Hotrod magazine LA BUILD VERSUS LS

In our first installment, we focused on the engine’s block enhancements and short-block assembly, outlining a number of unique and custom modifications designed to shore up the LA’s foundation. Valley Performance started with an early Magnum 360 block, largely for its overall strength and taller lifter bores.

The block mods and short-block details included:

The cylinder were overbored from 4.000 inches to 4.100, mostly to unshroud the valves.

The stroke was reduced slightly, from 3.580 inches to 3.556 inches, to achieve the desired displacement and use 2.100-inch rod journals.

The water jackets were partially filled with Hard Blok to promote optimal ring sealing.

Windows were cut into the main web area to alleviate windage.

Custom, splayed four-bolt main caps were made to provide greater main bearing support.

A lifter valley reinforcement plate was added to tie the valley to the block’s rear bulkhead for additional strength.

Extensive oil-control block modifications were made to reduce windage, including closing off the lifter valley from oil drain back and drilling an oil drain tunnel through the block to drain oil externally to the oil pan.

Bullet roller camshaft with 0.775/0.774-inch lift and 255/265 degrees duration.

An Eagle forged crankshaft with the counterweights refined to minimize windage.

Eagle 6.250-inch H-beam connecting rods with 0.927-inch pins (stock 360 rods are 6.123 inches long), to reduce piston height.

Custom Ross gas-ported pistons with thermal and friction coatings. The heads were custom made, per Valley Performance’s molds of the cylinder head combustion chambers

A compression ratio of 11.66:1.

That brings us to the rest of the buildup: airflow. In the Race Engine Challenge, the engine would be judged on its average power production between 4,000 and 7,500 rpm. That would take the basic, truck-based Magnum 360 out of its comfort zone, when it came to engine speed.

“That’s one of the reasons we took so many precautions with the block,” says John Lohone, the engine’s co-builder. “The flip side of that is we needed exceptional airflow to achieve the power numbers we were aiming for at that rpm level.”

With the rules stipulating carburetion and natural aspiration, that proved more than a small challenge, as aftermarket parts options aren’t as plentiful as they are for other engine families such as the RB family.

“Before we agreed to go with the LA-based small-block, we took a long, hard long at the available parts out there, knowing we’d need a killer set of heads,” says Barna. “When it came down to it, the recent Edelbrock Victor small-block head sealed the deal. Without them, I don’t think we could have achieved the airflow we needed.”

There was another problem: drawing enough air and fuel into the heads.

“A single-plane, single-carb intake just wasn’t going to get it done,” says Barna. “We opted to modify a 25-year-old, W2-style Holley Pro Dominator tunnel ram and make it fit the Edelbrock Victor heads.”

Besides adapting the manifold to the heads, extensive work was done to reshape the tunnel-ram’s passages in order to blend seamlessly with the heads’ intake ports.

“We believe line of sight is important for the intake path,” says Lohone. “The changes made with the manifold provided the air/fuel mixture an unobstructed path to the combustion chambers, with excellent velocity.”

Topped with a pair of 880-cfm Holley four-barrels, the engine spun to 7,500 rpm in testing and produced 771 hp and 601 lb-ft of torque. It was a result that bolstered Valley Performance’s confidence as they headed in to the Race Engine Challenge, even if the dyno results during the competition didn’t quite match.

“All the engines were competing on the same dyno and test conditions, so we were satisfied with the parity of the challenge,” said Barna. “When it was all said and done, our engine produced the greatest average power per displacement, which was the goal in the first place.”

The little LA engine that could slayed some bigger competitors and raised some eyebrows, all while earned some well-deserved respect for the Mopar small-block.