A Guide to V8 Conversions for the MGB

Published with permission from V8 Conversions


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Since the Rover V8 engine appeared in the UK. It has been used in a variety of production vehicles and an endless number of kit cars and specials during this time it has acquired an excellent reputation. The block and heads are constructed from aluminium resulting in a very light power plant considering it is 3.5 litres in the original form. The weight difference between the 1800 B and the Rover V8 is very slight. The complete V8GT weighed in at just 40lbs heavier than the 1800GT equivalent, and do not forget the V8 has larger discs, tyres and prop.

The engine has remained fairly standard over the years and any Rover V8 engine is suitable for a conversion. Many compression ratios have been used and this has been achieved by different piston design. The cylinder heads were standard until the introduction of the SD1 that has been fitted with single value springs and large inlet values for more efficient breathing. The SD1 has also been fitted with an uprated oil pump (giving higher flow rate), improved crank oil seals and electronic ignition instead of points. British Leyland used the unit in automatic and manual cars and the only difference in these engines is the rear crankshaft or spigot bush that can easily be changed.

The most daunting problem with the conversion is the choice of a suitable engine. A new Rover V8 will cost well in excess of 1,600 and a factory rebuilt unit in the region of 1,200 (beware if you opt for a new or reckon Austin Rover engine they will not extend the warranty to cover its use in an MGB). This is rather expensive, also if you decide on one of these units it will normally be supplied minus such items as starter motor, distributor, inlet etc. and these are extremely expensive to buy, so most people opt for a complete used unit. The most effective way of doing the conversion is to purchase a complete donor vehicle as they can be found at very reasonable prices. The most suitable being a SD1 5 speed manual, an added advantage of a done vehicle is that in most cases you can ascertain the condition of the power plant and also many of the other components will be useful.

When you first see a complete Rover engine out of a vehicle, it is obvious that it is quite a monster. Removal of the power steering pump and associated hardware and the air conditioning, if fitted will reduce the problem but it is still too wide, long and tallfor a small sports car like the B. When MG produced their original V8 the Rover P5B and early P6 was around, the water pump, crank and alternator bracket were utilised but the inlet and exhaust manifolds, oil pump base and mountings had to be redesigned. Later type P6 Rover saloons and SD1s are fitted with a viscous cooling fan, longer crankshaft pulley and a different design of alternator and mounting. The earlier components will have to fitted to this unit to shorten it. The SD1 crank pulley can be machined to do the job of the earlier unit. All Rover V8 engines have an external oil pump mounted on the front cover, the base of which carries the oil pressure relief valve and oil filter. Unfortunately there is no room for this in the MGB because of the proximity of the steering rack.

A special oil pump base is available that is bolted onto the oil pump after removing the original base. This unit contains the oil pressure relief valve and oil galleries, a connection for the oil pressure gauge and two 1/2" BSP outlets to enable a remote filter to be used which is usually mounted on the GT V8. As the remote oil pipes exit the pump base, they are very close to the lip of the chassis and it is best to tap this over to increase clearance. If required the oil cooler can be plumbed into the system. On the original chrome bumper V8 the cooler was mounted on the rad ducting panel under the offside fan motor and because of limited space a 10 row unit was used. With the advent of the bumper V8 it was mounted underneath the same panel. Engine mounting brackets, for either chrome or rubber models are available for the sides of the engine block so that MGB GT V8 rubber mountings can be used. These engage in the existing mounts on the black bumper chassis rails and the modified units on the chrome bumper models.

The engine mounting brackets have been manufactured to mount the engine as low as possible, bearing in mind the problems with the steering etc. However if required, as with the production V8, packing pieces are available that fit between the bracket and the mounting rubber. If these packing pieces are needed they can be fitted to the steering side only in order to raise the engine and position it away from the steering. The engine oil filler and the flame trap at the front of the engine are very tall but fortunately the rocker covers can be interchanged.

