Fantasy 1275cc engine build spec suggestions.

[IslipMinor]

Making some assumptions - road use, maybe the odd track day, reliability, usability and fun

Engine - 1275 Sprite/Midget, or Marina/Ital

Bore - either +0.060" to give 1330cc, or offset bore 73.5mm to give 1380cc - any more and head gasket reliability can be a problem.

Head - 11-stud 12G940 with later Cooper S valve sizes, which are 1.4" inlet (~36mm), 1 5/32" exhaust (~29mm). Any larger and the head is very prone to cracking between the valve seats, and cannot be converted to unleaded. Obviously properly flowed, ported and 3-angle valve seats. CR minimum of 10:1, and preferably 10.5, converted to run with super unleaded fuel.

Cam - either Kent 266 for torque by the bucket full, or 276 for a bit more top end power, and still very driveable. More than a 276 may be great for a while, but for day-to-day??

Rockers - 1.5 ratio roller tipped - claimed to be worth going up 1 cam.

Carb - single SU HIF6 or HIF44 on flowed/matched Titan manifold, connect the water heating for easy 'warm-up' driving. Filter K&N with short stub stack.

Ignition - Aldon 'Yellow' distributor with vacuum (100AYV), Aldon Ignitor electronic trigger pack, high output coil e.g. Lucas 'Sports' and best quality silcone plug leads, e.g Magnecor.

Exhaust - large bore LCB (1 3/4" bore minimum) and enough straight-through silencers to give you a blend of 'nice noise', but not tiring on a long journey.

Crankshaft - ideally the EN40B version, but quite rare so more likely the EN16T, then tuftrided and balanced. Centre main strap.

Clutch - standard Spridget 1275 cover plate and driven plate to suit the gearbox being used.

Miscellaneous - full crank, rods, flywheel balance, maybe lightened flywheel (no more power, but better 'pick-up'), duplex timing with vernier adjustment (maybe belt, but no more power).

Result?

With 266 cam and everything else as above but the K&N filter/stub stack (used the MG Metro airbox cleaned up, and fitted with a K&N element) gave 100 bhp at 5,400 rpm with a very flat torque curve of >=100 lbf. ft. from 2,500 to 5,000 rpm.

With 276 and all above, 112 bhp at 5,800 rpm and maximum torque of 108 lbf. ft. Changing the air filter from the MG airbox with K&N element to a round K&N filter with short stub stack, increased the power from 104 bhp to 112 bhp! Same day same RR.

Fitting a Weber DCOE45 added 4 bhp, but the much reduced driveability and increased noise made it quite wearing on long journeys, so I put the SU back.

This is the spec of the 1380 Midget engine fitted in our Minor for the last 30,000+ miles. Is it the ultimate? Well it meets all of the 'assumptions' in spades!!!

[plastic_orange]

I used a 45 weber on my fully tweaked MGB engine in my Minor, and reverted to twin 13/4 SU's for similar reasons as you mention.
I've got a 1275 midget engine lying unused in my garage which allegedly is 1293, fully balanced with minisport stage 3 head - no idea of which cam though. I keep meaning to take it to bits to rebuild it, but haven't for the last 20 years. I swapped it out of a mate's minor when it started performing poorly I got to keep the engine for putting a 1098 in his. I discovered the head had a burnt valve, and couldn't get another one (didn't try very hard though), so it sits under my bench along with a tweaked B motor.
One day -----

Pete

[heathy12]

I think Islipminor has the idea!

Sounds quite a spec. Something to be said for reliability and regular use - who wants a tempramental car - most of us have enough tempramentality in the kitchens (gets coat!) so to have a car like that maybe too much!

I'm currently running thru my cars build spec and seeing what ive got to change from my dead engine to my decent A+ block this winter. Lots of goodies but its tricky determining what you actually have!