Diff. year 8.1L blocks, diff. cylinder wall thinckness? Diff. bore size ability? - Diesel Place : Chevrolet and GMC Diesel Truck Forums
 
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Old 11-17-2017, 01:34 PM   #1 (permalink)
Igotgas
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Diff. year 8.1L blocks, diff. cylinder wall thinckness? Diff. bore size ability?

Is it true that the earlier blocks have thinner walls and can't be bored as far as some of the older blocks?

Thank you.

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Old 11-17-2017, 09:52 PM   #2 (permalink)
Drakito
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The only change I know of is that some of the early 01's got a factory forged crank. Everything else was bolt up differences like the newer style timing cover.

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Old 11-17-2017, 11:54 PM   #3 (permalink)
Igotgas
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Thank you Drakito.
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Old 11-18-2017, 11:55 AM   #4 (permalink)
Drakito
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If you can count it, the PSI 8.8l block has thicker castings around the pistons and some revised and updated oiling, block clearancing for the longer stroke, and other minor upgrades. Those blocks aren't cheap though.

Edward Coss on Facebook and/or Raylar Engineering are probably your best bet for minor year differences on the 8.1l. Ed is probably your best bet if you are gunning for a PSI block.

The PSI 8.8l is based on the 8.1, but has the larger stroke/bore. PSI bought the 8.1 rights and changed the design for school buses, industrial pump engines, etc. The heads have been revised with smaller ports for more torque, on a normal build they make 565ftlbs, but only 250hp. They even have turbo propane versions which can push 750ftlbs. Since the 8.8l is an evolution of the 8.1l all the accessory mounting bosses, heads, intake manifolds, etc all bolt right up. They also run forged cranks rated to over 1000ftlbs.

However for the price of an assembled PSI long block(ranging from $11-15k) you could buy a Dart Big M Gen VII block($2k), get it machined and punched out to 565cuin with normal water blocks, or go siamesed block and punch it to 638cuin(~$1k), go fully forged rods/pistons/crank($2k), buy Raylar heads/cam($3k), get SW works long tubes($1k), and have somebody fabricate an intake manifold for you($1k) and only be around $10-11k

I saw a PSI bare block go for $3000 on ebay, without any machining, no main caps, nada.

Dart blocks:
Big M GEN VII – Dart
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Old 11-18-2017, 12:28 PM   #5 (permalink)
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Wholly crap! Great info. I need to go research the: “PSI” block. I have never heard of it. I am familiar w/the Dart.

I am going for a more low buck hot rod here. After putting the CC270/springs in my 8.1 truck, I love this motor. What a 35” tire-frying truck it was w/just a cam, springs, and an aggressive tune. So far I have accumulated an 01 core and a Dart Carb intake. The core is a 100k+, 2001 motor which lost rod bearings on #’s 5&6. I was thinking of selling it and buying a low-mile, good running 8.1L and just changing the bearings, adding another CC270 (not Raylar, but not too expensive), popping on the carb intake & putting it in a pre-smog,1975 car. I know the factory pistons suck, but there will be no boost or extended time, high RPM use. One interested buyer said he wanted a later block because they can take much more bore. It just got me curious.

Thanks so much for illuminating me on the block options Drakito!!!!
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Old 11-18-2017, 12:55 PM   #6 (permalink)
Igotgas
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Interesting

http://www.irv2.com/forums/attachmen...2&d=1323110685
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Old 12-15-2018, 06:44 PM   #7 (permalink)
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I have built more than a few 8.1s and the cylinder walls look like they are the same and in some cases thicker than 1970s 454s. Those blocks all tolerated an overbore of .125" (that's an 1/8" to you decimally challenged readers.) Overbore alone made them 482" and I never had any problems with them on street or strip. We have done them +.140" also (486"). When I freshen my 8.1, I will sonic test the cylinder walls and decide how big to go.
I have had Autotech Pistons make me forged flat top +.030" replacement pistons as a shelf stocking part number. Mine use the newer metric sized narrower rings too. They will also make them in other oversizes for the same cost. Any well equipped machine shop should have a sonic tester, so why not measure and go .060 or .100/.125 over? The boring charge is not that much more, and piston/ring costs are the same. This also unshrouds the valves more for better flow. At +.125 or more the HP gains in unshrouding are more than the gains in cubic inches. An 1/8" overbore should net 525" or so. I may go bigger, as the valves will still be shrouded somewhat. I know how to address that too.....
P.S. the 8.1s are cast from better grade of iron than the old 454s so I may get greedy!
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Old 03-26-2019, 08:53 PM   #8 (permalink)
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I have 3 of the PSI 8.8L block in my garage right now, just the bare blocks with main caps for 2 of them finish bored to 4.35 needing a hone. The third is bored to 4.4" and using a forged Kellog 4.75" crank and custom pistons to make 577 cubic inches. The bare blocks with main caps were under $1000 are the blind head bolt versions with coolant passages between the cylinders vs. the siamesed large bore versions. The other 2 I plan to finish out with just 4.5" cranks to net 535 ci motors that will be N/A. The 577 is getting a Raylar whipple kit and going in a 2003 suburban.
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