Tech Talk #81 – Takin’ It to the Streets

DavidTechArticlesBy David Reher, Reher-Morrison Racing Engines

“It’s astounding to think about driving a car with 1,000 horsepower on the highway.”

One of the recurring themes in automotive advertising is the notion that racing improves the breed of production cars. There’s strong evidence to support that idea, at least in engine technology. Not too many years ago, 300 horsepower was a stout number for a showroom engine. Now it seems that every four-door sedan has 400+ horsepower, and high-performance models have more than 600 horses under the hood.

The distinction between race and street engines is even less defined in hot rods and street machines. Although the sign on the front door says “Reher-Morrison Racing Engines,” our shop builds powerful street engines as well. It’s astounding to think about driving a car with 1,000 horsepower on the highway, yet with today’s engine technology that is certainly possible.

This abiding interest in high-horsepower engines led us to develop a variety of powerful street engine combinations. Many enthusiasts prefer the “legacy” engines that have been the bedrock of hot rodding and racing for decades, such as Old School small-block and big-block Chevy V8s with carburetors and distributors. We’re also working on combinations for modern computer-controlled engines such as GM’s LS family of engines.

Displacement dominates, so we typically build 427-cubic-inch small-blocks and 540 to 565-cubic-inch big-blocks for our street-oriented customers. We’ve even built several street engines with more than 600 cubic inches for guys who are really serious about performance. It’s relatively easy to get an impressive horsepower number from these big-inch engines. For example, a 540-cubic-inch big-block that produces 600 horsepower is making just a little more than one horsepower per cubic inch. That’s a relatively mild motor compared to a racing engine that makes more than 2 hp/ci, so it’s tractable enough to take out on cruise nights and extended tours. A power adder – a supercharger, turbocharger, or nitrous oxide injection – can increase power output dramatically without sacrificing driveability or reliability if the engine is assembled and tuned properly.

When we build a racing engine for a specific drag racing class or index, the guidelines are fairly clear. We know how much power it takes to propel a car of known weight to the elapsed time and speed that’s necessary to be competitive in its category. There aren’t any corresponding rules on the street, however. There the engine’s performance level depends more on the driver’s perception. Some guys want an engine that purrs, others want a motor that roars. That’s why a powerful street engine is ultimately a custom build that’s based on understanding the customer’s expectations and experience.

Driving a purpose-built race engine on the street is seldom a rewarding experience. A street-driven engine needs to start, idle, and operate reliably without constant maintenance. It needs to be able to run on readily available unleaded gasoline and not overheat in traffic. Advances in technology have made it possible to build fantastically powerful street engines that meet these criteria.

While most naturally racing engines have compression ratios that range from 12:1 to above 15:1 (depending on the rules and the application), we usually build our street engines with a 9.5 to 10.5:1 compression ratio. A relatively modest compression ratio is essential for survival with today’s pump gas, and it permits the use of a power adder without overstressing the engine.

Hydraulic roller camshafts make it feasible to use cam profiles that rival the valve lift and acceleration used in racing designs not too many years ago. The hydraulic roller lifters eliminate the hassle of frequent valve adjustments, although we do use solid roller cams in some high-rpm applications. The constant improvements in valve spring materials now permit valve lifts well over .750-inch without sacrificing longevity. A street engine responds to the same enhancements as a race motor: more aggressive lift and duration, coupled with corresponding improvements in cylinder head airflow, are the path to power.

Regardless of its power level, an engine needs adequate cooling and lubrication to survive on the street. I strongly recommend using the largest radiator and oil cooler that’s practical to install in the vehicle. Drag race engines can get away with marginal cooling systems because they operate for extremely short periods of time – street engines don’t have that option. Something like a NASCAR-spec radiator is really what’s required for a high-horsepower engine, along with a high-volume water pump. And don’t forget to install an oil cooler – oil plays a significant role in internal engine cooling. (In fact, many “air-cooled” engines are effectively cooled by the oil circulating through them.)

Use a 160-degree thermostat to help the cooling system maintain control of the engine temperature. I know that most modern automobile engines run at well over 200 degrees, but that’s driven by emission regulations. It’s easier to maintain a reasonable coolant temperature than to regain control after the engine has overheated. The cooling system has a finite capacity to dissipate heat, so keeping the coolant as cold as possible provides a reserve when things start to get hot under the hood.

Most street engines can’t run a deep oil pan because of ground clearance considerations, and the expense and complexity of dry sump systems makes them unrealistic for most customers. However, a large capacity wet sump oil pan with extended side wings will help to ensure continuous lubrication while enhancing cooling. A reserve of oil really helps to transfer heat away from the valvetrain, pistons, and cylinder walls.

Don’t be tempted to run low-viscosity synthetic oil in a street engine. These lubricants are fine for all-out racing engines when every horsepower counts, but that’s not the goal in a street-driven engine. Good quality multi-grade conventional oil will provide all the lubrication a street engine needs – at less cost and without the risks associated with extremely low viscosity oil.

When I look at the current crop of production engines, I see components and techniques that were developed in racing. Cylinder head port designs with deep valve bowls, thin piston compression rings, low-tension oil rings, smooth cylinder wall surfaces, and lightweight valvetrain parts originated in competition engines. In that respect, the familiar adage is true: Racing does indeed improve the breed.