If you’re building a naturally-aspirated engine that’s going to make big horsepower, you’ll want a top end and valvetrain that’s been well thought out. In this article, we’re going to take a look at these key areas of our naturally-aspirated 427 cubic-inch LS engine that SAM Tech has built for Project Number Cruncher.
The last time we saw Project Number Cruncher’s engine the short block was being finished by the students at SAM Tech. The Dart block was built out with great parts to ensure the engine would be very strong and not have any issues making well over 700 horsepower without a power-adder. The SAM Tech students had a lot of fun putting the finishing touches on the 427 cubic-inch engine before bolting it to the school’s engine dyno to see how much horsepower it would make.
Project Number Cruncher’s LS-based engine features a set of Dart’s Pro1 LS7 cylinder heads. In a previous article, we covered the technical specifications of these cylinder heads and explored their development. The cylinder heads play a crucial role in horsepower generation for a naturally-aspirated engine build like this, so it made sense to use Dart’s Pro1 heads.
Dart put a lot of effort into improving the overall design of the OEM LS7 cylinder heads with its Pro1 unit. Mike Sanders from Dart spoke to why these heads are a great fit for this build.
“Our 12-degree LS7 285cc CNC head was designed to be used in naturally-aspirated or forced induction applications. Like all heads we develop, we adhere to strict cross-sectional formulas and maintain specific velocity numbers to make sure the port doesn’t become turbulent. This allows the fuel to stay in suspension for maximum fuel shear off the valve job, and increase cylinder fill for the duration that the valve is open.”
A naturally-aspirated engine doesn’t have a way to stuff a more dense air charge into its cylinder bore thanks to a power-adder, and that means you need to make the engine as efficient as possible. Aftermarket cylinder heads like Dart’s Pro1 LS7 head are designed to maximize efficiency.
Andrew Hachmeister from SAM Tech explains the benefits of going to an aftermarket cylinder head for a high-horsepower, naturally-aspirated build.
“The pushrod holes being wider on these heads allow the entrance of the port to become closer to being square. This means we don’t have to pull so much material out of the floor of the port. This creates an optimal path for the air to make it around the turn and get inside the engine easier. An aftermarket cylinder doesn’t require us to alter an existing port that was designed for efficiency at lower engine speeds. This allows us to create our own port with more freedom to do what we want. There’s more material where we want it, and also more material around the port so we have less of a chance of hitting a water jacket when we are designing a port for high airspeeds.”
All Aboard The Valvetrain
A naturally-aspirated engine that’s going to make serious horsepower must have a stout valvetrain. The team at SAM Tech spent a fair amount of time accounting for our goals and selected parts to make sure there wouldn’t be any stability issues. The final result is a rock-solid valvetrain that can spin to nearly 8,000 RPM without batting an eye.
The lifter bores of Project Number Cruncher’s block are fitted with .904-inch Race XD REM Finished Bushed Solid Roller lifters from COMP Cams. These lifters are ultra-strong and have REM finished bodies with bronze alloy bushings for extra durability. The lifters also feature tool steel pushrod seats and dual oil feed holes to the lifter’s axles. Basically, these lifters are made to take abuse in a high-horsepower engine.
SAM Tech wanted a lifter that could transfer the rotational movement of the camshaft into a linear movement as smooth as possible. The .904-inch Race XD lifter was a great choice for this thanks to its bushed wheel assembly, captured link bar, and pressurized oiling design.
“When choosing a lifter, you have to consider your options and application, so the .904-inch Race XD lifter from COMP made sense. Going to a larger diameter lifter will allow you to fit a larger wheel on the bottom to create less force pushing sideways; this will have less strain on the parts internally. Also, with a larger diameter lifter, it creates more surface area for the load to spread out more evenly, creating less drag,” Hachmeister explains.
Cam selections are really critical when trying to make the most power for a high horsepower application, especially when a power-adder isn’t being used. – Chris Mays, COMP Cams
The camshaft inside Project Number Cruncher’s Dart block isn’t’ an exotic grind that requires top-secret clearance to see its specs, it’s just an off-the-shelf COMP Cams unit. This particular cam uses COMP’s Low Shock Technology (LST) — these are lobe profiles that make a lot of horsepower while providing plenty of stability higher into the RPM range. The LST cams don’t beat up your valve springs as much, have more durability, and keep load loss to a minimum.
