In the world of performance engines, Keith Newcomer has carved out a niche in the Jeep community based on his fantastic success with the brand’s iconic straight-six engines. While most shops chase horsepower with LS or other more modern engine builds, Newcomer Racing has been wringing big power out of the AMC and Jeep engine — engines most people still think of as farm-truck powerplants. And that includes everything from big-torque, low-budget builds using mostly stock parts to an outrageous, record-breaking turbocharged monster that pumped out over a thousand horsepower on the engine dyno.

Jeep motors don’t enjoy the same aftermarket support as many performance V8s, so Newcomer Racing regularly overcomes that obstacle by fabricating and manufacturing its own components. That includes everything from billet thermostat housings to valve cover spacers, custom intakes, and even cam position sensors for EFI conversions. If there’s a bottleneck in performance, the Newcomer team will machine their way around it.

Now they’re tackling one of the biggest limitations in the Jeep six: the camshaft.

Instead of just throwing the new roller cam setup in a new Jeep engine, builder Keith Newcomer wanted to test it against a known commodity. So they pulled this test mule with a practically identical solid flat-tappet cam for an A/B test.

The Flat-Tappet Bottleneck

From the factory, every Jeep engine rolled out with a flat-tappet camshaft. That setup works fine for stock applications, but it can be troublesome for anyone wanting aggressive ramp rates, big lift, and long-term reliability. In stock form, a straight-six can live practically forever. But, when you start trying to make big power with larger, more aggressive cams, high spring pressures, and flat tappet lifters, valvetrain lifespan becomes a gamble. Aggressive cam lobes move the initial contact point on the face of the lifter closer to the edge where friction spikes and bad things can happen.

Plenty of people have talked about building a roller cam option for these engines. A few have even done it, at least for a while. But every system until now has been plagued with problems. Nobody’s actually put a complete, working roller lifter system in the hands of Jeep owners.

The test mule is a 4.7-liter stroker with .060-over cylinder bores and 3.895 inches of stroke thanks to a fully-counterweighted crank from a 4.2-liter engine. It was already quite stout with solid flat tappet lifters, putting out 368 lb-ft of torque and 365.9 horsepower.

That’s where Keith Newcomer comes in. His shop has been quietly developing a full roller valvetrain — cam, lifters, rockers, everything — that could finally drag the Jeep six into modern performance territory. And we had a front-row seat for the dyno test of their latest prototype.

The Test Mule

Instead of starting with a fresh build, Newcomer wanted to test the roller setup against a proven flat-tappet combo in a direct apples-to-apples comparison. His test mule was a 4.7-liter stroker, well broken-in after about 15,000 miles of real-world use.

The short-block packs .060-inch overbores and a fully counterweighted 4.2 crank with
3.895 inches of stroke. An aluminum Edelbrock cylinder head that Newcomer has hand ported himself tops things off. On the exhaust side, a gorgeous six-into-one header from American Racing Headers with 1-5/8-inch primaries feeding a 3.0-inch collector handles spent gases.

A cam swap in a Jeep straight six isn’t exactly a walk in the park. To get the cam out, the lifters will have to be removed, and that basically requires stripping the engine down to the short-block.

This is no mild build, and it’s been making strong numbers for a while. Baseline pulls with a hand-fabricated R&D intake manifold showed 368 lb-ft of torque at 4,600 rpm and 365.9 horsepower at 5,800. Solid, repeatable, and tough to beat.

Swapping cams in a Jeep engine isn’t exactly a 30-minute job. Before you can pull the cam, you have to remove the lifters, and that requires pulling the valve covers, intake, rocker arms, pushrods, and cylinder head. Oh, and getting the cam out also means pulling the timing cover and the timing chain.

Newcomer did what he could to get the flat-tappet setup to perform as well as possible. The flat tappets were lightweight, solid units that also had an EDM hole in each lifter face to inject pressurized oil between the lobe and the lifter face. It’s a smart upgrade over stock, but still not immune to wear. Once the cam came out, we noticed early signs of lobe wear. Not catastrophic yet, but inevitable with big springs and a flat-tappet profile.

The new stick is a high-quality billet steel roller cam, built to match the specs of the outgoing flat-tappet grind for a true head-to-head test.

Others have tried to offer roller cams for the Jeep straight-six, but almost always with a cast cam core, like the flat-tappet versions. Newcomer Racing’s roller cam (foreground) is ground from a billet core for extra strength and durability.

