The question of Spit engine mods is a reoccuring theme on this list.
There are lots of things to do or can be done. I do however, disagree
with one comment, that with increased performance you decrease reliability.
When a high performance racing engine is built, the goal is to make it
bullet proof so it will be reliable under extreme useage. When you beef
up the Spit for "boy-racer" use, you should also take steps to increase
reliability.
When modifying, this will involve removeal of emmissions equipment (this is
another story as to the ethics involved, not to mention the legalities).
You will want to replace the air filter (K&N always get great reviews),
then probably the exhaust system including manifold. The next things
almost have to be done together: increase CR, to increase breathability by
changing carb, head flow characteristics, and cam. Roller rockers will
help as will lighter (and if needed, shorted) push rods, lighter valve
spring retainers, cam followers, and appropriate springs. IF DONE
CORRECTLY, you have increased potential power output. Now you need to
increase reliability to match. Balance and blueprint the moter. Lighten
the crank, rods, and flywheel to make the engine freeer reving. Replace all
bearings (use 77 MGB rod bearings). If you have tonnes of cash use titanium
rods, obtain from special order place (I can give you the name of such a
place). The use of an oil cooler is MADATORY as is converting the
half circle thrust bearing to a full circle type. Now you have to set up
the motor. YOu will need to take it to a place with a dyno set up, and
the parts and knowhow to set the cam timming (vernier adjustable
timming gear will kelp), the carb settings and the ignition. Oops, you
may need to get a hotter ignition to increase the spark intensity at the
higher CR. You will certainly need a custom advance curve. This will all
cost you an arm and a leg, at least $2000-$3000.
You could replace the engine with a 1500 set to UK specs, or rebuild
to UK specs. UK Spits have no emmissions, a nicer 4-2-1 exhaust manifold,
a nice inlet manifold with twin SU carbs, a more radicle cam and CR.
Don't think the head was ported any better, and can't remember if the
valves are larger. BUT the UK Spit does not have any of the reliablity
improving mods. It is however, fully set up and all bits are presumably
compatible so you won't need (or it is not as dire) to take to be dyno
tunned.
Have fun, get your cash out, and rev that motor....
Cheers Dennis
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