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MG MGB GT V8 Factory Originals Technical - 3.5 and beyond

I have an old 3.5 V8 block (1970) in my MGB at the moment with new parts.
I would like to increase the engine size and keep the new bits, but as I have power Steering etc I have no more room to expand.
Would a larger engine (4.6?) have a larger block/height ?
I would appreciate any help on this matter
D M Tetlow

Power steering on an MGB?

Externally the 3.5, 3.9, 4.0, 4.2, & 4.6 are all the same.
Carl Floyd

Thanks Carl

You have answered a question I have always wondered about.
I currently have a 69 3.5/Edelbrock Carburetor (totally rebuilt) but of course would like more power.
So would a 4.6 be the way to go?


Bruce Mills

Thanks Carl
Yep, just fitted the MGOC Power Steering. I have 195-65 tyres on MGC 15" wires. The car was a pig to park. Now I can do it with my little pinky. Normal driving is OK too.
When you say the same does this mean all my ancillories, will also fit? as my water pump altenator, distributor, exhaust, and carb are all new, and I only have a tiny clearence in front of the pulley and under the standard bonnet.
Are the engine mount pickup points the same too?
D M Tetlow


As long as the engine you intend to fit has a distributor and a cam driven oil pump – like the 3.5 you have now – all the ancillaries will fit. Serpentine drive belt and later distributor-less engines with crank driven oil pumps can still be made to fit, but its more complicated. As Carl says, externally all Rover V8s are more or less identical, engine mounts will bolt straight on as will exhaust manifolds etc. You could even, but don’t, fit your small valve heads from the early 3.5 onto a 4.6. probably tells you all you want to know.

Geoff King

If you are going to spend more money on your engine you should bear in mind that the non-cross bolted Rover V8s have a serious problem with main bearing cap stability.

The most effective cure is to replace the block with a cross-bolted block; these are available in many capacities but the usual are 4.0 or 4.6 litres.

The problem will be that you will also need a new or reconditioned crankshaft, as the cross-bolted block has bigger main bearings.

The alternative is a stud kit, which, it is alleged helps with the main bearing cap stability problem.
Nigel Steward

This thread was discussed between 27/09/2006 and 28/09/2006

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