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LS1 Dirt

Increasing Gen III Block Displacement on a Budget

Ro McGonegal Feb 9, 2004
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According to the mail, you thought the the LS engine tech we ran a few months ago was interesting but too expensive to replicate for everyday use. Indeed, we have the mild 550/575 C5-R engine ready to go in our Biscayne as well as a '98 LS1 block fitted with a 393ci stroker crankshaft and blower pistons. Neither is a basic buildup, and we apologize for jumping out of sync. Check out the less expensive methods for expanding the internal dimensions of the block noted here as well as those on the Internet.

Hank The Crank (HTC) supplied the rotating assembly for our 451ci C5-R combination. One of his 4340 billet stroker cranks, Carrillo H-beam connecting rods, and CP dished pistons create a combo that, although more expensive than a Mercedes, is virtually indestructible and stems from HTC's Winston Cup experience. These parts form the basis of a much wilder combination, one founded on a twin-turbo application. >>

The all-alloy LS1 engine and its considerable offshoots are rather remarkable in their deep-skirt cylinder-block architecture, free-flowing cylinder heads, reduced mass, and compact dimensions. It is an engine of stature in the high-performance community and therefore should be complemented by the best parts for the money. Hank The Crank is one of the most knowledgeable crankshaft builders on earth, but he is also a businessman. Certainly, the high-buck stuff is intimidating and needs the balance of viable but less expensive alternatives.

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On the Ground

One scenario is to offset grind the stock LS1/LS6 nodular-iron crankshaft, decreasing crankpin diameter from 2.100 inches to 2.060, thus increasing the stroke to 3.650 inches (from 3.620). Then you diddle the bore a little, opening it from 3.897 to 3.908 for a yield of 351 ci. Plug in Speed-Pro hypereutectic pistons (PN H868CP, 0.25 mm) with 0.945-inch-diameter pressed-in pins and reworked (polished beams, shot-peened, big-end honed 0.002-inch oversize) OE powdered-metal connecting rods. Finish the rods with ARP 8740 capscrews (PN 134-6006) that have a 190,000-psi tensile strength or ARP 2000 capscrews (PN 234-6301) with a tensile strength of 220,000 psi.

On the Ground Too

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These BHJ honing plates are an excellent way to ensure repeatable honing procedures in every cylinder. In effect, the plates emulate the weight dispersion of the cylinder heads, making certain the bores remain as straight and true as possible during the process.

Use the LS1/LS6 crank, with its 2.100-inch-diameter crankpin, >> and increase the stroke to 3.700 inches by offset-grinding the pin to a 2.000-inch diameter. In a 6.0L iron block with a 4.030-inch bore and using Carrillo's new A-beam connecting rod, the yield is 379 ci. Combined with an HTC-sleeved alloy block (4.065-inch bore), the displacement becomes an ever-popular 383 ci.

Waist Level

Our recipe for an upgrade to 383 ci (4.030x3.700) is as follows: Add forged HTC/Speed-Pro pistons on 6.125-inch HTC connecting rods with tapered, full-floating pins (2.50x0.927). The flat-top pistons (PN LW2625F) ensure excellent flame travel and include two small valve reliefs. The ring pack (PN R10603) features a 1.5mm plasma-moly top, a 1.5mm second, and a 3mm oil scraper with 10 pounds of tension. For the 383 combo, go with the late '03 cylinder block that uses the standard-flange rear-main seal and Speed-Pro PN LW 2625F +0.060 pistons (4.060x3.700).

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...A Goodson installation fixture attaches to the reluctor wheel and to the flywheel bolt hole.

Differences Between All Gen III LS1 and LS6 Blocks

Federal-Mogul provided the following values, the differences between camshaft-bearing od and the corresponding housing bore (id) in the cylinder block. As you can see, block clearances are not created equally. (All dimensions are measured in inches.) LS1 cam bearing set (1888M)

Position; Min. Shaft; Max. Shaft; Min. Housing; Max. Housing

1 & 5; 2.1650; 2.1669; 2.3276; 2.3295
2 & 4; 2.1650; 2.1669; 2.3177; 2.3197
3; 2.1650; 2.1669; 2.3079; 2.3096

LS6 Cam Bearing Set (1898M)

Position; Min. Shaft; Max. Shaft; Min. Housing; Max. Housing

1 & 5; 2.1650; 2.1669; 2.3675; 2.3476 (GM 12574413)
2 & 4; 2.1650; 2.1669; 2.3276; 2.3295 (GM 12574414)
3; 2.1650; 2.1669; 2.3079; 2.3096 (same as LS1)

Engine Prep and Dyno Results

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Vector (HTC) harmonic balancers with 17 percent underdrive for the LS1 Camaro and Corvette (far left). The others are 7 percent underdriven for the same engines.

Talk is cheap. We wanted a graphic demonstration and some hard numbers to back up the babble. For that round, we went to Glen Elsberry and a 351ci LS1-block-based engine that he'd taken fresh from the dyno cell. Glen arrived at the displacement with an HTC Budget Kit featuring a 0.010-inch overbore and a 0.030-inch-longer stroke (3.905 inches). The Speed-Pro hypereutectic pistons were installed 0.005 inch above the deck surface and cohabit with some port-tweaked 5.3L cylinder heads. The compression ratio is about 11.0:1 with a 63cc combustion chamber that Glen massaged to meet the outer limits of the bores.

Elsberry poured the bumpstick to his LS1 freak: a GM ASA road-race cam (0.525-inch lift, 219/236 degrees duration) with corresponding valvesprings. To feed the thing, he plopped on an LS6 intake manifold, attached an 87mm throttle-body, tapped in 30-lb/hr fuel injectors along with a 60-psi Mallory fuel pump, and used an ambient air temp sensor rather than the MAF. The primary pipes on the special dynamometer headers were 17/8 inches in diameter. Fuel was 91 octane. With the mild ASA cam, the gritty LS1 produced 479 hp. The torque curve was flat from 3,000 rpm.

What It Costs

Speed Pro hypereutectic pistons: $224.00
HTC main caps and ARP studs: $599.00
Reworked OE connecting rods: $190.00 (labor with customer rods)
ARP 8740 connecting-rod bolts: $84.00
ARP 2000 connecting-rod bolts: $120.00
HTC/Carrillo A-beam rods: $1,250.00
Reworked OE LS1 crankshaft: $575.00 (labor with customer core)
BHJ bolt-stretch gauge: $158.69
Vector harmonic balancer: $325.00


CP Pistons
Irvine, CA 92614
Mahle Motorsports
Fletcher, NC
Winona, MN 55987
Automotive Balancing
South Gate, CA 90280
Vector Dampers
South Gate, CA 90280

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