► Bentley’s ballsy L-Series V8 in detail► The central adventure of a 60-year old engine► From the backward ’50s to 2020
Magnificent motor cars like Bentley’s afresh retired Mulsanne are ambrosial of a ancient age. And aloof as time eventually bent up with the Mulsanne – Bentley’s flagship bows out this year, with 30 Mulsanne 6.75 Edition by Mulliner cars – so it has bent up with the Mulsanne’s arresting engine, the pushrod V8 that remained in connected assembly for added than 60 years. In that time some 36,000 were built.
Originally advised in the aboriginal ’50s, the L-series V8 was no added (thanks to its all-alloy construction) and almost any bigger than the six it replaced (it had to fit in the aforementioned agent bay, that of the ’59 S2) and, at 180bhp, some 50 per cent added powerful. Half a aeon later, in the Mulsanne Speed, it would be acceptable for 530bhp and an amazing 811lb ft of torque.
Tim Seipel abutting Bentley in 2005, in time to baby-sit a brace of key phases of the 6.75’s evolution. Here’s what went down.
Fit for purpose‘The 6.75 was deployed in the big affluence saloons – the Arnage and the Mulsanne – and it ill-fitted them brilliantly,’ says Seipel. ‘The added avant-garde engines aloof weren’t the same. There was a BMW agent in the Arnage back VW bought Bentley, and the actual aboriginal engineering assignment issued by Ferdinand Piëch was to accept the 6.75 re-installed in the Arnage. The big capacity, beyond aloof eight cylinders – best battling engines acclimated 12 – meant you didn’t charge to rev it to admission its performance.’
Faster, stronger‘The agent fabricated 400-450bhp on the old Garrett turbos; 450-500bhp and added torque with the MHIs. For 2010, and the Mulsanne, we angry the wick up afresh application acquaint abstruse on the Brooklands coupe. That was our aboriginal attack into the branch of 750lb ft, and we adequate the agent to cope.’
Just add lightness‘In that 2010 overhaul, a lot of assignment went into abbreviation the weight of the basal end. It’s a amateur win; you abate the all-embracing weight of the engine, you access achievement and you abate ammunition consumption. We adored 6kg with a new crankshaft, 130g per agent and 100g per conrod.’
Slick coatings‘The pistons and arbor pins were coated with diamond-like carbon [DLC], while the agent skirts were coated with graphite. These coatings helped abate abrasion and ammunition consumption, and they helped the genitalia in catechism accord with actual aerial loads.’
Cam phasing‘Pushrod architectonics fabricated it accessible to add cam phasing [variable valve timing] almost amount effectively, and it’s article we capital to do for abounding reasons: bigger butt fill, low-speed torque, accelerated power, part-load cleanliness and a bland turbo delivery. We army the cam phaser on the advanced of the block, area the camshaft drive is, and ran an oil augment to it. Adding the technology to an overhead-valve agent would accept been a abundant added complex process.’
Cylinder shutdown‘For the deactivation [enabling the agent to shut bottomward some cylinders beneath low load, for added efficiency] we bare to put cyberbanking switching units on the tappet blocks, and accommodate two oil feeds; one for lubrication and one to act as a burden arresting to the tappet, cogent it to actuate or de-activate. We additionally had to run affairs central the crankcase and allowance a adapter to the crankcases. Really, it wasn’t a lot of change for a actual avant-garde bit of technology – that was the able affair about it. And this was the aboriginal agent beyond the accomplished VW Group to get butt deactivation; thereafter we were apparent as the experts. The abate Bentley V8 is a Porsche engine, of course, but it was Bentley engineers who accomplished Porsche about butt deactivation.’
Promoting swirl‘The agent was adapted afresh in 2017, with changes to the appearance of the ports and the agitation chamber. That assignment was about cleaner combustion, to accommodated Euro 6 regulations, and a added abiding idle. The differences were appealing detail – they’d be adamantine to atom to the green eye – but they fabricated for a abundant faster burn. Previously we had affluent pockets aural the chamber, and we bare a added constant mix to apple-pie the agent up. The changes gave added swirl, and that turbulence gave us a bigger fuel/air mix. The agent remained two valves per butt of advance – two actual ample valves per cylinder…’