In my experience, the 2 litre conversion is often bodged. People tend to want
to go as big as they can bore the block, and Lawrie correctly pointed out
some of the potential problems with that.
I had one block that looked great until I honed it and it perforated a wall -
had the casting inclusion been a few thou less deep, it would have lasted
until it was built and running before giving up, with much attendant cost and
agony.
I tend to be a bit conservative and limit engines to 1950 cc or so.
The other problem is that almost all of the 'kits' for big bore Bs I have
seen have incorrect pistons. Once upon a time, some bright light realised
that Lotus pistons had the right bore, and correct pin size to fit an
over-bored MGB engine. They likely got a heck of a deal on NOS pistons, as
these things keep cropping up - not enough old Cortinas and what not in need
of pistons, I guess.
Unfortunately, the Lotus pistons DO NOT have the correct deck height, which
means you have to carve off a large chunk of the top of the B block, further
compromising rigidity. And to top it off, the crown shape had cut outs for
the valves on the DOHC Lotus that do nothing except lower compression in an
MG.
People - if it's worth doing, surely it's worth doing properly. It doesn't
cost all that much to have one of the custom piston firms make up a simple
flat top piston, forged, with correct deck height. It never fails to amaze me
how cheap some people can be - they'll save $100 on pistons, then spend
almost that much having the block modification that they wouldn't have needed
if they had spent the extra money for the right parts in the first place.
I would have to agree with Lawrie, that the so called 2 litre mod isn't
really needed for most street engines, that it can take the engine into the
area where you are fumbling around looking for the correct carb needles, and
that it mostly produces more torque rather than appreciable horsepower, as
the same guy that was too cheap to buy the right pistons, is also too cheap
to get the head work done that is needed to produce much more power, or else
he finds some 'friend' with a grinder than can do it cheap for him and ends
up with lower flow from overly hogged out ports than he started with.
Power costs money - there is no secret, cheap path to glory here, and
Lawrie's way will save you a bundle even if it deprives you of bragging
rights. For the few that are really building performance engines, the carb
stuff is de rigeur and expected, and won't put anyone off.
Bill Spohn
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