Originally Posted by: abi Not really related to this thread but 1974 Holden studied the potential for a 3.40 inch stroke 4 inch bore derivative of the Holden V8. I read this only a few nights ago in some online notes from an ex GM Holden engine development engineer. 342 cubic inches.
This would have been a fantastic prospect. A dished piston 9.0 compression version for long wheelbase automatic models and a flattop version with bigger valves for the sporty models, shame it was not pursued.
Interesting to read that.
Some 12-13 years later, HDT offered a very similar stroker in the VL series - I own one. It's well known that HDT had lots of inside help from GMH, and the VL stroker was developed before the split (my car was ordered in the days after the split - the original owner fearing HDT would be closing there & then).
According to the HDT paperwork, it's a 3.375" stroke and a 40" thou overbore to 4.040" = 346ci.
Without the overbore, the capacity would be around 339/340ci - so this is pretty close to the 342ci you mention above.
The 3.375" stroke was the largest stroke they could fit in the block without having to relieve it so the rod bolts/nuts would clear the bottoms of the bores & pan rails.
The later VR onwards HSV strokers were 350ci, but included the additional block clearancing to allow for the longer 3.48" stroke that they ran.
Brock (optimistically) rated the 5.6L at around 231kw, but in reality it wouldn't be up there. It does have plenty of torque, and with counter-balancing on the rear crank flange (as well as the dynamic balancing of the whole rotating assembly including flywheel & pressure plate that I had done during the rebuild) it spins up to 6000rpm as smooth as any jap multivalve short-stroke engine. Despite having the big valve heads, cam, ported manifold etc, it's very well behaved, and very smooth to drive.
Knowing what my stroker is like, GMH really missed an opportunity by not going ahead with that concept in '74 - it certainly would have made for a nice powerful, torquey, and smooth luxo-barge motor, and if fitted with the L34 bits (which is effectively what Brock did - less the cam) - would have given the L34/A9X Toranas an even bigger advantage on the track.