>I am not very familiar with MG products, so I have a couple of questions.
>Does the 1275 engine have three exhaust and two intake ports, as in some of
>the smaller displacement (A series?) engines?
The 1275 is the largest version of the A Series engine. This
began as an 803cc four in about 1950 and has gone through a
number of displacements. It has been used in all kinds of
vehicles from Austin and Morris Minis, Minors, A35s and other
economy cars through somce very potent Formula Junior racers
of the late Fifties, not to mention the Mini-Coopers that won
the Monte Carlo rally several times in the Sixties.
All *production* versions of the A Series engine did in fact
have two intake and three exhaust ports. Two variations should
interest us:
1 - the Healeys designed, built and raced with an aluminum
8-port crossflow cylinder head. In conjunction with the
Lucas petrol injection unit, an overbore to 1293cc, and a
generally mild state of tune (suitable for a 24-hour race),
the engine put out 120 bhp, consumed a gallon of petrol every
22 miles *during the race*, and propelled the little Sprite
coupe to a top speed of 147 mph on Les Hunaudieres.
2 - When Honda introduced the S600 and S800 convertible to
Europe in the late Sixties, it was seen by BMC as a potential
threat to the Spridget, for obvious reasons. Though the
handling was described as "diabolical," it was putting out
about 100 bhp/liter, meaning either about 60 or about 80
bhp (but at astronomical revs for the time). The 80-horse
version was quite a bit quicker than the 1275 Spridget of
the time. Eddie Maher of Morris, their engine wizard, put
together a prototype cylinder head that would be produceable,
add little to the overall cost of the car, but which made
a dramatic improvement in the car's performance -- dropping
its 0-60 time from 13-14 seconds down to 9 or 10. Unfortunately,
Honda cancelled plans to sell the S6/800 in Europe, BMC did
their usual thing about spending "unnecessary" money on cars
that were selling, and Maher's design got the can. (There is
also some speculation that this motor was politically unpopular,
since it made the Spridget faster than the MGB.)
For what it's worth, an example of the aluminum head is supposedly
in the hands of Stan Huntley, owner of FASPEC, and he keeps
threatening to make up a few for an exorbitant price. (He has
one of the Le Mans coupes.)
The siamesed intake and exhaust ports pose some interesting
problems for the tuner. For one thing, the pushrod holes go
between the ports, meaning you can't take too much metal away
from the ports if you are so inclined. For another thing,
the reflective pulses (the backwards pressure wave when the
valve closes) can be very distracting to such things as
fuel metering or exhaust scavenging. There are tricks, though.
One of the simplest is to leave a step at the cylinder head/
manifold interface. That is, rather than matching the ports
exactly, you grind the exhaust manifold a little bigger than
the exhaust port, and the intake port a little bigger than
the intake manifold. This flows like a matched port in the
right direction, but it causes huge amounts of turbulence for
reverse-flow conditions.
The best reference for anyone interested in Spridgets or Mini-
Coopers is David Vizard's amazing _Tuning BL's A-Series Engine_.
This is the OED or _Larousse Gastronomique_ of the A-Series.
In fact, this book is so comprehensive that it's almost a
deciding factor in whether to get a Spridget or a Spitfire! :-)
Seriously, though, this is an amazing work, not only for owners
of A-series equipped cars but also for other British car buffs --
maybe not to buy but certainly to browse through. His tests on
various proprietary parts (air filters, exhaust systems, ignitions,
etc>) not to mention his thoroughness in examining different
setups make this a tremendously eye-opening work for anyone
interested in engine tuning.
>Is the MGB engine directly
>related to these little guys, or does it boast a separate lineage?
The MGB's engine is the Austin B Series engine, and is basically
a 1.5X version of the A Series. The B Series was originally
designed as a 1200cc engine and has been produced in a number
of dimensions, up to the 1798cc version as used in the MGB.
This included a 1500cc version, a 1588cc version, and also a
1622cc version used in the last MGAs.
