Making Boost And Getting Fuel Into The SBF

0
14
Making Boost And Getting Fuel Into The SBF


This is the new Golden Age of horsepower. It’s never been easier to make big power than right now. But it’s always been easy to make big power if you are willing to unleash the funds for the best components. The key is assembling the right combination of parts to not only make the power but to build it so the engine will survive run after run. In the capable hands of Jon Bennett and KBX Racing, this engine features the best of the best.

If you’ve been following the countdown to Project Evil’s full assembly, then you already know it’s a 434ci small-block Ford built around a standard-deck, billet aluminum Dart block stuffed with a Callies billet steel crank, GRP aluminum rods, Diamond Racing forged pistons, a Moroso dry sump, and a combination of a COMP Cams solid roller and a T&D shaft-rocker package.

All of that has led us to this episode, where we will dive into the induction and exhaust systems. For the various classes this car will run, there are rules that limit just how large you can go in this area. Engine builder Jon Bennett was quick to assemble the combination of a Vortech XB105 centrifugal supercharger with all the advantages of methanol fuel. We’ll get to the fuel in a moment, but let’s start with the pressurized power offered by this Vortech blower.

CFE built this angled-inlet manifold to maximize power through equalized entry into all eight intake ports. The upward angle reduces the tendency to affect flow in the leading runners. With all the magic happening in the CFE intake, Bennett matched it with a Wilson 123mm billet throttle body.

Under Pressure – the XB105

The Vortech XB105 specs out with a 5.0-inch inlet O.D. and an inducer diameter that’s rules-limited to 106mm. This supercharger is capable of 35 psi and as much as 1,700 horsepower, but in this application, Bennett isn’t pushing it quite that hard. On the surface, it may appear that the way to make more power is just to turn up the wick, push the blower to its limit, and let it eat.

The reality isn’t quite like Teddy Roosevelt swinging a saber and charging up San Juan Hill with the Rough Riders. It’s more subtle. Basic physics and the Vortech’s engineering data suggest that all superchargers have a sweet spot where they can move the most air without creating an overheated intake charge.

Any type of device that compresses air adds heat, both through the natural act of squeezing the molecules closer together, along with the conduction of heat from the compressor itself. One key to making horsepower with a blower is to minimize the heat as much as possible since cooler air is denser air.

Inlet air density is a term that references the amount of oxygen in a given volume of air. As the air is pressurized, its density increases while simultaneously decreasing due to its increasing temperature. In this case, the XB105 blower is capable of moving a large volume of air at a given boost pressure. That volume of air is capable of making the required power for this project.

Boost pressure is often mistakenly identified as the primary factor in making power. In reality, gauge pressure (PSIg) is actually an indicator of resistance to flow. Pushing air through a large-enough inlet tract, the Vortech supercharger could move its maximum volume of air with near-zero gauge pressure.

The Vortech XB105 fits within the limitations of the rules for this X275 Mustang yet can still move some serious air, sufficient enough to produce maximum output figures of up to 2,900cfm, and 35psi of boost. The flow numbers will support up to 1,700 horsepower.

But presented with downstream restrictions (inlet ducting, a throttle body, the intake manifold, ports, and of course, the intake valve), pressure is created. Another key to power is selecting the right size intake tract to create the least amount of restriction while also producing power within the engine’s intended RPM-band.

Any supercharger can be evaluated by measuring the amount of air it moves at a given pressure, and by how much the blower heats the air as it performs this task. The most popular way to express this performance is with a compressor map that indicates “islands” of efficiency ratings.

The Vortech XB105 offers a 75-percent adiabatic peak-efficiency rating, which is very close to the typical best numbers for a centrifugal supercharger. Without going into extreme detail, the higher the percentage, the more efficiently the blower creates pressure while minimizing heat buildup.

Chris Alston’s Chassisworks builds this Component Driver Systems (CDS) blower mount that uses a six-lug drive to step up crankshaft RPM in this application by a ratio of 2.15:1.

Adding boost pressure certainly can improve power, but as the boost goes up, so does the charge air temperature. Discharge temperatures from the blower at 25 psi can be as high as 275- to 300-degrees Fahrenheit, which is not good for power. The increased air temperature reduces the density and, therefore, its oxygen content.

According to Vortech engineer Lance Keck, the 75-percent efficiency numbers are with the blower operating in its most efficient range, so heat in this area is a real issue. Adding a water-to-air intercooler makes a lot of sense, but in this case, the rules don’t allow it.

Keepin’ Cool

An excellent way to reduce the discharge temperature from the blower is to run methanol instead of gasoline. If you’ve ever had a nurse swab your arm with alcohol before sticking you wth a hypodermic needle, then you know that as the alcohol evaporates, it pulls heat out of your skin, leaving your skin cooler for a moment.

The same thing happens to the inlet air when combined with massive volumes of methanol in the airstream. Reducing the inlet air temperature by 50 to 75 degrees is certainly possible, which improves the air density and power at the same time.

