The GEN-3 HEMI is now decades old and has been produced in mass quantities since it made its debut in the 2003 RAM 1500 truck. But even after all these years, people still make avoidable mistakes when modifying GEN-3 Hemi engines.

It started life at 5.7-liters, but would grow in size and horsepower levels, peaking in 2023 with the 2023 Demon 170s 6.2L supercharged beast, which made a stratospheric 1,025 horsepower on E85 fuel. The modern HEMI has been embraced and accepted by enthusiasts, custom car builders, hot rodders, racers, and just anyone who bleeds Mopar Blue, Turquoise or Orange. Modifying GEN-3 Hemi engines has naturally become a huge part of the hobby.

Whether you’re doing a G3 Crate HEMI install or trying to make more power from your late-model Mopar, make sure to follow the advice of experts and not random strangers on social media.

Used GEN-3 HEMI engines are finding a second life in everything from 1969 Dodge Darts to 1985 RAM D150 pickups. With that, many enthusiasts are making good and bad choices when it comes to rebuilding, tuning, and picking the right parts combo for their modern HEMI.

With that, we reached out to some smart dudes in the GEN-3 HEMI world who’ve spent years thrashing and developing a wide array of parts for this 21st-century HEMI. They’ve learned the hard way on what works and doesn’t on
these modern engines, and are ready to share their depth of knowledge with us.

Blackbird Performance

Geoff Turk knows a thing or two about G3 HEMIs. Back in 2018 he was the first the break the 7-second barrier in his NHRA/NMCA legal Factory Super Car Challenger Drag Pak.

First on deck is Geoff Turk from Blackbird Performance. Turk was a regular at NHRA and NMCA events with his Blackbird Factory Super Car Challenger Drag Pak. About a year and a half ago, Turk and his wife and business partner Jena, started Blackbird Performance, a company specializing and focused on helping folks with their G3 HEMI-powered projects.

A GEN 3 HEMI can do everything Chey LS can, even better and very cost competitively if you understand and exploit the inherent strengths of the engine design and the factory parts, said Geoff Turk.

Geoff Turk is a firm believer in using the production cast-iron block and factory aluminum cylinder heads on many of his builds. The stock core parts can support well over 1000 horsepower and for customers on a budget, they don’t have mortgage the house to go fast.

Here are some tips Turk shared when it comes to GEN 3 HEMI modifications.

1. “Don’t modify the stock valvetrain unless you’re building an all-out race engine. For 80 percent of the street and strip builds, the stock rocker shafts and rocker arms work very well unmodified — even all the way up to the most aggressive hydraulic cams,” Turk said.

“Since the new HEMI still uses a dual shaft per  head, they’re small, relatively lightweight rockers and will work very well in applications up to 1,500-plus HP,” he said.

2. “Another fallacy is thinking real GEN3 HEMI performance begins and ends
with modified supercharged 6.2L Hellcat variants, and this is not true. The
basic factory stock 6.4L/392 HEMI platform is blessed with a 1,500-plus HP
capable factory cast iron block, production heads which flow a lot of air,
and a stock crank that’ll work on many high winding engines. In almost
any configuration and build budget, the production core parts can make
impressive and cost-effective power in naturally-aspirated, as well as
power boosted applications, Turk noted”

3. “Replacing the stock coil packs in pursuit of more ignition power won’t
yield any significant increase in power. Maybe five horsepower on the
dyno, but you won’t see that on an ET slip. More ignition power often
does not translate to more engine power. The stock, factory dual plug coil
packs perform very well up to 1,700-1,800 HP.  Even the factory
production coil packs were used on the 2021 Challenger Drag Pak’s 354
cubic inch supercharged HEMI and are very reliable.”

4. “Look at taking some weight out, as it’s the enemy of going fast. “The
HEMI-powered Challenger, Charger, and 300C production street cars are very rigid, precisely built, and structurally very strong. Unfortunately, they’re also fairly heavy and have many factory-installed features and comforts. In terms of performance improvement, every pound that no longer needs to be accelerated or stopped is often far more bang for the buck and beneficial than just making more power. Look at smart ways to
lose weight. Aftermarket wheels, removal of the back seat, use of a lightweight battery, and other reduction initiatives will pay out with improved ETs.”

5.  Do not go looking to “Social Media Crowd Sourcing” for advice on
building/modifying your GEN 3 HEMI.

“It amazes me that people go on Facebook and ask random strangers what camshafts, headers, tuners, and mods they should use on their builds. Choosing wisely is not best
completed by getting input from ‘self-proclaimed” experts, as they can take you down the wrong path.”

Geoff Turk and his wife, Jena, founded Blackbird Performance a few years back with a focus on developing, engineering, and manufacturing parts for the G3 HEMI. His engines can be found in street machines to all out race cars.

Mancini Racing

Ryan Radcliffe represents the next generation of Mopar enthusiasts. Behind his youthful face is a decade of G3 HEMI knowledge. He’s on the front lines at Mancini Racing making sure G3 HEMI customers get the advice and parts for their builds.

We also got some great GEN 3 HEMI advice from Ryan Radcliffe of Mancini Racing. Despite being relatively young at 28-years-old, Ryan has spent over a decade in the Chrysler performance parts business and has performed many GEN-3 crate HEMI swaps on vintage Mopar vehicles.

He has walked many enthusiasts through the intricacies of a G3 HEMI swap and has common-sense approach. Unfortunately, many enthusiasts get blinded by horsepower numbers on a dyno and overlook many basic steps and can help enthusiasts have a
consistent and reliable G3 HEMI-powered machine.

Here are Ryan’s top five things he sees that too many enthusiasts overlook.

