Holden 253 timing chain.

[Smitty2]

OK, so OZ introduced grp A before we had FIA grp A?
I thought the year Tom and Larry drove they had an engine failure due to that?

no, Australia went to FIA Group A rules the same time as the rest of the world.

But Holden only had the standard Commodore with the 5044cc (aka) 308 engine in the road car available
that allowed them to go racing. (read the original FIA Homologation papers for the Commodore, they are on the internet)

So Australian Commodore racers originally went out racing under Grp A rules with small valve, single row chain, standard pressed steel valve
rockers in the standard road car 308 (yup, complete with std ignition and Quadrajet carby)
Failures were frequent PLUS... the standard car had a weight penalty applied as it had an engine over 5000cc

Plans were put into place.... reduce the cars weight by destroking the 308 (5044cc) to 304ci (4987cc)... woot ! race car can be 75kg lighter
so road cars got the 'new' 304c LV2 engine and the first 5,000 cars produced after the new engine was introduced got the V7X version

V7X? that meant big valves heads, big open inlet manifold, lighter flywheel, baffled sump PLUS a double row chain.

Then Holden got really serious and introduced a new model Commodore... the A9L which is what we know as the Blue Meanie or SS Grp A
and it got another 'special evolution' A9L engine. Based on the V7X version of the new LV2... it got some extras. Crane roller Rockers
Crane high lift camshaft, extractors and big bore exhaust system (extractors made to Holden specs by HM exhaust, big bore exhaust by Lukey))
The Blue Meanie was lighter again (wind your own windows on all), lighter seats, bigger wider alloy wheels (16" diameter)

and there is your history lesson

[SL/ENUT]

Smitty, V7X doesn't have the large valve heads, they have the small valve ones, VG prefix.
Its the V5H VB prefix 304...

[Smitty2]

Smitty, V7X doesn't have the large valve heads, they have the small valve ones, VG prefix.
Its the V5H VB prefix 304...

hmmm...... my VK 234 pack Berlina (GMH co car) had an LV2 engine (+M21 box) with V7X
that included B Cast heads on the engine (no small valves there)

will have to dig out the original employee invoice for it now (to check the engine prefix)