Although not fitted to the works V8, a tie bar can be fabricated to relieve the load on the engine mounts and assist with the problem of the limited clearance between the offside exhaust manifold and the steering shaft. This is mounted on the front of the nearside cylinder head and the nearside inner wing just below where the wing joins. If you decide that the engine needs a little love before the conversion do not be put of by its size. It is a fairly straight forward unit to rebuild and after market components are a lot cheaper than Rover. The engine block and also the heads on these units are quite often in very good condition even after high mileage people are surprised how little work is required. The oil pressure on the V8 is very low, the oil light warning switch on saloons operates at less than 10psi ! With regular oil changes no problems occur but if not sludge builds up with resultant wear in the valve chain and these may need attention.


On the first MGB V8 conversions before Leyland produced theirs the original 4 synchro overdrive gearbox was utilised. The 4 synchro non-overdrive unit can be used but the extra overdrive ratio is very useful with a low revving unit like the Rover. The earlier 3 synchro gearbox is not suitable as the smaller bell housing will not accommodate a large enough clutch.

The overdrive seems to cope with the increased power but if the unit is switched in and out with full throttle in third gear it can put a strain on the unit. British Leyland, in their production V8, removed this overdrive from third gear by modifying the side of the level selector that switches the overdrive inhibitor switch.

The MGB gearbox is retained in its original position and mated to the Rover V8 by means of an adapter plate. The original B flywheel is machined to accept a larger clutch and this is attached to the Rover crankshaft adapter fitted with the crank bush. The 1800 B starter is retained and mounted on to the adapter plate after the starter mounting has been removed from the Rover block. A cut-out is also required in the bell housing to clear the nose iof the starter and the motion shaft will need to be shortened. This system utilises a MGC clutch cover MGB GT V8 centre plate and an 1800 standard or roller release bearing. The clutch hydraulics remain standard with the exception of an MGB GT V8 slave cylinder. Some dressing of the transmission tunnel at the front may be required to clear the adapter plate.

The B.L. MGB GT V8 utilised a modified 4 synchro overdrive box that is identical to the 4 synchro 1800 B unit except for the ratios and the bell housing, which mates direct to the Rover block. The case and the internals have proved to be very weak and extremely costly to repair. Moreover the unit is no longer available from B.L. and used units are very scarce and expensive.

The pre-SD1 4 speed Rover P6 3500 S manual gearbox has been used but the poor reliability of this unit, coupled with the fitting problems and the lack of a fifth overdrive gear ratio have made the unit a poor choice.

The SD1 five speed gearbox is the ideal gearbox for the conversion and this is the unit that has been used in the RV8. The gear ratios are superior to the B box and the fifth gear is an overdrive ratio. This gearbox seems to be the strongest unit for use with the V8. The box is narrower, higher and shorter and modifications are required to the gearbox cross member, prop shaft, clutch hydraulics, speedo cable and transmission tunnel. The standard MGB prop shaft is not suitable as it is far too short also the Rover one is unsuitable. Early boxes have a manual speedo cable and once the speedo cable has been charged this can be utilised obviously the speedometer will need re calibrating. The latter boxes are fitted with an electrical transducer this can easily be removed and the earlier type fitted. The tunnel on chrome bumper models will have to be cut and an extension fitted. On black bumper models the tunnel can be dressed up to accommodate the 5 speed unit although many people have found it easier to cut the tunnel and make good in a similar manner to the chrome bumper mod. Some minor dressing of the tunnel will be required to clear the edges of the larger bell housing. The gearstick fortunately is an approximately the right position and slight modification of the cut-out in the tunnel, towards the offside, will allow the gears to be selected. The remote on the top of the gearbox is a separate unit and this can be repositioned with shim washers if required. Be careful when purchasing a second hand 5 speed gearbox separate from the engine, because this unit was used in a variety of different BL vehicles and apart from the different bell housing the clutch release arm pivot, release bearing carriers and gearstick remotes were different.

With such a powerful engine the Rover automatic gearbox is another suitable alternative but this requires similar modifications to the five speed unit. The size of the torque converter housing requires extensive modifications to the bottom of the heater unit. The gear selector mechanism has to mounted and obviously the auto has the added problems of an oil cooler and kick down cable. Because of the limited demand for this application we are unable to offer components for this gearbox.

