Modifying the LS for more power is as easy as falling off a log, to apoint, then some tough issues arise, especially if you are building ahigh-rpm race engine. But until you reach that point, the LS respondsnicely to boring and stroking, improved cylinder head flow and theyrespond especially well to power adders.
The only real chink in the LS armor is that GM’s cylinder headdesigners didn’t leave any room for a proper high-lift, high rpmvalvetrain. It’s essentially the same problem the Gen III Hemi’s have −no room under the valvecover. The stubby LS rocker is just aboutstanding on end at lifts above .650?, and there’s not enough realestate to install a longer pivot length rocker and shaft assembly thatprovides good rocker geometry. Some companies like Mast Motorsports aretaking matters into their own hands and designing heads like its Mozezthat has a larger rocker area and uses an SB2 small-block valvecover.
But that’s okay, especially if you decide to build for torque insteadof rpm. The LS engine readily responds to stroker crankshafts withcorresponding cylinder heads capable of feeding the increaseddisplacement. The LS has always been thought of as a replacement forthe small-block because of the similar 5.7L displacement, but inreality, the engine responds more like a big-block. You rarely hear ofanyone with a truck complaining that they want their old 454 back inplace of their new 6.0L LS, because he 6.0L tows almost as well with alot better fuel mileage.
Speaking of displacement, GM has built several production versions ofthe LS ranging from a 4.8L truck engine to the 7.0L Z06 Corvette ratedat 505 naturally aspirated horsepower. They did this with twogenerations of engine blocks Gen III ’97-’05 and Gen IV ’05-’11),available in both aluminum and iron. GM even produced a front wheeldrive version, the LS4 that has a unique bellhousing bolt pattern, sobe aware of that one when scrounging the salvage yards for cores. GenIII engines were built with three different bore sizes 96.01mm (4.8Land 5.3L truck blocks), 99mm (LS1, LS2, LS6) and 101.6mm (6.0L truckblocks). Gen III stock stroke cranks were 83mm (4.8L truck) and 92mmfor both LS1-LS6 and 6.0L truck engines.
The LS series of engines uses a cam position sensor that provides theECU with timing information. Part of this system is a reluctor wheelattached to the crankshaft. It is important to take note of thereluctor wheel tooth count as most Gen III engines (up to 9/05) used24-tooth reluctor wheels and 58X-tooth reluctors for the Gen IVengines. There’s actually much more involved than tooth count becausethe reluctor wheel is ECU specific. How and where the cam positionsensor is mounted, and with which type sensor 1X, 2X or 4X, adds to theconfusion. If your customer is converting to drive-by-wire, it addsanother layer of complexity. We don’t have room to completely coverthis subject, but there is lot of information available on the LSforums like LS1Tech, LS2.com and others. Just understand that this is acritical consideration with any LS engine build.
In 2005 Gen IV engines were introduced with now recognizableperformance icons like the LS3, L98 and the awesome LS7. A couple ofthings that could trip up the average engine shop is that some of theseengines came from the factory with variable valve timing (VVT) and/oractive fuel management. So do your research when building a strokerengine for a customer and make sure you know what you are dealing with.Gen IV blocks came in four sizes 96mm (4.8L and 5.3L truck), 101.6mm(LS2, LS98 and 6.0L trucks), 103.1mm (LS3, L92 and L99) and 104.8mm forthe LS7. Stroke selection remained the same as the Gen III with 83mmand 92mm, plus the addition of a 101.6mm stroke for the LS7.
Another LS block from GM worth mentioning is the aftermarket LSX ironblock with a raised cam and deck height that accepts bores and strokesto 108mm x 114.3mm (4.25? x 4.5?). These blocks are capable of handling2,500 hp with the proper rotating assembly, cylinder heads and poweradder.
