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MG Midget and Sprite Technical - A Series inlet manifold

I went to great effort to get Vizards book and reprofile a spare inlet manifold I had to replace the one on the car.

Only to discover the one on the car looks to be a non BMC possible even a performance inlet manifold.

Most noticeable and the hardest to photograpgh are the 'huge' ports connecting to the cross tube.

It has a 'P' on the underside - no other info.







Malc Gilliver

I have just fitted one of these to my 1275 engine
Tim Carter

Tim
Any idea where they come from ?
Malc Gilliver

Have you measured across the inlet? I’m wondering if it’s to suit the H4 1.5” carbs.
Dave O'Neill 2

Dave O'N has it. Modified to fit a pair of H4s. A very popular mod in the day. Try finding a pair of H4s now.
Rob
MG Moneypit

Dave and Rob.

Thanks, just searched for an H4 carb setup and sure enough, that looks like the manifold I have.

Do we know if the H4 manifold is better than the correct HS2 manifold for performance, I would assume that the later HS2 manifold 'should' be better ?

Thanks
Malc Gilliver

IF you were wanting to run H2's on that H4 manifold you'll need to make up a tapered spacer (plastic-aluminium) to reduce that tapered throat area back to a straight 1 1/4" diameter otherwise the depression straight after the carb. into the manifold will play hell with the airflow--
William Revit

William.

I am beginning to wonder if my previously documented oil sucking/burning issue ( which I assumed was due to a worn out engine is related to this inlet manifold as I didn't realise it was not standard.

I have the engine out ( to replace the clutch thrust bearing ) and found what I feel was excessive oil in the intake - despite having a catch tank - so I feel you are on to something.

Maybe this goes all the way back to https://mg-cars.org.uk/cgi-bin/or17?runprog=mgbbs&access=&mode=archiveth&subject=97&subjectar=97&thread=2014091416212710294

from 2009 !


Malc
Malc Gilliver

That thread started in 2014, not 2009. Last post 2021 by Nigel

Worms. Cans of. 🤣🤣
anamnesis

AHH but this isn't your manifold, it's a spare----??
and not saying it'll cause crankcase breathing issues at all----------
All that will happen with that manifold as is with 1 1/4" carbs is that the airflow through the carbs won't be perfect and will expand out into the larger diameter section , velocity will drop off then have to pick up again to travel through the manifold--As a guess I'd say probably down a bit on outright power and possible flat spots at lean running cruising speeds maybe
William Revit

I can see all those as possible, do next job is the fit the correct manifold and compare
Malc Gilliver

That manifold would be quite ok for 1 1/2" carbs with it tidied up a bit inside but yeah for 1 1/4's it would be better with that tapered section filled to suit 1 1/4' bore----------it's ok -don't discard it
William Revit

Looks the same to mine off my 1965 MKII.
I have the HS2 1 1/4" carbs on it. Thought it was original.




James Paul

Yes It looks the same as the one I have for HS2's. It came off a 10CC 1098 engine. I believe you can fit H4 carbs to this manifold suitably opened out.There was a special tuning kit C-AJJ 3304 and C-AUD 194 I think just for this purpose
The HS4's won't fit the manifold as the body is different
Bob Beaumont

Agreed it is a std manifold which will take both size carbuettors but not perfect for either--For 1 1/2" carbs the throat area needs opening out and blending.
For 1 1/4" that front tapered area needs reducing back to match the carb at 1 1/4" to eliminate the step from the carb to the manifold, then blended in.
It'll work as is but not properly-
William Revit

My car is a 1965 1098cc car - maybe the manifold was fitted as standard on these cars - or BMC just used up excess MG A stock from 1962
Malc Gilliver

Looks like I have one, as well. The openings are 1/16” under 1.5”.

Not MGA, as B-series ports are further apart.


Dave O'Neill 2

I also have that manifold on my 1964 MKII midget.

Done know if the opening has been altered though.
Philip Sellen

Dave O'Neill 2

Your casting has different details - no centre pad and larger firing order - but I did wonder if a B has wider ports than an A series
Malc Gilliver

The 1275 and 1098 manifolds I have slight differences but are escentially the same. I wonder if Dave's is off a 1275 engine?
Bob Beaumont

This thread was discussed between 19/07/2025 and 24/07/2025

MG Midget and Sprite Technical index

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