Induction System

The variety of inlets available for the Rover V8 is endless but, unfortunately, the very limited bonnet clearance has always been a problem with the MGB, especially the chrome bumper model.

The standard Rover saloon inlet uses twin 1 3/4" S.U.s or Strombergs mounted back to back in the centre of the engine. This inlet works very well but a bonnet bulge will have to be fabricated. The standard air filter is rather large and will require modification alternatively pancake or K+N filters can be used. The original conversions used the standard HS6 SU carbs on the saloon inlet, with shortened carb dashpot, pistons and dampers that still required quite a large bulged bonnet. The latter inlets utilised HIF carbs on a different inlet which mounted the carbs even higher.

Later Rovers and also the RV8 were fitted with fuel injection and this system works well, however compared to normal carburation this is very complex. Quite a few extra components will have to be added and alterations to the fuel system and electrical wiring will be required. Some owners have managed to get this system under the standard bonnet but it has required machining of the manifold. On the RV8 they opted for a bulged bonnet. Because of the complexity of this system it would be best to obtain the complete unit from a donor vehicle also most of the components are only available from Rover and are very costly.

The MGB GT V8 used a pair of special 1 3/4" S.U.s mounted side by side on a special 2 part inlet that positions them rearward, between the rocker covers where bonnet clearance is at a maximum. Unfortunately this set-up is no longer available from Rover.

The Rover V8 engine was originally designed in the U.S.A. by Buick and was known as the 215, fortunately performance parts are still manufactured in America for this unit. The most readily available inlet is the single plane Offenhauser, which has been available for many years. This unit will require modifications for the servo take-off and temperature sender and a bracket for the acceleration mechanism. A new Offenhauser has been manufactured specifically for the Rover V8 and is known as the 7001 Dual Port. This unit is designed for street performance, it is a lower profile manifold than the single plane, giving increased bonnet clearance. It also has the same water temperature sender outlet as the Rover, a brake servo take-off and extended gasket sealing tabs.

There are two possible carburettors: the Holly and the Carter. The Holley is the 4160 series 8007 version, which is a 4 barrel unit with vacuum operated secondaries and a flow rate of 3990CFM. This unit has proved the most suitable for road applications. The Carter is a similar unit to the Holley, and is slightly lower than the Holley this unit is now marketed by Weber who have also started to market another inlet manifold called the Edelbrock however at the time of going to press we are not sure about the height of this manifold.

On black bumper MGs a 14" low rider air cleaner can be used after removing or resiting the central bonnet strengthener. On chrome bumper cars be very careful with bonnet clearance a very small mini can be possibly be used or a remote air filter will have to be fabricated.


Due to the restricted space in the MGB engine bay none of the production cast manifolds used on the Rovers will fit. MG used a special cast manifold that did have a tendency to corrode and crack at the present time this is not available, so tubular mild or stainless steel exhaust manifolds are used. This is manufactured to be as tight as possible to the block and the down pipes are routed centrally down the sides of the block. The water drain tap on the right hand side of the block will have to be blanked off to clear. On the nearside of the block, where the dipstick tube enters, it may need relieving to clear the manifold.

The right hand down pipe is routed between the rear of the sump and the front of the gearbox to mate up with the left hand down pipe and then a standard MGB GT V8, or competition large bore exhaust will complete the system. The standard exhaust mountings can be used with the exception of the very last mounting, which will require larger saddle clamps to accommodate the larger pipe except on the large bore system that has fittings welded to it.

If Koni rear shock absorbers have been fitted, clearance problems may have to be overcome.

Because of the redesigned front suspension on the MGR V8 the manifolds exit straight out through the inner wings through quite a large opening that does result in a great deal of road spray entering the engine bay.

Many people have asked if a twin system could be used, to give the famous V8 burble. This is possible but as there is no space between the offside rear spring and the tank, the latter would have to be modified.


The 1800 B has used two types of axle. The early cars used a banjo axle, up to GHD3 and GHN3 132923. Later vehicles were fitted with a Salisbury or tube type. The production V8s and Cs were also fitted with the Salisbury type. Many owners run their converted vehicles on the standard axle but the Rover engine in standard form is not high revving and produces its maximum torque at 2750 r.p.m. Consequently a high final drive ratio will improve the top speed, consumption and general drivability. The standard 1800 B tube axle has a ratio of 3.07:1. Unfortunately no suitable ratios have been made up for the banjo axle.

