Motovicity And Duttweiler Build A Custom Spec LS3 427 Stroker

duttweilerleadMany of Power Automedia’s online magazines are covering the assembly of this custom 427ci LS3 that will be given away by warehouse distributor Motovicity and built by Duttweiler Performance, a highly-respected engine shop in Ventura, California.

LS3 Parts Supplied By Industry Giants

  • Dart: SHP LS Next block and LS3-type cylinder heads
  • Scat: crank and connecting rods
  • Mahle: pistons, pins and rings
  • Comp Cams: camshaft, lifters, pushrods, valve springs, and timing chain
  • ARP and Dart: head studs and engine fasteners
  • Comp Cams/FAST: fuel rails, throttle body, intake manifold, injectors, and EZ EFI 2
  • Holley: water pump, valve covers, and oil pan
  • Accel: spark-plug wires and MSD for the coils
Readers of LSX Magazine, Chevy Hardcore, Corvette Online, Street Muscle Magazine, Dragzine, Rod Authority, Engine Labs, Turnology, and Off-Road Xtreme will want to take note of the quality of the engine. And since the April 29th deadline to enter for the chance to win it has passed, we will announce the winner as soon as we learn who it is.

But we still believe that this engine is going to have a broad appeal across many of our online magazines, and you can be assured that it isn’t just going to be a standard run-of-the-mill LS3 crate motor. Rather it’s a complete purpose-built engine that will be equipped with the best components from a variety of manufacturers.

In fact, major players in this build read like a who’s who of the performance aftermarket. When we read the list, we were quite excited to see what the finished project would be on Duttweiler Performance’s dyno. We were not disappointed in the results, and figure you won’t be either. Whether you decide to continue reading here, or jump straight to the dyno numbers below now, you will certainly get a good sense of what we are talking about.

The quality of the parts is really only half the picture. A knowledgeable and careful engine builder is the critical other half. And Duttweiler Performance is about as top-quality as you can get.

Here is the completed LS3 on Duttweiler Performance’s engine dyno. As you can see in the below results, this one is a pretty respectable runner, making more than 560 horsepower. It’s enough for big fun on the street or track in just about any car or truck you can think of.

Ken Duttweiler has been building high-performance engines for decades, and got his start with turbo Buick V6s in the ’80s and ’90s. Those engines powered some of the quickest and fastest Buick Grand Nationals with numerous cars routinely running in the 7s.

Subsequently jumping into Ford and Chevrolet engines, Ken has built some seriously powerful Chevys including, for example, the 2,300 horsepower small-block that powered the Potent & Main Streamliner to 462 mph at Bonneville. He also built 351 W-based twin-turbo small-block Fords making more than 1,500 horsepower and running mid 6s in the NHRA’s Sportsman Comp Eliminator ranks.

And now, Ken has built this stroked LS3, that if fitted with forced induction, will be capable of producing upwards of 1,000 horsepower. Not too shabby for an engine definitely built to run on the street.

Cast Iron Dart Block 

The Dart block has numerous other features including scalloped water jackets that increase flow around the cylinders for better cooling, as well as an incorporated clearance for up to a 4.100-inch stroke with steel rods, and splayed outer bolts on the middle main-bearing caps. The block also accepts GM OE front and rear covers, which were used in this engine. It also has all OE bolt holes for the starter, water pump, and other accessories.

Now that you have the basics of the build, and who is putting it together, we’ll get into the details beginning with the short-block.

Setting Oil Pressure

Ken fitted a Melling standard-pressure oil pump (PN 10295) to the engine. It comes with two springs and the red higher-pressure spring was in place out of the box. He removed the red spring and installed the blue, lower pressure spring in the pump to slightly reduce oil pressure, which is what he wanted to do with the Dart block.

“The standard-pressure pump with the higher pressure spring would yield upwards of 100 psi with the Dart block. This is probably a little on the high side, so I installed the lower-pressure blue spring to lower operating oil pressure a little bit,” Ken said. “It still results in about 80 psi of oil pressure, certainly plenty, because the Dart block has several oil-passage upgrades over a stock LS3 block. The Dart block’s main-oil galleys provide better oiling to the lifter bore passages and Dart’s priority oiling better ensures more oil gets to the main bearings. Thus, the oil pump doesn’t have to produce as much pressure as it would with a production GM, OEM block.”

The Dart SHP LS Next cast-iron block (PN 31867211) has extended pan rails. “It’s a very nice piece, I like it because it doesn’t need as much machine work as some other blocks that need to be decked and bored. Just finish the cylinder bore and that’s about it,” Ken told us. “The lifter bores and the mains are also finished. With the Dart block, we mounted the oil pickup on the fourth main cap with an ARP 7/16-inch stud and nut.”

Given that aluminum-block LS engines routinely make upwards of 700-plus horsepower at the flywheel, you can bet the Dart iron block is — very conservatively — good for at least that. “With forced induction, this engine will easily survive near or at the 1,000-horsepower mark,” commented Ken.

