Fellow Correspondents,
A lucky find at what was probably one of the last Jumbles of the year in
England was a pile of old "Automobile" magazines and a few "Motor Sports"=
=2E
I chanced upon an article by Bill Boddy on the Turbo charged Bentley of
Jumbo Goddard. I remember that this monster was in the entrance foyer of
the Donington racing car museum when it first opened. Where is it now, I
wonder? I hope Mr Boddy does not mind my reproduction of his article. =
I leave the reader to come to his own conclusions as to the appropriatene=
ss
of this conversion. Please bear in mind that the perpetrator is Austraili=
an
(I believe). My prelidictions are well known.
A TURBO-EXHAUST-SUPERCHARGED VINTAGE BENTLEY
WHEN the commentator at the B.D.C. Silverstone meeting spoke of John
Goddard's 8-litre
Bentley as having exhaust-driven turbo-superchargers, there must have bee=
n
those, myself
included, who thought he was mistaken and was referring to twin
engine-motivated blowers.
Not a bit of it. One never quiteknows what " Jumbo'; Goddard will do next=
and sure
enough, he now has a couple of exhaust-turbo-superchargers on the Bentley=
=2E
The car is the previously-described 3-litre into which an 8-litre engine=
was installed. To
prepare this engine for forced-induction it had to be somewhat modified.
When the late
Forrest Lycett was running his well-known 8-litre he had two special
crankshafts forged by
Laystall in I935, one being put in the car and the other, unmachined, kep=
t
as a spare. The
spare remained on a shelf at McKenzie's for 30 years. It was presented to=
John Goddard
by McKenzie, machined by Laystall and put into his engine.
The crankshaft has big-end journals of 65 mm. dia., compared to 60 mm.
journals of the
normal 8-litre crank and, being nicely matured, was just the job for the
contemplated
conversion. In conjunction with this crank new con-rods were designed by
Phil Irving, forged
by E. Haddaway in Melbourne, and machined by Johnsteads in London. Made o=
f
Comsteel
R4 2 1/2per cent. nickel-chrome steel equal or equivalent to EN25, these
rods have a tensile
strength of about 45 tons. Final hardening was achieved by soaking the ro=
ds
at 850"C. for an
hour, quenching them in oil and tempering at 550C. The gudgeon-pin dia. i=
s
increased from
7/8in. to an inch. The big-ends are white-metal lined with Johnstead's "
Brigramet " standard
graphitised alloy, the small-ends phosphor-bronze, The c.r. was lowered t=
o
approx. 6.5 to 1
by inserting a 7/16in. plate between cylinder block and crankcase, which
also serves to
stiffen the notoriously flexible crankcase of a vintage Bentley.
The superchargers are standard produclion exhaust-turbo vane compressor=
s
made by
Garrett of Los Angeles in their Industrial Research Division fur diesel
engines. They were
responsible for the exhaust-turbo-supercharger offered as an optional ext=
ra
for a time by
Oldsmobile. American buvers did not show sufficient enthusiasm, the proje=
ct
was
abandoned, and Garretts were left tooled-up for unwanted equipment.
These Garrett TEO-6-series turbo-superchargers are hung from the Bentley=
exhaust
manifolds without anv other form of mounting. Each one sucks from a 2 in=B7=
dia. S.U.
carburetter and feeds to the engine through a pipe curving over the top
ofthe camshaft cover
and dropping into the standard Bentley in!et manifold. At present these
Pipes have a flat-
section to clear the bonnet and look untidy, but they will be replaced in=
due course with
properlv-fitted stove-enamelled piping. The dimensions of this remarkable=
induction system
were calculated by Garrett's engineers.
From each supercharger an exhaust pipe runs rearwards, either to outlets=
in the side of the
car or at the tail, the previously contrived side exhausts normally being=
closed by adapted
petrol filler caps to provide rather more back-pressure for the blowers.
How does it add up, in action? Well, although Goddard does not usually
exceed 4,000
engine r.p.m., the new crankshaft should enable 5,000 r.p.m. to be used
safely. At tick-over
the superchargers run at 1200 to 2000 r.p.m. At 3500 r.p.m. of the Bentle=
y
engine they are
revolving at 55,000 - 60,000r.p.m. and at its present maximum of 4000
r.p.m. they are doing
60,000 - 65,000r.p.m. Hardly a cool 65,000, because under bonnet
temperature is something
of a problem, although it is now down to a maximum of 120F., which is qui=
te
satisfactory.
Plans are afoot to use a baffle to deflect hot air from the rear
carburetter.
Manifold pressures are difficult to quote, due to the turbulent pulsatin=
g
gas flow, but at an
exhaust back pressure of 8 Ib./sq. in. it is in the region of 8 1/2a
Ib./sq. in. and each blower is
then giving 15 - 20 h.p.--200b.h.P. has been measured at the road wheels
at 2,500 r.p.m. and zero boost.
To cool as much as lubricate them the superchargers require an oil feed =
of
at least I0 Ib/sq.
in.--the supply comes off the engine filter and a tell-tale light warns t=
he
driver should the
pressure drop below this figure.
This turbo-supercharged 8-litre Bentley is no freak. Since he has been
back in this country
from Australia Mr. Goddard has driven it I,500 miles on the road and
competed with it at
Silverstone, Firle, Shelsley-Walsh, Brighton and in other sprints and dra=
g
contests. The
penalty of conversion is exclusion from V.S.C.C. events. Fuel starvation
was a problem at
first but at Shelsley-Walsh a practice run was made in 45 sec. in spite o=
f
the rough road, and
at Brighton it just broke Lycett's record, doing the s.s. kilo. in 27.3
sec.; of course, the timing
is different now and Lycett's Bentley was not supercharged. The car runs =
on
the best grade
ESSO petrol giving 6mpg at Silverstone, 10 - 12 mpg on the road, and is
lubricated with
Castrol XL.
W.B.
Yours plagaristically, with all acknowledgements to William Boddy and
"Motor Sport" magazine,
JH
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