Q:For the LS1 aluminum block, exactly how much overbore is safe for a turbo? What is the largest bore for this block? i would need to go 0.020-inch over to clean up my cylinders; is this block tho usable?




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A:Compared to beltdriven superchargers or nitrous oxide, today"s digital controls make it fairly easy to manage big power profit on a turbocharger. Back officially GM claims an LS1 block "has to be tested at over 400 hp," real-world ar experience suggests short-duration competition LS1 blocks have endured at least double that through the conventional bore size—for a while, anyway.


Note we claimed "with the standard bore size." Bluntly, in terms of accepting traditional standard overbores, LS1 blocks should be considered "throwaway" castings: castle accept practically no overbore at all, even if running generally aspirated. Prior to the advent of aftermarket aluminum blocks, trick (and high-buck) cylinder sleeving methodology was essential to achieve large bore size on manufacturing LS1 block castings (see Pit Stop, Mar. 2014).


The reason: Aluminum LS1 block have an extremely thin, centrifugally cast iron liners. The blocks space actually actors in place roughly these liner (rather than the normal practice of pressing the liners right into the block after ~ it has actually been cast). Top top the really earliest LS1 blocks created in 1997 and 1998, the sleeves may not constantly be positioned 100 percent perpendicular within the block casting, meaning that the final-bore sizing and honing process left one side of the walls thinner 보다 the main engine architecture specs referred to as for. Therefore, 19971998 LS1 5.7L aluminum blocks can only be safely honed (not also bored!) simply 0.004-inch over the stock bore diameter. Improved liner placing in 1999-and later 5.7L LS1 blocks and also all LS6 blocks permit boring up to 0.010-inch oversize. Either way, you room SOL in ~ wanting to walk 0.020-over because that a reputable LS1 aluminum block rebuild.


There are several ways to identify early from so late LS1 block castings. One is by check the oil-passage configuration situated on the rear block face. Visible with the rear cover removed, 19971998 blocks the can"t it is in overbored likewise have a shallow oil-transfer i that boundaries equal oil flow to the key lifter oil galleys (photo). Finish original beforehand assemblies likewise have perimeter-bolt valve covers, matches the center-bolt covers offered on 1999-and later engines. Of course, over there are always the block casting numbers situated at the back of the block on peak of the driver next of the bellhousing flange. Back there might be others, verified casting No. 12550592 absolutely designates one early, first-design, "undesirable" block.


So if your LS1 block is supplied up, what space the realistic alternatives? If on a budget, the best approach is grabbing a sleeveless iron van block out of the wrecking yard. Plentiful, cheap 4.8L and also 5.3L iron truck blocks are typical as dirt and also usually have actually sufficient wall thickness to expropriate at least a 0.118-inch overbore (with about a 0.020 "safety margin" left over because that future cleanup rebuilds). A 0.118-inch overbore bring them the end to 3.898 inches, the exact same as the LS1 aluminum block.


Although fairly rare (and hence an ext expensive 보다 their steel sibling), there are additionally some 5.3L aluminum blocks; several sources report the the external diameter that the sleeves provided in those blocks is the very same as the sleeves used in 5.7L LS1 blocks—which would allow boring 5.3L aluminum block to the LS1 5.7L block size without occurs the 7080-pound load penalty incurred once using the stole block.


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Then there"s the larger-displacement iron 6.0L truck blocks that have 4.0-inch bores; they have the right to be punched 0.060-over come 4.060 customs (although for serious power-adder usage I"d back that under to 4.030). Manufacturing iron blocks v moderate overbores have survived with 1,100 hp in turbo apps without filling the block with concrete.


Incidentally, some rare 4.8L/5.3L iron block castings deserve to be bored all the way out to the 6.0L engine"s 4.0-inch boring size. Together reported by Lingenfelter Racing"s Jason Haines, that"s since (you guessed it), this is a rarely universal spreading used interchangeably at the foundry to make 4.8-, 5.3- or 6.0L engines. Look for "4.3L-5.3L-6.0L" (all three displacement designators) cast into the block"s front passenger side.


For the dad Warbucks crowd, heavy-duty nonproduction GM (Chevrolet performance Parts/CPP) and also aftermarket blocks room available—some of them have the right to accept up to 4.200-inch bores and have lived at the 2,500hp level. They likewise have much more clearance for big stroker cranks, six-bolt head-bolt patterns, optionally obtainable taller deck heights, and plenty of hardcore, professional-engine-builder-friendly features.


Production GM Gen III/IV"LS-Series" Overbore GuideCompiled using info from a range of sources, this table is exactly to the best of our knowledge—but corrections or comments room welcome. Constantly sonic-check the block first before going for the max provided overbore. Gen III and IV architectures execute not directly interchange together a finish assembly. All dimensions in inches uneven otherwise noted. GenLitersTypical RPO CodesBlockmaterialStock CIBoreStrokeMax OverboreMax Bore-SizeMax Overbore CIIII4.8LLR4Iron293.63.783.270.1303.910314.1III5.3LL59, LM7Iron325.23.783.6220.1303.910347.9III5.3LL33, LM4Aluminum325.23.783.6220.1283.908347.6III5.7LLS1 (19971998)Aluminum345.83.8983.6220.0043.902346.5III5.7LLS1 (1999up), LS6Aluminum345.83.8983.6220.0103.908347.6III6.0LLQ4, LQ9Iron364.14.03.6220.0604.060375.1IV4.8LL20, LY2Iron293.63.783.270.1303.910314.1IV5.3LLY5, LMGIron325.23.783.270.1303.910347.9IV5.3LLC9, LH6, LH8, LS4Aluminum325.23.783.6220.1283.908347.6IV6.0LLY6Iron364.14.03.6220.0604.060375.1IV6.0LL76, L98, LS2, LFA, LZ1Aluminum364.14.03.6220.0304.030369.6IV6.2LL92, L94, L99, L9H, LS3, LS9, LSAAluminum376.14.0653.6220.0204.085379.8IV7.0LLS7Aluminum427.64.1254.0000.0054.130428.7Notes: some rare 4.8L/5.3L iron truck blocks deserve to be bored out to 4.00-inch (see message for details). LS4: modification block because that transverse engine installations only.


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Aftermarket and Nonproduction LS Block Overbore GuideBrandSeriesMaterialAs-Delivered boring OptionsMax BoreMax StrokeMax CICPP (GM)C5RAluminum4.1174.1604.10445.8CPP (GM)LSXIron3.880, 4.065, 4.1854.2004.50498.8DartLS next BlockAluminum4.00, 4.1254.165Not listedDartLS following BlockIron4.00, 4.1254.220Not listedRHSGM LS Aluminum race BlockAluminum4.100, 4.120, 4.125, 4.160, 4.1654.1654.600501.4WorldWarhawk LS1/LS7 ChevyAluminum3.990, 4.1204.1554.500488.1WorldMotown LS steel BlockIron3.995, 4.1204.200Not listedNotes: Achieving provided maximum stroke might require optionally-available "tall-deck" variation plus little base circle camshaft. Darton MID sleeve option permits up to 4.220-inch bores.