A couple of weeks ago I was picking my A15 block from the machine shop and I happened to mention to the owner that we spin these motors past 8000 rpm.

When I said that he said that woud explain why the blocks were so stout, noting that it explained why Nissan used so much metal in the block.

I am in no way going to do so but his comments did make me wonder if it would be possible to pull 10-15lbs out of the block. Given the bare block is all of 75lbs I doubt it but it does make me wonder.

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Tomei took this approach with the Formula Atlantic/Pacific A-series power-plants.

At least you could remove all those unused /unnecessary external bosses and mounting points. No point carrying around mass if you don't need to.

For sure many mounting point even back of block some jagged edge corners can go
Also interesting is les Collins did an L series for a customer a belt drive conversion
Which got rid of the dizzie but was using dry sump pump, yet front of crank snout
was quite long much like the a series. You can shorten the crank snout when running
A belt driven ohc head like the e series or the Mazda head. Not sure you are want
that but belt driven engines spin easier than chain driven all else being equal.
Factory Cam in block can be kept if running stock oil pump but shortened substantially.
Water pump can be electric and you have eliminated various power robbing items and
Weight but then all this is no use if allowed to run the e series or ga series.

Block lightening isn't an issue if the strength is still there
Ford teams in V8 supercar used to send their blocks to a local engine centre here who had a fancy CNC machine that took weight out of the outer of the block for lightening
Blocks came out looking like they were billet instead of the rough casting we are used to

angle grinder is cheaper and a lot of fun
My L16 had at least 2kg off it when I finished
with it and only weighed 37kg from the start.
The A15 block I had to compare was 35kg so
yes very stout and heavy but has a cam in there.
While the L series head is like 18kg vs 12kg
A series heads.
Bore out the L16 or A series 3mm and thats
4 X 3mm pipes worth of weight removed

Benny does anyone know where they took weight from? I figured you can cut the lugs off the left side of the block, mill out some metal around the fuel pump boss (using electric pump), mill the outer edge of the oil pan mounting lip, also it seems to be possible to take some out of the block breather hole. Will that add up to more than a few pounds is the question. I'd hate to be the guy who takes 20lbs off the block only to start breaking cranks.

D yes bore the block out will definelty make it lighter but how much heavier are the pistons, obviously not as much as the steel liner but there must be some offset there. The big reason I've yet to bore my blocks out to 78mm is the compression ratio gets crazy past 77mm.