So with a better understanding of the different LS engines produced bythe factory, let’s take a look at stroking them for more performance.We contacted Horace Mast of Mast Motorsports for some advice as hiscompany is dedicated solely to engineering and supplying complete LSengines to the aftermarket. His best advice is limiting the stroke to101.6mm (4.00?) in any standard deck height LS block. (Horace says thatmost of his engines end up with a 9.230? deck height after surfacing.)This will provide up to 416 cid for an LS3 and 427 cid in an LS7. Hehas built LS3 and LS7s with 4.100? stroke cranks, but says that thehave poor long-term durability, and he doesn’t recommend them,especially for daily driven street cars.
The problem with strokes in excess of 4.00? in a LS motor is that thepiston skirt is not properly supported at the bottom of its travel,causing a lot of rocking and premature wear. In fact, Mast’s 4.00?stroke engines use specially designed Mahle pistons to minimize thisproblem and to provide a more stable ring package. Horace maintainsthat the same holds true when using the taller deck LSX block – Mastlimits displacement to 454 cid even though 511 cid is possible. Eventhen Mast warns its customers about using these engines as dailydrivers because there are too many compromises in the area of pistonstability.
Other companies like Flatlander Racing who sell K1 stroker kits for LSengines agree with Mast on the 4.00? stroke for normal deck heightmotors, but are more aggressive on the LS7 putting the limit at 4.120?stroke and 4.250? for the LSX blocks.
Another issue with LS engines is making sure that your bore size iscompatible with the cylinder head you will be using. Most companiesselling stroker kits do a good job at listing what heads will work withwhich kits. However, if you are unsure, take a little time to researchwhat combination will work for you. It’s just one of those quirky LSthings that you didn’t have to worry about with traditional 23-degreeChevys.
So let’s look at what’s available in LS stroker kits from some of theaftermarket’s top vendors. Prices vary widely from top shelf U.S. madecomponents to lower priced imported components. Another contributor toprice is the completeness of the rotating assembly, and whether itcomes balanced or not. You can piece together your own assembliessourcing a crank from supplier X and pistons from supplier Y, but bythe time you are done with ordering, shipping and deadlines, you aremoney ahead sourcing a complete rotating assembly from a single source.Virtually all of these kits contain forged cranks, forged rods andpistons plus complimentary rings, bearings and pins.
Eagle has a large number of rotating assemblies for sale that cover awide range of displacements and compression ratios. Its kits forstandard LS engines feature 4340 forged cranks in 3.622?, 4.000?,4.100? and 4.125? strokes, which depending on the block and bore sizecan net engine sizes from 347 cid to 434 cid. They all use 6.125?-longforged H-beam connecting rods with either Mahle or Arias forged pistonsin various compression ratios. They also offer 4.250?-stroke rotatingassemblies with 6.460?-long rods for GM LSX tall-deck blocks for up to454 cid, and 4.250?-stroke cranks with 6.560?-long rods for WorldProducts Warhawk tall deck blocks.
Lunati offers engine assemblies for LS1, LS2 and LS6 applications in avariety of bore and stroke combinations. All of its assemblies featureLunati Pro Series non-twist forged cranks and Wiseco Forged andCNC-profiled pistons. They are available in the followingdisplacements: 347 cid, 383 cid, 395 cid, 408 cid and with a 4.125?bore block − 427 cid. You also have a choice of the more expensiveI-beam or less expensive H-beam rods, all 6.125? long.
Scat breaks its LS rotating assemblies down into two groups: street andstrip and competition. They also offer these kits balanced orunbalanced, you decide. They offer three different stroke 4340crankshafts at 4.000?, 4.125? and 4.250? strokes. Two different rodstyles, forged 4340 H-beam and forged 4340 Pro Comp I-beam 6.125?-longare included depending on the kit. Forged pistons, rings, pins andbearings are also included. Displacements from 365 cid to 461 cid areavailable.
