Reprinted.
Increasing Gen III Block Displacement on a Budget
By Ro McGonegal
Photography: Ro McGonegal
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.
On the bottom side, HTC applies billet-steel main caps and secures them evenly with ARP studs and the factory torque specification. |
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To hold the price of the conversion down, HTC reworks the OE powdered-metal connecting rods for durability and strength. They are fitted with ARP rod bolts. |
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In the interest of longevity and durability, the stock LS1/LS6 rods are shot-peened and polished, and the big end is honed 0.002-inch oversize. |
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Upgrades include a forged-steel spiff, an HTC/Carrillo A-beam... |
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...and a more expensive Carrillo H-beam variant. |
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HTC reworks the stock LS crankshaft (right), streamlining the core, and subjecting it to an ionization process. |
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For $1,995, the ultimate application, HTC's E-4340 forged crank, as designed by Scott Bechtloff and Marty Cimaglia, packs more than 40 years of drag race, Winston Cup, and hot street experience. |
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A BHJ bolt-stretch gauge is used for properly setting up the connecting rod for resizing, obtaining the proper torque load when the bolt is installed in the engine, and monitoring the condition of the bolt while in use. Measure the length of the bolt in a relaxed (untorqued) state. Record the number. When it's time to tear the motor down, take another measurement. Anything greater than 0.001-inch stretch is reason to replace the fastener. |
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Budget variants includes the Speed-Pro hypereutectic flat-top pistons and OE pressed-in 0.945-inch pins. Static compression ratio with a 63cc chamber is 11.0:1. |
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Our piston upgrade is represented by CP/HTC dished-top forgings... |
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...Note the sly gas-port holes peppering the top ring land (arrows) that aid cylinder sealing by forcing the ring outward to the cylinder wall. |
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Mahle Motorsports offers a lightweight alternative for the HTC budget build. Though relatively new on the hot-rodding scene, Mahle has been the OE supplier to Porsche and other high-dollar imports for decades. |
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Thank guru Russ Hayes for this hot-off-the-forge Speed Pro piston... |
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...It carries PN L2621F and is available in 3.898- and 3.908-inch bore sizes. |
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Questions concerning the efficiency and longevity of Mahle products should be answered here. This piston was taken straight from a C5-R 427 Corvette that went the 24-hour distance at Daytona. |
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ARP is now producing connecting-rod bolts for the LS-series Gen III engine. |
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Hank relies on Speed Pro 152M main-bearing shells and PN 8-2555CP 40x2 connecting-rod inserts for all conversions. |
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In order for the reluctor wheel to work properly, it must be installed flat and straight on the crankshaft flange... |
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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
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
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