Performance Perspectives
Contents
1. LS6 LS2 LS3 and LS7 engine cylinder head bolts are 11mm in diameter the LS9 block uses 12mm diameter bolts Valves and Rockers A few early LS engines feature solid valve stems while most feature hollow sodi um filled exhaust stems The LS7 uses ti tanium intake valves and hollow sodium exhaust valves As for rockers the LS family of en gines breaks down like this the LS1 LS6 and LS2 have a rocker arm ratio of 1 7 1 with intake and exhaust rockers identical the L92 LS3 L99 and LS9 also have a 1 7 1 rocker arm ratio but with the intake rockers offset the LS7 has a 1 8 1 rocker arm ratio with the intake rockers offset Two different rocker arm pedestal rail versions are used One rail is designed for use on the LS1 LS6 and LS2 The other isfor the L92 LS3 L99 and LS9 The rail for the LS1 LS6 and LS2 features the pedestals centered height wise on the rail Each edge of the rail s length is straight The rail for the L 92 LS3 L99 and LS9 locates the pedestals a bit offset with one side of each pedestal extended out The rail for the LS1 LS6 and LS2 fea tures each cylinder s pair of pedestals lo cated 1 901 in on center The rail for the L92 LS3 L99 and LS9 features the pedestal centers located 2 227 in apart center of hole to center of hole LS7 cylinder heads feature individual radiused rocker stands and require no separate rocker arm mounting rail All LS series rocker arms feature a2. 1 70 1 ratio and are semiroller type fea turing a trunion bearing at the rocker s pivot point H ardened rocker tips contact the valve stem tips no roller bearings at the valve contact Aftermarket full roller rockers are readily available through the performance aftermarket All LS rockers are interchangeable for intake and exhaust except LS7 rockers LS7 rockers are unique as the intake rocker features an offset and the LS7 rocker ratio is higher at 1 80 1 as op posed to 1 70 1 for all other LS engines All original equipment style LS series cylinder heads feature beehive shape valve springs All OE spring retainers are steel even in the LS7 This single bee hive spring design eliminates the need for dual springs and allows the use of smaller and lighter retainers E arly LS engines featured composite type cylinder head gaskets Around 2002 GM switched to multilayer steel MLS cylinder head gaskets All remaining gas kets throughout the engines are formed elastic seal type gaskets that are reusable depending on condition of course Regarding MLS gaskets it s very com mon on any engine not just LS when using MLS cylinder head gaskets that you may experience a slight external coolant weeping during the initial engine run This is normal The MLS gaskets feature a special heat cured coating that will con tinue to seal during the initial run As long as the deck surfaces have been pre pared properly and you ve
3. press fit at the rear of the crankshaft and sends crank location signals to a crank shaft position sensor that mounts to the right rear side of the block 24 MOTOR October 2010 Photos Mike Mavrigian blocks with iron heads and in some applications iron blocks with aluminum heads The E scalade is the only SUV application that used an aluminum block and aluminum heads In Corvette Camaro and Firebird applications all LS engines featured aluminum blocks with aluminum heads While there are some similarities between Gen III IV and Gen engines 4 400 in bore spacing 2 10 in rod journal diameter 842 in lifter diame ter valve train oiling through the pushrods and a single piece rear main seal similar to late Gen I II engines the differences far outnumber them F or example OEM block deck height is 9 240 in up from 9 025 In The firing order on all LS engines is 1 8 7 2 6 5 4 3 on Gen I II it s 1 8 4 3 6 5 7 2 eBank offset was changed to 9488 in from the previous 8800 in eGen III IV engines are approximately 100 lbs lighter than Gen Is Connecting rods are shorter 6 098 in vs 5 700 in Piston pin diameter is 940 in vs the pre vious 927 in Crank thrust has been moved from the rear to the No 3 main bearing There is no distributor provision with Gen 11 IV and the list goes on and on The LS1 LS6 feature two different length hex head cylinder head bolts 11x100mm and 11x15
4. 5mm later LS2 LS7 LS3 and L92 engines use only 11x100mm head bolts All LS heads also feature additional 8x1 25x45mm pinch bolts which are located at the inboard edge of each cylin der head All LS heads require ten primary cylin der head bolts plus five 8mm pinch bolts All GM OE head bolts are torque plus angle and torque to yield TTY types which should not be reused and feature OEM thread locking compound All head bolts enter blind holes so none are open to water or oil All LS blocks feature a 4 400 in bore spacing and a bank angle of 45 The blocks are cast from 319 aluminum and feature vent holes cast continued on page 26 Performance Perspectives or drilled in the main webs LS blocks and cranks feature the thrust bearing located at the No 3 main aS compared to the rear located early Chevy engines Crankshaft rota tion is clockwise Note While the Chevy service manual states that the damper bolt should not be reused this is not be cause the damper bolt is TTY it s not Rather damper bolt replacement is rec ommended only because the underside of the bolt head features an OE friction reducing contact surface that may be worn away on a damper bolt that has been installed and removed All LS series blocks feature individ ual main caps that are secured with six bolts four primary vertical bolts plus two side bolts that enter through the outside of the block above the pan rail Because
