaway one when even we in Nowheresville used to have an annual car show. Not only did it have a similar pushrod arrangement as the Busso to run the exhaust valves from the SOHC but twice as many for good measure, and it was a 90 degree V6 with one of those warped-up cranks with offset throws to give even firing, as Buick had started and the gutless PRV engine finally adopted. Elephantine in physical size as well, that first V6 Honda, the most complicated piece of nonsense cylinder head ever designed to my mind that prompted the question – why? I could go and drag out all my old mouldy CARs and find out if LJKS bothered to mention it, but after those earlier cutting remarks on the Busso design, perhaps he was discreetly quiet about its layout being a Honda man, so I won’t bother.

    One thing’s for sure, the Alfa slayed the Honda engine despite the latter’s 24 valves. Never read a bad review on any Alfa with any version of the Busso V6 – it dominated the car it was mounted in. Just one of those rare occasions where things turn out right – I’m yet to be persuaded that the Jaguar V12 was ever great – when people can substitute a Chevy V8 smallblock and the result is better in every way but smoothness, something wasn’t quite right in the first place.

    1. “I’m yet to be persuaded that the Jaguar V12 was ever great …”

      I think that is right. One of the things I am increasing able to understand is the importance of swirl and tumble of the intake charge for part throttle low rpm efficiency, detonation resistance etc. , especially with port fuel injection. All the fuel gets dumped on the intake valve and in-cylinder air motion is required to mix it. Swirl and tumble do that mixing more completely.

      One thing Jaguar got unlucky on the V12 was, with a SOHC and the valves inline and straight down into the cylinder, there was almost no inherent swirl or tumble in that design. With any pushrod inline valve engine, the port flows in at an angle and significant swirl is automatic – it would probably be hard to not have it.

    2. I leave the finer points of engineering details to those with intimate knowledge of the subject, but as a long-time owner/user of a Jaguar V12-powered motor car, I feel compelled to point out that I’ve never experienced a car of squarely the same vintage that offered even remotely the same levels of smoothness. No six, eight or V12 engine produced at the same time as the 5.3 litre Jaguar engine I’ve sampled remotely matched it in this regard – including American V8 units and Mercedes’ 6.3 V8, as well as BMW’s far more advanced 5.0l V12.

      So with all due respect to American engineering, not everyone who doesn’t substitute a Jaguar V12 with a Chevy V8 is a listless buffoon.

  5. On the subject of the Alfa Romeo Twin-Cam and early Alfa Romeo Twin-Spark engines (as opposed to the later Fiat Pratola Serra / B Family 16-valve Twin-Sparks), does any information or specific details exist regarding alleged 16-valve prototypes developed in-house by Alfa Romeo?

    1. Read elsewhere there was no room in the heads of the Twin-Cam and early Twin-Spark engines for 4-valves, yet have heard of unbuilt experimental 4-valve prototype engines being tested by Alfa Romeo and am mainly after information on power / torque for the latter.

    2. How in earth do you get performance numbers from unbuilt engines?
      Not enough room for four valves in the Busso engine’s head is nonsense. There was room for four valves in the ‘modulare’ engine with 83 x 91.5mm bore/stroke, so there surely was enough room with 84.5 x 88 mm.
      The above picture clearly shows a four valve engine, so at least one has been built.

    3. Am defining an unbuilt engine in this instance as an experimental prototype engine that did not reach production. Even if an unbuilt / experimental engine never reaches production, such performance numbers is still usually available for such engines whether online and in books with countless examples (e.g. all-alloy water-cooled 54 hp 950cc Simca Flat-Four at CAAPY, 59-84 hp 970-1275cc A-OHC, 120-170 hp 2.2 Rover P10, 270-280 hp 4-litre Maserati V8 for Quattroporte II as tested in a Citroen SM, etc).

      The reference on there was no room in the heads of the Twin-Cam for 4-valves comes from a Curbside Classics article on the Alfa Romeo Twin-Cam, AFAIK there has never been an actual production 16-valve Alfa Romeo Twin-Cam / early Twin-Spark engine beyond the odd prototype as well as few Autodeltas and another 16-valve head developed by the tuner Franco Angelini (along with other small references in Jim Kartalamakis’s How to Power Tune Alfa Romeo Twin-Cam engines).

      To clarify am aware the later Fiat-based Twin-Spark engine did feature 16-valves as well as aftermarket tuning companies, however am only interested if available in any information on the experimental 16-valve Alfa Romeo Twin-Cam / early Twin-Spark prototype engines developed by Alfa Romeo themselves.

    4. Look for ‘Francetti’ engine or ‘Autodelta 16 v marino’. Autodelta built 16 v engines mainly for marine use with 1.300 cc/180PS or 2.000 cc/260 PS some of them were used in racing Alfas.