This efficiency effort goes beyond just discharge temperatures. It requires power to drive a centrifugal supercharger, given the huge volumes and pressures of air the blower must deliver. Belt-drives for blowers tend to increase the power demands, which is why Bennett opted for a Chris Alston Chassisworks Component Drive Systems (CDS) crank-driven blower drive package.

This particular CDS version is a gear-driven package that overdrives the Vortech by a ratio of 2.15:1. Combine this ratio with the XB105’s internal step-up ratio of 4.21:1, and that establishes the blower’s peak impeller speed.

This side view reveals the significant length this drive adds to the front of the engine. The drive also mounts the Aeromotive electric fuel pump as well as the dry-sump system.

The XB105’s factory-rated redline speed is 69,000 rpm. If we multiply an 8,000-rpm engine speed by both the external ratio of 2.15:1 and the XB105’s internal step-up ratio of 4.21 (2.15 x 4.21 x 8,000), we get 72,412 rpm, which is just slightly above the blower’s maximum rated speed.

One reason racers have converted to the crank-drive is to reduce the bending moment on the end of the crankshaft that results from the load created by the blower’s horsepower draw and belt tension. This is no small amount of load, and that tension translates into a measurable loss of power.

Plus, the friction applied by the belt is also a factor eliminated by the use of the crank-centerline mounting of the drive unit. Smaller centrifugal superchargers only realize minor power reductions at low boost. But big blowers can demand 400 horsepower (or more), creating insane belt loads and bending-moments that cannot be ignored. As an example of drive power requirements, Keck told us that current Pro Mod blower parasitic losses can be as high as 900 to 950 horsepower!

Moving On Up

For all that boost to be efficiently distributed and ingested, no standard intake manifold would do. It wasn’t a difficult decision to have Carl Fult’s team at CFE Racing perform their magic. The team’s approach began by establishing the proper runner length and taper angle required for this particular application.

While the runners are often fabricated from sheet aluminum, in this case, CFE stepped up to a set of billet aluminum CNC-machined runners whose tapers were then matched to CFE’s calculated plenum volume. They also chose to include a monstrous Wilson Manifolds 123mm (4.84 inches) throttle body to complement the airflow requirements.

The ideal position for the throttle body on a turbocharged or supercharged application is on top of, and in the middle of, the intake plenum. Since this wasn’t possible in this case, CFE angled the leading edge throttle position to aim the incoming pressurized air up toward the top of the manifold to more evenly distribute the incoming air across all eight inlet ports.

Note the intake runners on this CFE intake are CNC’d billet pieces that are carefully machined to produce an optimal port taper and length. The injectors are 770 lb/hr, low-impedance Billet Atomizers.

Previous experience has shown that when the throttle body is positioned at the front of a short plenum, high-velocity, high-pressure air across the front two intake ports can cause a siphoning effect that can literally pull fuel out of these intake ports, causing those cylinders to run lean.

Located roughly halfway down the ports are the electronic fuel injectors with only one injector per port. When dealing with methanol, it’s not unusual to see a pair of injectors per cylinder. But in this case, Bennett opted for a single set of 700 lb/hr injectors from Billet Atomizer. That might seem like a huge injector size — because it is! Obviously, Bennett has done his homework for selecting these injectors, but let’s run through it to show you how the math works.

Fueling the Fire

First, let’s start with brake specific fuel consumption (BSFC). This spec represents the pounds of fuel burned to produce one horsepower for one hour (lbs/hp/hr). A properly-tuned, naturally aspirated engine on gasoline will be somewhere around 0.45 lbs/hp/hr. Aeromotive’s recommendation for a supercharged engine on gasoline is 0.65 lbs/hp/hr, which is substantially more (nearly 45-percent) than the naturally aspirated number. Part of this increase in fuel use accounts for the power required to drive the blower, as we’ve discussed earlier.

The rule of thumb for methanol is it requires roughly twice the amount of fuel consumed compared to gasoline. So a normally aspirated engine on methanol would have a BSFC number of 0.9 to 1.0. But for supercharged methanol engines, Aeromotive recommends doubling that number to a staggering 1.8 to 2.0 lbs/hp/hr.

To determine a sufficient injector size, we first must have a horsepower goal — in this case, we chose 1,800 horsepower. 1,800 divided by 8 equals 225 horsepower per cylinder to be fed by each injector. Multiply that by a BSFC of 2.0, and it equals 450 lbs/hr of fuel required by each injector. Most injector companies aim for an 80- to 85-percent duty-cycle number as a safety margin.

Because the injector is now turned off for 20-percent of the time, this means we must add 20-percent to the size of the injector. Doing the math, we end up with 1,800 / 8 = 450 x 1.2 = 540 lbs/hp/hr for an injector size. We used 1,800 horsepower because it’s important to account for the power required to drive the blower. This horsepower does not show up at the flywheel but still requires fuel to produce.