One of the variations on the B Series engine was a Twin Cam,
similar in lineage to the Lotus Twin Cam. The most potent
version of this engine was supercharged to 30 psi and put
out just over 300 bhp. It was used to set speed records;
Stirling Moss and Phil Hill drove the car to speeds in
excess of 254 mph, a record that stood till Olds spent a
boatload of money to make the Quad Four go faster about a
year ago.
>Also, do the Spridgets have lever arm shocks front and rear?
Yes, at both ends. The Spridget front suspension was derived
from the Morris Minor of Sir Alec Issigonis, and uses stamped
lower control arms, coil springs mounted between the lower arms
and a chassis mounting point, and a single upper link that
serves as the upper A-arm (or I-arm in this case) as well as
the connection to the shock absorber. What's surprising is that
it works as well as it does for its really ludicrous specs.
Conversions exist for changing both front and rear shocks to
modern tubular dampers. In addition, The Winner's Circle in
Ohio sells a complete coil-over suspension conversion for both
ends of the car. They're not cheap; I think the rear setup
was something like $800 four or five years ago.
As for Spridget motors, it's really easy to tune these up to
respectable power outputs. The basic steps are as follows:
1. Set the valve lash to 0.015" hot (up from 0.012"). This
changes the cam timing slightly and moves the power peak
up in the RPM range. Yes, you can feel the difference.
2. Install a decent exhaust system, starting with the muffler.
The header is surprisingly good on Spridgets made before
September 1974; you won't exceed its flow capacity until
you start making internal engine mods.
3. Drop the mixture adjusting nuts one or two flats. This
isn't as good as swapping in a richer needle (to compensate
for better scavenging by the improved exhaust system) but
it is free.
4. Remove the air pump (if any and if your conscience permits).
The 4 to 6 bhp that this uses are noticeable in an engine
that will put out about 65 bhp when you're done with it.
5. Advance the distributor a good amount -- I guessed by advancing
till it pinged and retarding with the vernier knob till it stopped.
6. Install low-restriction air filters; K & N's kit has a nicely
shaped mini air horn for the carb mouths, and also have that
million mile warranty. I used the old standby Weiand foam-type,
which worked okay.
This made for a quick 1275cc Midget, one that regularly outdragged
fuel-injected Rabbits (not GTIs) and Sciroccos. The next stages
involve significant outlays of cash either for parts or for labor,
as in gas-flowing the cylinder head. This is a wonderfully streetable
engine, with great low-end torque (for a 1.3L, anyway) and a nice
6300-rpm redline. It's cheap, it's dependable, and it's fun.
The ultimate Spridget motor that *I* know of belonged to Greg Neal,
who autocrossed it in Southern California. He ran something like this:
- Overbored .120 for displacement of 1380cc (this also had
tremendous effects on the valves, which are normally some-
what shrouded by the cylinder walls)
- Single Weber 45DCOE (George Emery's trick of using two that are
cut in half is expensive, but it does produce a marginally
measurable increase, for reasons I'll be glad to explain)
- Factory-style long-center-branch header (10" tubes on the
#1 and #4 ports, 23" tube on the center port, followed by
a collector) and SuperTrapp muffler
- 13.5:1 compression (racing fuel only, please!)
- Complete gas-flow of cylinder head for maximum airflow
- 1.5:1 rocker arms (increased lift versus the stock 1.25:1)
- One of David Vizard's hot cams for the A Series engine, complete
with a vernier cam sprocket to help dial it in faster (worth the
cost because you save in time!)
The dynamometer said this put out about 130-135 bhp. There are
reputed to be FP racers (Comptune and a few others) who have
even more extreme power levels. I've *seen* one of these motors
in a Lotus 7A put out 110 bhp *at the rear wheels* on the dyno
at Willow Springs, which works out to about 130 bhp at the flywheel
if I recall Neville's formula from the last dyno day.
Neat motors. Will cost you just under four grand at The Healey Store.
I might have one for 1991, if the savings account is big enough by then
('cause I'll have to get the Spridget to put it in, too...)
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