Magazine Cover - Classic Cars For Sale - 1000s of Classic Car Reviews, How To Service & Maintenance Guides

Morgan Plus 8

Published: 14th Nov 2011 - 0 Comments - Be the first, contribute now!

Morgan Plus 8
Morgan Plus 8
Magazine Subscription
The latest issue of Classic Cars For Sale is on sale now - Pick up your copy from all good newsagents including WHSmith or click here to subscribe now

Subscribe to Classic Motoring Magazine and save over 20%

Subscribe NOW

Available at all good newsagents including WHSmith

The Plus 8 Morgan was quite a performance car when it was launched back in 1968, a fact that’s often overlooked these days.

The Plus 8 Morgan was quite a performance car when it was launched back in 1968, a fact that’s often overlooked these days. With the evergreen Rover V8 engine shoehorned under the bonnet, this retro roadster weighed less than 1000kg, making it a serious sports car that could match the very best for pace – 0-60mph in just over six seconds was terrifi c going back in ’68. It still is, for that matter, but such is the tuning potential of this versatile V8 that many owners are tempted to give their cars a bit more zip, to show those MX-5s a thing or two!

Get One Now

Which classics still have the potential to get up and go? Alan Anderson remembers the cars, the people… and how to make a class

Mechanically this American-derived V8 is almost burst-proof, so long as the oil has been changed regularly – annually, irrespective of mileage, we’d say – to avoid sludging, which will hinder and hurt the engine’s hydraulic tappets. The only other issue is in the retention of the cylinder heads;Buick engines had 18 retaining bolts for each head, whereas on ‘SD1’ motors of the late 1970s one outer row of four bolts is not used, and this creates uneven stress on one side. This does not necessarily cause the head gasket to blow, but allows unspent petrol and exhaust fumes to ‘weep’ into the centre of the Vee, and contaminate engine oil, resulting in bore wear and cam and crank bearing failures.

Amazingly, Rover did not finally solve the problem until 1994, when the other row of four bolts was deleted and the heads were attached to the block by just 10 equally spaced bolts. A ‘fi x’ for 14-bolt heads is to torque down the centre two rows of fi ve and simply leave the outer four fi tted but un-tensioned and held in place by Loctite. The engine that Rover inherited from Buick was already old when it arrived on UK shores. Earliest versions had rope oil seals on the crankshaft and mains bearing caps that were apt to ‘float’ and knock out the bearings. Rover’s development of the engine was somewhat reluctant, but by 1982 most of the major problems had been ironed out – with neoprene oil seals and a stiffer alloy block with cross-bolted mains caps.

‘Stiff’ blocks can be identifi ed by wider and more uniform strengthening webs in the centre of the Vee, between the cylinder banks, and the cross-bolted type by the bolt heads low down along the sides of the block.

Hotting One Up

The V8 has enjoyed a long and legendary service life and, even in standard tune, kicked out a 155bhp. If still in good nick, perhaps with a thorough decoke, electronic ignition and setting up on a rolling road, it may well still suffi ce.

Post SD1, Rover upped the power by increasing its capacity. The original 3528cc engine has 89.5mm bore and 71mm crank throw, with the later torque-fi lled 235lb.ft 3.9-litre unit achieved by using 94mm bore. When the engine went to a 4.2-litre, the crank was changed to one with a 77mm throw and the 4.6 litre unit is obtained by further stroking to 82mm. The 94mm bore is as large as the can be safely obtained within the block because some of these engines have been known to crack behind the cylinder liners – but remember, Morgan offered a 220bhp 4.6-litre engine for two years in 1997.

Whilst upping capacity is sure way to up power, there’s plenty of scope for modifi cation of the heads. Careful attention to the shape the ports and matching to the appropriate manifolds is worthwhile, as is cleaning out the shallow dish-shaped combustion chambers. Valve guide bosses can also be shortened and smoothed to improve gas fl ow, and valve throats opened out. Standard 39.9mm inlet and 34.3mm exhaustvalves are fine for road tune engines, whilst 41.4mm inlet and 35.5mm exhaust are about as far as you can realistically go.

A 9.75:1 compression ratio is best for most purposes; with so little chamber in the cylinder head, this usually obtained by the correct combination of pistons and the type of gasket used, either tin or much thicker composite type. With valve seat inserts used in the alloy heads, damage due to the use of unleaded fuel is not a problem no matter how hard you drive.

A camshaft change should be pretty early on the list of modifi cations, as the engine benefi ts from better breathing. If you stay on hydraulic tappets (there’s not much point in swapping to solid lifters on a road engine) the engine is limited to just over 6000 rpm and so tuning for good mid-range torque is the best way to go. The timing gear and chain on early engines is likely to wear, and warrants fi tting a Duplex set-up, although this is not practical on post-1994 engines.