    5. Managed to find the following link on engine developments of the Twin-Cam at Autodelta, though nothing specific about any detuned road-going 16-valve versions of the Twin-Cam / early Twin-Spark engines or on anything Autodelta did in the 1980s-1990s for the engines before they were replaced by the Pratola Serra-derived engine. – https://www.alfabb.com/threads/engine-developments-at-autodelta-in-the-1960s-and-1970s.283985/

      Otherwise was unable to find any reference to the Francetti engine though assume it ties back to Baron Franchetti?

    6. I’d say that a racing GTA 1300 junior or 2000 GTAm is a road going vehicle, if anything. Autodelta built 16V engines for such cars, so definitely there were road going 16V Busso engines and compared to the marine versions they were slightly detuned to make them more usable on the track.
      The Twin Spark Busso engine as used in 75/164/155 used a head based on the GTAm race engine’s but did without the monobloc wet liner because the road going 2,000cc engines had even cylinder spacing and therefore could use separade wet liners. So it clearly is a detuned version of the race engine.

    7. The Autodelta 16-valve engines may be road-going in a manner of speaking though cannot really envision them being something Alfa Romeo would enter production themselves, had they produced a production version of their 16-valve Twin-Cam / early Twin-Spark engines as would expect a fairly moderate increase in power roughly comparable to the later Pratola Serra 16-valves a decade prior in the mid-1980s (yet still with scope for such power gains via tuning).

    8. Maybe it would be helpful if you stopped to use ‘road going’ and ‘series production’ as synonymous terms.
      Alfa did a series production version of the old twin spark, it was used in the 75, 164 and 155. The engine is a direct relative to the Autodelta race engines but with equal cylinder spacing. These engines were able to produce significantly more power than they had but were kept at distance to the V6. It’s relatively easy to get reliable 170hp from a twin spark with perfect everyday road usability.

    9. Guess standard would be a more accurate term.

      For the old 113-146 hp 8-valve Twin-Spark engines that were used in the 75, 164 and 155. Would it be correct to say a moderately tuned 16-valve version of the former had it appeared in the mid-1980s would have roughly matched (or even slightly exceed) the figures of the later 102-153 hp Pratola Serra 16-valve?

    10. Then let’s say that the Autodelta 16V was the ‘standard’ engine for late GT Am and Junior racers. ‘Standard’ and ‘road going’, but still far away from ‘Series production’.
      A 16V series production simply wouldn’t have made sense as Alfa already had to limit the twin spark’s power outpup to 148 PS to keep a certain distance to the 2.5 12V V6 with 155 PS. AS 16V racers had up tp 260 PS any de-tuned version would have had 170 to 180 PS, making it a direct inhouse competitor ti the 3.0 12V. Even if Alfa at that time generally had no idea about product management even they saw that this wouldn’t have made sense.

      As Autodelta was the official race department any development done by Autodelta was an inhouse Alfa development. Tipo 33 racers and Formula One engines always were developed and raced by Autodelta (Carlo Chiti) but were offically known as Alfa Romeo.
      Here’s a picture of an Autodelta 16V head (intake side):
      https://www.alfabb.com/attachments/2-head-disassembled-jpg.274051/
      And the block with monobloc liner
      https://www.alfabb.com/attachments/4-monosleeve-block-jpg.274053/
      and a complete engine
      https://www.alfabb.com/attachments/ebay-006-jpg.276360/

    11. Thanks for clearing things up, can understand Alfa Romeo’s rationale for not wanting a detuned 2000cc 16-valve Twin-Cam / Twin-Spark to overlap with the V6. Am sure the company’s other issues and the low range torque of a 16-valve engine compared to the 8-valve engine (as mentioned in the Jim Kartalamakis book) also played a role in Alfa Romeo deciding not to offer it as a production option.

  6. Bob it is not “Franchetti” it is “Facetti” one of the famous tuners in ITaly along with Angelini, Conrero, Balduzzi.

    Also regarding Alfa Romeo twin cam engines progression, Alfa Romeo twin cams always had a superior torque curve across the rev range in the 1950s (when the engine first appeared) and the 1960s and 1970s. This is something that Alfa Romeo did not wish to give up on seeing as 16v engines tend to lose out on low end torque. However the combustion chamber they found on the single plug twin cam 1600 race engines had poor flame travel due to the shape of the pistons and was the main reason it is said for the twin spark change because the bottom end of the twin cam engine was excellent design.
    The 16v head engine used by Autodelta in rally/race engines in the beginning of the 1970s and also the Angelini 16v engine had input from Cosworth in their creation apparently.

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