Tech Talk #97 – The Pump Gas Project


By David Reher, Reher-Morrison Racing Engines

“A powerful engine that runs reliably on pump gas has a lot of appeal for performance enthusiasts.”


The sign on the door reads “Reher-Morrison Racing Engines,” but in fact a surprising number of engines we build end up on the street.

The relentless pursuit of performance has been the hallmark of hot rodders since the days when Wally Parks and his friends conducted speed trials on dry lakes in fenderless Ford roadsters. Now with the arrival of 707-horsepower Dodge Hellcats and 650-horsepower Corvette Z06s in dealer showrooms, the performance ante has been raised to a staggering height.

Consequently I’ve decided to redefine what I once called “street engines.” Now I simply call them “pump gas engines,” which is a more accurate description of how these super high-performance engines are designed to be used.

Over the years, I’ve learned that the definition of a street engine is purely subjective – one man’s street engine is another man’s race engine. Some guys intend to drive thousands of miles on cross-country tours, while others only want to drive 20 miles to a local cruising spot or two blocks to a neighborhood car show.

A powerful engine that runs reliably on pump gas has a lot of appeal for performance enthusiasts. A pump gas motor can power a Saturday night cruiser, a weekend warrior that sees double-duty on the street and drag strip, or an affordable bracket racer. Gasoline is relatively cheap these days (at least compared to what we were paying a few years ago), and many customers would rather fill up at the corner station than store a drum of racing gasoline in the garage.

With the parts and technology available today, we can build pump gas engines that rival (and sometimes outperform) the engines that once won Pro Stock championships. For example, manufacturers offer conventional big-block aluminum cylinder heads with port volumes that range from 275cc to 365cc, with a choice of as-cast or CNC-machined runners. With such a wide variety of port volumes and shapes, we can match the engine displacement, operating range, and maximum rpm with great precision.

One of the variables in assembling a pump gas engine is the variability of the gasoline itself. In Texas, we have 93-octane premium at the pump, but in California it’s 91 octane – while my customers in Australia tell me they can buy 98-octane gas! So an engine that is optimized for 93-octane fuel must have less spark advance (or a bottle of octane booster poured into the gas tank) to avoid detonation when it’s burning 91-octane gas.

In back-to-back dyno tests, we’ve seen significant differences in horsepower depending on the brand of gasoline. Consequently I strongly recommend buying premium unleaded from a major brand rather than using the cheapest gas on the market.

The key to keeping any pump gas motor alive is controlling the coolant and oil temperatures. The hotter the engine, the more prone it is to detonation. Radiators designed for drag racing have no place on the highway – they simply don’t have the cooling capacity that’s need for the long haul. I look to NASCAR and heavy-duty trucks for cooling system inspiration, because those vehicles must maintain a reasonable coolant temperature under heavy loads. It’s not just the water temperature that’s important – oil plays a crucial role in engine cooling as well as lubrication. A large capacity oil pan and an auxiliary oil cooler can go a long way in keeping an engine cool.

Maintaining a high-performance engine does requires a little more effort and diligence than servicing an econobox. I don’t recommend changing oil at fixed intervals like every 3,000 miles. Instead, I tell customers to look at the oil. The chief culprits in shortening oil life are condensation and contamination. Street engines are prone to condensation and contamination because they typically spend more time idling than race engines. Oil is cheap compared to the cost of a new engine, so if there is any question about the oil’s condition, I recommend changing it.

We include a tool with our engines that’s used to cut off the top of the oil filter so the paper filter element can be inspected. It’s normal to see some fine metallic flakes in the filter, but anything more than that indicates a possible problem.

Hydraulic roller camshafts and single-coil conical beehive valve springs are popular in pump gas engines, but frankly we have encountered problems with them in high-horsepower big-blocks. Steel big-block valves are heavy, and hydraulic roller tappets limit the spring pressure that can be used to control valve motion at high rpm. Oil bleed-down in hydraulic lifters can also be problematic.

That’s why I now favor solid roller lifters on a tight-lash cam profile in pump gas engines. There is almost no discernible difference in engine noise with tight-lash solid lifters (.006 to .008-inch valve lash) compared to hydraulic rollers. The solid rollers enable the use of dual valve springs with higher seat pressure (typically 225 pounds versus 175 pounds for hydraulic lifters) and more open pressure (620 pounds versus 340 pounds with hydraulics). The dual springs are less prone to catastrophic failure than a single-coil conical spring because if one coil breaks, there is a second coil that will control the valve long enough for the problem to become apparent.

It’s true that solid lifters require periodic valve lash adjustments, but that’s a small price to pay for superior valvetrain reliability. Setting the valves is also the perfect opportunity to inspect the springs, rocker arms, and pushrods. And remember, back in the days when a Duntov solid lifter cam was the hot setup in a small-block Chevy, knowing how to adjust valves was the hallmark of a real hot rodder.