5. Performance Perspectives TN Mike Mavrigian mmavrigian motor com GM Gen Ill and Gen IV engines offer a seemingly unlimited number of assembly choices for performance engine builders Here we sort through those choices to explain what works and what doesn t he Gen III and Gen IV families of GM engines build upon the pre vious generations of GM small block engines With the LS1 debut in 1997 the family has been in con sumers hands now for almost 14 years and has gained substantial momentum in the performance aftermarket Its high time we took an in depth look at the new small block which is pre dicted to be as popular as the original Gen Chevy small block that began production back in 1955 It was replaced by Gen II engines including the LT 1 LT4 group which were built from 1992 97 The Gen III engine LS1 LS6 started with a clean sheet of paper in terms of design Aside from cylinder bore spacing rod journal diameter and lifter diameter Gen III IV engines have nothing in common with previous Chevy small blocks Gen III IV engines encompass more than just the 5 7 and 6 0L versions Variant engines in clude the 4 8L LR4 the 5 3L LM4 the 5 7L LS1 LS6 the 6 0L LQ4 LQ9 the 6 2L LS3 and LS9 and the 7 0L LS7 Trucks and SUV Gen III engines featured iron Whether you re running injection or a carb without distributor you ll need the reluctor wheel This multitooth steel signal wheel is
6. ash the OE rods and buy some high quality forged steel rods Whenever servicing cracked cap rods the caps must be kept with their respective rods a must The new liners are installed at 270 F and liners are then torqued three times during the cooling process Liner bottoms must also be notched for rod clearance The block is then decked the main caps are installed and the main bore is bored or honed The block is then dou ble vacuum impregnated The liners are then bored and honed for individual pis ton fit M y point is that the LS aluminum block sleeves are not installed in the tra ditional method If resleeving is needed it must be handled only by a shop that is Skilled and experienced in LS sleeving All LS cranks are created equal sort of All feature a 2 65 in main journal and 2 100 in rod journals and all use the same rear main seal All OE cranks are iron except for the LS7 and LS9 which are fitted with forged steel cranks Also the LS7 features a 4 00 in stroke others feature a 3 62 in stroke Although not a permanent component of the crankshaft the reluctor wheel tooth count can vary with either a 24 or 58 tooth count Early LS engines fea tured the 24 tooth wheel which was phased out in favor of the 58 tooth wheel It really doesn t matter as long as you match the tooth count with the appropri ate ignition controller and crank sensor Also be aware that the crankshaft snout is longer by a
7. bout an inch on LS7 LS9 applications to accommodate the two stage dry sump pump drive You can adapt an LS7 or LS9 crank to other LS engines but it s not so easy when try ing to use a short snout crank for a dry sump drive unless an aftermarket suppli er offers a snout extension hub N ote that the LS crankshafts feature a toothed reluctor wheel also called a tim ing wheel or tone wheel used for refer encing crankshaft position The crank Shaft position sensor is at the right rear side of the block and the reluctor wheel is press fit onto the rear of the crank A Different Firing Order All LS series Gen III IV engines feature a firing order of 1 8 7 2 6 5 4 3 This represents four cylinder swaps as com pared to the standard Gen I II small block big block Chevy order of 1 8 4 3 6 5 7 2 Keep this in mind when connect ing spark plug wires The unique firing order was chosen to help smooth out en gine harmonics and theoretically provide a smoother power band The firing order swap is accomplished via the camshaft the layout of the lobes differs from older generation Chevy cams so the change in firing order is not simply a matter of spark plug wire switch ing The LS uses a unique firing order camshaft different from earlier genera tion Chewy firing orders Only an LS style camshaft may be used in an LS engine All OE threaded fasteners in the LS series of engines are metric All OE cylin der head b
8. ctives All Gen III IV LS engines feature a front mounted crankshaft driven gerotor style oil pump that s keyed to the crankshaft snout This is one example of the improve ments that GM designed into its LS engines The oil pump is mounted after the tim ing set is installed This performance build happens to feature head studs LS7 rod requires a unique rod bearing If you re building a real go getter engine from scratch and especially if you re building a stroker nix the OE rods and buy some forged steel rods from one of the performance aftermarket sources such as Scat Oliver Callies Lunati etc Offering high strength and durability quality aftermarket rods are available in a variety of lengths to accommodate a range of popular stroke combinations While the standard small block big block Chevy engines featured an offset connecting rod the LS series features on center connecting rods pin bore in relation to big end bore According to Katech the OE powdered metal rods are surprisingly strong while the primary weak point is the OE 9mm rod bolt Changing to high performance aftermar ket rod bolts such as those from ARP or A1 is recommended At this point there are plenty of aftermarket forged rods from which to choose to provide much greater durability than the OE PM rods The OE rod bolt is 9mm but K atech and other rod makers offer a 10mm rod bolt to work with their connecting rods If you plan to build a h
