Quadrajet
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'''So, all Q-jets are the same, right?''' | '''So, all Q-jets are the same, right?''' | ||
| − | Not hardly! These are a few | + | Not hardly! These are a few differences: |
Generally, there were the ‘small’ and ‘large’ casting carb bodies. These were 750 and 800 cfm, nominal- other cfm requirements were met by tailoring the air valve and/or the secondary throttle stop. Then there was the rare (one year-‘71) Pontiac HO carb that used a smaller booster to get even more flow than the “normal” large casting (800 cfm) carb. | Generally, there were the ‘small’ and ‘large’ casting carb bodies. These were 750 and 800 cfm, nominal- other cfm requirements were met by tailoring the air valve and/or the secondary throttle stop. Then there was the rare (one year-‘71) Pontiac HO carb that used a smaller booster to get even more flow than the “normal” large casting (800 cfm) carb. | ||
| − | There were straight or 90° fuel inlets, w/short and long filter housings. There were at least 4 different choke arrangements. There were 5 different idle mixture screws. 4 different float pivot pins, 5 different float bowl inserts. There were both | + | There were straight or 90° fuel inlets, w/short and long filter housings. There were at least 4 different choke arrangements. There were 5 different idle mixture screws. 4 different float pivot pins, 5 different float bowl inserts. There were both Torx and straight blade screw heads used to secure the air horn. |
| − | There were two different needle and seat arrangements regarding the type, and at least 3 different floats made from 2 different materials (nitrophyl and brass. | + | There were two different needle and seat arrangements regarding the type, and at least 3 different floats made from 2 different materials (nitrophyl and brass). |
| − | Later carbs (~’76-up) have | + | Later carbs (~’76-up) have an adjustable part throttle feature (aka "APT"). Some have idle air bypass, others don’t. Most had only two primary rods, some had three- one hooked to an aneroid. Sort of like 2 power pistons. |
| − | Various carbs had different bowl vents, some had a hot air compensator. Many had secondary fuel booster outlets (passive accelerator pump) that were located above the air valve, others below (below better for high performance). Some secondary air valves were slotted, others not. | + | Various carbs had different size and shape bowl vents in various locations, some had a hot air compensator. Many had secondary fuel booster outlets (passive accelerator pump) that were located above the air valve, others below (below better for high performance). Some had a primary arrangement similar to the secondary system just described. Some secondary air valves were slotted, others not. |
| − | Accelerator pump pistons varied by length and spring rates (at least 6 different), inlet seats were different sizes (at least 6 different sizes available, 0.095” to 0.149” [0.149” is aftermarket only]), power piston spring rates varied (10 different OEM springs, others available through the aftermarket), obviously jets (at least 13 different OEM sizes, from #64 to #78), primary metering rods (15 different ‘65-’67 rods and 18 different ‘68-up rods. Sizes range from 0.033” to ~0.060”), secondary metering rods (93 to select from), secondary hangars (20 different p/n’s) varied between carb applications. There are [b]millions[/b] of different combos possible for the ‘68-up carb alone! And this doesn't even consider all the different linkages, choke pull-offs | + | Accelerator pump pistons varied by length and spring rates (at least 6 different), inlet seats were different sizes (at least 6 different sizes available, 0.095” to 0.149” [0.149” is aftermarket only]), power piston spring rates varied (10 different OEM springs, others available through the aftermarket), obviously jets (at least 13 different OEM sizes, from #64 to #78), primary metering rods (15 different ‘65-’67 rods and 18 different ‘68-up rods. Sizes range from 0.033” to ~0.060”), secondary metering rods (93 to select from), secondary hangars (20 different p/n’s) varied between carb applications. There are [b]millions[/b] of different combos possible for the ‘68-up carb alone! And this doesn't even consider all the different linkages, choke pull-offs, the two different CFM ratings, etc. ad infinitum. |
Throttle linkages varied greatly- some were made for manual trans apps, these can be used w/a TH400 if the kickdown switch is relocated (or is at the throttle pedal), some were only for a TH400 apps w/carb-mounted kickdown switch, some were used w/the TH350 (has the ability to "pull" a detent cable), some for the Powerglide trans. Some have cruise control studs, some not. Early carbs used throttle linkage, later used a cable. | Throttle linkages varied greatly- some were made for manual trans apps, these can be used w/a TH400 if the kickdown switch is relocated (or is at the throttle pedal), some were only for a TH400 apps w/carb-mounted kickdown switch, some were used w/the TH350 (has the ability to "pull" a detent cable), some for the Powerglide trans. Some have cruise control studs, some not. Early carbs used throttle linkage, later used a cable. | ||
| − | There were at least 20 different front choke pull offs, at least 10 different rear choke pull offs, carbs with front only or both front AND rear choke pull offs. Vacuum port size, number and locations were all over the place. | + | There were at least 20 different front choke pull offs, at least 10 different rear choke pull offs, carbs with front only or both front AND rear choke pull offs, some used no pull offs at all, instead relying on a piston in the fuel bowl to damp the secondary opening rate. Vacuum port size, number and locations were all over the place. |
There are two different length primary rods, there are stepped and tapered rods. | There are two different length primary rods, there are stepped and tapered rods. | ||
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