Engine blocks
Safety Car
Joined: May 2006
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From: Northern Virginia
St. Jude Donor '08
Melting Slicks
Joined: Feb 2006
Posts: 2,172
Likes: 103
From: Des Moines Iowa
The LS6 and the LS1 use an all-aluminum cylinder case. It’s a "deep-skirted" design (block structure extends below the crankshaft centerline) with six-bolt main bearing caps (four vertical bolts and two horizontal bolts per cap) and head bolt threads deep in the main bearing bulkheads (for minimal block distortion and maximum head gasket clamping force). LS1/6 blocks are semi-permanent mold castings of 319-T5 aluminum. The LS6 case is different from LS1 blocks in the design and strength of the main bearing bulkheads.
As the pistons move up and down, they force air in and out of the spaces (or "bays") beneath them. At high rpm, this reciprocating air flow is violent and really whips up the oil. While the LS1 block has some machined openings between bays, the LS6 block, because the engine has about 500 more usable rpm, needed larger windows at the base of each cylinder to better accommodate "bay-to-bay breathing."
We got the GMPT guys to cut up a LS6 block for us. To above-left of the #2 main bearing bulkhead, at the bottom of the cylinder bore, you can easily see the rectangular bay-to-bay breathing window. Photo: author
Click Image For Larger View
Obviously, cutting windows at the bottom of each cylinder reduces the strength of the block’s key structural area, the main bearing bulkheads. With 40 more horsepower, 400-500 more rpm and even more powerful derivations of this engine to come, the block needed to be even stronger than it would be without the windows. It doesn’t take a rocket scientist to figure, in their ruthless pursuit of power, Dr. John and his engineers had to do more than simply reprogram their CNCs to cut those windows.
Finite element design work along with a lot of thrashing engines to death (in a few cases, literally) on the dyno eventually resulted in the special LS6 block having both the bay-to-bay breathing windows and more overall strength than the LS1 block.
Like the LS1, LS6 uses centrifugally-cast, gray-iron liners which are cast into it at the foundry. Their bore is 99 millimeters (3.8976-in.). ’97 and ’98 LS1s could not be overbored. For 1999, liners changed such that a service overbore of .010-in. was possible and this carries over to the LS6.
LS6’s valley mounted oil separator is similar in concept to the system used a decade before in the LT5. It uses internal baffling to force the crankcase vapors in a circuitous flow. In the process, the oil separates and drains back into the engine. Photo: GMPT Communications
Click Image For Larger View
The LS6 crankshaft is the same cast, nodular iron unit with rolled-fillet journals used by LS1s since 1997. Its stroke of 92 mm (3.6620-in), makes the LS6's displacement 5.665 liters or 345.69 cubic inches. Drilled main bearing journal centers reduce weight and assist in bay-to-bay breathing. For the 2001 model year (MY01), the reluctor wheel, pressed onto the crank to trigger the crankshaft position sensor, was redesigned to enhance sensor signal output. For MY01, all Gen IIIs use a new main bearing that has reduced diameter variation. That allowed a slight decrease in main bearing clearance which reduces the potential for bearing knocks during starts in extremely cold weather from engines having bearings on the high-side of the variation. Lastly LS6 cranks use a lightweight harmonic damper with an aluminum hub which is 2.6 pounds lighter than the LS1 damper.
The sintered, forged and shotpeened, PF1159M steel, 6.1-inch connecting rod introduced in 1997 carries over to the LS6. Beginning in MY01, all Gen III rod cap screws are stronger through a change in manufacturing process used to heat-treat and roll the screw’s threads. This particular change came as a result of the LS1’s use in the American Speed Association (ASA) race series during 1999.
LS6 puts out more power and runs faster so it has a brake-mean-effective-pressure (b.m.e.p.) that peaks about 15% higher than LS1’s. Because of this, LS6 needs a more robust piston. The new piston, as well as all other Gen III and Gen II pistons, are made by Mahle. The LS6 unit is cast of a eutectic aluminum/silicon alloy called "Mahle 142". Both M142 and the previous material, M124, also contain small amounts of copper and nickel, but M142 has slightly more of both. Mahle 142, offers increased strength and less expansion at high temperature. That offers better control of piston-to-bore clearance, both at the skirt and the ring lands. The improved dimensional stability prevents piston noise along with enhancing durability and oil control. Because the LS6 piston material has more favorable expansion characteristics, the slight barrel-shaped profile used in the machining of the piston had to be changed, too.
Above was copied from "Ruthless Pursuit of Power" written by Hib Halverson, and found on the Idaho Corvette web page.
