Our Cars : Martin Williamson and his re-engined MGB GT

AROMG… a little play on what might have been had the MGB continued selling under the Austin Rover Group banner with the planned O-Series engine and written for ARO!

MGB - Martin Williamson

Where to start with this one? Among the various Longbridge-built cars I have owned, one power unit that I found most compelling was the T-Series engine in a Rover 420 I had as a company car in 1998. The T16 unit just seemed to have bags of torque combined with a willingness to rev despite its modest manufacturer-quoted power figure of 143bhp, even managing to pull the 820 around with reasonable pace.

With my second MGB back in 2002, a 1980 MGB GT, I started getting into the ‘Special Tuning’ side of the hobby and, as a result, the engine was built up by a well-respected Market Drayton firm, Bradbury’s Engineering, to a mild, 1860cc, Stage 2, fast-road specification that revved willingly to 6000rpm putting 99bhp out at the rear wheels in third gear. Various improvements were made to the handling and braking. However, as is always the case, that little bit of extra power and road-holding was great initially, but then there was the insatiable desire for more.

One relatively new option in the early 2000s for the MGB owner searching out more bolt-on performance was supercharging the B-Series engine, not forgetting that Shorrocks had offered a kit back in the 1960s. However, the cost of the supercharger alone before any changes needed for the engine meant this was not an economical route to follow. A notable difference between my tuned engine and driving several supercharged B-Series MGBs at the time was that they had much more torque than mine and did not need the revs to get into the power band, making for more relaxed cruising.

As was always the case, for similar money to the supercharger, the more obvious, tried and tested, choice would have been the Rover V8, but I have always had an aversion to V8s in MGBs on the basis that MG was all about handling and that an inline four- or six-cylinder powerplant was what defined MG.

All of which lead to me following various builds of MGBs using the Rover K-Series, KV6 and T16 engines as documented on my website, Upgrades4MGs. Whilst the Mazda MX-5 and Ford Zetec units are also a common option now, as were Fiat Twin-Cam engines previously, 20 years ago, there was still a reasonable choice and supply of parts from the Rover stable so to focus on the Rover units seemed much more of a case of keeping it in the family. The K-Series and KV6 were not an ideal choice in the way that the RWD MX-5 is, simply because the K=Series and KV6 were all utilised in FWD applications bar Caterham offering the K-Series in their RWD cars. This made the installation of these engines more complex.

This led to my focus on the T16. Firstly, there was the fact that the T16 was distantly related to the B-Series in that it had evolved via the O-Series SOHC unit through to the DOHC M16 and then to the DOHC T16. More importantly, the original gearbox could be retained and, apart from modifying the front cross-member, the effort to fit was the lowest by comparison to most other choices.

What was really appealing was the fact that MG toyed with the idea of the O-Series as an update for the MGB in the early-1970s and there were twelve development cars on trial at Abingdon – some of these still exist, although they were sold off to the public with B-Series engines refitted, and a number of these are still on the road. In discussion with the MG Owners’ Club’s (MGOC) very own Technical Officer, Roger Parker, it transpired that he’d had been involved with an M16 transplant in the early 1990s, and that variations of the O, M and T units had been used in vehicles as diverse as the budget Rover SD1 2000, Leyland Sherpa, Ital and Land Rover Discovery models, so adapting to the RWD set-up wasn’t an issue. The T16 even made an appearance in the Morgan Plus Four in the 1990s.

MGB - Martin Williamson
One of the original MGB development cars fitted with an O-Series engine – this one with EFI as planned for the US specification and smog pump

In 2008, I even went as far as buying a T16 turbo engine for my 1980 MGB GT, but it never made it into the engine bay despite doing significant preparation work with the assistance of several others, who were already doing similar conversions. But in 2010, as increasing work and travel meant there was no longer the time to play, I ended up selling both my MGB GT and the T16 engine and settled to a quiet decade of being a purist with a very original 1966 MGB GT Mk1 and 1967 MG 1100 Mk1, while new, much more powerful cars arrived and went on the driveway to satisfy the urge to go quicker on a day-to-day basis.

Prior to this, though, I had met another local MGB GT owner, Stephen Whitham, in Wrexham, and like me, he fancied the Café Racer look as I had done on my previous 1980 MGB GT – as his father had a Rover 820, I jokingly suggested we relieve it of its T16 engine. This spurred Stephen to acquire a 2.0-litre O-Series engine out of a Rover SD1 and a 1972 failed restoration MGB GT. Over the next few years, he set about creating his ultimate track day car by converting the 1978 shell into a chrome bumper specification with much attention to swapping out the dash, the front cross-member and even the pedal box.