Moving 10 gallons of methanol per minute is a job meant for a mechanical fuel pump, which in this case, is an Aeromotive 12-series. It can deliver enough fuel to feed a 2,500-horsepower race engine.

Bennett spec’d a set of 700 lbs/hr injectors, which offers a substantial safety margin, and also reduces the base fuel pressure required to feed these injectors. This is an important consideration because starting at a base pressure of 50 psi means the pump does not have to work as hard to create the additional pressure required by the boost.

This lower base pressure allows the tuner freedom to use a 1:1 boost reference to match the fuel pressure as the manifold boost pressure climbs to its peak number. With a base fuel pressure of 50 psi and a maximum projected boost of 40 psi, this means the total peak fuel pressure will be 90 psi.

Consider the total fuel flow of methanol pushed by as much as 90 psi. Even multiple electric pumps would be challenged to get the job done. For this task, Bennett stepped up to an Aeromotive 12-series mechanical fuel pump, capable of a massive 126 pounds-per-minute capacity.

Plumbing an engine like this is not a simple matter. But, using Earl’s Ultra-Flex 650 Kevlar braided hose in -12, -10, and -8 sizes made the job a little easier. The hose requires specific crimp-collar fittings but ensures leak-free connections, especially when exposed to 90-psi fuel pressures.

This equals over 7,500 pounds of fuel per hour. Eight 700 lbs/hr injectors at a 100-percent duty cycle represents only 5,600 lbs/hr of fuel through the injectors, so the Aeromotive pump can supply this engine’s needs while offering roughly 25-percent excess capacity. There’s plenty of pump here to do the job.

With the hydraulic side of the fuel system engineered, Bennett decided on using FuelTech’s new FT600 ECU to control the electronic side of the engine. The FT600’s display can be used as a dashboard while monitoring all the information the driver may need. Plus, the system also runs eight individual ignition coils that are powerful enough to get the fire started, even with all that fuel in the cylinders.

Bennett chose the FuelTech FT 600 EFI system to exert control over the fuel and spark curves. The system is ultra-sophisticated with tiers of control mechanisms that include gear-based timing control to give the engine tuner more command over the engine as it accelerates down the track.

The software package on the FT600 is robust, allowing fuel control that includes manipulation over spark and fuel in each individual gear, along with multiple other features far too numerous to mention here. Tuning for this engine is not like a typical gasoline engine. With gasoline, the optimal air-fuel ratio falls within a very narrow range. Methanol’s lower energy content means you burn roughly twice as much fuel as gasoline, but methanol also brings with it massive inlet evaporative cooling on the way to the cylinder.

Bennett says his ideal air-fuel ratio is somewhere between 3.75:1 and 4.0:1, which means only four parts air to one part fuel, instead of gasoline’s stoichiometric point of 14.7 parts air to one part fuel. Unlike gasoline, methanol air-fuel ratios can run significantly on the rich side with no detriment to power.

Bennett says ignition timing for methanol engines isn’t really all that much different from gasoline engines. Also with boost, the numbers are substantially more conservative. Still you can understand why he’s reluctant to discuss specifics. That’s how all racers are.

Burns Stainless constructed the 304 stainless stepped headers starting with a smaller 1 7/8-inch primary that increases to 2-inch before the collector. Note the use of a Burns four-into-one merge collector before it transitions into the bullhorn exhaust.

With everything buttoned up, the engine was bolted up to the dyno to validate everything and get a baseline tuneup for the engine. In an engine of this caliber and design, elapsed time is a much more important factor than a number on a dyno sheet. Also, keep in mind, this is an engine destined for a heads-up racing series, so the fact KBX and the DragZine team are allowing us to share these numbers at all publicly is a pretty big step.

After a couple of pulls to sort out fueling and ignition timing, Bennett set the engine dyno for a 5,000 to 8,000-rpm sweep and gave it the business. The engine’s performance at full-song was something to behold, and the final number left everyone smiling. However, those numbers aren’t meant for public consumption. Instead, we were given a dyno sheet from one of the pulls where Kolivas was sorting out the fueling.

Those numbers are still extremely impressive, coming in at 2,282 horsepower at 7,900 rpm and 1,566 lb-ft of torque at 7,600 rpm, but with a flat 1,500 lb-ft torque curve from 6,100 rpm to 7,900 rpm, which will be very useful on the dragstrip.  In addition to having plenty of power, this engine should withstand the abuse of repeated runs down the eighth-mile better than most.

As you can see from this dyno pull, KBX tuner Jon Kolivas was working on smoothing out ignition and fuelling between 6,200rpm and 7,100rpm. While we weren’t given the final run data, these numbers aren’t anything to sneeze at.



DragzineDragzine – Making Boost And Getting Fuel Into The SBF

Facebook Comments