Hand in hand with any camshaft change must come an overhaul of the ignition system. Most original distributors are likely to be well worn by now and so (as far as tuner RPi is concerned) the only way to go on an early (pre GEMS management system) engine is to fi t a Mallory distributor. This operates as a six-volt system (retaining 12 volt for starting) and so needs its own coil and ballast resistor. Having said that, many other companies, such as Aldon and H& H Ignition Systems, can provide a similar performance system.

Early SD1 engines were fitted with either SU or Zenith-Stromberg carburettors, and with these new needles and some fi ne tuning on a rolling road can accommodate mild stages of tune, but the fi rst fuel injection systems offeredin 1983 (Lucas L-Jetronic) are fairly crude on the electronic front and are not responsive to usual performance chipping. Really, the best course of action for anyone with a pre-GEMS engine looking for a decent increase in power is to fi t a fourbarrel Weber carb conversion, which sits neatly in the centre of the Vee. RPi’s Weber kit mates the carburettor to an Offenhauser inlet manifold. A Lucus fully electronic ignition was utilised on the 3.9-litre model, incidentally.

Other carburettor installations have been tried with the engine; notably BL fitted both Pierburg fuel injection and four Weber DCOE carbs on the rally TR8’s – but, for a good power hike, increased response, and simplicity of installation at a reasonable enough cost, the four barrel Weber can’t be beat still.

As an indication, a pair of modifi ed heads, fast road camshaft, four barrel Weber carb and some decent extractor exhaust ‘headers’ will see the basic 3.5-litre nudge the 200bhp mark; up it 3.9-litres and 250bhp is available – which, given the performance of even a basic Plus 8, is plenty for road and mild competition use!

How Did It Drive?

There’s no doubt about it, Morgans are an acquired taste and not for everybody. Even the cars’ many devotees will admit that they are not exactly daily drivers and the early Moss-gearboxed models are particularly not for the meek and mild. The steering feels as vintage as the design suggests, while the buckety ride is nothing but uncompromising. But, on the right day, and smooth roads, these cars are exhilarating, with all that V8 grunt on tap. It will come as no surprise to learn that Plus 8s can take a lot of taming on wet roads, thanks to the crude suspension. “Totally impractical but great fun – when it’s in contact with the road” is how one road test summed the Morgan up!     

Handling The Power...

We spoke to Peter Mullberry Fabrications, one of the most established Morgan tuners, with almost 40 years experience, and with whom the factory itself often consults. He has developed a wide range of equipment to make a Plus 8 handle better, although he says that the majority of owners alter their cars purely to gain a better ride. In the mid 1980s Morgan switched to rack and pinion steering, which was a great improvement, and there are numerous power assistance kits now available; sadly, converting an older car to rack and pinion is involved, and only for the dedicated. Mullberry does market a steering bearing conversion kit costing £160 for all cars, which helps. Unless you want to spend almost £8000 on a modern-style Librands front suspension conversion, you’re stuck with the vintage sliding pillar design – but it can work effectively enough. Adjustable dampers are essential and Peter markets AVO types with his own valving requirements. Being adjustable they allow the owner to tune the ride for individual requirements. As the Plus 8 rides surprisingly high, lowering is the next step, and front springs are £66 a pair. At the rear, Mullberry Fabrications has developed a fi ve-line coil design – there was also an earlier De Dion idea by Librands – but both are a bit exotic for the road. Just ensure the standard items are okay or replace with standard new items. Early Plus 8s featured lever arm dampers, and conversion kits to later coil types are readily available. The factory-developed brakes are barely adequate for V8 power! A switch to Mintex F4R pads is the fi rst step and there are more in depth upgrades. Tyres? The Morgan uses a rim that was also fi tted to the Rover P5B, Vauxhall Ventora FE and the Jensen Interceptor. A 205/60 is a good compromise for road use. For more details call Peter (who is a mine of Morgan information!) on 02476 397666 or click on

Share This Article

Share with Facebook Share with Facebook

Share with Twitter Tweet this article

Share bookmark with Delicious Share bookmark with Delicious

Share with Digg Digg this article

Share with Email Share by email

User Comments

This review has 0 comments - Be the first!

Leave a comment

Keep it polite and on topic. Your email address will not be published. Please do not advertise products, all posts of this nature will be removed. We do not stock or supply any of these products, we independently review these products.

Subscribe Today
Latest Issue Cover - Click here to subscribe

Subscribe to Classic Motoring Magazine and save over 25%

Britians top classic cars bookazine