> I'm sure someone has the answer to this question at their fingertips.
> What are the differences between a 1275 (12V ?) in a 1973 MG Midget and
> a 1275 in a 1967 Sprite (12CC ?) ? I have a friend who has a 1973 Midget,
> and I'm curious about the potential for performance enhancement.
There are three years of Midget that I'd consider buying if I were
going to get back into A Series sports cars: 72, 73, and 67. (74
would come a close fourth, as my first Midget -- my first M.G. --
my first sports car -- was a '74 Midget, Blaze Red, which is bright
orange.) I think the '72 and '73 are the prettiest and with the
round arches they're the easiest to hot-rod for handling; the '67 is
the most "collectible, as the first year with the 1275 and the last
year without smog. If I were building a hot-rod Midget, I'd want a
'72 or '73, though. Good place to start!
Have your friend buy Vizard's Tuning the A Series Engine. That will
tell him how to get up to about 120 bhp out of the A Series block,
with gobs of torque and reasonable reliability. I've driven a couple
of hopped-up Spridgets, and they can be loads of fun.
> I'm
> aware that the 1967 Sprite had a detuned Mini Cooper engine in it, but I
> don't know how that differs from the later 1275.
Not quite true. The Cooper engines and the Spridget engines were always
different, both in crankshaft construction and cylinder head (more head
studs on the Cooper, but less meat between the valves). The Cooper
cranks were made of EN40B alloy, while the Spridgets got EN19B (compared
to EN16 for the ordinary A Series cars). I'm not sure a Cooper crank
(made for transverse engines) will fit in a Spridget (which uses the
inline engine). I vaguely remember something about the way the flywheel
sets up on Minis and how that's different from the way Spridgets do it.
For a hot-rod A Series, the 12G940 head (post-68 "smog" head) is the
recommended one, as it has more metal in most of the castings to handle
the extra heat from the air injection reaction (air pump) in the ports.
This means that you can safely shave more metal off the 12G940 head to
get a higher compression ratio with less fear of warping. In addition,
the metal between the #2 and #3 exhaust valves (which share the central
siamesed port) is thicker and better cooled on the 940 head than on
the Cooper head.
In sum: for a bolt-on, a Cooper will give you a little better performance
than a stock Spridget head. But as the basis of a high performance motor,
the 12G940 is the way to go.
(BTW, "12G940" is cast into the top of the cylinder head, in the area
under the rocker arms. They're also recognizable by the presence of
tapped holes for the air pump injectors. Plain 5/16" fine bolts, or
Allen-head screws if you're cool, will fill those nicely.)
> BTW, are there any advantages/disadvantages to the 1971-1974 Midget with
> round rear wheel arches? The arches seem to be the only real differences
> between this car and earlier (post-1967) Spridgets.
Actually, it's 1972-74 (look for VINs beginning with GAN5UC through
GAN5UE -- no HANs as the Healeys' contract expired in 1970.) The '72
and '73 models have the pretty bumpers; the '74 has big black cubes
instead of the chrome overriders. On the other hand, those prove
handy for getting push-starts from tow trucks. Ask me how I know... :-)
Pluses: Better rustproofing beginning about 1970. Fewer holes in the
body (the chrome waistline strip on Midgets disappeared in 1970) mean
less opportunity for rust. Big one: the rear round arches make it
simple to add wider tires if you get the offset right -- if you're
silly, you can fit 185-60 tires on the stock Rostyles, but a) they
rub on the inside of the fender unless you add 1/4" spacers and b) the
wheels really aren't wide enough and the car feels sluggish in steering
response (though it sticks like a slot car). Recommendation: go with
185-60HR-13 tires on rims at least 5.5" wide, with >= 1/4" less back-
spacing than the Rostyles. That will also widen your rear track,
which (ummm...) decreases oversteer. (I'm away from Carroll Smith,
and I welcome anyone who's got a copy to correct me if I'm wrong.)
And round-arch Midgets all have three windshield wipers, which I
have always thought is just way cool.
Minuses: the extra metal in the outer fenders *does* add some minor
structural rigidity in the event of crashes; note that they returned
to the early-style arches in 1975 for the rubber-bumper SpitFidget,
which required extra gusseting for the 100+ pounds of bumpers. I just
figured I'd drive fast enough that nobody would rear-end me. :-) Also,
the dashboard on post-68 Spridgets is almost as bad as the one on
68-71 MGBs, with the mitigating factor that the Spridgets still have
a glove box under the dash while the B has only that map pocket down
by the passenger's right calf. And if you're in a state with hard-nosed
smog laws, it's going to be a little trickier to get performance out
of the relatively low compression ratios used on the post-68 motors.
No big deal if you're going to rebuild it from the inside out; put in
higher-compression pistons (you can get as high as 10:1 without much
knock, Sir Harry Weslake's cylinder head design is very good at this),
flow the head, and use a nice cam, plus go with a big overbore -- if
you run .120" oversize, you can get 1380cc, which has a nice synergistic
effect as not only is there just more area for combustion, but the
larger cylinder bores unshroud the valves to help breathing as well.
As with the larger cousin, the B Series, SUs are the best overall
carburetor for the hot-rod A, until you get over the 130 bhp level
and want to wring out the last few bhp at high cost. You can use
1.5" SUs on a hot 1275, which will give you all the breathing you
need with SU's traditional throttle response and midrange; you'll
need a modified or aftermarket manifold. Call Mini Mania in Milpitas
(in the 510 area code) for the parts, or the Austin Healey Store in
Canoga Park (the 818 area code).
That ought to give your friend something to chew over for a few months.
Hope he has fun with the car in the meanwhile.
--Scott
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