Exhaust options

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ORIGINAL EQUIPMENT

None of the original equipment fitted to the Magnette or the MGB offers the ideal solution for the modified car, so this is the one area where the owner is most likely to have to compromise or pay for a custom-made solution.

The ZA manifold was always restrictive of engine breathing and is best replaced at least with a ZB type.

The MGB manifold simply will not fit the Magnette engine-bay (unless you fancy a system that exits through the wheel-arch!)

LOW COST COMPROMISE

The ZB manifold will fit the MGB engine and allow the standard exhaust system to be used but by doing so one is choking off a fair percentage of the newly-acquired performance. Nonetheless this is probably the best solution where cost is a real issue. Some of the down-side can be overcome with a straight-through silencer and pipework that is fabricated to pass under the rear axle, so as to avoid the usual convoluted "up and over".

THE MIDDLE WAY

By the time the MGA was designed, the B-series manifold had developed further. Because of the MGA's engine-bay lay-out, the manifold is swept more to the rear than the Magnette's. However, the Magnette manifold shape is only what it is because of the need to route the down-pipe past the steering column on LHD cars. On RHD cars, there is a pointless kink and it is difficult to understand why the factory did not develop different down-pipes for LHD & RHD cars. The MGA manifold is actually very suitable for the Magnette and it has the added advantage that the down-pipe is attached using a studded flange rather than the difficult clamped arrangement on the Magnette. A new down-pipe has to be made up but for best performance it is better to get a whole system made up using a larger bore pipe as fitted to the MGA. This is the approach used by Stephen Tickell and is described in his separate article.

BEST SOLUTION

The best solution is to have a free-flow or extractor manifold fabricated, preferably in stainless steel so that the job only has to be done once. To have one specially made up will undoubtedly be expensive so if you have the necessary welding ability it is possible to modify one of the tubular manifolds supplied by most MGB specialists. This is a lengthy process involving many saw-cuts and welds. The system will need to be repeatedly offered up and checked for clearance over the bell-housing. This is tight enough as standard so if you have limited patience you are advised to pay someone to do it, thereby preserving your own sanity! Previous remarks about straight through silencer and re-routed tail-pipe will certainly apply to this option. Use a larger bore pipe to suit the manifold or, again, the benefit will be lost.

Editor's Note:

Trevor Jones' comment below refers to a bespoke system that he has had made up as a batch. Here is a picture, showing that it includes a 3-branch manifold:

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