MGB Intake manifold alignment

[steve00136]

Having recently swopped carburettors I took the opportunity to check how well the joints between the carb and cylinder head were mating.
I noticed a pronounced ridge of about 3mm where the inlet manifold mates onto the head. This may only affect performance at high revs - but it is not ideal.
It seemed as if the manifold needed lifting a little which would be a quick and simple solution to centre the manifold to the head. So I slotted the inlet manifold mounting hole and repositioned the manifold which cured the problem.
Can't say I've noticed any improvement in performance but it's satisfying that I know these parts are properly aligned and fitted correctly.

 

[Mickey Richaud]

As long as the ports on the manifold and the head are aligned, all should be well. But as you say, having things lined up does make one feel better!


Mickey

 

[YakkoWarner]

Never even occured to me that this COULD be wrong - I just always assumed they were designed to line up. I have mine off now to do some cleaning and paint touchup on the engine, so when I reassemble I will be sure to check this...

 

[DrEntropy]

Mass production takes into account a certain amount of "slop tolerance." That leaves it up to us as caretakers, to correct and finesse things to their optimum. The intake and exhaust runners in most MGB heads are left as rough-cast ports. It pays to clean them up and check the alignment with the manifolds. The "old ways" treatment for intake ports was to polish to a mirror finish, unfortunately that lead to a laminar flow issue and less efficiency. An 80-grit finish after cleaning all the sharp points and rough parts of the casting and aligning the manifolds to the head will noticeably smooth out the running of the engine. Worth doing if the head is coming off.

 

[billspohn]

Doesn't matter at all on a street car.

Standard procedure on race cars to index the manifolds and install roll pins to ensure automatically perfect fitment.