Jet Performance Engine Tuning and Transmission Setup - CHP Insider

Stephen Kim Oct 1, 2008 0 Comment(s)
0810chp_03_z Jet_performance_engine_tuning_and_transmission_setup Dyno_tuning 2/9

Dyno Tuning
"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."

0810chp_04_z Jet_performance_engine_tuning_and_transmission_setup Efi_tuning 3/9

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."

0810chp_05_z Jet_performance_engine_tuning_and_transmission_setup Q_jets 4/9

"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.

Custom Carbs
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.

Seasonal Changes
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.


Connect With Us

Get Latest News and Articles. Newsletter Sign Up

subscribe to the magazine

get digital get print