Number Cruncher’s camshaft has .672-inches of lift on the intake side and .688-inches of lift on the exhaust side. The duration measures 258-degrees at .050-inches of lift on the intake side, and 272-degrees at .050-inches on the exhaust side. The camshaft has a lobe separation of 113-degrees. An adjustable timing set from Cam Motion connects the camshaft to the Dart crankshaft.
Chris Mays from COMP Cams explains why this camshaft was a solid choice for our engine.
“Cam selections are really critical when trying to make the most power for a high horsepower application, especially when a power-adder isn’t being used. The additional duration and lift increase the engine’s ability to make a lot of power between 4,500-7,000 RPM. The duration and lobe separation are a great match to this engine’s RPM operating range too. This camshaft’s LST technology is going to make it reliable and help it make really good power across the board.”
The Dart Pro1 heads come with a custom five-angle profile that has copper impregnated powdered metal seats, or optional copper seats. The heads are machined to use a 2.200-inch intake, and 1.625-inch exhaust valves that have special profiles designed to move the most air possible while also maximizing fuel distribution.
“We received Manley valves for this build; since we are not spinning this engine to a really high RPM level where every gram on the valve side matters, and since there are no power-adders being used, we decided to go with stainless valves. Stainless steel valves will allow the engine to run longer between refreshes, and they will be more durable for this application,” Hachmeister states.
Dart has the ability to create a custom valve spring package for its Pro1 heads based on your specific build. You can choose from PAC or Manley springs based on what you need.
“With all of our valvetrain components that were selected, we decided not to skimp on the valve springs. We went with PAC 1238x springs for this build; these springs will provide enough spring pressure to control everything that is happening inside of the engine, and they will last a long time,” Hachmeister says.
Pushrod selection is another task that SAM Tech took seriously with this engine build. A pushrod experiences a lot of stress and not having the right one will cause valvetrain issues. SAM Tech had to look at multiple factors before it decided which Trend pushrod would go into the engine.
“When you’re choosing a pushrod, you have to consider the RPM level the engine will be operating in, the spring pressure, and how big of a push rod can you physically fit in the engine without any issues. We went with a Trend 7/16-inch double tapper pushrod. We chose the double taper to allow for clearance on the tie bar of the lifter, and for clearance of the rocker arm. The Dart heads will accept a 7/16-inch diameter pushrod with ease, and that size pushrod will also be rigid enough for this engine,” Hachmeister explains.
The last stop on our valvetrain ride is the rocker arms. Project Number Cruncher’s naturally-aspirated engine will sing a pretty RPM-based song, so with that in mind, we wanted to make sure the rocker arms we used would be up to the task. The last thing you want with a high-winding, naturally-aspirated engine are rocker arms that can’t control the valvetrain.
Sheldon Miller from T&D Machine explains the features you want in a set of rocker arms that will be used on a high-horsepower, naturally-aspirated engine.
“Stability is one of the biggest things you need to look for in rocker arms. Way back when, stud mount rockers were common — racers would use a stud girdle to keep the studs from moving under high load or high RPM. A superior way to do this is with a shaft mount rocker system. The rocker can’t rotate on the shaft, so you lose the guide plates, you have far more adjustability to fine-tune the geometry, and better yet, the rocker is fastened to a stand that won’t allow any movement. This gives you far more stability over a single stud attempting to hold everything together.”
With that information in mind, it made our rocker arm selection easier.
“We decided to go with T&D’s aluminum rockers on this build,” Hachmeister says. “With the aftermarket rockers, we now have an adjuster to adjust lash. We also have a rocker stand that has a wider footprint to create less deflection, along with the shaft mount setup of the rocker arms that are fastened down on either side of the rocker arm which will create a more stable rocker that will not deflect as much.”
