Dan Nicholas of Jet Performance
While people may have biases over which method of administering fuel they think is best, engines don't give a rip. Feed them well, and they will treat you well. This is evidenced by the fact that great carb tuners often make great EFI tuners. Although Jet Performance is best known for boosting horsepower through electronic wizardry, it cut its tuning teeth in the '60s modifying carburetors for NHRA Stock and Super Stock drag cars, showroom stock road racers, and circle track machines. The company's talents didn't go unnoticed, and Jet served as an OE consultant during the '70s, lending its expertise to designing cleaner, more efficient fuel systems. Naturally, with the proliferation of EFI performance cars in the '80s, Jet tapped into its vast pool of technical aptitude to unlock the potential hidden inside computer-controlled vehicles.
Today, Jet offers a full line of chips, hand-held programmers, and custom tuning software to electronically maximize the performance of just about any modern fuel-injected Bow Tie ever built. Jet has also expanded its reach by developing transmission components and various engine accessories in addition to a bevy of custom-calibrated race and street carburetors. To get the lowdown on the latest developments at Jet and pick up a few tuning tips along the way, we consulted Dan Nicholas. Here's the skinny.
"Chips were used on earlier fuel-injected GM vehicles where you would actually remove the stock chip (aka EPROM) from the computer and replace it with an aftermarket unit," says Dan. "Hand-held programmers are for newer vehicles that don't have removable chips, and they allow modifying far more programming parameters than the set program that was written on chips. It's just like the older computers that had 20 megabyte hard drives while today's computers often have hard drives larger than 500 gigs. Whether via a chip or a hand-held programmer, the major tuning changes made on gasoline vehicles are in the fuel and ignition advance maps. With our tuning, we typically see an 8-10 percent gain in horsepower and torque at the wheels. Additionally, newer vehicles allow modifying cooling fan thresholds, shift points, speedometer calibration, rev-limiters, and shift firmness."
Modern diesel motors are different animals than their gasoline counterparts, and therefore require a different approach to tuning. Since they implement bulletproof short-blocks pressurized by turbochargers, and burn their air/fuel mixture through auto-ignition, diesels pick up tremendous amounts of power through tuning compared to gasoline engines. For instance, a Jet Performance programmer can add up to 130 hp and 205 lb-ft on a GM Duramax diesel. There are some tradeoffs, however. "Getting the tuning right on a diesel is definitely a balancing act," explains Dan. "You want to get the perfect tune of air and fuel, because too much fuel without a sufficient amount of airflow to go along with it will dramatically increase exhaust gas temperatures and decrease the life of the motor."
"As density, altitude, and air temperature change, so must your tuning," Dan advises. "If you designed the fuel map for a 32-degree day, but it's 104 degrees at the track, then the thinner air will make the air/fuel mixture rich and reduce power. One of the best tools for tuning at the track is a wideband O2 sensor for accurate air/fuel ratio readings. This allows you to pick your proper jet sizes, or to dial in the correct fuel map in the case of EFI motors, and to set the proper ignition advance. Since running too lean can destroy a motor, it's not a bad idea to start by tuning it in the other direction first by running rich before leaning it out, just to be safe."
"On the dyno, you typically tune a motor by running the vehicle up to a certain load point, then increasing the load on the inertial dyno," Dan explains. "This will set the air/fuel ratio and optimize timing. You then go to the next load point and repeat the process in 500 rpm increments. The result is tuning that maximizes power, torque, and throttle-response under all driving conditions, not just WOT. The final test is thorough track and street testing to make sure the tuning works well under real world conditions."
Carb VS. EFI Tuning
Fuel injectors and carburetors achieve their objectives through different means, and they each have their pros and cons. If you have owned hot rods with both types of induction systems, understanding how each works will pay dividends when dialing in their fuel curves. "While a carburetor reacts to the actual vacuum a motor produces through mechanical means, an EFI system senses the load on the engine via throttle position sensors [TPS] and manifold absolute pressure [MAP] sensors," says Dan. "The benefit of using TPS and MAP sensors is that they allow a tuner to have much more precise control over the fuel map at different rpm and engine loads for improved drivability. On the other hand, an EFI motor with a big cam will tend to run excessively rich because of the decrease in manifold vacuum at idle and under light loads. That's why proper tuning in so important in internally modified EFI vehicles."