9. der heads within the LS family are interchangeable among blocks with the exception of the LS7 heads LS7 cylinder heads cannot be mounted to other LS blocks as the wider valve layout would result in valves con tacting the bores Basically we re dealing with two separate cylinder head castings when addressing this later generation of LS engines The LS3 LS9 and L 92 all use essentially the same cylinder head foundation featuring a four digit iden tification number top of head just outside the valve cover rail 5364 The LS7 cylinder head is unique with identification number 8452 The LS3 LS9 and L 92 head is an as cast head with intake and exhaust ports and combustion chambers shaped during the casting process The LS7 cylinder Performance Perspectives OEM Gen III Gen IV cylinder heads feature tapered beehive style valve i springs and small diameter spring retainers Beehive valve springs take ad vantage of the coil shape to minimize unwanted harmonics eliminating the need for dual damper springs However some engine builders prefer to use traditional dual springs especially where higher spring pressures are desired head features intake and exhaust ports and combustion chambers that are fin ished by CNC machining Distinguishing an LS7 head from an LS3 LS9 and L 92 head is fairly easy The LS3 LS9 L92 head features flat rocker pedestals to accept separate rocker arm rails and the port
10. followed cor rect assembly procedures this minor leakage should disappear quickly mM
11. igh performance LS en gine an array of rods are available from aftermarket firms such as Lunati Scat E agle Crower etc These are forged rods that feature machined cap mating sur faces Only the OE rods feature pow 28 MOTOR October 2010 dered metal cracked cap construction The LS6 will safely overbore to the same diameter as the LS1 but the LS6 features a sturdier engine case and is a better choice for overboring The larger displacement LS2 is a less expensive block and features a superior block compared to either the LS1 or LS6 and offers much more interchangeabil ity with L S6 parts H ow large a displacement can you easily obtain by increasing bore diame ter and stroke The LS1 or LS6 origi nally 345 cid can be sized to a max of 427 cid using a 4 000 in stroke The L 2 originally 364 cid can be oversized to 427 cid maxas well Why cant you or shouldn t you go further with an overbore The problem lies with the very common sloppy place ment of the LS aluminum block cylinder Sleeves t s common for the sleeves to be placed slightly eccentric likely due to core shift during the block casting If the sleeves were symmetric and located ex actly where they re supposed to be you could go further H owever to be safe you should consider a max overbore by about 030 to 032 in otherwise you run the risk of thinning out the sleeves in certain spots which can get pretty ugly G eneral ly stick to overbo
12. l OE LS pistons are hypereutectic cast type alloy with high silica content except for the LS9 piston which is a forged aluminum piston required to handle the higher cylinder pressures as sociated with supercharging forced in duction Again this refers only to origi nal equipment strong forged aluminum performance pistons are readily available from aftermarket performance piston WORK FROM makers for any LS application JE Dia mond Ross Probe CP etc Be aware that when areluctor wheel is in place LS type piston No 8 requires a narrower profile at the pin bosses in or der to clear the crankshaft reluctor wheel used for picking up crankshaft timing This is especially important if a stroker crank is being used This is referred to as a siderelief or side notch piston Since the No 8 piston requires this relief all eight pistons must be of the same style in order to accommodate piston weight bal ance matching Common piston height is 006 to 008 in above the deck All OE LS connecting rods are con structed of forged powdered metal and feature cracked caps with the exception of LS7 LS9 rods which are made of forged titanium for both strength and re duced weight Center to center length of most rods is 6 098 in while the LS7 rod is 6 067 in Also only LS7 rods will work with LS7 style pistons due to the design of the piston s inner bracing Finally the October 2010 MOTOR 27 Performance Perspe
