Is the 4.2/258 as durable as the 4.0/242?
I assume it is but my knowledge is very limited.
Is the 4.2/258 as durable as the 4.0/242?
I assume it is but my knowledge is very limited.
AFAIK yes
Searching right now for stroke, bore, rod length, main bearing count and such for each engine.
They are nearly identical motors. In fact, you can combine bits of both of them together to make a 4.6L version.
4.2:
3.75 in (95 mm) bore and 3.895 in (98.9 mm) stroke, 5.875" connecting rod
4.0:
same 3.895 in (98.9 mm) bore as the 258 with a shorter 3.414 in (86.7 mm) stroke, 6.125" connecting rod.
From what I've been able to find the 4.0 was a 4.2 with some slight improvements. I haven't found anyone declaring a difference in reliability or durability between the two, unless it's a carbureted 4.2. 
LOL Just noticed the discrepancy in the bore size. That's copy pasta from wiki.
In reply to Javelin:
Nice!
I'm not digging the rod/stroke ratio of the 4.2, though.
I’d say they are equally reliable but the 4.0L was a better engine. More power with EFI, better cam profile, and head design.
The engines are roughly identical. The difference comes from whether it is topped with a Carter BBD or not. With Carter, carbon buildup and worn out cylinder walls. With EFI, less worn out stuff.
I put a 4.2 short block in my 93 ho with all the 4.0 efi and head on it. It ran great. Everything bolted up just fine.
Don't the 4.0L head coolant ports need to be modified to bolt onto a 4.2L block?
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