"One huge advantage of the Q-jet is that its spread-bore baseplate features smaller primaries, which will give you nice crisp acceleration and excellent fuel mileage," Dan says. "That's a huge plus with today's gas prices. Also, Q-jets transition very smoothly and quickly at heavy throttle, since you don't have to wait for a set of vacuum secondaries to open up. That's not to say Q-jets are necessarily better, because they definitely have their limitations, but they're more capable than many people give them credit for." For GM buffs, Jet offers a line of rebuilt Q-jets. Features include properly sized circuits, custom-calibrated metering rods and jets, new floats, choke pull-offs, throttle-shafts, and casting plugs that are sealed with epoxy to prevent leak-down. Some applications also include custom-matched needle-and-seat assemblies.
Out-of-the-box carbs do an excellent job for most applications. "More radical combinations may require a custom carburetor," says Dan. "Fortunately, Jet offers everything from Dominators to Q-jets custom-calibrated to any racing or street application." Jet's custom carbs are modified with custom-sized circuits, modified metering blocks, and premium hardware. Available options include removable air bleeds, modified floats, high-flow needle-and-seat assemblies, increased venturi diameter, modified boosters, and radiused throttle-shafts.
Depending on what part of the country you live in, common sense says that seasonal changes in temperature might require tweaking carb calibrations. "If you're living in an area like Southern California, then you probably don't have to worry too much about seasonal changes, but if you're living in an area like Denver where temperatures can range from 90 degrees in the summer to 20 degrees in the winter, then changing your jet sizes from the stock calibration is critical," say Dan. Additionally, ignition advance shouldn't be overlooked, especially if warmer weather yields detonation issues. Running a motor overly rich to compensate for too much ignition advance is a no-no. While hotter temperatures may only require backing off the total advance a few degrees, engines generally require a greater reduction in initial advance since they see far greater loads during part-throttle, low-rpm operation.
"Jet started out 40 years ago as a racing carburetor shop," Dan says. "As we started to tune and find ways to make power, we moved into other areas of automotive performance. Today, this includes our carburetors, chips, programmers, transmission components, and various engine accessories. Our tuning expertise eventually led to working with EFI systems in the mid to late '80s, and that's when our company experienced its most dramatic period of growth. This allowed us to grow and develop new applications for a whole new market of vehicles. Over the years we have been extremely lucky to have worked with some of the brightest minds in our industry. We are extremely proud to manufacture all of our products in the USA."
Although Jet is best known for its electronics expertise, the company also has a full line of performance accessories. "We manufacture everything from high-performance mass air-flow sensors to throttle-body spacers, to low-temp fan switches, to underdrive pulleys, to low-temp thermostats, to fuel pressure regulators, to speedometer calibration boxes," says Dan. "We also carry a lot of carb rebuild components. Currently, we're also developing a Q-jet that's compatible with E85."
LS1 & LT1 Tuning Software
Late-model GM vehicles, particularly those equipped with LS-series motors, come with extremely advanced computers from the factory. Tuners are taking advantage of this, and Jet is no exception. "We offer software that allows tuning your own vehicle via your personal computer," Dan explains. "With it, you can access every part of an LS1 or LT1 computer for an unbelievable range of custom changes. We actually allow consumers to download the software free of charge off of our Web site, and try it out to see if it's something they can handle. It can't be used on the vehicle without our hardware, but they can see how the tables and different parameters work."
In addition to standalone trans computers and billet servos, Jet also manufactures high-performance torque converters and shift kits. "Our torque converters feature furnace-brazed fins, Kevlar clutches, a reinforced hub assembly, computer balancing, and stall-speeds that can be customized to any application," says Dan. Additionally, Jet's Power Shift controller allows for the selection of four transmission shifting firmness settings at the touch of a button in many computer-controlled vehicles. It plugs into the trans wiring harness, and increases line pressure on demand.
Unlike newer EFI systems whose computers can be reflashed over and over again, early computer-controlled vehicles required swapping out chips each time tuning calibrations needed to be changed. To lessen the hassle, Jet offers a nifty compromise called the Six-Pack, which is available for select '88-'95 GM vehicles. "The Six-Pack was basically the early version of our performance programmer," says Dan. "It allows you to select from one of six different chips at the touch of a button without having to manually remove and replace them. It has one chip set up for lower octane fuel, one for higher octane fuel and mild bolt-on mods, one for improved fuel economy, one with timing curves designed specifically to boost low-end torque, one with a valet mode that reduces engine power, and another with a security mode that shuts down the injectors."
Jet Performance Products