Hotrod magazine LA BUILD VERSUS LS

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Let’s cut to the chase: The LA small-block racing engine we’ve been following, built by Michigan’s Valley Performance for the Race Engine Challenge, took home the gold.

Based on average horsepower per cubic inch, the 376-inch underdog surprised and overpowered more than a few LS builders in the event, punching out 1.963 hp for each genuine Mopar cube and claiming the class win.

“We were confident we had a competitive combination and would give the LS engines and other well-developed engines a run for their money,” says Jack Barna, Valley Performance’s owner. “But it was still somewhat of a surprise to see our engine come out on top. It had something to prove and really did.”
 
As we detailed in the first installment of this story, the engine was built for the inline-valve class in the competition, which had a displacement range of 370 to 490 ci. The other class was for canted valve/Hemi designs. And while those engines expectedly posted big peak numbers, Valley Performance’s output was right with them when it came to power-per-inch.

Our number was within 1 hp of the top Hemi engine,” says Barna. “So when it came to overall output, our LA really brought it home.”

The engine posted an average horsepower rating of 737 hp, which was about 4.5 percent lower than Valley Performance’s test pulls on a different dyno. Barna attributed the difference to a variety of contributors: a different dyno, different atmospheric conditions, a different altitude correction factor and more, but the bottom line is the engine squeezed out more per cube than its rivals.

“We believed a smaller engine would be more efficient when it comes to making the most average power per displacement, with less friction and more airflow per cubic inch,” he says. “The results speak for themselves.”
 
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.
 
On the dyno at the competition, the engine Valley Performance nicknamed Mopar Disadvantage spun its way to the win, recording 738 hp — or 1.962 hp per cubic inch. It’s performance that proved a point and demonstrated what two knowledgeable Mopar builders and a carefully constructed plan could achieve.
 
Valley Performance started with an early Magnum 360 block that was reinforced with Hard Blok in the water jackets and underwent a number of modifications for windage-reducing oil control. Valley Performance also had a splayed four-bolt main caps made for it to provide extra support for the mains. The cylinder was bored out to 4.100 inches to unshroud the valves.

Inside the block is an Eagle forged crankshaft the slightly reduces the stroke from 3.580 inches to 3.556 inches. The rods and pistons include Eagle 6.250-inch H-beam rods and custom Ross forged pistons that contribute to an 11.66:1 compression ratio. The camshaft is a Bullet roller unit with 0.775/0.774-inch lift and 255/265 degrees duration

The relatively new Edelbrock Victor cylinder head is credited with helping push this small block project to the winner’s circle. They offer large, 225cc intake ports, raised exhaust ports and a revised 16-degree valve angle (stock is 18 degrees). Out of the box, the head is good for about 345 cfm on the intake side and 237 cfm through the exhaust ports.

Valley Performance enhanced airflow in the new heads by opening up the walls a bit to eliminate the pushrod inch, along with a little guide work, resulting in a strong 372 cfm at 28 inches of water. Note, too, the 5/16-inch bolt at the upper left of the stock bolthole. It was to bolt up the W2-style tunnel ram intake manifold.
 
Thermal-coated exhaust ports help keep in heat and move air faster. Valley Performance says the ports flowed well stock, but they nonetheless opened the bowls and worked on the short-turn radius, bumping flow to 265 cfm.

Out of the box, the Edelbrock Victor heads have 58cc combustion chambers, complemented with Valley’s insertion of 2.175-inch hollow-stem intake valves and 1.600-inch exhaust valves. Valley Performance blended the valve seats and combustion chamber area to enhance airflow, ending up with 61.5cc chambers.

For oil control, the oil drains in the heads were plugged, forcing the oil to exit externally through the front and rear of the head casting and preventing it from draining back into the lifter valley.

Moving up to the valvetrain is a set of PAC Racing Springs dual-coil springs with titanium retainers. Specs include an installed height of 1.88 inches and a 675-pound spring rate.

