SBC power up to 750hp.
By Bertie S. Brown:
Does a heavier engine block harm the prospects of a race car?
If you sought the support of savvy oval track engine builders about a 750hp block that has every admirable feature except one—it weighs 30lbs more than the lightest available—they’d state their position in two words: Too heavy!
As a rule, oval track race cars require a greater proportion of their weight at the rear, usually 55 to 60 percent of the car’s total mass. It follows, therefore, that if the front of the car is carrying an additional 30lbs an equal amount or more is required at the rear. This affliction introduces a substantial handling disadvantage, particularly for those cars competing in classes restricted by a minimum weight ruling.
Though mindful of the drag racer who wants to build a lightweight small-block Chevrolet, World Product’s new Motown Pro Lightweight was devised principally to meet the needs of the oval track racer. In this regard it marks a new chapter in engine development for both manufacturer and competitor.
Significantly, the first tangible insight of its potential struck immediately when WISSOTA star Cory Crapser’s prowess won first time out in a Modified race at Cedar Lake Speedway. The engine was built by Tim Ludwigson of Tim’s Automotive Machine in Bloomer, Wisconsin.
Weighing 178lbs, the Motown Pro Lightweight is about 18lbs heavier than GM’s standard 350 Chevrolet block and about 8lbs more than their popular 400 casting. The 350, which is produced in Grade 30 cast iron and giving a yield strength of 32,000psi, uses cylinder walls exposed to 360-degree cooling, while the stronger 400 type features Siamese-style cylinders. The central feature of Siamese cylinders—cylinders attached to each other—is that they sustain less cylinder wall distortion and consequently achieve better ring seal.
The virtues of light weight are irrelevant if the cylinders crack.
The most desirable 400 casting carries the nomenclature 817 and with 4.155in bores employs cylinder wall thicknesses of 0.160 to 0.0180in. Still, it is frequently devastated by fractured cylinders, which is no joking matter to the sufferer’s racing budget. “When they exceed 600hp,” comments engine designer Dick Boyer, “the 817 casting is often destroyed by cylinder wall fractures after about 1000 laps.” With cylinder wall and main web strength foremost in his mind, Boyer’s new lightweight block with similar bore size (4.155in) exhibits a wall thickness of around 0.240in. Further, he cast it in the more robust Grade 40. “Grade 40,” he noted, “possesses yield strength of 42,000psi and, to date, there is no other aftermarket lightweight block made of this grade.”
Why adopt ductile iron main caps? “Because they are adequate for up to 750 hp race engines,” he explains. “Another reason for running them is that their properties are similar to those of the block. The block and main caps expand and contract similarly and bearing wear patterns usually demonstrate a more desirable uniformity.”
As expected, the Pro Lightweight is fitted with 4-bolt splayed caps on numbers 2, 3 and 4 with 2-bolt caps allocated to numbers 1 and 5, which allow easy oil pan fitment. For peace of mind, the main caps are secured by high strength 7/16in ARP bolts.
Extolling the merits of SBC or BBC cam journals
The new block, which is 100 percent US-made, is available with standard small-block cam journals and lifters or, alternatively, with big-block cam journals and 0.904in lifter bores without the added cost of bronze lifter bushings. In addition, a priority-mains oiling system has been revised to accommodate the 0.904in lifter upgrade. The “904 lifters” are considered a worthwhile option when engine speeds exceed 8,000rpm and, conveniently, this block complete with big-block Chevrolet cam tunnels and lifter bores is furnished as a stocking part number.
One further comment on the oiling system is that attention has been paid to the drain-back flow. “The reason for restricting the oil flow in oval track race engines,” explains Dick Boyer, “is that at sustained high rpm the engine will pump the oil up into the valve covers and in a wet-sump engine there is often insufficient oil in the pan to lubricate the engine properly. But on this engine the oil drain-back flow has been increased.” Yet, the block can be drilled and tapped for further restriction should engine builders wish to do so.
Clearance for a 4.000-inch stroke crankshaft is accommodated and connecting rods that offer clearance for the big-block Chevrolet camshaft option with the 4.000in stroke are available. The Siamese cylinder bores come in either 3.995in or 4.120in (resulting in finished sizes of 4.000in or 4.125in) with a maximum bore of 4.185in to allow for large cubic inch displacement.
Dick Boyer, 53, was born in Oskaloosa, Iowa. Probably a gearhead from birth, he bought his first car, a 1969 Chevelle, at age 14. At his Shop Class in High School he built an engine for the machine and drag raced it for two summers.
His career path began in foundry work, continued in an auto repair shop, followed by eight years at Dave Bruns Mid-America Racing Engines. In 2000, he took employment at JR Motorsports managing it for three years. During his tenure he elevated it from a three-person shop to a fourteen-person operation. In 2007 he joined PBM Performance in Louisville KY. During his career he devoted fourteen years to businesses he established himself.
Recently, Boyer, who remains one of the most influential US race engine developers, has pioneered several notable engine blocks including the Man ‘O War (454), the Motown LS and now this innovative Pro Lightweight model. Dick Boyer has wanted a top-flight lightweight racing block for World Products for some time; now they have one.
Part numbers for the new Motown Pro Lightweight blocks are as follows:
083010 – 3.995in Bore, 350 mains, standard SBC cam journal & 0.842 lifters
083020 – 4.120in Bore, 350 mains, standard SBC cam journal & 0.842 lifters
083010-BBC – 3.995in Bore, 350 mains, BBC cam journal and 0.904in lifters
083020-BBC – 4.120in Bore, 350 mains, BBC cam journal and 0.904in lifters