I was involved on the side lines advising and was even present when he first got the engine running in 2011. The O-Series proved to be a simple swap as, with a Sherpa 1700cc engine backplate fitted to the 2000cc engine, the original flywheel and clutch from the B-Series can be used along with the MGB’s four-synchro gearbox and overdrive. With the early O-Series also having a more suitably located oil pump, there was no need for chopping up the cross-member as there is with the later versions. With a distributor and twin SU HIF carbs, it is also a simple hook up on the wiring loom and fuel supply, unlike the later fuel-injected engines with ECUs requiring additional modifications for the timing sensors etc. Shortly after completing it in 2012,

Stephen moved to Dubai with his job and the car eventually ended up sitting in his parent’s garage in Wrexham having only covered a few thousand miles with the subsequent odd trip to the MOT station.

Fast-forward to 2020 and, through the MGOC, I met Mark Burton and his son, Harvey, who were building a superb MGB GT Sebring tribute, and their engine of choice was the T16. I was delighted to hear that my website had been the inspiration for this decision, and honestly, I don’t think there is a better way than what they have achieved to pay homage to the possibilities that the O/M/T-Series engines offered for the MGB. When I first saw the engine in the car back in the Summer of 2020 with the custom, polished cam covers, it struck me as the ultimate Twin-Cam MG that should have been a production model. I blame this visit to see their GT for the itch to revisit the world of engine tuning and customising once again and thinking about the unfinished business with the T16 and my plans from back in the day.

Coming back to Stephen and his O-Series MGB GT, we had maintained contact over the years but, with him now living in Denmark, and his parents wanting his MGB GT out of their garage in Wrexham, the GTO, as it has since been christened, found its way into my garage at the beginning of 2021.

I’d briefly toyed with buying another O-Series car, in late 2020, though. In this case, the MGB in question was a replica of the concept built by Aston Martin in 1979 during their negotiations with British Leyland to take over MG. This tribute replica was a 1974 MGB GT that had been converted from chrome to rubber bumpers, probably the only one in existence but never let it be said that no one has ever converted an MGB in reverse! That really appealed to me. The original builder of this replica, Trevor Broadbent, had fitted the same 2.0-litre O-Series engine in the belief that this is what Aston Martin would have done had the proposed deal gone ahead. However, I suspect Aston Martin might have gone with the Rover V8, but that is a debate for another day.

The replica of the concept MGB built by Aston Martin now owned by James Hargreave
The replica of the concept MGB built by Aston Martin now owned by James Hargreave

Unfortunately, I was outbid on the auction, so it never happened, which is how I came to buy Stephen’s MGB GT with the O-Series engine.

Ownership has not been plain sailing until about nine months ago owing to a number of problems that resulted in me pulling the engine and gearbox twice in order to resolve them. The first time was to rebuild the engine following a strip down highlighting worn bearings after a head gasket failure had been identified. Parts were easy enough to source in the main, although the timing belt tensioner is no longer available, but an enterprising Ital owner has come up with a solution. New old stock of other items is generally easy to source on eBay and Rimmer Bros. also stock a number of engine items.

During the refit of the engine the first time, a number of changes were made to take it from a lightweight track car to more of a Café Racer better suited to road touring. This entailed researching the original layout of the development cars and looking at issues such as the routing of the coolant hoses and heater controls to re-incorporate the thermostat, inlet manifold heating and the interior heater.

MGB - Martin Williamson

One area that did show up as an issue was heat from the exhaust manifolds and social media comments suggest that this was always an issue with the RWD vehicles with the O-Series engines. I was able to overcome this when removing the engine for a second time to sort the slipping overdrive by getting the exhaust down pipes ceramic coated and to put heat-shielding on the side of the block. This has resulted in improved cooling in the engine bay and reduced coolant and oil temperatures.

I am informed that originally the US specification MGBs were planned to be fitted with the usual smog control equipment as well as fuel injection. Ironically, these were stated to be around 105bhp as opposed to the expected 110bhp of the UK market cars that were to be built with the twin SU carburettors as used on the Rover SD1 2000.

By contrast to the, by then, aging B-Series in 1800cc format making 95bhp, it is somewhat surprising that the SOHC 2000cc new design engine was only capable of an additional 15bhp. These days, one expects better than 100bhp from a 1000cc engine, but as always with British engine designs it is not the power so much as the torque they produce which is the real difference between the B-Series and the O-Series.

MGB - Martin Williamson

In principle, the SOHC engine should be able to rev easily compared to the older B-Series with push-rods and that is one of the things that always surprises me with this engine is how smooth it is. Yet, despite that, this O-Series seems reluctant to go above 4000rpm in the lower gears, although as it beds in it may improve.