1. “Too many folks don’t plan out their GEN-3 HEMI build. They need to define their goals and determine if their GEN-3 HEMI project will be a cruiser, drag and drive, or car show trailer queen. Determine what you want and then begin thinking about supportive mods like brakes, cooling, chassis, suspension, and other things.”

2. “Build the car with an end goal rather than just [throw] parts at it. I’ve seen so many situations in which the wrong items, such as intake manifolds, timing covers, and other items, were just thrown at the engine in hopes it would perform to their owner’s expectations.

One of the big things I tell people is to delete the MDS lifters, and if the HEMI had a VVT set up, it does not need to be deleted unless you want to lock out the timing.”

3. “Choosing the right electrical systems to support the engine functions is important. Do your homework, as the aftermarket has many options and kits out there, and they’re all basically good.

“The big mistake with some novice tuners and first-time builders is choosing the wrong kit and getting lost in a tuning maze. The Mopar Direct Connection Install kit is by far the easiest to navigate and works great on 90% of GEN 3 HEMI swaps.”

Among all the aftermarket install kits for G3 HEMI swaps, Ryan Radcliffe recommends the Direct Connection until. There’s many versions available (NA 5.7L/6.4L and SC 6.2L Hellcat/Demon). They’re user friendly and can be installed by any novice. However, if the engine mods are more radical, Ryan recommends the Holley kit, it offers the capability for more tuning.

4. “Another area that’s often overlooked is the fuel system on GEN 3 HEMI swaps. The wrong fuel pump, whether it’s an in-tank or external setup, can ruin your day. Make sure the overall system can support the pressure and volume your engine will need. Also, don’t cheapen out when it comes to AN fittings and hoses. Get the best parts so you’ll avoid breakdowns.”

Ryan also stresses running a proper fuel system when doing a G3 HEMI Crate Engine swap or modifying your street car. Not doing so can potentially damage the engine by creating a lean condition and ruining your day.

5. “Camshafts also seem to be a big mystery among enthusiasts looking to modify their GEN 3 HEMI engines. If you grew up on the old Mopar ‘Purple Shaft’ cams, none of that applies to the modern HEMI. Along with choosing the right torque converter, gear ratio, headers, and other things, tuning the engine for an aftermarket camshaft is hypercritical. Don’t go too big on the duration, overlap, and go one size smaller. Play it safe and don’t spend weeks just trying to tune the engine so it can idle in gear.”

High Horse Performance

We also got some great advice from Josh Schwartz, owner of High HorsePerformance, Inc. He and his staff have been making GEN 3 HEMI engines more powerful since 2004 and have supported the modern Mopar community for a longtime. He thinks you can avoid the big mistakes with these words of wisdom.

1. “Not modding with a goal in mind or educating yourself on the parts you’re using. Most customers progressively build their cars, very rare do customers do everything at once. You need to know what the final outcome you’re working towards is and have a plan on getting there. We have customers who will have us complete major work then decide a year later to change directions and we have to redo all of the previous work we completed, from changing camshafts, changing pistons or other engine
components, rebuilding transmissions, or performing additional upgrades to fuel systems, brakes, and suspension just to be able to support the new direction.

“We can usually tailor a multi-stage build so that it progresses along the best path for a customer to reach their ultimate goal and this can save anywhere from 10 to 20 percent in the end.”

As Josh Joshua Schwartz of High Horse Performance pointed out, “If modding is brought about by necessity, i.e. a lifter failure, engine bearing, driveshaft coupler, suspension bushing, or similar issues that cars experience especially with higher miles, waiting is your worst enemy since collateral damage increases and the repairs become more expensive the longer you wait to have the problem addressed.”

2. “Making poor decisions based off advice they received from someone they don’t know on Facebook. Adding larger fuel rails or fuel injector when it’s not needed does not in any way make more power. The internet is overwhelmed with bad advice that 99 percent of the time comes from people who think they know more than they actually do. First-hand experience is rarely the basis for most online groups.”

3. “Trying to be cheap. It rarely pays off. The old cliché ‘You Get What You Pay For’ applies. The cheap parts normally fail quicker and the lowest bidder on the installer side usually results in less than stellar results. We get way too many repair jobs where the repair ticket is much higher than the original install job would have been.”

4. “For big horsepower builds, don’t try and over build your car beyond what you are capable of supporting yourself, both from a financial side or from a mechanical side. If you are trying to build a 1,500-plus horsepower car, you should at a minimum be willing to support the vehicle, whether it’s changing spark plugs, changing belts, making data logs when necessary or even being able to transport the car to your mechanic when it needs to be serviced or inspected. Don’t go over your budget and especially never get a loan to build your car.

With bigger builds, there’s always a chance parts can break and if you don’t have the finances to cover the repairs you may have to park the car for months or years until you can afford to fix it. Bigger builds should be inspected regularly to ensure everything is in
working condition and keep up on your tune-ups. Even if you don’t drive the car much, at a minimum annual spark plug changes, oil changes, filter cleanings, injector cleanings, fuel pump testing, it all goes a long way.”

5. “The ‘KISS’ method makes the mechanics and tuners life easier. Keep It Simple Stupid! If it’s complicated, expect complications. There’s many ways to accomplish the same outcome. The simplest way is typically the most reliable. Don’t over complicate a build. Don’t use non-standard parts, use the trusted and reliable ones. And new parts that are fresh to the market rarely live up to their hype. Just because a part fits or says it works, that doesn’t mean it will. The experienced shops know which of the parts are reliable and which aren’t.”

So there you have it, important tips from some smart dudes that live and breathe the G3 HEMI lifestyle every day. When it comes to modifying a gen 3 HEMI engines, follow their advice and your hot rod will live a long, happy life.