Summary of the Many Gen I, II, and III Similarities and Differences
In case you are wondering what is similar and what is different on the Gen III V-8 versus the previous Chevy small-block design, here is a chart.
Similarities
* Gen III has the same 4.4-inch bore spacing as Gen I and II
* 90-degree angle spacing of cylinder banks
* Two overhead valves per cylinder
* Valvetrain oiled through lifter gallery/lifter/hollow pushrod system
* Connecting rod crank pin diameter of 2.1-inches
* Lifter diameter of 0.842 inch
* Single-piece rear crank seal (like on later versions of Gen I and II)
* Starter located on lower passenger side of block
* Oil filter located on lower driver side of block
| Differences | Gen III | Gen I and II |
| Block length | 519.0 mm (LS1) | 553.2 mm (LT1) |
| Block width | 460.0 mm (LS1) | 434.6 mm (LT1) |
| Block deck height | 9.240 inch | 9.025 inches |
| Firing order | 1, 8, 7, 2, 6, 5, 4, 3 | 1, 8, 4, 3, 6, 5, 7, 2 |
| Cylinder bank offset | 0.9488 of an inch | 0.8800 of an inch |
| Crank main caps | 6 bolted – 4 verticle, 2 horizontal, | Mostly 2-bolt mains, some splayed with 4 bolts |
| Distributor Drive | No distributor capability | Distributor drive at rear of cam |
| Sensors | Engine block–mounted; | No direct electronic crank
and cam location cam sensors |
| Weight | 430 lbs for a complete LS1
(add approximately 88 lbs for iron truck block) | 531 lbs for most complete Gen I/IIs |
| Connecting rod | 6.098 inches long | 5.700 inches long offset |
| Piston pin diameter | 0.940 inch | 0.927 inch |
| Crank thrust bearing | No. 3 (center) | Rear main bearing |
| Cylinder head ports | All Replicated | Mirrored images of each intake
and exhaust ports |
| Crank flange location | 0.040 of an inch closer to bellhousing mount on block than Gen I/II | |
| Thermostat location | Intake side of water pump; | Exit side of water pump |
| Intake design | No coolant or hot water passes through oil; | Touches intake and oil hits bot tom of intake |
| Intake construction | Intake made of nylon; | Intake made of cast-iron or
aluminum |
 If you like what you see here,...  If you like what you see here, make sure to order this book, as it has much more detail on everything that is in this story. The full history of the engine's creation, a full breakdown of the factory engine components and assembly methods, installs of aftermarket components with dyno testing, and details on removing and replacing the Gen III engine from production vehicles. |  The book is loaded with multiple...  The book is loaded with multiple engine buildups that show step-by-step details of everything from bolting on 100 hp without tearing down the short-block to building complete Gen III V-8 engines that make everything from 500 hp to more than 1,000 hp. | |
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