The pushrods are strong, 3/8-inch-diameter with 0.120-inch walls, from Smith Brothers.

Hughes Engines supplied the 1.7-ratio roller rocker arm assemblies, which have been cryogenically treated to enhance strength. They’re actually big block Wedge-style assemblies to accommodate the offset that comes with the heads’ 0.600-inch-longer intake valves.
 
The intake manifold was a large challenge for the project. Besides adapting the W2-style bolt pattern to the W5-pattern heads, the passages had to be reshaped to match the intake ports. It took Valley Performance’s Jack Barna two months of scouring the internet before he found the vintage Holley Pro Dominator tunnel ram.

The manifold’s intake runners were originally D-shaped and didn’t line up with the heads’ intake ports, so Valley Performance went to work reshaping them until they did. The goal was to make the runners blend with the ports, with the larger radius of each runner at the top to optimize velocity.

Despite the comparatively small 376ci displacement, the airflow capability of the heads and intake manifold demanded significant fuel and air delivery, so a pair of 880-cfm four-barrels from Pro Systems Carbs (with annular boosters) were crafted by Patrick James.

The carbs are used with anti-reversion plates — also known as shear plates — to help prevent high-rpm airflow reversion. They’re designed to redirect hot gases that can rise into the manifold via camshaft overlap; and with a tight lobe separation angle of 106 degrees on this engine’s cam, that’s a concern.

An MSD crank trigger system was selected for more precise cylinder-to-cylinder ignition timing. With it, the conventional distributor mounted on the engine is essentially gutted, containing only the rotor and shaft to support the secondary ignition.

The headers are from Schoenfeld, with 1-3/4-inch-to-1-7/8-inch stepped primary tubes and 3-1/2-inch collectors. Valley Performance cut the collectors from the primaries and experimented with various primary lengths on the dyno, finding the original length delivered the best average performance.
 
Note the oil drain-back hoses at the front and rear of the heads. Plenty of pre-challenge testing found the engine liked 34 degrees of total timing and delivered peak ratings of 771 horsepower and 601 lb.-ft. of torque.
 
There’s a couple of misprints, proof reading errors.

“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.”

How does a Eagle 6.250 rod reduce the piston height when it’s taller than the stock rod length of 6.123?

“The intake - Besides adapting the W2-style bolt pattern to the W5-pattern heads”

Port wise, yes, bolt pattern, NO!

Nothing like having quality tech proof readers!

Where’s RustyRatRod when you (the magazine!!!) need him?
 
Longer rod requires less compression height on the piston. Lighter piston
 
rumblefish360 said:
There’s a couple of misprints, proof reading errors.

“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.”

How does a Eagle 6.250 rod reduce the piston height when it’s taller than the stock rod length of 6.123?
Click to expand...
Maybe they meant to say 'to work with the reduced compression height pistons' ......
 
rumblefish360 said:
There’s a couple of misprints, proof reading errors.

“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.”

How does a Eagle 6.250 rod reduce the piston height when it’s taller than the stock rod length of 6.123?

“The intake - Besides adapting the W2-style bolt pattern to the W5-pattern heads”

Port wise, yes, bolt pattern, NO!

Nothing like having quality tech proof readers!

Where’s RustyRatRod when you (the magazine!!!) need him?
Click to expand...
.
Did they shorten the stroke to compensate for the longer connecting rods?
 
No. The stroke was shortened .024 to suite there wants. If they had it in there minds to take that route....

The OE rods are 6.123 vs the 6.250 they used.
A .127 lengthening.

A .103 difference between rod length and stroke shortening going upwards.

The slugs were custom.

All in all, I loved it. First thing I did was send this to my Chevy friends.:p Nice to see someone use the new heads and use them well.
 
rumblefish360 said:
No no no, did they state they shorten the crank for clearance?
Click to expand...
Did they state they didnt shorten the crank for clearance?

They came up with an ideal this and that, be it lesser bob weight, higher desired rod ratio, keeping the CID down ...or even all of thee above...
 
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