Engineering Around a Jeep Engine Quirk

The lifters are where this project gets tricky. Jeep’s block casting puts a big divider between each lifter pair, so conventional link-bar roller lifters won’t slide in as a unit. Newcomer’s solution? A slotted tie bar on one side so each lifter can be installed individually, then reconnected as they are slid into the lifter bores.

It can be a bit of an involved process. Newcomer drops in the lifter with the link bar riveted on, then uses a magnet to hold the link bar up so that the second lifter can be slid into place. It took a minute, but Newcomer got all 12 lifters seated and tied together. The link bars have a “dogbone” dip in the center to clear casting ribs in the block, with strategic rivet reliefs where needed. That may evolve before production, depending on how the design shakes out across the Jeep’s many block variations.

One difficulty with upgrading to a roller valvetrain is the lifters must remain properly oriented in the bores. Link bar lifters are the obvious solution, but one side must be slotted so that the lifter can be removed for installation.

With the cam degreed in and lifters secured, the team reassembled the head and valvetrain. They kept the same Comp Cams 313-pound-per-inch beehive springs for both tests to keep the comparison fair.

Once everything was back together, the stroker was ready for round two on the dyno.

Newcomer says the main goal for the new roller cam was longevity by eliminating the lobe wear that comes with flat tappets under heavy load. Any power gains would just be a bonus. Remember, the specs on the two cams are basically identical. But, the reduced friction of the roller lifters delivered a surprise.

Peak torque jumped from 368 lb-ft to 380.4, a 12.4 lb-ft gain. Peak horsepower climbed from 365.9 to 373.4, an extra 7.5 ponies on tap. Even better, the improvements weren’t just at peak. Across the entire pull, average torque was up 9 lb-ft, and average horsepower increased by 7.6.

It’s these posts cast into the block between each pair of lifters that require the slotted tie-bar. The installation system Newcomer has developed is to install the lifter with the bar still attached, then use a magnet to rotate the tie bar up and drop the second lifter into position, both in the lift bore and the tie bar.

And the high-RPM concerns? Gone. The heavier hydraulic roller lifters stayed stable all the way to the test’s 6,500 rpm redline with no hint of valve float.

While the roller cam was the star of the day, another development quietly stole a bit of the spotlight. Newcomer’s R&D fabricated intake manifold made some pretty serious gains over a hand-ported aftermarket cast intake that previously had been about the best thing out there. This has practically nothing to do with our roller-cam test, but we thought it was very interesting. In fact, based on how well it performed here, he’s likely to turn it into a cast piece for production. Given the scarcity of serious performance intakes for the Jeep six, that could be another game-changer for the platform.

Here, you can see the lifters in position. Another difficulty with the Jeep engine block is this big divot in the center that requires the retainer for the link bar to be relieved on one side.

Worth the Effort?

Let’s be clear, if you are looking into a roller cam conversion, this isn’t going to be a budget upgrade. Between the custom lifters and camshaft, there are several other upgrades that will be required if you don’t already have them. For example, the lifters require between 0.010 and 0.015 inch of preload. It is impossible to be this precise with the stock stamped steel rockers, so you need a set of aftermarket roller rockers with lash adjusters.

Unfortunately, aftermarket rockers are usually too tall for the stock valve covers, so a valve cover spacer will also be necessary. And then that compounds further, because normally the stock thermostat housing won’t fit with a valve cover spacer — so that will need to be upgraded too. Unfortunately, that means the cost will add up. By the way, Newcomer Racing has developed products to get around all these problems.

On this test, both the flat-tappet and the roller cam were big enough to require aftermarket valve springs, so we used a set of Comp Cams beehives. But Newcomer Racing will offer smaller roller cams that will work with the stock springs.

But for Jeep engine owners chasing both power and reliability, the numbers speak for themselves. More torque everywhere, more horsepower up top, and the promise of a valvetrain that can live with aggressive profiles without eating itself alive.

Keith’s next move is to drop this engine into one of his Cherokees for road testing. If the street miles go as well as the dyno pulls, Jeep fans might finally have the roller valvetrain they’ve been dreaming about.

For now, it’s one more example of Newcomer Racing pushing a platform most people overlook, and proving there’s still plenty of untapped performance hiding in an engine that first appeared all the way back in 1964.

On the dyno, we saw surprising gains with the roller cam setup, even though it had the same lift and duration. Both torque and horsepower went up (12.4 and 7.5, respectively), but more impressive is the total area under the curve all the way through the pull.