|The MGA With An Attitude
MGB Exhaust Manifold on MGA - EX-204
This page is posted on popular demand. The question is, "Can the MGB Exhaust manifold be used on the MGA"? The answer is yes for right hand drive cars only, but not for left hand drive cars (unless you may be a glutton for punishment).
MGA above - MGB below
This question usually arises when someone has trouble finding a good used MGA exhaust manifold. They have a tendency to crack at the crotch of the "Y" shape. I have tossed out a few broken ones myself. I like to keep a spare in hand just for this reason, so I don't have to go searching on short notice when I might need one. There are still lots of parts cars around, but good used manifolds are getting more rare as time passes. I can still pick one up cheap enough on occasion at a swap meet or from eBay, but more often than not they need some repair, like replacement of a broken stud, Helicoil for a stripped thread, or welding (re-casting) of part of the bottom flange (see EX-201).
The problem fitting the MGB part is that the wonderful long center branch part of the casting will interfere with the steering column on LHD cars, and it is a royal PITA trying work around this situation. Some people have gone so far as to cut the pinion shaft near bottom end and install another universal joint, allowing them to relocate bottom end of the steering column slightly to the left (with an additional bulkhead modification and maybe bending the clutch pedal a bit).
I have seen a drawing (sketch) showing a modification to the MGB exhaust manifold. Someone machined the top gasket surface at a slight angle to move the bottom end closer to the engine block. That made the bottom flange(s) hit the block somewhere around the sump flange. Then they cut horizontally through the manifold casting about where it would pass the steering shaft. Removing a slight wedge shape piece, the bottom end was then tilted back outboard to clear the block, and it was welded back together. I don't have enough confidence in anyone welding cast iron to do that, especially where the manifold is subject to extreme temperature swings in operation. In any case this modification would be somewhat expensive to contract out, or time consuming if you happen to be talented enough to do it yourself.
A few people have reported grinding a notch in the side of the long center branch to clear the MGA steering column (and they claim it has worked for them). It strikes me that if you didn't grind it too thin it would end up being a very close fit to the steering column, giving some difficulty in assembly, and risking some bumping or rubbing as the engine rocks on the rubber mounts. I haven't tried it, so I don't have first hand experience with it, and I can't recommend it without some reservations. An alternative in this approach could be to grind it back farther until you have a hole, the weld in another concave piece of iron to have a thicker wall with the desired depression. This involves some of the same problems and risks with the prior welding scheme.
Fairly recently Moss Motors has a new cast iron exhaust manifold available for the MGA (for a price of course). It would be neat if someone would produce a casting similar to the MGB manifold but configured to fit around the steering shaft in the MGA. The cost of producing this part might have been more palatable before the new MGA iron manifold was available. Considering the price of the new stock type MGA manifold, someone may yet take the proposition to fruition.
An alternative is to use tubular headers, but not particularly to my taste (considering noise, heat, and originality issues).