K1 is part of the Wiseco/JE/SRP piston group and has collaborated withWiseco to build a really comprehensive catalog of LS rotatingassemblies, plus they have the advantage of designing components as aunit, which reduces mass and results in assemblies that are easier tobalance. The K1 cranks are forged out of 4340 steel, core-hardened andnitrided for journal surface hardness. K1 connecting rods are offeredin two styles – forged 4340 and billet 4340. They are weight-matchedwithin a gram and come with pin bushings for improved frictionreduction. The pistons are all forged lightweight Wisecos with metricring packages. K1 offers kits from stock stroke 3.622? as well as4.000?, 4.125? and 4.250? stroke cranks. Rod lengths vary from 6.098?to 6.365? depending upon stroke and compression height. Displacementsrange from 347 cid to 471 cid.
Probe has divided its LS rotating assemblies into two categories – itsDominator series features lightweight forged I-beam connecting rods andits Pro-Street series features forged 4340 H-beam rods. Both series useforged SRS pistons in a wide variety of compression ratios with toolsteel pins for the Dominator kits. The forged Probe rods come in 6.125?or 6.200?-lengths depending on the assembly. The forged 4340 steelcranks are available in 3.900?, 4.000? and 4.125? strokes. All kits arecomplete with rings, bearings and piston pins.
While these manufacturers are just a sampling of what’s available forLS stroker kits, it gives you an idea of just how many combinations areavailable so that you can build almost exactly what your customer wantsor needs.
Going to really long strokes and huge displacements require theaftermarket blocks mentioned previously. The choices are GM’s iron LSXblock, RHS’s LS Race Block and World Product’s LS Warhawk block. Let’slook at GM’s LSX engine first introduced by GM Performance Parts at the2006 SEMA show. The LSX is an all-new cast-iron racing block based onthe LS7 engine. It was designed with help from drag racing legendWarren Johnson. It offers displacements ranging from 364 cubic inchesto 511 cubic inches (4.25? (108 mm) bore x 4.5? (114.3 mm) stroke) andis capable of withstanding 2,500 hp. This block incorporates two extrarows of head-bolt holes per bank for increased clamping capacity. Thesix-bolt steel main caps are the same ones used on the LS7 engine. Ifyou can handle the weight penalty of an iron block over aluminum, theLSX is a good value.
Racing Head Service’s (RHS) LS Race Block is cast out of A357-T6aluminum with press-in spun cast iron liners that are available in twobore sizes 4.125? and 4.165?. The raised cam position can handle up toa 60mm cam core and a relocated oil galley provides room for a 4.600?stroke crankshaft and directs oil to the main bearings first. Two deckheights are available: standard (9.240?) and a tall version at 9.750?.The RHS block is chocked full of other features like multiple enginemount options, dry sump connections and access to the two additionalhead bolt hold downs per cylinder.
World Products Warhawk LS Race Block is another max effort blockcapable of handling huge power numbers. Cast out of 357-T6 aluminum theWarhawk features beefy 1045 steel cross-bolted main caps retained withmassive 7/16? main studs and cross-bolts. The Warhawk comes in two deckheights, a tall 9.800? and the standard 9.240? deck. Optional head bolthold-downs (two per cylinder) help seal combustion pressures on highlyboosted engines. Two bore sizes are available – 4.000? and 4.125? andthere is room inside to clear a 4.500? stroke crank. Like the RHSblock the Warhawk has several engine mount locations.
As you can see there is virtually limitless ways to build a largedisplacement LS engine. And when you consider the plethora ofaftermarket cylinder heads, intake systems, and power adders, it makessense that the LS engine is going to represent a big piece of anyperformance shop’s business. We hope this brief look into LS strokerengines has whetted your appetite to build a few large LS derivatives.Hot rodders are stuffing these engines into anything they can get theirhands on because the combination of lightweight and big power is toohard to resist. With very little effort you can get old fashionbig-block power in a tight little package.
To download stroker kit charts, click here (Stroker Charts.pdf)
For a complete list of stroker kit suppliers, click here (Stroker Suppliers.pdf)
LS Stroker Sources:
K1/Wiseco Performance Products
Eagle Specialty Products
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