A Look Inside One Of The Winningest TT-Unlimited Engines Ever

Often times when we write articles about competition engines—especially engines for classes with the word “Unlimited” in the name—they feature some of the most advanced parts and pieces that are currently available on the market. However, sometimes an engine program comes along that is deceptively simple, and its sheer simplicity is part of its beauty. Enter the engine program from Horsepower Research for Paul Costas and his Super Unlimited (SU) / Time Trial Unlimited (TTU) Camaro known as “Scratcher”.

No ordinary weekend race program, Costas and Scratcher not only win, but they win a lot. The team has some incredibly impressive stats, with 59 starts, 58 podiums, and 50 wins in-class since January of 2014, with the unofficial title of longest winning streak, at 38 consecutive class victories. “How many folks can say they finished the last 38 races in a row, much less won them?” says Costas of his impressive winning streak.

One of the keys to Costas’ unmatched success has been his engine program, and he certainly isn’t shy about heaping praise on the backbone of his engine program, Horsepower Research. Nor is he shy about revealing to us the parts and breakdown of his engine. Designed and assembled for him by Erik Koenig of Horsepower Research, Costas’ powerplant is a 355 cubic-inch Gen I small-block Chevy engine, which gets quite impressive as you peel back the layers.

Surprisingly, the parts used in Paul Costas’ engine by Horsepower Research aren’t any crazy, custom-ordered pieces. Thanks to the suggestions of the HPR team, his money was spent on quality parts that would hold up to a serious amount of abuse.

Starting with a two-piece rear-main seal Gen I block, Koenig bored the cylinders .030-inch and added Callies straight four-bolt main caps to ensure longevity. A Callies Compstar Comet forged 4340 steel lightweight 3.48-inch-stroke crankshaft, with gun-drilled mains, pendulum-cut counterweights, and a lightened “star” flange was chosen as the centerpiece of the shortblock. Koenig chose to go with a Honda rod bearing journal diameter (1.880-inch) to reduce friction, and chose 6.00-inch Callies Compstar rods, which have computer-modeled weight reduction built into the rod design and come with ARP 2000 rod bolts straight out of the box.

Attached to the rods are Diamond Pistons 4.030-inch flat top pistons, with a standard 1/16, 1/16, 3/16-inch ring package – no crazy custom slugs here. Truth be told, that is probably one of the most surprising parts of this impressive engine build, as we are used to seeing engines using pistons with custom features. The bearings used in the mains and the rods are Clevite, but have been coated after the fact by PolyDyn with their PolyDyn DL coating, which has had an incredible effect on the engine’s longevity.

“We pulled the engine after about 20 weekends—I’m not kidding—and the coating that Erik specifies on the bearings was almost entirely intact,” Costas says. “A few of the bearings had scuffed the top of the coating away but none of them had any bearing wear at all.”

The latest refresh of Costas’ engine by Horsepower Research consisted of sending the bearings out for recoating, cleaning and reusing the piston rings, and giving the cylinders a light hone. Incredible for 20 race-weekends-worth of hard use.

The timing set is a simple double-roller chain affair, and contrasting that simplicity is the oiling system. Utilizing a three-stage dry-sump oil pump from Stock Car Products, the system is manufactured to insanely tight tolerances to not only be as efficient as possible, but as reliable as possible. An oil pump that loses efficiency in the middle of a road race will end your weekend quick, fast, and in a hurry.

The camshaft is spec’d out by Koenig, and he had no problems sharing those specs, which was another change from what we’re used to. It is a .680-inch-lift solid roller, with 262 degrees of intake duration and 268 degrees of duration on the exhaust side, with a 107-degree lobe separation angle. In addition, it’s installed three-degrees advanced.

Koenig used Morel offset solid lifters with full-time pressure oiling to actuate 3/8-inch CV products 4130 chromoly pushrods. A Jesel Pro Series shaft rocker system with standard slot lightening on the lifter body reduces weight and translates the camshaft movement into valve movement, with incredible stability at high rpm levels—key in this application for long-term health of the engine.

Horsepower Research utilized Clevite bearings that were coated by PolyDyn in an advanced wear-mitigating coating. By the results seen in the refresh, it works incredibly well.

The cylinder heads on the combination are again deceptively simple out-of-the-box pieces: Trick Flow‘s Ultra 18 cylinder heads with—as the name suggests—18-degree valve angles. A 250cc intake runner and 100cc exhaust runner have been fully CNC-machined from the factory to flow 343 cfm on the intake side and 269 cfm on the exhaust side.

The 56cc heart-shaped combustion chambers house 2.150-inch stainless steel valves on the intake side, and 1.600-inch stainless exhaust valves. The valves are controlled by PAC Racing 1.136-inch OD dual valve springs, with 240 pounds of seat pressure and 598 pounds of open pressure, perfect to handle sustained-rpm jaunts.

Jesel Pro-series shaft rockers with a single lightening cut allow the small-block Chevy to spin to the moon, if need be. However, Costas prefers to trade the high-rpm power for a stout, wide torque curve and increased longevity.

Providing the fuel to the combination is a Holley 830HP carburetor that comes from the Holley Pro Shop, which sits atop a GM Performance Parts (now Chevrolet Performance) Bowtie Competition 18-degree intake manifold, which was designed specifically for NASCAR short tracks and Trans-Am series engines. Again with the simple, reliable parts, an MSD 6-AL ignition box keeps the spark going lap after lap, and 1 7/8-inch stepped headers scavenge the exhaust gasses out of the engine as efficiently as possible.

When compared to other engines powering similar cars, Costas admits that he’s not at their horsepower levels, specifically to increase the engine’s longevity.

“Mine is a healthy motor, but down from the low-800s that the current Trans-Am and GT-1 cars produce,” says Costas. “Those motors spin much higher than mine to make that power and the valve spring and bearing life is dramatically shorter than mine. With the Jesel top end, we could spin the motor a lot higher and pick up decent power, but this is club racing and I’m self-funded. So we went with lower revs and a broad powerband to give me a long engine life, which I can spend developing and tuning the chassis and driver on track.”

There is nothing exotic about the cylinder heads or valvetrain. Out of the box Trick Flow CNC’d Ultra-18 cylinder heads, stainless steel valves, and off-the-shelf PAC valvesprings work exceptionally well together.

In addition to increasing engine longevity, Costas’ style of driving lends itself to a broader powerband as opposed to more peak power.

“With a smooth, flat torque curve, it is so much easier for both the driver to get on the gas early coming out of a corner and also for the chassis to accept and deploy the power,” says Costas. “This helps on starts as well, whereas most drivers are trying to pace and keep the motor ‘in the power’, my powerband is wider. A tactic I use is to start pretty slow and it has worked well. Other times the run to first turn is too long and I get walked when they come up on the power, but then I simply have to get to work and find a way back by them.”

“Driving a higher-horsepower car to its potential is incredibly difficult. Doing it in a car with no ABS, stability, or traction control is even harder. Thankfully when the 14-inch-wide tires are hot, they grip pretty well, but I am modulating the throttle a ton every lap,” says Costas. “With this in consideration, the HPR motor that Erik built has a nice broad torque curve and while a lot of my competitors easily beat me on peak power, we all know area under the curve is what sets good lap times.”

The GMPP competition 18-degree intake manifold, which was designed for Trans-Am-style road racing, is topped with a Holley 830HP carburetor from the Holley Pro Shop and makes for an easy fueling solution.

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About the author

Greg Acosta

Greg has spent over a decade in automotive publishing as Senior Editor of Race Pages magazine. In his free time, he is a firearms instructor and volunteer in the police armory.
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