However, rather like a diesel, it doesn’t really need to rev so high as with all that torque, it pulls strongly from low rpm in any gear. The let-down with the O-Series in the MGB using the original four-speed overdrive gearbox is that, whilst the installation is made much easier by retaining the transmission, the gap between second and third gear on the standard MGB gearbox is quite large. This is a throwback, I gather from Roger Parker, to the earlier MGBs with no synchro on first.

The 2.0-litre O-Series as fitted in the Rover SD1 2000 had the LT77 five-speed gearbox and, whilst this is an option on the MGB, it would mean additional work in the transmission tunnel potentially for clearance, and the LT77/R380 units are not known for their finesse. With the O-Series crank being the same as the B-Series at the flywheel, and with using the B-Series flywheel and clutch this means one can look at the usual MGB alternatives. Obviously, the Ford Type 9 is another possibility utilising an adaptor kit, but these transmissions are starting to get expensive now. The increasingly popular alternative is the MX-5 gearbox. Having had an MX-5 in the past, and on trying a friend’s MGB, albeit with V8, the MX-5 box is decidedly superior in terms of the shift – slick, but not clunky, and very precise. I’d certainly recommend going this route if considering the O-Series.

An alternative to using a different gearbox would be to find a differential offering the 3.7:1 ratio rather than the standard 3.9:1 to reduce the rpm even further at cruising speeds. I don’t believe the O-Series would be able to manage the MGC and V8 differential at 3.1:1. Another possibility is increasing the rolling radius of the tyre but, as with a taller differential, this would blunt the acceleration, the speedometer would need recalibrating and it does not solve the gap between second and third gear as would be the case with a newer gearbox. The fact it is even a consideration is testament to the additional torque of the O-Series but, on the other hand, I am a fan of the overdrive box – I still like having the overdrive for that semi-automatic shift in third or fourth.

MGB - Martin Williamson
The seal of approval from Dr. Ian Pogson!

So, what is not to like? The O-Series does lack the distinctive exhaust note of the siamesed exhaust port on the B-Series. Much more power could be got from a newer engine swap such as the MX-5 or even the T16. Parts are not as easy to get hold of now, and nor is it easy finding an experienced mechanic that knows these engines.

Would I recommend the swap to others? The short answer would be no. If you are looking for the easiest way to get more power, then it’s still cheaper and more reliable than rebuilding and tuning a B-Series and offers comparable torque to a supercharged B-Series. But with more budget and effort a lot more performance can be attained from newer engine choices or by going the traditional V8 route. However, in the context of the mid-1970s, then this engine would have offered a fresh approach to the then aging MGB and its B-Series with its design dating back to 1948. More importantly, what may now seem like a minimal power gain would have been quite reasonable then. Perhaps if the MGB had soldiered on well into the following decade the EFI engine from the Montego, and dare I suggest, the turbo version…then that is a whole different story! But like the Triumph TR7, the MGB never saw the light of day with the O-Series despite the development cars that were built.

I have covered quite a few long journeys on mixed roads including motorways and added a few more thousand miles. Aside from the fact it’s a bit noisier than a standard car owing to the motorsport themed bare interior, it is a world away from the B-Series with the grunt to be able to rapidly accelerate in fourth overdrive thanks to the additional torque and making for much easier overtaking when needed. The lighter engine has also had an impact on handling to some degree making it more agile on turn in, although some of this may be down to the period handling upgrades at the front and rear.

I was recently asked what’s next? A good question. History suggests I will get bored with this MG and find another project. However, I suspect not with this one! The O-Series has resulted in an MGB with comparable performance to a supercharged B-Series MGB and there are more ideas in hand such as an LSD for the differential.

Another reason is that my wife and I have invested in a small business to fill our spare time, the result of recently becoming empty-nesters. Over the last ten years I had been buying quality stainless-steel and high tensile fastners from the original owner for my various projects and restorations, and a chance conversation in 2021 about his future plans led to him contacting me late last year and the upshot is, I am now tied to a new business venture, Grove Components. There frankly isn’t time for any projects currently while running two businesses and this MGB GT makes for a great advertisement for the products from the new endeavour.

As the saying goes, no project is ever finished, and I am sure there will be modifications to come. Funnily enough, Mark Burton keeps mentioning the spare Rover T16 engine he has, which is where all this started…

MGB - Martin Williamson


  1. Don’t forget the T16 was installed in the Defender 90 for the Italian Carabinieri. It was so good, I wanted to offer it in a successor to the SV90. But the 2.0-litre Discovery was getting such a bad press in the company that it never happened. Good project for someone, though…

  2. Recall reading that along with proposed O-Series states of tune in NA and Europe, also being capable of putting out up to 127 hp for possible use in the updated MGB.

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