Affordable Small Block Race Engine - Cheap Street Secrets

Cylinder head choice came down to the less exotic, less costly iron GM Vortec head (PN 12558060). Cheap Street rules permit milling of the heads, but porting and other mods are strictly forbidden-especially if you're caught!

Although not the best-flowing head available, the iron Vortec does have a relatively efficient combustion chamber. Thomson admits milling the heads "as far as possible" while preventing valve/piston interference. Maximum valve sizes permitted are 2.025, intake, and 1.610 exhaust. "That's exactly what we used," says Thomson. "We wanted the biggest valves possible while still staying in the rules."

Other inexpensive, off-the-shelf parts include the Crane "Gold" roller-tip 1.5-ratio rocker arms. Why only a 1.5 ratio, and not a 1.6 or 1.7? With the cam's relatively low lift, Thomson says there's nothing to gain with a higher ratio rocker arm.

The single plane intake manifold was sourced from GM Performance because of its need to fit the Vortec heads. The manifold has slightly raised runners that provide a straight shot into the heads' intake ports.

Per the rules, the carb meets the 750-cfm limit. Thomson used a Barry Grant Mighty Demon 750, which, for racing, offers benefits like billet metering blocks, a glass window to check the level of the float bowl and easily adjustable air bleeds. Described by Barry Grant as an "aggressive" street carb, the Mighty Demon takes only minutes and about $30 worth of materials to transform into a full race carb. The basic carb runs about $499.C

Another lightweight addition to the engine was this set of contoured valve retainers. The contour shape trims weight, as do the drilled faces. Pretty cool, huh? Also, Thomson says two sets of valve springs were used to build the engine: one set of "soft" springs to break in the cam, the other used on the engine for racing.

Cheap Street's nitrous regs also stipulate a single plate with no more than two spray bars (one for nitrous, one for fuel) and a maximum jet size of just .063-inch. That's not a large jet by anyone's measure, but it's enough to give most Cheap Street competitors a 150-horse shot. Wise racers know, too, there are ways to get more from the nitrous system while sticking to the .063 jet size.

Cheap Street's only legal power adder is nitrous oxide, and it's limited to a single-stage system and a 10-pound bottle. Barry Grant's Nitrous Works system (PN 10010) was used on Thomson's build-up.

Along with the carb and nitrous system, Barry Grant also supplied the engine's fuel pump, pressure regulator and fuel filter.

A GM/MSD electronic distributor was used on the small block so that the corresponding ignition box could be used to help retard ignition timing, as needed, with the nitrous system.

In addition to the nitrous system plate, Thomson also added a 1-inch phenolic spacer to the top of the intake manifold. It helps maximize intake volume, providing help to the somewhat restrictive Vortec heads.

Without nitrous, Thomson's 355-cube, mystery-cam Cheap Street small block peaked at 479 horses at 6,100 rpm and 447 ft-lb of torque at 5,100 rpm. With the juice, output jumped to 649 hp at 5,900 rpm and 611 ft-lb at 5,700 rpm. Even without nitrous, however, the engine makes more than 400 ft-lb at 4,400 rpm and doesn't trail off until 6,300. The power is more than reasonable for a 355 with flat-top pistons, proving there are a few speed secrets within the small-block's confines that Brian Thomson is keeping.