It really depends on what you want to do.....If you want to go fast and tow big loads, the 6.5 is for you, if you want to get the best possible fuel mileage, and do it on the cheapest possible budget, the 6.2 is for you.
Of course some will argue that a 6.2 turbo is the best combination of the two......
the 6.5 599 block is a better stronger block than the majority of the 6.2 blocks and it rarely cracks... I have three 6.2's and one 6.5... like said above, it depends on application.
Not all 6.2s are the same, nor are all 6.5s. Probably one of the strongest blocks ever made are the ones that both the 6.2s and 6.5s used in 1992, casting #10149599 . Since the 6.2 version has a smaller piston bore, the cylinder wall is heavier and more rugged. So, depends on how you want to look at it. The 6.2 version is more rugged, and the 6.5 version has more power.
Ford had the same thing going on with their IH 6.9s and 7.3s. Same engines with different bores. The 6.9s are more resistant to cyliinder-wall corrosion because they are thicker.
The 1982 engines had a lot of problems other then the block. Head gaskets leaked something awful (needed an update from GM), valves too big causing cracking, injector pumps with short lives due to the plastic governor rings falling apart (eliminated in 1985), etc. For those reasons, as well as the 700R4s failing often, many of those early 6.2 rigs got parked with low miles. So, I'm not sure if they were actually better or not.
I've got three of those engines sitting under my work-bench. All with less then 50K miles. I did a spark-test with a grinder, and the metal on the blocks makes sparks a different color than later blocks. So, I assume the alloy is different somehow. The theory is it has more nickel content, just like the new 6.5s being made now have.
With the 1992 engines, in 6.2 or 6.5 version, they pretty much had the best of everything. Different crank, block, injection pump, heads, etc.
6.5 Turbo hands down. Has decent power and no smoke. (same 200HP, 1993, as a 1995 5.7 gas and more TQ.) The 6.2 without a turbo in a 1500 suburban can’t get out of it’s own way and will roll the coal factory like the new diesel guys wish they could. (and have to spend money to do so.) Only the 5.7 olds diesel smoked worse.
...The 6.2 without a turbo in a 1500 suburban can’t get out of it’s own way and will roll the coal factory like the new diesel guys wish they could....
Bah! I'm running a non-turbo K10 'Burban - only way I can make that baby smoke is to lock the tranny in 1st and stand on the loud pedal, then she gets up and hollers!
But even normally, she's no slouch and I find 150hp of V8 is enough to scare the bejesus outta' these pantywaist Messican taxi 'drivers' around here.
What Block Were They Running in 1991 6.2L Original. Also GM Had a Replacement 6.2L "GM Goodwrench 6.2 Engine" Was the Original Better Compared to the Replacement.
Also I think The Original Was Built By Detroit Diesel, 6.2 Replacement & the 6.5 GM built I Think Not to Sure
91's were the 660 block. the goodwrench's were 660's also, even after 93. i had a goodwrench and it said allison on the sticker, and i'm pretty sure they didn't make it lol
the goodwrench i pulled apart was the worst for cracks. i pulled an 84 apart with more miles and it was in better condition
The 660s are actually pretty decent blocks also, even though they are not highly sought after, many guys use them for their 6.2/6.5 hybrids. They are one of the more available blocks, and seem to hold up fairly well.
In response to the Goodwrench post above-every Jasper or Goodwrench rebuild I've seen has been a 660 block-my advice is to pull the main caps and look for hairline cracks on anything you buy. I've even seen 660 6.2s bored out to 6.5 specs & put in newer turbocharged DS IP trucks-good luck with that holding up!
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