Spec me an engine / gearbox

Spec me an engine / gearbox

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edthedead

Original Poster:

210 posts

138 months

Sunday 14th June
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I have a Mk1 which I brought with a 1275 a+ engine apparently from a metro vanden plus. It has run for the last 14 years with no problems what so ever. I have changed the (badly fitted) RC40 to an RC50 but other than that, and the obligatory K&N and electronic ignition it is standard as far as I know.

I am going to be spending some cash getting the mins body work and interior refurbed as it wasn't done particularly well when I brought it and it is long overdue.

I would also like to do some bits to the engine/gearbox to get a bit more power and make it a bit of a nicer drive over distances (we live in Surrey and do the North Devon run most years), not sure what gearbox or dif it has the moment but it seems quick to about 50 then just get noisy!

I am thinking a 1293 with twin carbs and a 5 speed box but haven't really got much more ideas than that.

What do the experts suggest? And who is recommended to supply/fit?

Cooperman

4,418 posts

206 months

Sunday 14th June
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I would suggest that twin HS4 carbs combined with a nicely gas-flowed head with 35.6 mm inlet and 29.5 mm ex. valves would be a good start. Combine that with a lighter flywheel and a Kent 266 cam and that will work well with the exhaust system which you already have.
Match the manifolds to the head and clean out the inlet manifold to remove the nasty casting flash.
That will give max power at 5700 rpm and max torque at c.4000 rpm. Expect c.80 bhp.
With regards to gearing, a 3.44:1 final drive ratio is a good all-round choice and it gives 70 mph at just over 4000 rpm, which is OK for the old A-Series engine. That is the ratio which the original 1275 Cooper 'S' had and that spec is not far from the 'S' either.
If you can get a set, the original Cooper 'S' gear ratios are good, with slightly up-rated 1st, 2nd & 3rd, but with top still at 1:1.
I have no experience of 5-speed gearboxes in a Mini as my cars are kept mopstly original or built as rally cars which have to comply with historic regulations.
For pistons use the 21253 and have the compression ratio at about 10:1. That way you will not need octane booster in the petrol. It is a good idea to have the flywheel/clutch assembly balanced. I like a pre-Verto clutch & flywheel.
K & N air filters with stub-stacks work well with the HS4 carbs. You could use HS2's, but they will be at the limit of what they can flow, especialy if you later decide that you want a bit more grunt.
As it is a Mk.1 I guess you want the engine bay to look a bit more 'original Cooper', but an HIF44 is also a good carb and requires less setting up.
Let me know if I can help further.

edthedead

Original Poster:

210 posts

138 months

Monday 15th June
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Thanks very much for the reply, very helpful, sounds like what I am after!