Affordable Small Block Race Engine - Cheap Street Secrets

Builder Brian Thomson Reveals And Hides Power Secrets During Our Look Inside PRO "Claimer" Engine

Barry Kluczyk Jan 1, 2004 0 Comment(s)
Sucp_0401_03_z Affordable_small_block_race_engine 355_ci 1/22

Cheap Street rules dictate a 385-cid maximum displacement, although there's a 10-pound penalty for every cube over 365. And with this engine destined for a Third-Gen Camaro, which already carries a weight penalty compared to pre-'75 cars in the class, the owner didn't want to add even more weight with a bigger-inch engine. So, this 350 block received just the standard .030-in. overbore, for a grand total of 355 ci.

The rules are pretty simple: build a low-dough motor with an iron block, off-the-shelf heads, an off-the-shelf carb, and a shot of juice. Don't go overboard on the trick parts, though, because the guy next to you can buy your engine for $3,000.

Welcome to Cheap Street competition. PRO bills it as the ultimate "real world" class in its pro series, with the competitors driving street-based combinations-more or less. And to keep the competition relatively attainable to checkbook-challenged racers, the class has adopted a longstanding tradition in the sportsman circle track world: claimer engines.

In Cheap Street, a racer who believes another competitor might have an unfair edge can claim that competitor's long block for $3,000, as well as a transmission for $2,000 and even the carburetor for $500. It keeps the players on a level playing field on oval tracks, and, theoretically, ought to do the same in this heads-up, wheels-up class.

But drag racers are a notoriously crafty bunch, and being competitive in Cheap Street requires at least 600 horses and high-9-second e.t.'s. That's a lot to ask of car weighing a minimum of 3,200 pounds and powered by a stock-headed small-block.

Sucp_0401_04_z Affordable_small_block_race_engine Main_bolts 2/22

Fortunately, the engine was a four-bolt-main 350. Because main bolts stretch when installed and removed, which is likely to happen during the course of the racing season, a few bucks was spent to install studs for securing the main caps. This also makes removal and re-installation a little quicker.

We recently followed the build of a Cheap Street engine at Thomson Automotive, a Detroit-area shop run by longtime racer Brian Thomson. He's been building drag race and circle track engines for more than 20 years and he said he was confident he could find the maximum power with the parts allowed.

But what are the parts allowed? Good question. Here's an overview of the Cheap Street rulebook:
*Iron small-block displacing no more than 385 ci
*Mass-produced cast iron or aluminum heads; milling
permitted, but no porting, welding or epoxy allowed
*Maximum valve sizes of 2.025 intake, 1.610 exhaust
*Flat top pistons only
*No roller cam allowed
*Nitrous oxide allowed, but only with single stage system, maximum jet size of 0.063 inch.
*No more than a single 750-cfm carburetor; "typical" carb mods allowed
*Exhaust pipes have a maximum 3-inch tubing diameter
*Supercharging, turbocharging, and fuel injection prohibited

Sounds simple enough, right? Yes, but keep in mind that flat-top pistons with stock heads isn't exactly the recipe for excess horsepower-and a 0.063 nitrous jet won't make the Pro Mod guys tremble.

Sucp_0401_05_z Affordable_small_block_race_engine Cement_filler 3/22

A relatively inexpensive method to ensure the racing engine's longevity, especially since it'll be on nitrous for each pass down the track, is filling the water jackets with cement, which prevents the cylinders from deforming. In this case, Thomson Automotive used Hard Blok jacket filler, which is a cement-based product designed for use in racing engines. Its coefficient of thermal expansion is the same as iron engine blocks. Thomson leaves enough room in the water jackets to allow water to get to the heads.

"It's harder than it looks," says Thomson. "The easy way to make power, even with stock-type heads, is to add compression. The flat-tops limit compression severely, and the tiny nitrous jet certainly won't double the engine's output."

And, there's the weight factor: Pre-'75 cars and all trucks in Cheap Street must weigh 3,200 pounds if equipped with at least a 365-cid engine; it's 3,250 for '75-and-later cars. However, a weight penalty of 10 pounds per cubic inch is assessed for each cube over 365.

The engine Thomson built for this story was headed for a Third-Gen F-car, meaning it would have to weigh at least 3,250 pounds.

"The owner wants to avoid adding weight, so we decided to keep the engine under 365 cubic inches," says Thomson.

Firm Foundation
Although cognizant of the claimer rule, Thomson and the engine's owner knew there was no way to build a competitive engine for $3,000-and make it last for an entire racing season. The decision was made to use the strongest parts where possible, knowing that items like the unmodified heads, intake and carb would be relatively affordable.

Rather than start with an all-new short-block, however, Thomson started with a used block and cleaned it up. By giving it the standard 0.030-inch overbore and a 350 crank, the engine would displace 355 ci.

The rotating assembly was built for durability, low mass and low friction. The lightweight Diamond aluminum pistons and GRP aluminum rods from GRP aren't exactly cheap, but they provide a necessary performance edge, according to Thomson.

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