The tube axles fitted to the 1800 and V8 are basically the same except for the crown wheel and pinion, differential cage, pinion oil seal and prop shaft flange. One point of interest is that the tube axle for the wire wheel and bolt-on wheel cars are different as the half shafts and axle tubes of different lengths. The MGC used the tube axle in bith wire wheel and bolt on (5 stud fixing) forms. These two ratios, 3.3:1 and 3.07, although very similar these axles were fitted with Girling rear brakes instead of Lockheed.

Although V8 crown wheels and pinions are no longer available form Leyland, reproduction items are. The 1800 differential cage can be machined to accept the V8 crown wheel. The settings up of the crown wheel and pinion is rather complex and requires some specialised tools(refer to the MGB workshop manual). A limited slip differential cage can also be obtained for the MGB axle.

The MGR V8 uses a different axle with a 3.31 ratio and limited slip however at approximately £2,000 this is not a very attractive option.

Axles from different cars, i.e. Rover SD1, 3 litre Capri, Jaguar Mark II, have been used but obviously extensive modifications have to be carried out.


The standard single circuit MGB 1800 braking system seems to cope well with the increased power. The original V8 conversions ran with standard brakes fitted with competition brake pads. These can be used if brake fade is experienced but these require greater pedal pressure and obviously disc wear is increased. If the vehicle is not fitted with one, a remote servo is a worthwhile extra to reduce the amount of pedal pressure required.

On the Production GT V8 a thicker disc was used along with a different calliper and a larger pad these components fit straight on the B stub axle/hub. The rear brakes are the same as the 1800. Although the V8 discs and pads are easily obtained the callipers are normally only available on an exchange basis. Some converters have successfully utilised the 2 pot SD1 callipers the mounting holes are on the same centres as the B calliper and the disc lies in the centre. The calliper mounting holes are too large so special bolts will be required or sleeves fitted to the hole, also the connection which accepts the brake flexi pipe has a thread that will require a special brake hose. Some insurance companies may request the brakes to be modified.

The later tandem, twin circuit brakes can be utilised as the servo does not obstruct the V8 installation, however some owners have noticed that this system feels rather spongy and does not seem as positive as the earlier one.

Competition front brakes can be purchased from a number of sources. These comprise twin 4 pot callipers and ventilated discs but these systems are very expensive and for a road car it is debatable if this is wothwhile.

Suspension and Steering

Because of the similar engine weights the standard MGB suspension, with the addition of the competition wishbone arm bushes, is what MG used in their original V8, and this seems to cope with the increased power quite well. However the system will need to be in a good condition as any slight weakness will be shown up the V8. The only problem with fitting the Rover relative to the suspension is that clearance is very tight between the crank pulley and the anti roll bar. On the V8 the bar is slightly cranked alternatively it can be spaced down.

Having said this the whole topic of suspension becomes a confusing maze as there are so many different options available on this particular subject. You have to consider ride comfort, ground clearance and your own taste. After all for many owners one of the attractions of the B is the rather out dated but predictable handling.

A 3/4" front anti roll bar will improve cornering and the V8 lower wishbone bushes are an improvement over the 1800 types.

The ride height of the black MGB is higher than the earlier models and consequently road holding has suffered. This can be improved by fitting a lowering kit, comprising front coils and rear springs, or alternatively the front spring pans and rear spring anchorage points can be altered. If the car is going to be driven hard it is well worth considering anti tramp bars at the rear to locate the rear axle.

This question of different crossmembers and steering set up is rather difficult to explain but I hope the following information is of some assistance.

On a standard Chrome Bumber 1800 the steering joint, between the steering shaft and column, is far too large and would obstruct the exhaust manifold on a V8. So when the first chrome bumper cars were converted a special steering shaft was fabricated. This had a much smaller joint that was much closer to the bulkhead and the steering column was dropped as much as possible on its brackets. This resulted in line up problems between the rack and the column so another small joint was used on the steering shaft close to the rack and under the offside engine mounting. The engine in these early conversions was quite high in the engine bay because of the proximity of the engine to the crossmember and steering.

