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Mild tuning for 948cc engine

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Jerram Avatar
Jerram Silver Member David Jerram
Reading, Berkshire, UK   GBR
My Bugeye's 948cc engine has a cracked head despite the DPO doing a 'complete engine rebuild'... so the engine is now with a professional builder getting a complete re-refresh.

While it is there, are there any worthwhile upgrades that could / should be made to improve the engine - without going overboard?
Ultimately I don't want to run larger carbs as I'd prefer the motor to look stock under the hood.

I am going to get lead-free valve seats and a duplex vernier timing chain set. Anything else worth upgrading while I am at it?

Thank you all.

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AN5L8016 Avatar
AN5L8016 Mark Haynes
Nederland, CO, USA   USA
You can step up the cam to a hot road cam, and putting flattop pistons and a ported 1098 head will help it breathe. I built a 948 +.040 10.5:1CR, NOS hot road cam (BMC 2A948 cam), adjustable timing set, 12G295 head ported, milled 0.080",NOS flat top Hepolite pistons, HS2s, header from Winner's Circle that ran great. I should never have sold that engine.



'58 Bugeye
'66 'Stang

westburn70 Eric Flack
Glasgow, Lanarkshire, UK   GBR
Flat top pistons. Double valve springs, Crankshaft pully with rubber insert. These were on
later minis etc. I got mine from a scrap metro engine. Cheap upgrade to a basic 948cc
Port out exhausts and skim head. Plus as above. Read Vizards book on tuning BMC A engines.

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Jerram Avatar
Jerram Silver Member David Jerram
Reading, Berkshire, UK   GBR
Thank you Eric and Mark,
I do have Vizards book, but it generally expects owners to 'upgrade' to a 1275 - or go so far that you need a much larger carb.
Your recommendations look great, and I will speak to the engine builder about them:
  • Over bore +.040
  • Hepolite flattop pistons
  • 12G295 ported head (or a 1098 head)
  • Skim head for 10.5:1 compression ratio
  • Double valve springs
  • BMC 2A948 cam
  • Verier & duplex timing chain
  • HS2s carbs
  • Maniflow inlet
  • LCB exhaust header

Thank you very much. Happy holidays!

westburn70 Eric Flack
Glasgow, Lanarkshire, UK   GBR
I have the BMC competitions dept tuning booklet for the 948cc engine. In the UK
in the late 50s and 1960s there was a "junior" class for racing cars under 1000cc
A laste of such vehicles used the BMC 948cc engine- plenty about in those days.
In 1965 my BE had the flat top pistons, double valve springs,skimmed and "ported"
stage two head,. You could go to stage 3. Eventually I got the engine with tuning to
do nearly 100 mph! With drum brakes! Yep the engine sort of gave up as the
bearings gave up on the fancy crankshaft. But I had two years of fun and
that's what it was all about! I will dig out the BMC tuning stuff. Might help you.
I did "play about" with various carburettors and engine tuning. Now back to
bog standard original 948 and carbs.

carlinacton Avatar
carlinacton Bruce Acton
Midrand, Gauteng, South Africa   ZAF
Above is a great recipe for a fast road 948 engine. I can add:
Minispares sell a decent set of flat top piston as well.
Alden Yellow Distributor highly recommended for this spec engine.
Maniflow make a small bore LCB just for 948 Sprite.
Kent 266 cam very nice fast road cam and similar characteristics to 2A948. Any bigger on a 948 and too much bottom end lost.
12G295 head fantastic period head for 948 (as fitted to early small bore Cooper and MG1100).
HS2 carbs with K&N filters.
Fully balanced bottom end nice touch.
Good luck!



Edited 1 time(s). Last edit at 2018-01-05 01:23 AM by carlinacton.

boom132 Jason Dupuy
Manchester, ME, USA   USA
Just checking in... did you actually do all the things on your list? I’m starting out on my 948 rebuild adventure. Would like to know from where you purchased your parts, and how much the machine shop charged you... thank you, Jason.

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