The as delivered jetting from holley is very close to optimum for the majority of high performance applications. The ducting will help even out the seasons a little but the engine transferred heat is still hanging around causing troubles and requiring a little bit of attention from you.
Carburetor Basics 101 A Quick Overview Of Primary And
Holley carb jetting 101. Holley carburetors powered every monster energy nascar cup team and nearly every nhra prostock champion for four decades. Holley 4 barrel carburater information list numbers and stock jetting. Lets say you have a 750 double pumper holley 0 4779. This is more complicated than a simple spring change. Tuning a performance street car for its best performance even if you have outside air ducted to the carburetor is a constant job or at least seasonal. In fact it is not at all complex but it can be time consuming.
Tuning the accelerator pump is required to prevent a bog. They can also be used to give the driver more control. In a holley carb the jets are located in the metering block behind the fuel bowl. For every 2000 foot increase in altitude you can reduce the jet size by one size. Power valve tuning theres more to tuning the holley power valve on the primary side than just choosing when the valve opens. Holley carbs are calibrated for sea level operation and an inlet air temperature of 70 degrees fahrenheit.
Since the pilotslow jet is supplying fuel at wide open throttle we always recomend starting with the slowpilot jet. One of the things we noticed over the years is the lack of information concerning holley list numbers and the specifications for individual carburetors and their stock jetting. Air valve carbs provide the best throttle response on street cars. Holley has been the undisputed leader in fuel systems for over 100 years. Many will look at jetting charts and infer from it the jet which is affecting carburetor circuit. For example at wide open throttle the engine runs poorly according to a jetting chart the jet to adjust is the main jet.
Vacuum secondary tuning. Air valve style carbs with. Mechanical secondary carbs are used in race cars that operate at max throttle. As mentioned earlier by selecting the correct spring for the vacuum chamber you take care of 90 percent of the tuning of the secondaries. For the most part the jets delivered with the carburetor should suffice as your tune up baseline. Now holley efi products power these cars and are dominating the performance world.
Considerable mystery surrounds the tuning of the secondaries on a holley carb. Lets say you. Once you know the correct stock jetting for your particular holley carb you can determine whether you live or race at an altitude above sea level.
Gallery of Holley Carb Jetting 101