When Leyland produced their V8 the crossmember was redesigned to be further away from the chassis and the steering rack was mounted further forward. The joint, between the column and shaft, was dropped lower and mounted further back in the bulkhead resulting in the engine being mounted considerably lower. This set up was retained with the advent of the rubber bumper 1800 model.

Cooling System

On all MGBs fitted with an engine -driven cooling fan, the radiator is not large enough to cool the V8. The larger MGB GT V8 radiator should be used, mounted towards the front of the engine bay.

Unfortunately there is no room for an engine-driven fan, so twin electric fans are fitted under the slam panel. Be sure to check the clearance between the bonnet release lever, in both the open and closed positions, and the left hand fan blade as it is very close. A Kenlowe thermostatic control is used to switch the fans (however it is best to wire the fan motors through a relay as they do consume a large current), some converters have wired in a manual over-ride switch. A guard can be mounted over the blades.

The V8 radiator requires a separate header tank, which is positioned on the left hand inner wing, adjacent to the distributor.

On the late model MGBs, with an electric cooling fan, the core in the original radiator is the same as the V8, but the top and bottom tanks will require reversing and modification. The late model MGB is already fitted with a header tank.

On most production Rovers the radiator is normally mounted higher than the engine and the top hose is at an angle. In the MG the radiator is on the same level, so problems may occur with air locks. If this is the case a special thermostat housing is available

A rear water outlet should be fabricated to enable the 1800 B heater valve to be used.

Wheels and Tyres

The MGB has been fitted with 14" diameter wheels. There have been three types: 4 J bolt-on steel wheels, 4 1/2 J wire wheels 5 J Rostyle wheels. The standard tyre fitted to the 1800 was 155 or 165 SR 14. With the increase in power and possibly in top speed there will be a greater strain on the tyres. If you have changed the axle ratio you will have to fit HR rated tyres to comply with insurance requlations.

The works V8 was fitted with 5 J Dunlop wheels and 175 HR 14 tyres. This size tyre is the largest you can fit to the wire or Rostyle wheel, although some owners have increased to 185.

The MGRV8 is fitted with 6J alloy wheels with 205/65 VR 15 but do not forget the wheel arches have been modified.

Once the tyre size is increased beyond 175, problems may occur with the wheel arch to tyre clearance. If you decide to change your rims, the choices of profiles, rim sizes etc. are very extensive. Smaller track rod ends are available if the clearance on the inside of the rim is a problem. 15" diameter wheels are another option.

The standard B wire wheels have been used in the past but these will obviously have to be in good condition. If the car is driven hard it is well worth considering the wider competition wire wheels with extra spokes.

Electrical System

The standard twin 6 volt or single large 12 volt batteries as fitted to the 1800 MGB are adequate for the V8 application.

The amount of alteration to the wiring loom, compared to many other conversions is quite straight forward. The starter motor is in the same position with similar connections as is the alternator. However clearance between the rear of the alternator and the rocker cover is limited which may require the plug to be modified or individual insulated connectors being used. Wiring will have to be extended to the new position for the ignition system. On late models a second cooling fan motor will have to be wired in parallel with a suitable relay and a Kenlowe control and on the earlier models wiring will have to be provided for both motors and controls.

Because of the twin cooling fans, an alternator with an output of 45 amps or more is needed. This is normally mounted in front of the offside rocker cover and this unit has to be quite short and of a small diameter. The normal B alternator is not suitable for this application, and the standard MGB GT V8 alternator or equivalent should be used. The new Valeo alternator that we supply comes less the pulley and fan however these items can be used from the original 1800 alternator.

The standard tachometer will need modifying for use with the 8 cylinder engine. Some owners have managed to mount the movement of the SD1 tacho in the MGB case alternatively your tacho can be sent to:

The Mews
St Paul Street
London N1 7BU
Telephone: 0171 226 9228
Who will carry out the mod, they will also carry out any speedometer modification should be needed.

