The 1984 VK was released with the 308ci (5044cc) or
5.0L V8 as it was more commonly referred to.
Brief specs:
Bore: 4.00" (101.6mm)
Stroke: 3.06" (77.8mm)
Cubic capacity: 308ci (5044cc)
This motor was available in 2 versions.
The standard engine (L31 on option plate) featured the engine number prefix
of VT, a continuation since the VB, and it was rated at 126kW@4400RPM, and
361Nm@2800RPM.
The high output version of this motor, production option V5H (V5H stamped
on plate) first appeared in the VH commodore as the basis upon which the HDT
engines were built (as well as being optional on manual BT-1 equipped police
interceptors). This motor was stamped with the prefix VZ in both the VH and
VK models, and it was rated at 177kW@4800RPM and 419Nm@3500RPM. It was
only available with the M21 4 speed manual gearbox.
The V5H featured the following "revisions" as GMH called them:
* B-cast higher flowing heads fitted with larger valves
* Brock inlet manifold (with the open style plenum)
* Lightened flywheel
* Baffled sump with scrapers & windage tray
* Cold air intake
* Larger snout on air cleaner
* Less restrictive exhaust
* Blue printed distributor & advance mechanism.
Note that some of these figures were measured under the old SAE measuring
system, and are not a true representation of "installed" (referred to as DIN)power
figures. SAE measuremnts were obtained with minimal exhausts (usually just
headers), no air filter, and no accessories driven off the crankshaft. Installed
(DIN) power figures are a truer representation of output and are the norm
today, where the motor is equipped with all ancillaries, exhaust & air filter.
1984 was the last year of the "big bangers" Group C touring car class, dominated
by aussie-built V8s, culminating in Bathurst every october. The upcoming Group
A "international" formula for 1985 had strict minimum weights for various
engine capacities. The 5001 to 6000cc class required a minimum weight of 1400kg,
but if GMH could squeeze the capacity to under 5.0 litres, it would fall into
the lesser category with a minimum weight of 1325kg. Brock & Holden did the
maths, and worked out what little they would lose in approx. 50cc of capacity,
would be far greater offset by the 75kg weight saving.
Thus in early 1985, the 304 was born.
The 304 featured the same 4" bore of the 308, but the stroke was reduced by
1mm to 76.8mm, for a total capacity of 4987cc - a mere 13cc under the maximum
allowed capacity.
Brief specs:
Bore: 4.00" (101.6mm)
Stroke: 3.02" (76.8mm)
Cubic capacity: 304ci (4987cc)
Although the actual cubic capacity was close to 5.0 litres, it was referred
to as the 4.9 to differentiate it from the earlier 308 motors.
As part of the Group A homologation regulations, GMH had to build and sell
a minimum of 5000 high-output V8 powered & manual shifted commodores, followed
by a further 500 specials built much closer to race trim, in order to qualify
to race in the Group A category.
There were a number of versions of the 304.
The standard version fitted to automatics, featured the engine prefix VA.
The High Output version dropped the V5H tag to become the production option
LV2, and featured the same performance enhancing equipment of the 308 V5H,
only in 304ci capacity. It featured the prefix VB, and was part of the 5000
needed to comply.
After the 5000 were made, GMH no longer fitted the B-cast heads, and renamed
these motors V7X, prefixed with a VG. The VG was rated at 122kW. All the other
high performance equipment remained however.
The VG engine became standard in all manuals (apart from the HDT cars) from
break points at body numbers: J9 53597 (Vic plant) and L1 80871 (SA plant).
The body number can be found on the radiator support panel, and is a thin
aluminium plate, usually painted over.
The Group A SS (engine option A9L) was prefixed VC, and in addition to the
LV2/V5H changes, also featured a high lift cam, roller rockers, a blueprinted
carby & extractors for a total output of 200kW@5200RPM and 418Nm@3600RPM
In conclusion, this is the easiest way to show it:
Information was gathered from a number of souces, including personal experience
rebuilding these motors & cars, factory issued service bulletins, the factory
parts guide for the VK model, see the scan below, as well as road tests from
various motoring publications of the era.
