Editing Quadrajet (section)
Jump to:
navigation
,
search
==Tuning== [[File:POWER PISTON SPRINGS.gif|thumb|200px]] ===Power Piston Springs=== The power piston (PP) spring is seldom mentioned when Q-Jet tuning is being discussed, but it need to be addressed just like if it were a Holley. The same principals apply when tuning for low vacuum cams, etc. The power piston spring allows the power piston to behave like a Holley's power valve. That's to say the power enrichening system is vacuum controlled. At high vacuum, the vacuum exceeds the PP spring rate and the primary rods are pulled down into the main jets, leaning the fuel/air mixture. Conversely, when vacuum drops like when under a load or the accelerator pedal is whacked WFO, the PP spring rate exceeds the vacuum, which lifts the rods up to their smaller diameter "rich" position. If a “medium” PP spring = a Holley 6.5 in/Hg, a "soft" PP spring (allows enrichening to come in at a lower vacuum) would be like a 3.5 Holley PV; a “stiff” PP spring = a Holley PV of, say, 8.5 in/Hg. Longer duration cams will “like” a softer PP spring. Below is an image showing a variety of different springs, another shot shows three different types of power piston. The springs vary in length, coil diameter and wire diameter (0.012"- 0.020" in my collection). Edelbrock has different PP springs in a "Race Calibration Kit" that contains a selection of main jets and rods, secondary rods, hangars, PP springs, high flow needle and seat and an accelerator pump. Gessler and Ruggles both carry a selection of PP springs as well as many other tuning and repair parts. GM p/n 7029922 is a rather weak spring that was OEM for HO Pontiac engines from the early '70's. It delays enrichment until vacuum drops to 3 in/Hg. This spring will work with durations >/= 230 degrees @ 0.050”. Another GM p/n is 7037305 for a PP spring that is set for 6 in/Hg, and would work well w/a high vacuum, smooth idling and/or wide LSA-type cam. Thing is, unless the parts counter guy is cool w/you, they come in packs of 10 springs. ===Secondary metering hangars and rods=== [[File:Secondary rods 002.jpg|thumb|left|250px]] <br style="clear:both"/>
|
Editing help
(opens in new window)
Personal tools
Log in / create account
Namespaces
Page
Discussion
Variants
Views
Read
Edit
View history
Actions
Search
Navigation
Main Page
Recent changes
Random page
Help
All articles
Start a new article
Hotrodders forum
Categories
Best articles
Body and exterior
Brakes
Cooling
Electrical
Engine
Fasteners
Frame
Garage and shop
General hotrodding
Identification and decoding
Interior
Rearend
Safety
Steering
Suspension
Tires
Tools
Transmission
Troubleshooting
Wheels
Toolbox
What links here
Related changes
Special pages
Terms of Use
Copyright
Privacy Policy
Your Privacy Choices
Manage Consent