Bringing The Air In
Naturally-aspirated engines are very sensitive to airflow and how it’s presented to the engine. You therefore have to take into account what the engine needs to run as efficiently as possible since there’s no power-adder making up for any inefficiency the engine might have. That means you need to make sure your intake will work as a part of the naturally-aspirated horsepower team you’re building.
Dart sent us one of its Pro1 LS intakes to match the heads we are using — this is a two-piece intake that includes some great features.
“Like all manifolds we design, line-of-sight and port entry is our number one focus. Since this is a two-piece intake, we can fully CNC-port the complete intake manifold from top to bottom, and our design offers an exceptional line of sight to the cylinder head port opening. In addition, our manifold has multiple options including 4150 carb or throttle body mounting provisions, and is available with or without fuel injection machining,” Sanders says.
SAM Tech had a good idea of what RPM range our engine would operate in and how much horsepower it could potentially make. Those are two important factors when you’re looking at which intake you want to use.
“The air inside of the intake tract doesn’t have a constant direction of flow…it pulses. This is why there are so many different varieties of intakes on the market that go together with different port designs and camshafts to fit each engine as best as possible. We pay close attention to the shape of the intake’s runners, length of the runners, the taper, and the volume of the plenum. The Dart intake was pretty close to perfect and needed almost no work, besides fitting a 4500 throttle body onto the 4150 flange. Our students also brought it into shape to work together with our intake port in the cylinder head for the operating range of the engine we were shooting for,” Hachmeister says.
The final part of the induction equation is the throttle body. You have to treat the throttle body selection just like you treated the intake selection and make sure it will match your goals. SAM Tech wanted to be sure we had plenty of air to feed our Dart-based LS engine, so itselected a Wilson Manifolds 4500 Dominator throttle body.
Keith Wilson of Wilson Manifolds explains how the company approached the design of this throttle body and why it works so well.
“We put a lot of effort into the shape of the throttle body to make it flow as much as possible. This throttle body will deliver an immense amount of air into the engine very evenly. It controls the velocity of the air that’s coming into the manifold, and that’s really important for a naturally-aspirated engine. This throttle body will flow over 1750 CFM of air, but it will still be controllable and won’t hinder tuning.”
We pay close attention to the shape of the intake’s runners, length of the runners, the taper, and the volume of the plenum. – Andrew Hachmeister, SAM Tech
The job of the throttle body in an EFI system is to help meter the air. A throttle body like this Wilson Manifolds 4500 Dominator is great because it makes sure all the air is going where it needs to go.
“We wanted a throttle body that had smooth action and was large enough to not pull a vacuum at the top of the run. One big trade-off with going to a larger throttle body is drivability goes down. This is because a small movement in the throttle blades makes a big change in the amount of air it allows by. With this Wilson throttle body, they addressed that issue by running a progressive butterfly on the rear of the throttle body. This makes the drivability more manageable and helps with tuning,” Hachmeister states.
To help the engine breathe as deeply as it can, SAM Tech added one of Wilson’s throttle body spacers to the mix. This move served two purposes; first, it made converting the intake from a 4150 flange to a 4500 flange easier. Second, it would make it easier for air to be directed where it needed to go inside the intake.
“The reason why we opted to run a spacer was not for more plenum volume, but more for guiding the air. The air does not like to go from a small space into a large space, just like the air behind your car when you’re driving. This spacer gives the air some guidance so it does not block off the throttle body as bad and create a restriction,” Hachmeister explains.
Fuel And Spark
Now that we’ve covered how we’re introducing air into Project Number Cruncher’s engine, it’s time to talk about where the fuel and spark are coming from. These are two of the most important components in the combustion process, so you need to have plenty of each in a high-performance engine.
Our engine will be controlled by a FuelTech FT550 ECU, a pair of WB-O2 Nanos will monitor the AFRs, and a FuelTech LS1 harness will deliver instructions to the engine. This EFI system will control the fuel and spark for the engine — we will do a deeper dive into these parts in a future article.
To ensure we were getting the right amount of fuel into the engine, SAM Tech used a set of fuel injectors from Fuel Injector Clinic. Darren Smithers from SAM Tech explains how they calculated what size injectors our naturally aspirated mill would need.
