LS ENGINE TECH
The current new generations of GM engines are here to stay and represent the hot ticket for today’s and tomorrow’s hot-dog smallblocks for both street performance and racing applications. It’s time to get up to speed.
by Mike Mavrigian
photos by author
LS6 aluminum 5.7L block.
LS2 aluminum 6.0L block.
The Gen III and Gen IV (Gen IV is the most current) family of GM smallblock engines. With the LS1 debuted in 1997, the LS, or Gen III, has been in consumers’ hands now for over 10 years and is beginning to gain momentum in the performance aftermarket. It’s painfully obvious that it’s high time we started taking an in-depth look at the new smallblock, which is predicted to be as popular as the original Gen I Chevy smallblock that began production back in 1955.
The Gen III engine started from scratch, a clean sheet of paper in terms of design. Aside from cylinder bore spacing, rod journal diameter and lifter diameter, the Gen III has nothing in common with previous smallblocks.
The entire Gen III family of engines includes more than 5.7 and 6.0L versions. Included are the 4.8L LR4, the 5.3L LM4, 5.7L LS1 and LS6, 6.0L LQ4 and 6.0L LQ9.
Truck and SUV Gen III engines featured iron blocks with iron heads and, in some applications, iron blocks with aluminum heads. The Escalade is the only SUV application that used an aluminum block and aluminum heads.
In Corvette, Camaro, Firebird, GTO and Cadillac CTS-V applications, all LS1 and LS6 engines featured aluminum blocks with aluminum heads.
GEN III SIMILARITIES TO GEN I
4.400″ bore spacing
2.10″ rod journal diameter
Valve train oiling through the pushrods
0.842″ lifter diameter
Single-piece rear main seal (similar to late Gen I and Gen II)
GEN III DIFFERENCES
Here are the primary design changes that represent the basics of the Gen III engine:
Block deck height is 9.240″ (up from 9.025″)
Firing order is 1-8-7-2-6-5-4-3 (Gen I/II is 1-8-4-3-6-5-7-2)
Bank offset changed to 0.9488″ (from previous 0.8800″)
Cast aluminum sump
No distributor provision
Lighter weight (approx. 430 lbs. vs. Gen I 531 lbs.)
Connecting rod length is 6.098″ (vs. previous 5.700″)
On-center beam connecting rods (no offset)
Piston pin diameter 0.940″ (vs. previous 0.927″)
Crank thrust has moved from the rear to the No. 3 main bearing
Cam-to-crank centerline distance is 4.914″ (vs. previous 4.521″)
The crankshaft flange has moved 0.40″ closer to the rear of the block
Water temperature is controlled on the intake side of the water pump
Replicated ports vs. mirrored ports
According to Katech’s Jason Harding, the LS1 and LS6 feature two different length hex-head cylinder head bolts (10mm x 100mm and 10mm x 155mm), later LS2, LS7, LS3 and L92 engines use only the 10mm x 100mm head bolt length.
Additional pinch bolts at the inboard edge of the cylinder head uses 8mm x 45mm hex head bolts. All LS heads require 10 primary cylinder head bolts, plus five 8mm pinch bolts. All primary head bolts are TTY (torque-to-yield) type and feature OEM thread locking compound. All head bolts enter blind holes, so none are open to water or oil.
BLOCK AND CRANK NOTES
All LS blocks feature a 4.400″ bore spacing and a bank angle of 45 degrees. The OE aluminum blocks are cast from 319 aluminum and feature vent holes (cast or drilled) in the main webs.
The LS series of blocks and cranks feature the thrust bearing located at the No. 3 main as compared to the rear-located early Chevy engines. Engine rotation is clockwise.
Note: While the Chevy service manuals may note that the damper bolt should not be re-used, this is not because the damper bolt is TTY, because it’s not. Rather, they recommend damper bolt replacement 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 individual main caps that are secured with a total of six bolts. This includes four primary (vertical) bolts plus two side bolts that enter through the outside of the block, above the pan rail. Because of this side-bolt design, which offers superior rigidity, main caps cannot be ground to reduce the bore size if align-boring is needed, as this would throw the side bolts out of register. If the main bores must be machined in order to correct a roundness or center issue, oversize-O.D. main bearings would then be required. The LS7 is the only version that came OE with billet main caps. All other LS main caps are PM steel. However, Caleb Newman with Katech noted that small changes can still be made to the caps without throwing them away, as a small bit of clearance exists at the side holes.
LS series engines utilize a front-mounted keyed, crank-driven oil pump.
All LS cranks are cast, again with the exception of the LS7 cranks, which are forged.
The LS1 and 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).
Crankshaft counterweights are cam-ground to clear piston skirts. Cam grinding also makes crank balancing a bit easier.
Newman noted that Katech developed a proprietary process for sleeving up to a 4.125″ bore on the LS2. If stock bores are desired, it’s more cost effective to buy a new block. If sleeving is required for an aluminum block, all eight cylinders are bored to size, then honed to size for each individual liner. The new liners are installed at 270 degrees F and 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 double-vacuum impregnated. The liners are then bored and honed for individual piston fit.
Katech notes that a GM performance Parts Race Case is available that features 356 aluminum, Siamesed bores, steel billet main caps and 7/16″ main and head bolt locations. This block will accept 4.125″ bores.