Other noteworthy features of the block include Dart’s priority main oiling system (see sidebar for more information) with provisions for stock oil-filter mounting. The cylinder barrels also extend .375-inch at the bottom of the bores and the thick decks of these iron blocks mean head-gasket sealing — especially with forced-induction applications — is reliable. There is also six-bolt-per-cylinder capability and the head-bolt holes are blind.

Crank, Connecting Rods, And Pistons

Scat Enterprises is well known for making bomb-proof crankshafts that easily manage 1,000 horsepower or more. Thus, Scat got the nod here with one of its 4340 non-twist forgings (PN 4LS140065) that weighs just 50 pounds, and is precision ground and micro-polished. The piece is also heat-treated and ion nitrided. Other features include straight shot and chamfered oiling holes. Furthermore, the Scat forging will be a good bit stronger than any cast GM LS3 nodular-iron crank. The crank has a 58-tooth reluctor wheel; however it can also be had with a 24-tooth wheel.

The Mahle pistons have a machined crown and Grafal anti-friction coating on the skirts. They are phosphate-coated to reduce micro welding and pin galling, and the pin bores are finished on CNC boring equipment. The Grafal skirt coating reduces drag, scuffing, friction, cylinder bore wear, and piston noise. The phosphate coating provides the grey appearance to the pistons and this dry-lubricant coating (not a thermal film coating) provides a lubricant film in the pin bores and ring grooves until the oiling system of the engine reaches operating pressure. This is very useful during break-in of an engine to protect against galling.

The crank’s 4.00-inch stroke is paired with a set of Scat Pro Sport 4340 forged H-beam connecting rods (PN 6612521A) that are 6.125 inches in length. The rod journals are 2.100 inches in diameter and are fitted with ARP 2000, 7/16-inch cap screws.

Atop the rods are Mahle PowerPak 4032 forged aluminum-alloy pistons (PN L92105125P25) sized for the Dart block’s 4.125-inch bore. A complete set of high-performance rings are included with the set, which are also made by Mahle. Their 25cc dish results in a 9.8:1 compression ratio; easily compatible with 93-octane pump gas in the East or 91-octane out West. Furthermore, Ken noted that, “The relatively low compression ratio of 9.8:1 was chosen so that whoever ends up with this engine has the option of going with forced induction should someone decide. Either a supercharger, a single or twin-turbo setup are all options.”

The 4.00-inch stroke crank and the 4.125-inch bore result in a full 427 cubic inches of displacement; basically the same as an LS7 which is a 428-cubic-inch (7.0-liter) engine found in the 2006-13 Corvette Z06 and 2014-15 Camaro Z/28.

While the Dart block comes with its own set of cam bearings, off-the-shelf Fel-Pro gaskets for an LS were used, and Clevite bearings for the mains and rod journals were fitted.

Top-End, Including Cylinder Heads, Camshaft, and Valvetrain

Recommended for engines with 4.00-inch bore or larger, the Dart PRO1 LS 15-degree square-port cylinder heads certainly take performance to the next level. Better airflow, more efficient combustion chambers and more user-friendly features are added benefits over production LS castings.

Most of this engine’s valve train was sourced from Comp Cams, including the custom-ground hydraulic-roller cam (PN 54-000-11). Specifications are as follows:

  • Max Lift: .578-inch intake/.596-inch exhaust
  • Duration at 0.050-inch lift: 236 degrees intake/248 degrees exhaust
  • Lobe Separation Angle: 112 degrees

The cam moves a set of GM OEM standard-style lifters and the Comp Hi-Tech pushrods (PN 8406-16) have a 5/16-inch diameter. “The Comp pushrods are good solid components and the 7.400-inch length is a standard measurement in an LS3 build,” Ken said.

Stock GM LS3 rocker arms with their standard 1.7:1 ratio work fine on the engine. While testing pushrods, Ken found that the stock GM LS3 rockers, with 128 pounds of pressure on the seat and 414 pounds with the valves open, worked well with Comp conical valve springs. “We also used a set of GM LSX lifter guides, which are in pairs rather than four to a group,” he noted.

As with the block, Dart also got the nod for its Pro1 LS square-port cylinder heads that are a 15-degree valve-angle, LS3-style design (PN 11030153) with a six-bolt-per-cylinder retention pattern. They also have dual valve springs, a 68cc combustion chamber, and a 280cc intake-port volume. Valve sizes are 2.165 and 1.600 inches on intake and exhaust, respectively. Stock valve angles, valve locations, and accessory mounting holes facilitate an easier stock-like installation.

We asked Ken about the heads after looking through Dart’s line of LS heads and noticed they are the top dog option in the company’s standard LS-architecture product line. He assured us that, “Although these are Dart’s biggest heads, we felt they would still be a good fit on this engine, that will have a good chance of being run on the street. Keep in mind this is a 427 cubic-inch engine, so it won’t have any problem using all the airflow these heads will provide.” We can imagine.