“We use the brake specific fuel consumption formula (BSFC) to calculate injector size. This formula looks at the total fuel flow required, divided by the number of injectors, and comes up with the minimum injector size required which would be at 100% duty cycle. In its current form, we think this engine could make about 825 horsepower. Generally accepted BSFC ranges for N/A gas engines is .45 to .55. Using .55 to error on the rich side, we take 825 horsepower and come up with: .55 BSFC = 453.75= 454 lbs/hr which is the total fuel flow required. That means 454 / 8 (1 injector per cylinder) = 56.75, so 57 lbs/hr is the minimum injector size we would need. We then multiply whatever percentage we want to offset for a target duty cycle (i.e. 1.2 as a multiplier will yield ~ 80-percent duty cycle). 57 * 1.5= 85.5 should yield about 50 percent duty cycle. Our 94 lb/hr injectors will be at slightly less than 50-percent duty cycle at full tilt boogie, leaving plenty of room to grow as is often needed.”
Jens Von Holten from Fuel Injector Clinic explains why you need to feed your engine the right amount of fuel when you’re trying to make big naturally aspirated horsepower.
“Working hard on equal air supply to each cylinder can easily be negated by unequal fueling causing inconsistent combustion. That is true for N/A builds as well as all others. The other advantage that Fuel Injector Clinic injectors offer is the matching at short pulse widths, which is where fueling is by far the most critical for good idle and part throttle characteristics. Not only do we provide the closest matching available in the industry today, but each Fuel Injector Clinic injector set is accompanied by a data sheet and downloadable tuning data that the tuner needs to accurately describe the injector characterization in the ECU.”
The air and fuel in the cylinder will need a spark to ignite so that horsepower can be produced. The FuelTech 550 ECU cranks out 175mJ of energy to create the spark required to fire each cylinder. A set of MSD coils got the call to provide the juice to run our engine. SAM Tech has used these coils on many of its LS builds, so they are more than capable to handle our spark requirements.
Evan Perkins from MSD explains why these coils work so well for a build like this.
“Our coils are designed with improved materials and windings to produce a stronger spark, which is going to improve performance in a naturally-aspirated combination. The additional spark energy helps maximize combustion and increases horsepower. Our coils are also a direct replacement for worn, factory coils which makes installing them extremely simple.”
The coils are just one part of the ignition puzzle — you need to transfer the energy they generate to the spark plugs so the engine will fire. Not all spark plug wires are created equal; for a high-performance application like this you need to use wires that offer low resistance, and can efficiently transfer the power to the plugs. With that in mind, that’s why we used a set of MSD’s Super Conductor spark plug wires.
“Race engines operate at higher loads and cylinder pressures than street engines, and those conditions demand a hotter spark to light the air/fuel mixture. Our 8.5mm Super Conductor spark plug wire sets offer only 40-50 Ohms of resistance per foot, which allows them to maximize the amount of energy delivered to the plug. They also offer exceptional RFI suppression which helps prevent noise issues with modern, electronic fuel injected engines,” Perkins says.
The students and staff at SAM Tech worked hard to get Project Number Cruncher’s engine ready. When this project was started the goal was to build a reliable LS-based engine that would make good horsepower and be a bracket racing workhorse. The only thing left to do was to bolt the engine to the dyno, wire up the FuelTech ECU, and make some pulls.
A big advantage of going with a naturally-aspirated engine with a build like this is the linear power the engine makes. That linear power curve will provide us with a solid base for power management no matter what track conditions we face. We will need that kind of control to help us print off consistent timeslips at the track.
The dyno graph tells the tale of how powerful Project Number Cruncher’s new heart is. The engine pulls all the way up to almost 7,700 RPM and generates 781 peak horsepower with 608 ft/lb of max torque. This will be more than enough to push our Firebird into the 9-second zone on a regular basis in even the worst atmospheric conditions.
A special thanks goes out to the staff and students at SAM Tech for creating this amazing engine. The next time you see this engine it will be resting between the fenders of Project Number Cruncher getting plumbed and wired for racing action. You can follow the build progress of Project Number Cruncher right here on Dragzine.com.