13. of this side bolt design which offers superior rigidity main caps can not be ground to reduce the bore size if align boring is needed as this would throw the side bolts out of register If 26 MOTOR October 2010 the main bores must be machined to correct a roundness or center issue oversize O D main bearings would be required The LS7 is the only version that came with forged billet main caps All other LS main caps are powdered metal PM iron LS series engines utilize a front mounted keyed crank driven oil pump All OE LS cranks are cast again with the exception of the LS7 cranks which are forged The LS1 LS6 blocks though sharing the same dimensions differ somewhat with the LS6 block featuring slight changes in main web design for crossover breathing the LS6 block main webs are slightly skeletonized Crank shaft counterweights are cam ground to clear piston skirts This cam grinding also makes crank balancing a bit easier If sleeving is required for a conven tional aluminum block the cylinders are bored to size then honed to size for each individual liner Sleeving an LS block is fairly tricky and L S specific experience is WORK FROM OE connecting rods in all LS engines except LS7 LS9 are powdered met al PM construction While surpris ingly strong for powdered metal if you plan to build additional ponies and especially if your plans include nitrous and or turbo or super charger boost tr
14. olts main cap bolts and rod bolts require torque angle tightening OE cylinder head bolts are also considered TTY style bolts and should not be reused For any high performance build it s highly recommended to use quality per formance aftermarket bolts or studs es pecially for the main caps and the cylin der heads Some main cap bolts or studs for example don t require the OE torque angle tightening procedure but allow torque only tightening All LS series engines feature roller tip lifters and all feature a 842 in lifter body diameter Instead of using dogbones or metal finger trays to locate the roller lifters to prevent lifter rotation in their bores special LS only composite plastic lifter trays are used E ach tray holds four lifters The cylinder block features a large recessed area above each set of lifters to accept these trays During assembly or disassembly the lifters and their tray can be installed or removed as a set Remember any roller lifter must not be allowed to rotate within the lifter bore since the roller tip must remain in plane with the cam lobe All roller lifter setups have some method of keeping the lifters in register to prevent lifter body rotation The LS engines simply use a different plastic tray retention approach F lat sur faces on the lifters align within flat face pockets in the lifter trays This flat to flat engagement serves to keep lifters in plane with the cam lobes Al
15. ring by about 030 in as your maximum Overboring is more safe ly accomplished using an aftermarket block such as those offered by D art RHS and World Products Actually you can order these blocks with your desired rough bore diameters already finished M odifications intended to achieve greater strength and durability include changing to aftermarket forged crank shafts forged connecting rods and forged billet CNC pistons billet main caps high strength aftermarket connect ing rod bolts the use of head and main studs in place of the original head and main bolts and oil pump modification among other techniques Oil pump mods include disassembly deburring the pump inside and out porting the oil entrance polishing the pressure relief section and reassembly Cylinder Heads All heads are aluminum All exhaust ports are standard LS All rockers are bolt downs except for shaft mount C5R and LSX CNC machined bare heads All LS family cylinder heads feature powdered metal valve seats and pow dered metal guides this PM formulation provides the lubricity of bronze and the longevity of cast iron guides All LS1 LS6 and LS2 heads feature tall cathe dral style intake ports LS7 L92 and LS3 heads have rectangular intake ports All LS heads with the exception of the LS 7 feature as cast chambers and ports The LS7 heads feature CN C machined chambers intake ports and exhaust ports According to K atech all cylin
16. s and chambers feature a cast finish The LS7 head has individual rocker arm radiused stands and all ports and chambers have a machined surface In addition the LS3 LS9 and L92 heads feature the tapered beehive valve springs while the LS7 head features straight valve springs Unlike the LS1 LS6 and LS2 heads that feature the tall skinny cathedral style intake ports the LS3 LS9 L92 and LS7 heads feature a conventional rectangular Shaped intake port style Intake port dimensions also vary be tween the two head versions The intake ports on the head used for the LS3 LS9 and L 92 are 1 250 in wide x 2 550 in tall while the intake ports on the LS7 head are 1 350 in wide x 2 40 in tall Which LS heads will physically swap out to the various LS blocks Basically you need to pay attention to the block s bore diameter Running a cylinder head intended for a larger bore size can result in valves crashing into the block F or in stance you cannot install an LS3 LS9 or 30 MOTOR October 2010 LS7 head on an LS1 LS6 or LS2 block at least not without some creative deck bore notching to clear the valves H ere s the rundown summary LS1 and L S6 blocks will accept only LS1 LS6 and LS2 heads LS2 blocks can use LS1 LS6 or LS2 heads as well as L92 style heads which includes LS3 and LS9 heads LS3 and LS9 blocks can use LSI LS6 LS2 LS3 or LS9 heads LS7 blocks can accept any LS head Be aware that while production LS1
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