Intake, Ignition, And Remaining Accessories

With the long-block pretty much assembled, the remaining bits and pieces will get us to a complete engine that will be ready to go on the dyno at Duttweiler Performance.

“The cam was selected so the engine would have just little bit of a nice lopey idle. I also consider it to be good overall grind, as it will have good street manners.” Ken Duttweiler, Duttweiler Performance

The Comp/FAST, LSXR 102 mm polymer intake manifold (PN 146102B) for rectangular port LS3 cylinder heads is a three-piece modular design that allows for easy disassembly and porting. Testing has led to a runner design that is longer and less restrictive than a stock manifold. It also gives the option to remove individual runners from the manifold for modification. We also like that the polymer material offers several benefits over aluminum, including a lighter weight, increased strength, and improved heat dissipating characteristics.

At the front of the intake is a Comp/FAST 102 mm throttle body, which is designed to match it. This piece has optimized cross-sectional flow, which eliminates airflow turbulence, especially at part throttle operation. In addition, it has increased throttle-blade thickness to eliminate deflection, which can be an issue with forced induction. A smoother-operating offset-blade pivot also improves throttle response, and a heavy-duty linkage and dual throttle-spring mechanism ensure optimum throttle control. A throttle-position sensor (TPS) and an idle-air controller (IAC) are also included with this version (PN 54103).

Mounted to the intake, FAST’s billet fuel rails (PN 146027) have a larger internal diameter that dampens the pulses and provides increased fuel volume to ensure the injectors won’t run dry. Better fuel distribution is another added feature. Made from high-strength billet, red (or black) anodized aluminum, they certainly add a nice touch to the top of our LS3 build.

Mounted in the intake is a set FAST 50 lb/hr fuel injectors (PN 30507-8) designed for direct installation into an LS3. These are correctly sized (shorter than common LS1/LS6 injectors) and feature the correct EV6/USCAR connector, enabling easy plug-in operation.  Stock LS3 operating fuel pressure is 58 psi.

The Holley water pump (PN 22-100) is a quality, reasonably-priced option that fits all LS engine blocks and has a forward facing water inlet. It works with standard (Corvette type) or middle (F-Body type) belt spacing.  OE applications include 1997-2004 Corvette, 1998-2002 Camaro/Firebird, and 2004-2006 Pontiac GTO.

Controlling it all is FAST’s LS self-tuning engine-control system (PN 30405-kit). It gets an LS swap up-and-running without the complex PCM flashing and GM harness reworking required with stock GM wiring and ECM. This setup includes an EZ-LS ignition controller and can be used with stock or aftermarket LS injectors, sensors, and coil packs.

The system utilizes an easy-to-use interface through the included handheld touchscreen and doesn’t require a laptop. After initial setup, the handheld can be used as a digital dash and the system actually tunes itself as the car is driven. And, because it keeps tuning, future engine upgrades are easier — meaning that trips to a shop for simple tune changes are not required. A purpose-built, OEM-quality wiring harness is also included, and has mesh wrapping that improves engine aesthetics over the factory harness. With the ignition controller, the user has the option to adjust timing. The multi-port installation kit is compatible with all LS-based car and truck engines. MSD Street Fire coils and Accel Extreme 9000 wires with ceramic boots complete the ignition system.

The Fluidampr harmonic balancer (PN 720102) is an LS1/LS6/LS2 application and has a 7 1/4-inch outside diameter. It has a hard-coat anodized finish and weighs 7.4 pounds.

Final results on Duttweiler’s dyno yielded impressive results; this thing is a beast! It made an average of 440.2 horsepower and 507.0 lb-ft of torque. Peak numbers are 563.7 horsepower at 5,800 rpm. The fat stroker-motor torque curve topped out at 555.7 lb.-ft. at 4,900 rpm. Ken told us, “As you can see from the dyno results with the cam we picked, the engine sings quite well in the 5,500-6,500-rpm range with peak power at just under 6,000 rpm.”

 Wrapping It Up

So, there you have it. A complete, professionally built engine put together by one of the country’s preeminent engine builders. As the dyno numbers illustrate, it’s clearly a well-rounded, high-performance LS3-based GM powerhouse that takes full advantage of what the LS platform has to offer. We would surmise that the whole package is good enough to impress most who are looking to put together a hot LS street motor. You can bet it would certainly be good enough for us.

Article Sources

About the author

Miles Cook

Miles Cook began his automotive writing career at SEMA, then spent a year at Turbo & Hi-Tech Performance covering the ’90s import scene. He then worked for Car Craft magazine, where he became the de-facto Ford guy on the staff. Next, he went to Mustang Monthly where all Mustangs were the mainstay. Miles is well versed in vintage and late model Mustangs as well as GM, Ford, and Mopar musclecars. His expansive background ensures that Miles is right at home writing for Power Automedia.
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