On a stock engine, the following upgrades can improve performance and fuel economy:
A stock LS6 does have more power than a stock LS1. However, they can both make the same power with common upgrades.
The aluminum blocks are not as strong as the iron block LQ4 and LQ9. But, they can be pushed to over 850 hp. with upgraded internals.
Below are some upgrades that improve the performance of the LS1 and LS6 engines.
Engine Block
The 1997-1998 LS1 blocks had thin cylinder sleeves. Honing them 0.005 in. oversized is the safe maximum. Later blocks had thicker sleeves that can be honed 0.010 in. Upgrading to a 4 in. stroke ups the displacement to 383 c.i. or 6.3L.
Another way to increase displacement is to re-sleeve the block. Generally, the 1999-2000 LS1 block is the preferred starting point. It has solid main webbing and better rear oil galley passage. The 1997-1998 LS1 blocks have solid main webbing, but less desirable oiling.
LS6 blocks are not good candidates for re-sleeving. These blocks have windows cast into the bulkheads for better breathing. When machining for larger liners, there is less material to support the cylinder. This will result in a weaker engine block.
With the right sleeves, the bore can be increased to 4.125 in. A 4 in. stroke is common, which increases c.i.d. to 427 or 7.0L.
With boost, sleeved blocks have been pushed to over 2,000 hp. These blocks have added bracing, oiling upgrades, and provisions for six head studs.
Rotating Assembly
The stock pistons are a known weak point. As horsepower increases, so does heat. The stock cooling system was not designed to handle the added heat.
The excess heat can cause the top piston ring to expand. Under enough heat, it will close the ring gap and the ends will butt together. When they do, a broken ring land can result.
Broken ring lands can happen with as little as 450 hp. in road racing or 600 hp. in drag racing.
Another weak point of the stock pistons is that they don’t have valve reliefs. This will limit piston to valve clearance. A set of Forged Pistons should be high on your priority list.
1997-2000 LS1 connecting rod bolts are another weak point. In 2001, the LS1 used the stronger LS6 bolts.
Rods with the 2001+ bolts are good to 500 hp. and 7,000 rpm (naturally aspirated). With boost or nitrous, 700+ hp. can be achieved if rpm is limited to 6,500. Forged Connecting Rods is another popular upgrade.
The stock crankshaft can handle about 900 hp and 7,000 rpm (for a limited time). A Forged Crankshaft upgrade will add strength to the bottom end. Stroker cranks will also add extra displacement. If rods and pistons are replaced, it makes sense to upgrade the crank at the same time.
Performance Balanced Rotating Assemblies make the job easier.
Cylinder Heads
The LS1 heads were good, but the LS6 were better. Both respond well to custom machine work:
- Porting - CNC machined factory heads (LS1 or LS6) can flow over 320 cfm.
- Milling/Decking: Without modifying the intake manifold, LS1 heads can be taken to 62cc chamber volume. The LS6 can be taken down to 60cc. This will create up to 11:1 compression on pump gas. However, be aware that piston-to-valve clearance will be reduced.
- Aftermarket Heads offer a range runner and chamber volumes. Additional deck thickness helps head gasket sealing with power adders.
- Lightweight LS3 valves can be cut to fit the seats.
- Performance valve springs will reduce Valve Float.
A 4-Corner Steam Kit can reduce hot spots that cause #7 ring gaps to butt.
Camshaft and Valvetrain
LS engines respond extremely well to Cam Swaps. Just match the other parts you choose to support it. This is not just Valve Springs and rockers. It includes intake, heads, exhaust, torque converter, rear-end gears, etc.
The trunnion bearings in the stock rocker arms are another known weak point. Retrofit Trunnion Kits fix this. Upgrading to Full Roller Rockers is recommended for over 0.600 in. lift.
Intake Manifold and Throttle Body
If you have an LS1, upgrading to the LS6 intake is inexpensive and popular. The throttle body diameters are identical. Aftermarket Intakes can produce strong gains with a 90mm (LS2) throttle body.
When changing intakes, take note of the throttle body. F-body cars and the 2004 GTO were cable operated. The Corvettes came with electronic throttle control (drive-by-wire).
LS1 and LS6 throttle bodies were both 78mm and had a 3 bolt mounting flange. Aftermarket manifolds usually have a 4-bolt flange.
If hood clearance isn’t an issue, Tunnel rams produce big gains at 6,000+ rpm. Single plane intakes don’t make as much torque or power as the tunnel rams. But, for engines turning 5,500+ rpm (minimum), or subject to nitrous backfires, they begin to make more sense.
Fuel System and Tuning
- Fuel Injectors: The standard 28lb. injectors only support about 390 hp. at 90% duty cycle. Upgrading to larger injectors is needed for more.
- Fuel pumps: The factory pump becomes a limitation at 450 hp. Drop-in dual pumps are a common upgrade.
- Fuel Rails: Factory rails need to be addressed around 700 hp. This will depend on how much extra fuel is being flowed in through Methanol or Nitrous nozzles.
Custom tuning will be required to properly adjust the fuel and ignition systems. Because of the popularity of LS upgrades, chassis dyno tuning with the factory ECU is most common.