Inside Scott Oksas’ Twin-Turbo Pro Mod Engine

Mating electronic and mechanical fuel injection on a 485ci Brad Anderson Hemi seems like a winning combination, as long they play nice together. But why not just stick with EFI and let the computer have full precision control over the fuel delivery?

“You could put in bigger injectors, but the smaller injectors idle better and it’s a little cleaner,” says Scott Oksas, leaning against his ’70 1/2 Camaro Pro Mod racecar at a recent NMCA event in Fontana, California. “Mainly, you have unlimited possibilities with the mechanical injection. You simply put in as much fuel as you need to.”

Left- and right-side turbos.

So far there’s been enough methanol to power the Chris Duncan-built chassis down the track with a best run 5.85 at 259 mph, which Oksas says is among the top 5 all-time trap speeds in Pro Mod.

Oksas makes about 65 passes before freshening the engine.

“Two years ago I decided to upgrade and said, ‘why not buy a top alcohol motor and put twin turbos on it?’ It’s pretty potent,” Oksas tells EngineLabs.

The former TAD engine sports two Precision Turbos Gen2 Pro Mod 88mm turbos pushing air through a pair of 105mm Accufab throttle bodies into a Hogan intake manifold. Both fuel systems rely on the same pump and are controlled with a Motec ECU. The Enderle mechanical injection is a simple steady-flow system metered with individual jets at each port and turned on/off with nitrous-oxide solenoids. The EFI is anchored by twin Siemens 225-pound injectors for each runner on the intake.

“The mechanical comes on about 200 feet down the track,” says Oksas.

The car has run a best of 5.85 at 259 mph.

The turbo system is a little unique, starting with the Precision Turbos that feature a one-piece, forged aluminum center housing and compressor backplate assembly along with a stainless-steel turbine housing. They’re mounted to 2.25-inch diameter headers fabricated by Bill Hickock, who also serves as the car’s crew chief, out of materials from Doug’s Headers. Boost is manipulated with TiAL wastegates before the pressurized air is routed through an Ed Thornton-built air-to-water intecooler — but no water is routed through the intercooler.

Fuel delivery is controlled by a Motec ECU. Note the dual EFI injectors and mechanical fuel-injection lines for each port. The mechanical lines are fed with nitrous solenoids, seen under the intake.

“It’s just an air straightener,” says Oksas, noting that the car leaves with about 10 pounds of boost and “gets to 46 pounds as quickly as possible.”

Owner/driver Scott Oksas, left, and crew chief Bill Hickock work on the ’70 1/2 Camaro Pro Mod car between rounds.

The engine is built around a BAE block and head combo. It carries a 4.380-inch bore and a 4-inch Bryant crank with GRP rods and Ross pistons. Compression ratio is 11:1. Controlling the valves are a Bullet camshaft, Cam Dynamics lifters and BAE rocker arms. Somewhat unique is the belt-driven pump to pull vacuum from the crankcase.

“It’ll go about 65 passes before I take it out, tear it down and put in new rods,” says Oksas. “Not too many run a vacuum system on a Brad Anderson. We feel it helps with the turbo and seats the rings a little better.”

The engine was built by QMP Racing and initially set up on the dyno (see video below for a run up to 18 pounds of boost making more than 2,000 horsepower).

“We got the baseline down and then tweaked it on the track,” sums up Oksas. “The key to tuning is having a lot of information and knowing how to use. We’re still learning about fuel pressures and putting fuel in the motor at certain spots.”

About the author

Mike Magda

Mike Magda is a veteran automotive writer with credits in publications such as Racecar Engineering, Hot Rod, Engine Technology International, Motor Trend, Automobile, Automotive Testing Technology and Professional Motorsport World.
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