As the pistons move up and down, they force air in and out of the spaces (or "bays") beneath them. At high rpm, this reciprocating air flow is violent and really whips up the oil. While the LS1 block has some machined openings between bays, the LS6 block, because the engine has about 500 more usable rpm, needed larger windows at the base of each cylinder to better accommodate "bay-to-bay breathing."
We got the GMPT guys to cut up a LS6 block for us. To above-left of the #2 main bearing bulkhead, at the bottom of the cylinder bore, you can easily see the rectangular bay-to-bay breathing window. Photo: author
Click Image For Larger View
Obviously, cutting windows at the bottom of each cylinder reduces the strength of the block’s key structural area, the main bearing bulkheads. With 40 more horsepower, 400-500 more rpm and even more powerful derivations of this engine to come, the block needed to be even stronger than it would be without the windows. It doesn’t take a rocket scientist to figure, in their ruthless pursuit of power, Dr. John and his engineers had to do more than simply reprogram their CNCs to cut those windows.
Finite element design work along with a lot of thrashing engines to death (in a few cases, literally) on the dyno eventually resulted in the special LS6 block having both the bay-to-bay breathing windows and more overall strength than the LS1 block.
Like the LS1, LS6 uses centrifugally-cast, gray-iron liners which are cast into it at the foundry. Their bore is 99 millimeters (3.8976-in.). ’97 and ’98 LS1s could not be overbored. For 1999, liners changed such that a service overbore of .010-in. was possible and this carries over to the LS6.
LS6’s valley mounted oil separator is similar in concept to the system used a decade before in the LT5. It uses internal baffling to force the crankcase vapors in a circuitous flow. In the process, the oil separates and drains back into the engine. Photo: GMPT Communications
Click Image For Larger View
The LS6 crankshaft is the same cast, nodular iron unit with rolled-fillet journals used by LS1s since 1997. Its stroke of 92 mm (3.6620-in), makes the LS6's displacement 5.665 liters or 345.69 cubic inches. Drilled main bearing journal centers reduce weight and assist in bay-to-bay breathing. For the 2001 model year (MY01), the reluctor wheel, pressed onto the crank to trigger the crankshaft position sensor, was redesigned to enhance sensor signal output. For MY01, all Gen IIIs use a new main bearing that has reduced diameter variation. That allowed a slight decrease in main bearing clearance which reduces the potential for bearing knocks during starts in extremely cold weather from engines having bearings on the high-side of the variation. Lastly LS6 cranks use a lightweight harmonic damper with an aluminum hub which is 2.6 pounds lighter than the LS1 damper.
The sintered, forged and shotpeened, PF1159M steel, 6.1-inch connecting rod introduced in 1997 carries over to the LS6. Beginning in MY01, all Gen III rod cap screws are stronger through a change in manufacturing process used to heat-treat and roll the screw’s threads. This particular change came as a result of the LS1’s use in the American Speed Association (ASA) race series during 1999.
LS6 puts out more power and runs faster so it has a brake-mean-effective-pressure (b.m.e.p.) that peaks about 15% higher than LS1’s. Because of this, LS6 needs a more robust piston. The new piston, as well as all other Gen III and Gen II pistons, are made by Mahle. The LS6 unit is cast of a eutectic aluminum/silicon alloy called "Mahle 142". Both M142 and the previous material, M124, also contain small amounts of copper and nickel, but M142 has slightly more of both. Mahle 142, offers increased strength and less expansion at high temperature. That offers better control of piston-to-bore clearance, both at the skirt and the ring lands. The improved dimensional stability prevents piston noise along with enhancing durability and oil control. Because the LS6 piston material has more favorable expansion characteristics, the slight barrel-shaped profile used in the machining of the piston had to be changed, too.
Above was copied from "Ruthless Pursuit of Power" written by Hib Halverson, and found on the Idaho Corvette web page.
Drifting
Joined: Sep 2006
Posts: 1,757
Likes: 13
From: Stillman Valley Illinois
I remember reading somewhere that one or the other had a "bulls-eye" casting mark in the block, just forward of the passenger side cyl. head but I cant remember which is which. Does anyone know?
Thread Starter
Burning Brakes
Joined: Jul 2004
Posts: 951
Likes: 0
From: La Plata MD
Thank you all
The reason for this post was to find out if it was worth the cheaper price to just buy a LS1 block to do a forged build up or spend a few $ more to buy a LS6 block to start with.
I have a Z06 so I guess I'll stick with the LS6 block
The reason for this post was to find out if it was worth the cheaper price to just buy a LS1 block to do a forged build up or spend a few $ more to buy a LS6 block to start with.
I have a Z06 so I guess I'll stick with the LS6 block