If a conventional early Rover points type distributor is used, a ballasted coil should be used along with a suitable ballast resistor, later MGBs have this already in the loom. The coil should be mounted on the nearside radiator mounting plate, adjacent to the header tank. SD1 V8's used electronic ignition. Early models used the Opus system and later vehicles used the Constant energy system either of these systems work well but it is best to obtain any associated components (i.e. ballast resistor, amplifier, wiring, coil) from the donor vehicle as these components are quite expensive. With high mileage Rover distributors the electronics may cause problems and replacement components are extremely costly however Luminition can provide some excellent alternatives at reasonable cost. When fitted in its normal position the vacuum advance unit, when viewed from the front of the engine is at approximately 8 o,clock relative to the distributor body, this would obstruct the top hose so the distributor will have to be rotated so that it is at 3 o'clock and the HT leads retimed.

With the early points ignition the drive on the bottom of the distributor for the oil pump is male and on all the latter electronic units it is female making it rather difficult to swap these units.

The standard 1800 electric fuel pump seems to cope quite adequately with the V8 engine in standard tune and this unit was in the production GT V8. The pre-SD1engines were fitted with a manual pump and this can be used if preferred. It is worthwhile fitting a fuel filter between the pump and the carburation. If you are modifying the engine output, you may find it beneficial to fit an uprated pump some of these produce a high pressure so a pressure regulator may be required.

Conversion of the Chrome Bumper MGB 1800 Engine Bay to suit Rover V8 Engine

Unlike the black bumper MGB, the chrome bumper model requires a number of modifications to the engine bay. Once these have been completed, the conversion is continued as for a black bumper model.

If you are using a pre SD1 Rover V8 engine i.e. P6 or P5 the front of the sump will have to be modified as clearance between the sump will fit the earlier engine but you will also need to use the SD1 oil pick up .

The following modifications have to made to the engine bay:

  1. Fit new chassis rail engine mounts
  2. Modify steering shaft
  3. Remove radiator mounts and fit later type
  4. Cut away front pan and strengthen
  5. Cut away bulkhead
  6. Recite brake light switch
  7. A dish is required in the inner wing to clear the exhaust manifolds
Details of these modifications are given below with a list of extra components for the chrome bumper model is attached.

Detailed Explanation of Modifications to Chrome Bumper MGB Engine Bay

  1. After removing both front cross-member fixing bolts, the original 1800 chassis rail engine mountings should be cut away completely and the surface cleaned up. The new chassis rail engine mounting for the steering side is relieved to give clearance around the steering shaft. Both engine mount front supports have to be formed around the front cross-member bosses. When the new mountings are in place, access to the studs of the engine mounting rubbers is very limited, so before the mounts are welded to the chassis rail, as shown in the drawing, a depression should be made in the side of the chassis rail adjacent to the slot in the mounting.

    It is advisable to tack the mounts and check the installation before finalising the welding.

  2. The original steering shaft is fitted with a large universal joint at the bulkhead. This obstructs the V8 exhaust manifold, so a special shaft and pinion have to be fitted, with 2 smaller joints, one at the bulkhead and one at the rack. The lower end of the column should be dropped in its brackets as far as possible.

  3. Because of the extra length of the V8 engine, the original radiator mountings have to be removed and the later radiator mounting plates welded in place, as shown in the illustration.

  4. The front pan has to be cut back to allow the V8 radiator to be fitted. A section of steel U-channel is fitted into the front to strengthen the structure. If the oil cooler is to be retained, it can be mounted in front this is best done when the cooling fans are fixed, as space is rather limited.

  5. The bulkhead has to be cut back as shown in the drawing, to give adequate clearance for the Rover heads and also to assist in engine/gearbox fitting and removal .

  6. The brake light switch mounted on the off-side inner wing is extremely close to the V8 exhaust manifold, and should be resisted.

  7. A dish will have to be fabricated in the inner wings to clear the front of the exhaust manifolds. This can be dressed back or a section could be cut out and a flat or concave panel welded in place. On later chrome bumper and rubber bumper vehicles a dish already exists however this will still increasing at lower edge.

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